Systems to safely store, handle, treat and dispose of medical (healthcare) waste are well developed in the 21st century. Yet across many parts of the Global South (low - and middle - income countries) such systems, resources and knowhow are lacking; to the extent that medical waste could be posing a serious threat to the health, safety and lives of millions of healthc are workers and waste handlers who regularly interact with this material. We present here a novel scope and dimension to investigating the risks and hazards to people who come into contact with medical waste, focusing on activity types and established medi cal practice. Based on a systematic review of the evidence (PRISMA approach, adapted), we critically analysed and comparatively summarised data, and identified prevalent combinations of hazards, exposure and risk with a global scope. Subsequently, we assig ned indicative comparative risk scores for such combinations. Our critical analysis unveils extensive mismanagement of medical waste globally, including the co -disposal with municipal solid waste (MSW), burning in open pits, and dumping even on public stre ets. Alarmingly, a small but non -negligible trade in reused medical equipment is proliferated by a cohort of waste reclamation specialists (sub -group of waste pickers): they collect hypodermic needles, and other single use medial items for resale to substa nce abusers and back into the healthcare system. We also highlight the dilemma faced by medical waste handlers in many parts of the world where a difficult choice is made between creating hazardous emissions from burning waste in the open or discarding it on land (e.g. in dumpsites) from where it risks accidentally infecting people with pathogens. Keywo rds: Healthcare waste, Solid waste, Health and safety, Risk, Global South, Resource recovery, Circular economy , Sharps injury, Medical waste incineration, Open burning , Medical waste. Graphical Abstract Abbreviatio ns As arsenic BC black carbon Cd cadmium CI confidence interval CO carbon monoxide Cr chromium Cr (VI) chromium IV DRC dioxins and related compounds DWH domestic waste handler EC elemental carbon EU European Union EWC European Waste Catalogue Fe iron haz. hazard HBV hepatitis B virus HCB hexachlorobenzene HCl hydrochloric acid HCV hepatitis C virus HCW healthcare workers Hg mercury HIC high income countries HIV human immunodeficiency virus I-TEQ international toxic equivalent L likelihood LIC low income countries LIMIC low income and middle income countries LMC lower middle income countries Mn manganese MSW municipal solid waste MWH medical waste handler NHS National Health Service (UK) Ni nickel NMVOC non-methane volatile organic compounds NO X Nitrogen oxides PAH polycyclic aromatic hydrocarbons Pb lead PM particulate matter PVC polyvinyl chloride R risk S severity SDG Sustainable development Goals SO 2 sulphur dioxide SO X Sulphur dioxides TSP Total suspended particles UMC upper middle income countries USEPA United States Environmental Protection Agency WASH Water, Sanitation and Health 1. Introduction Despite extensive global knowledge of the potential hazardousness of medical (healthcare) wastes, there are considerable shortcomings with medical waste management across the world, particularly in low and middle income countries (LIMICs) where medical waste is often stored, transported and co -disposed alongside other waste fractions (Harhay et al., 2009) . Whereas many of the materials, subs tances and objects that become med ical waste are similar in nature to household waste, t he World Health Organization (2014) (WHO) estimates that approximately 15% is potentially hazardous to human health , not least due to its potential to harbour pathogens that can subsequently cause infection at multiple points across a complex system ( Figure 1). In high income countries (HIC), systems to neutralise pathogens in medical waste are advanced, supported by protocols for sep aration at source, of for instance sharps (injection equipment), so that they can be stored, transported and treated or disposed of safely and efficiently. Infectious material is often incinerated or disposed of in specially designed hazardous waste landfi lls that prevent the risk of interaction with people or, the environment (Hossain et al., 2011; Windfeld and Brooks, 2015) . The specialist engineering required and effort undertaken to protect human health and the environment in this way, results in considerable cost. F or instance , a median o f $440 -620 per tonne for infectious waste treated in the UK in 2015 -16 (Royal College of Nursing, 2018) and $790 per tonne in the US (Lee et al., 2004) . For healthcare providers in LIMICs, these costs ar e often prohibitive, and r esearch undertaken by the Water, Sanitation and Health (WASH) team of W HO (World Health Organization and the United Nations Children's Fund, 2019) indicated that out of 48 countries that provided sufficient data , only 30 were able to provide data on healthcare waste generation and management and of those, more than 50% lacked b asic waste management services ( Section S.5 ). Figure 1: Generalised m aterial flow system for medical waste. System boundary denotes the parts of the system that fa ll within scope of this review . Red arrows highlight pathways through which single -use medical devices are reclaimed f or reuse. System boundary Self-care Collected for reuse or recycling (informal) Diffuse dump Aquatic environment Health centre & hospital open burning Medical devices & consumables supply Clinical service delivery Municipal waste collection Uncollected On site incineration Medical waste treatment facility Medical devices & consumables manufacturing Collected Disposal Dumpsite Municipal landfill Incineration Residential open burning Hazardous waste landfill Atmosphere 7 Fundamentally, medical waste is any object, substance or item that is discarded as a result of healthcare provision. Some of it may be hazardous, some infectious, and much of it is likely to be relatively benign. F or instance, Vaccari et al. (2017) found that approximately 44% of waste generated in an Italian hospital was hazardous , the Royal College of Nursing (2018) found that 32.8% of waste generated in hospitals in England and Wales was infectious in 2015 -16, and World Health Organization (2005a) reported that just 19% of waste generated in healthcare centres was poten tially hazardous. However, a globally unified definition of medical waste is absent, which means that there is ambiguity over how it should be stored, collected and transported. This basic lack of clarity may expose medical waste generators, handlers, trea tment and disposal operators to an unacceptably high risk o f exposure, due to interaction with wastes , some of wh ich have hazardous properties. Several reviews on medical waste management practice already exist. For instance, Ali et al. (2017) , Kerdsuwan and Laohalidanond (2015) and Khan et al. (2019) have each carried out mini-reviews of medical waste management in de veloping countries, listing information on medical waste generation, composition, manage ment and hazardousness, alongside narrative on the challenges faced by healthcare workers and medical waste handlers. On a national scale, reviews also exist for Ethiopia (Israel Deneke et al., 2010) , Jordan (Al-Momani et al., 2019) , India (Patil and Shekdar, 2001) and Turkey (Ciplak and Kaskun, 2015) amongst others. The World Health Organisation has also provide d several reviews, including an extensive global review on the safe management of healthcare wastes (World Health Organization, 2014) , one that focussed on Southeast Asia specifically (World Health Organization, 2017a) , and another that is dedicated to the safe management of sharps (used injection, phlebotomy and stitching equipment) (World Health Organization, 2019c) . Two global review s also exist in the academic literature. Hossain et al. (2011) provided more in depth context, also reviewing the main treatment technologies that exits to reduce the risk it poses to human health, including so me advanced methods such as the use of super -critical fluids and microwaves. Windfeld and Brooks (2015) briefly summarised the ge neral legislator approaches in Canada the U S and the UK , also very briefly discussing on developing countries. Lastly, Caniato et al. (2015) carried out a systematic review of global gover nance structures , which highlighted the widely varying approaches to the regulation and practices, particularly in LIMICs where investment in medical waste management was found to correlate with its effectiveness. 8 In common , these reviews provide an overv iew of the existing literature and general practices in medical waste management, describing and listing the general issues that relate to the topic . Yet , a comparative review of evidence indicating or assessing the potential or actual harm caused by estab lished medical waste management practice is not available. This research gap creates major challenge s for medical waste mangers and policy -makers to implement effective and efficient measures to ward mitigating the risk of negative interactions between medical waste, people and the natural environment. Therefore, we attempt here to bring three key contributions to the record to address these challenges , by way of a systematic review . First , we provide an overview of the medical waste system, generation, size of the sector. Second , we have systematically reviewed evidence that indicates hazards associated with medical waste to which receptors can be plausibly exposed through evidenced or inferred pathways. We focus on medi cal devices and consumables, specifically excluding pharmaceuticals , contraceptive devices and electrical equipment, for which more specialist reviews are needed . Third , we have aggregated and presented these data for comparison according to the hazards an d risks observed according to the phase of the waste management system to assist the reader with navigating the relevant concepts , namely : waste generation; waste storage, collection and handling; and reuse recovery and disposal (Figure 2). Fourth , we arrange identified risks into hazard -pathway - receptor combinations that enable a semi -quantitative comparison of relative harm so that risks can be ranked and prioritised for further research , innovation and wider interventions . 9 Figure 2: Phases during which hazard potential exists for medical devices after -use. Greyed out section is outside the system boundary of this research. The scope of the study encompasses the entire ‘after -use’ (end-of-engineered -life) phase which is defined here by the Directive 2008/98/EC (European Commission, 2008) , as the point in time at which the requirement to discard an item first takes place. For example, a needle that has been withdrawn from a patient’s arm after administering medication has complet ed its intended purpose and is considered waste because there exists a societal and/or institutional requirement to discard it immediately to prevent potential harm to others from a blood -born pathogen. Of course , there may be an unsan ctioned intent to reu se an item; however , there is almost always an expectation that this should not happen , and it is therefore considered ‘waste ’ for the purposes of our research. Collection, storage and handling phase Medical device has been used but not yet discarded e.g. injection equipment has been used to administer drugs but has not yet been disc arded into the sharps bin Medical device is collected e.g. by medical waste handler, informal waste collector Medical device is stored e.g. sharps container, medical waste container , flexible sack Medical device is transported e.g. from producer, or onward to treatment or disposal Medical device treated or disposed e.g. open burned, dumpsite, landfill, incinerator Medical device is used e.g. injection equipment is used to administer drugs, catheter is used to drain urine Use phase Medical device reprocessed into new materials e.g. a plastic syringe is shredded into flakes before being extruded into drinking straws Treatment, recovery or disposal Medical device prepared for reuse e.g. injection equipment is washed and repackaged for resale to hospital or pharmacy Waste generation phase Scope 10 2. Methods 2.1. Systematic review We followed methods reported by Cook et al. (2020) to carry out a systematic review based on PRISMA guidelines (Moher et al., 2009) , exploring three research questions (RQ) as follows:  RQ1 : What evidence exists to indicate risk to public and occupational safety posed by medical waste?  RQ2 : What are the comparative risks to public and occupational safety that arise from the management of medical waste?  RQ3 : What research could be carried out that would have the greatest impact on harm reductio n in the medical waste management sector? The Boolean search queries used to search three databases, Scopus, Web of Science and Google Scholar are shown in Section S.1 alongside the exclusion criteria ( Table S 1 ) and the basic statistical results of the r eview ( Figure S 1 and Figure S 2 ). These were tested using one at a time sensitivity analysis to obtain the optimum number of papers with the fewest terms. Further snowball and citation searching (Cooper et al., 2018) was undertaken as well as searches of databases from institutions such as The World Bank (2020) , International Labour Organization (2020) , World Health Organization (2020) , Health and Safety Executive (2020) (HSE). As described by Cook et al. (2020) , risks, hazards, pathways and receptors were combined into realistically experienced combinations according to scenarios reported in the literature , which enabled the production of source -pathway -receptor diagrams illustrating hazard flow to receptors , as shown in the unified diagram in Figure 3. 11 Figure 3: Conceptual overview of the main sources, pathways and receptors for hazards associated with medical waste . Receptor Route of human exposure Compartment Substance or material Transfer process Legend Glass fragments Biting and scratching Clearing up Healthcare workers Medical waste handlers Phlebotomy Administering medication Stitching Informal medical waste collectors Laundry workers Sources Pathways Used hollow needle Used suture needles Hepatitis B Hepatitis C HIV Other pathogens Adult Population Materials used in devices & consumables Accidental percutaneous puncture Trauma Mucous membranes Open burning Infectious soft waste Substances in materials Landfill Atmosphere Dumpsite Centralised incineration Ash Reclamation for reuse On-site incineration Reuse Deliberate percutaneous puncture Inhalation Dust Soil Deposition Ingestion Food Uptake in crops Mouthing Child Population Patients Substance abusers Receptors Waste container collection Secure container Insecure container Waste container storage Uncontained Open dump Informal waste collectors 12 2.2. Risk based approach A risk based approach, also described by Cook et al. (2020) , and adapted from World Health Organization (2012) , Hunter et al. (2003) , Kaya et al. (2018) and Burns et al. (2019) , assessed the likelihood and severity in each haza rd-pathway -receptor combination, assigning an indicative risk score ( Table 1 and Table 2) that was used to rank and compare them. It is important to note that this process did not and was not intended to quantify risk in each combination, but to be used as a decision support method that can be used to inform a future research agenda ; aggregated and ranked results are shown in Section S.3 . Table 1: Matrix used to calculate the relative risk of each hazard -pathway -receptor scenario. Consequence Very slight Slight Moderate Severe Very severe 1 2 3 4 5 Likelihood Very unlikely 1 1 2 3 4 5 Unlikely 2 2 4 6 8 10 Likely 3 3 6 9 12 15 Very likely 4 4 8 12 16 20 Inevitable 5 5 10 15 20 25 Table 2: Colour coding used to rank hazard potential qualitatively in each category. Red (R) High harm potential Amber (A) Medium/high harm potential Yellow (Y) Medium/low harm potential Green (G) Low harm potential Grey Insufficient data 2.3. Medical waste generation Data for medical waste generation were collected as a separate search exercise from the main review using the same pool of papers , and the same citation and snowball searching strategy. Descriptive statistics were illustrated as box and whisker plots. Outliers were defined as data points that were more than 1.5 times the length of the interquartile range distant from either end of the in terquartile range. 2.4. Other Calculation of cost of waste treatment in the introduction at 1.305 USD to 1 GBP) 13 3. Overview of medical waste 3.1. Definitions and scope Agreeing clear, shared definitions, for waste is critical to implementing policy and best practi ce to mitigate its harmful effects (Cheyne and Purdue, 1995) . However, our research indicates that there is still no unified global definition of medical waste and the terms ‘medical waste’ and ‘healthcar e waste’ are used interchangeably by different organisations and authors reviewed here. According to the World Health Organization (2017b) , healthcare waste includes: “[…] all the waste generated within health -care facilities, research centres and laboratories related to medical procedures. In addition, it includes the same types of waste originating from minor and scattered sources, including waste produced in the course of health care undertaken in t he home” . The Commission of the European Communities (2010) uses a similar definition for classification of healthcare and biological wastes, which includes all material generated in the pursuit of healthcare of humans and animals including: body parts and organs , sharps , bandages , plaster casts, clothing, diapers (from hospitals) and chemicals from hospitals and laboratories. The category also encompasses residential care activities, treatment of prevention care for humans and animals, human health activities, research. Despite these definitions, the medical and healthcare waste categories are not applied consistently , and are often used liberally to describe specific frac tions of waste generated by healthcare activities or often those that arise from specific healthcare facilities. For instance, the term ‘ medical waste ’ may be used as a proxy for:  The hazardous fraction of healthcare waste  The clinical fraction of health care waste  Waste generated in hospitals  Waste generated across a range of healthcare facilities . 14 3.2. Medical sector workforce Approximately 59 million people worked in healthcare worldwide in 2006, more than half of whom worked in Europe and the US ( Figure 4) (World Health Organization, 2006) . Health service providers mak e up the majority of the health care workforce , with significant managerial and support workers providing ancillary services in Europe and the Americas. Conversely, in the Western Pacific Region , Eastern Mediterranean and Africa, the healthcare workforce is primarily made up of healthcare providers with successively fewer management and support workers as a proportion of the total workforce in these regions. Figure 4: Number of healthcare workers by WHO region absolute numbers (World Health Organization, 2006) . WHO regions are det ailed in Section S .4. Europe and the Americas have considerably more (21.74) healthcare workers per 1,000 population compared to the global average of 9.3. Africa has comparatively few healthcare workers, with just 2.3 per 1,000 head of population, indica ting that countries with gr eater access to resources are able to provide more healthcare workers (Figure 5). 1.361.584.737.8111.5412.46 0.280.522.32.265.099.28 0 5 10 15 20 25AfricaEastern MediterraneanSouth-East AsiaWestern PacificEuropeAmericas Number of healthcare workers (millions)Health service providers Health management & support workers 15 Figure 5: Density of healthcare workers by WHO region (World Health Organization, 2006) . WHO regions are detailed in Table S 4. Red bar represents global average. 3.3. Medical waste composition As indicated by the data shown in Figure 9, medical waste is made up of both hazard ous and non-hazardous components. As a rule of thumb, World Health Organization (2005b) suggest s that HCW is approximately 20% non -infectious and non -hazardous, with the remaining 80% having similar properties to domestic waste. (World Health Organization, 2005a) provides the following indicative composition of healthcare waste, shown in Figure 6. Few studies provide more detail on the material composition of medical waste. O ne study (Eleyan et al., 2013) of medical waste generated at three hospitals in Palestine provides detail on both hazardous and non -hazardous fractions ( Figure 7). 2.344.35.89.318.924.8 0 5 10 15 20 25AfricaEastern MediterraneanSouth-East AsiaWestern PacificWorldEuropeAmericas Density (healthcare workers per 1,000 population) 16 Figure 6: Approximate proportions of HCW at public health centres reported by WHO. Data after World Hea lth Organization (2005a) . Figure 7: Material composition of waste sampled at three hospitals in Palestine . Data after Eleyan et al. (2013) . 3.4. Medical waste generation Medical waste generation data is reported using a variety of metrics and definitions worldwide. As revealed here, the most common convention in low income and middle income countries ( LIMICs ) is to report waste generated at healthcare facilities on a kg per bed per day basis. Here, 136 medical waste gene ration data points from 59 separate sources in 27 countries were reviewed and categorised by the World Bank income category at the time t hat the primary research was conducted ( Figure 8). The data showed some commonality in LIMICs, however few data points were found for high income countries (HICs ), as the convention is to report on a whole country or hospital basis, thus the arithmetic mean was skewed fo r HICs by two very high data points. The majority of the data identified were for LIMICs, with a n arithmetic mean of 2.8 kg and 2.9 kg per bed per day for low income countries ( LICs ) and upper middle income countries ( UMC s) respectively. LMCs showed a lower healthcare waste generation, with a n arithmetic mean of 1.1 kg per bed per day and median of 0.68 kg per day. Non-infectious 80%Pathological and infectious 15%Chemical and pharmaceutical 3%Sharps 1%Pressurised cylinders, broken thermometers 1% Waste mixed with infectious (HAZ) 22% Medical plastic (HAZ) 13% Absorbent cotton (HAZ) 7% Sharps (HAZ) 1%Pathological (HAZ) 1%Paper (GEN) 19%Other (GEN) 18%Plastic (GEN) 17%Glass (GEN) 1%Textiles (GEN) 1%Metals (GEN) 0% 17 Figure 8: Side by side comparison of central tendency and spread for waste generati on in medical facilities by income category; sources detailed in Table S 2 . Both UMCs and LICs showed a similar waste generation, more than a third greater than LMCs. Abbreviations: high income country (HIC); low income country (LIC); upper -middle income c ountry (UMC); lower middle income country (LMC); inter -quartile range (IQR). Though hospital waste is widely published on a per bed basis, statistics on the absolute mass of medical waste generated are less commonly reported outside the European Union. Eurostat (2016a) publishes data for European countries ( Figure 9), which reported collective 5.3 2.9 1.12.8 HIC UMC LMC LIC05101520 Income categoryMedical waste generation (kg bed d-1) 25%~75% Range within 1.5IQR Median Line Mean Data 18 healthcare and biological waste generation of approximately 2.1 million tonnes in 2016. Approximately 56% of Europe’s healthcare and biological waste is classif ied as hazardous; but, as shown in Figure 9, there are clear differences in the way waste is categorised in different countries. Moreover, there is wide var iation in the medical waste generation per capita, which is comparatively high for both Belgium and Ireland and low for Turkey and the average of all the other European countries. Figure 9: Healthcare and biological waste genera tion in selected European countries Eurostat (2016a) . High variability in healthcare waste generation is reported, possibly reflecting inconsistencies in definitions and variability in the level of accurate reporting between member states. Abbreviations: healthcare waste (HCW). Reporting of medical waste generation in the EU relies on the accurate submission of paperwork and correct classification of wastes according to Chapter 18 in the European Waste Catalogue (EWC) (European Union, 2018) . In practice , member states may have a variety of interpretations of the central EU requirements under Directive 2008/98/EC (The Waste Framework Direc tive) (European Commission, 2008) , and often businesses and individual instructions may not be provided with adequate guidance on how to report the waste they generate under the correct EWC code . 0.02.04.06.08.010.012.0 050,000100,000150,000200,000250,000300,000350,000400,000450,000500,000 HCW generation (kg capita yr-1)HCW generation (t yr-1) Hazardous HCW Non-hazardous HCW HCW generation per capita 19 As a way of contextualisi ng European healthcare and biological waste generation, it is shown in Figure 10 as proportion of MSW generation as reported by Eurostat (2016b) . As with the data shown in Figure 9, there is considerable variation between some countries, for which there is no obvious explanation. Again both Belgium and Ireland show healthcare waste generation as a proportion of MSW, with Turkey and the other European nations showing very low proportions in comparison to the mean average ge neration of approximately 0.7%. Figure 10: Healthcare and biological waste in Europe shown as a proportion of MSW (Eurostat, 2016a; Eurostat, 2016b) . There is no obvious explanation for the large variation in healthcare waste generation between member states. The considerable variation in reported categories and mass of medical waste by different countries suggests that it is unlikely that accurate esti mates of medical waste generation will be forthcoming at a country, regional or global basis. Furthermore, s everal other types of waste arisings that could be considered to be part of healthcare waste are unlikely to be reported at a ll, the majority of whi ch will be discarded alongside domestic MSW collected waste, such as self -care products (e.g. incontinence products , blood glucose testing kits, dressings and catheters ) administered at ho me. 0.0%0.5%1.0%1.5%2.0%2.5%Healthcare & biological waste proportion of MSW 20 4. Challenge 1: Medical waste generation phase 4.1. Context We summarise here data on the key hazards identified that exist at the point of waste generation in healthcare. With a few exc eptions, most of the studies focus on sharps and needlestick injuries, which are the dominant category of injury relating to medical waste at the point of generation in many contexts (Akpieyi et al., 2015; Elder and Paterson, 2006) . As shown in the co nceptual model ( Figure 11), the main hazards associated with both the sharps and needlestick injuries and also exposure to soft infectious medical waste, for example, dressings or personal protective equipment (PPE) , are identified as those from infection with hepatitis C virus ( HCV ), hepatitis B virus ( HBV ) and human immunodeficiency virus (HIV). In isolation, these pathogens pose little risk, however, there are several circumstances through which these pathogens may be carried by medical devices and consumables, and ther eafter could in principle enter the bodies of those who may come into contact with them (subject to specific conditions for pathogen survival) . Figure 11: Hazard exposure conceptual model (source –pathway –receptor) associated with medical waste at the point of generation phase. Sources Pathways Receptors Receptor Route of human exposure Compartment Substance or material Transfer process Legend Used hollow needle Used suture needles Recapping Clearing up HBV HCV HIV Other pathogens Nurses Doctors Clinical assistants Venepuncture Administering medication Stitching Glass fragments Biting and scratching Percutaneous puncture Trauma Mucous membranes Clearing up Infectious soft waste 21 Other less common pathogens are reported by NHS Employers (2015) and are summarised in Table 3. However, the studies reviewed here did not report exposure or risk of exposure to these patho gens, which may denote a gap in other relevant research efforts. Table 3: List of less common blood -borne pathogens other than hepatitis B virus ( HBV ), hepatitis C virus ( HCV ) and human immunodeficiency virus ( HIV) which are transmissible through needlestick injuries; after NHS Employers (2015) .  Human tlymphotrophic retroviruses (HTLV I & II)  Hepatitis D virus (HDV or delta agent, which is activated in the presence of HBV) hepatitis G virus (GB virus or GBV -C)  Cytomegalovirus (CMV)  Prion agents such as those associated with transmissible spongiform encephalopathies (TSE)  Parvovirus B19  Transfusion Transmitted virus (TTV)  West Nile virus (WNV)  Malarial parasites  Epstein -Barr virus (EBV) The terms ‘sharps injury’ and ‘needlestick inj ury’ are often used interchangeably by some authors and as separate, distinct categories by others. For clarity, here we report using the following definitions adapted from the Cana dian Centre for Occupational Health & Safety (2020) :  Needlestick injuries include all injuries that involve hollow needles for percutaneous removal or addition of fluids. Examples of hollow needles include fixed syringe or winged steel needles (butterf ly).  Sharps injuries involve all other injuries excluding hollow needles. Examples include injury by glass shards, suture needles and safety pins. While every effort was made to convey the findings of the reviewed studies using the above definitions, in several occasions where the terms were ill defined in the original text and therefore it is likely that there are occasional incidences where categories have overlapped, but it has not been reported as such. 4.2. Sharps and needlestick injuries to healthcare workers (HCW) Nine studies reviewed in our research reported rates of injury or prevalence of sharps and needlestick injury to healthcare workers at the point of waste generation ( Table 4). The review carried out by Elder and Paterson (2006) standardised findings from multiple studies on the basis of the number of exposures to sharps and needlestick injuries per 100 person years. While this standardisation was a helpful comparison within the paper, other authors reported on the basis of preva lence in the past 12 months of working life; that is whether a worker had experienced a single exposure or not over that timeframe. 22 Table 4: Needlestick injury rate and prevalence* among healthcare workers . Ref. Year Context Summary method Exposed workers Clinical /non/ both Type of injury 12 month prevalence* Lifetime prevalence* Injury rate per 100 person years Mean 95% CI Mean 95% CI Auta et al. (2017) 2017 Western Africa Meta -analysis (n=65) of occupational exposure to body fluid, mainly through percutaneous injury (2002 - 2017) Healthcare workers c Clinical Blood and bodily fluid exposure incl. needlestick (95% CI) 47.93% 31.52 –64.33 56.68% 37.2-76.17 Central Africa 51.68% 37.52 –65.84 68.01% 44.89 -91.13 Eastern Africa 47.29% 36.66 –57.92 67.98% 59.06 -76.9 Southern Africa 33.92% 16.48 –51.36 61.07% 48.35 -73.79 Northern Africa 60.70% 56.89 –64.51 82.9% 70.55 -95.24 Africa (overall) 47.96% 40.65 –55.27 65.66% 59.69 -71.64 Africa 2000 -2009d 49.7% 42.8–56.6 Africa 2010 -2017d 47.8% 34.5–61.1 Western Africa Needlestick (95% CI) 35.98% 24.43 –47.52 52.91% 45.7-60.12 Central Africa 55.00% 48.41 –61.59 Eastern Africa 33.26% 28.54 –37.98 53.07% 43.59 -62.56 Southern Africa 16.40% 10.64 –22.16 67.89% 64.76 -71.02 Northern Africa 47.92% 32.63 –63.22 Africa (overall) 35.97% 31.15 –40.79 54.35% 48.4-60.31 Africa 2000 -2009d 39.2% 31.6–46.9 Africa 2010 -2017d 31.5% 28.1–34.9 World Health Organization (2017a) 2017 LKA Survey at hospital Doctors, nurses, support staff (n=121) Both Needlestick 54% Kosgeroglu et al. (2004) 2003 TUR Survey at three hospitals over six months Nurses (n=595) Both Needlestick 56.4% Sharps 20% Enwere and Diwe (2014) 2014 NGA Knowledge assessment of injection safety HCW (n= 156) e Both Needlestick 50.6% Mercier (1994) 1994 GBR All HCW (n=4,000) Nursing Both Needlestick and sharps 3.33% 5.15f Medical 6.25% Medical student 5.88% Elmiyeh et al. (2004) 2004 GBR Clinical healthcar e professionals surveyed Doctors (n=125); nurses (n=175) Clinical Needlestick 38% 57-74%e 74 f Astbury and Baxter (1990) 1990 GBR Healthcare workers (n=1,800) Clinical Needlestick and sharps g 32% 116 f 1994 GBR Medical students Clinical Needlestick 22% 23 Ref. Year Context Summary method Exposed workers Clinical /non/ both Type of injury 12 month prevalence* Lifetime prevalence* Injury rate per 100 person years Mean 95% CI Mean 95% CI Cossart and deVries (1994) Survey of medical and dentistry students; nurse s Dentistry students 72% Nurses (medical) 17% Nurses (surgical) 42% Doctors (medical) 57% Doctors (surgical) 100% Emergency staff 50% Elder and Paterson (2006) nd GBR Review of needlestick injury research All HCW and support staff Both Needlestick and sharps 1.8 2002 All HCW and support staff 4 2003 All HCW and support staff 3.66 2004 All HCW and support staff 0.78 1995 Occupational health staff Both 0.9–4.4 1992 Medical students (n=275) Clinical 30 1990 Medical students (n=151) 65 2002 Dental students (n=183) 38 1993 Operating department staff (n=158) 284 * Unless specified, is the mean proportion of workers who have experienced one exposure over the time period; a collecting waste from producer premises and returning to depot for handling and onward processing; b exposure was reported as 1 per 29,000 man hours , adjusted for comparability on the basis of 1,864 working hours per annum; c category includes nurses, doc tors, auxiliary healthcare workers, students undertaking clinical training or gaining experience; d pooled results; e nurses (62.8%); waste handlers (11.5%); ward assistant (12.2%); doctors (8.3%); lab scientists (5.1%); abbreviations: healthcare workers ( HCW); confidence interval (CI); e rate reported in results does not match the abstract so both reported; f Calculated by Elder and Paterson (2006 ); g incl. scratches and bites. Abbreviations: healthcare workers (HCW); confidence interval (CI) 24 The Elder and Paterson (2006) review found a large range (0.78 –284 injuries per 100 person years) of reported injury rates, and suggested that this may be a result of reporting inconsistencies and variations in reporting rate. Closer inspection reveals that the much higher rates of injury were reported when the denominator is workers who are more likely to experience direct exposure to used hollow needles. For instance, the operating department staff showed a rate of 284 injuries per 100 person years, whereas when data is reported for the whole hos pital staff, or occupational health staff, rates of injury were within the range of 0.78-5.15 injuries per 100 person years , including Mercier (1994) . Needlestick injury data reported for clinical staff by Elmiyeh et al. (2004) , Astbury and Baxter (1990) were 74 -116 per 100 person years and for students , the rate was slightly lower at 30 -65 per 100 person years (Elder and Paterson, 2006) , reflecting the level of clinical involve ment of each group. Auta et al. (2017) reviewed 65 studies across Africa on the basis of prevalence of injury over 12 months or the lifetime of healthcare workers, finding a mean 12 month prevalence of 35.97% (C I 95%: 31.15 -40.79%) and mean lifetime prevalence of 54.35% (CI 95%: 48.4 - 60.31%). These data are a similar range to those re ported in other LIMICs such as World Health Organization (2017a) in Sri -Lanka, Kosgeroglu et al. (2004) in Turkey and Enwere and Diwe (2014) in Nigeria. However, they are also similar to those reported in the UK: Elmiyeh et al. (2004) , Astbury and Baxter (1990) report 38% and 32% prevalence over 12 months, respectively. Several other correlations can be observed between income level and prevalence of needlestick and sharps injuries among HCWs. For instance, the prevalence of these type of injuries in Southern Africa (Auta et al., 2017) are lower than those for poorer parts of Africa and in a similar range to those reported in Great Britain (Astbury and Baxter, 1990; Elmiyeh et al., 2004) . There i s also evidence of a reduction in prevalence over time in the first and second decades of the 21st century, as reported by Auta et al. (2017) . Three authors highlight considerable under -reporting rates of exposure to needlestick and sharps injury of between 22% and 58.3% ( Table 5). The obvious implication is that considerably more HCWs may experience needlestick and sharps injury than incident reporting data suggest; indicating that the reported rates of injury may nee d to be adjusted by between 30% and 50% to estimate e xposure to the HCW population. 25 Table 5: Reporting rates of needlestick and sharps injury . Ref. Worker Reporting rate Mercier (1994) All HCW 58.3% Elmiyeh et al. (2004) Clinical 51% Cossart and deVries (1994) Doctors 28% Nurses 44% Dentistry students 45% Medical students 22% Emergency staff 47% Abbreviations: healthcare workers (HCW) Survey data may be more reliable in comparison to incident reporting data as it does not rely on the volition of HCWs toward completing an incident report. However, surveys of people’s historical experiences are subject to recall bias, which may over or un der inflate the results. Furthermore, the probability that a HCW will participate in a survey may also be commensurate with propensity to complete incident reports, meaning that part of the workforce may always remain under -represented. While the prevale nce of sharps injuries, including non -reported rates, provide insight into the potential hazard exposure, they do not indicate risk of infection from blood -borne viruses that are the principle hazard aside from localised trauma (NHS Scotland, nd) . While it is acknowledged that other pa thogens may be contracted through needlestick injuries, the main infection risks ar e considered to be HCV, HBV and HIV. The global probability of infection by these three viruses has been modelled by Prüss‐Üstün et al. (2005) who estimated potential exposure incidents at: HBV: 926,000 ( upper estimate 340,000; lower estimate 1,490,000) ; HCV: 2,100,000 (770,000 to 3,30 0,000); and HIV: 327,000,000 (61,000 to 1,300,000) . The most notable number of potential exposures identified in Prüss‐Üstün et al. (2005) is the very high number reported in the West Pacific region for HBV ( Figure 12). This results from a combination of a mid -range estimate of the number of sharp s injuries per healthcare worker per year in China and the marginal sea states to its south, as well as the very large population in that region and hence number of healthcare workers. Furthermore, rates of HBV infection are high in this region, which incr eases the likelihood of needles containing the pathogen. 26 Figure 12: Number of healthcare workers potentially exposed to hepatitis C (HCV), hepatitis B (HBV) and human immune deficiency virus (HIV) through needlestick injuries in World Health Organization Regions ( Section S.4 ); data after Prüss -Üstün et al. (2016); Prüss‐Üstün et al. (2005) . HBV prevalence amongst healthcare workers in Western Pacific is very h igh as a reflection of large population and high population prevalence of the infection. Potential HIV exposures were low in most regions, except Africa where the population level of HIV infection is much higher than in other regions (World Health Organization, 2019b) (Figure 12). The number of modelled HIV infections ( Figure 13) is broadly proportional to the number of exposures ( Figure 12) and much lower as HIV has a very low risk of transmission (0.3%) compared to HCV (3%) and HBV (33%) (Cheng et al., 2017) . However, the lev el of HBV infection is not proportional to the modelled exposure in the Americas, Eastern Mediterranean and Western Pacific regions. No mention is made of this by Prüss‐ Üstün et al. (2005) ; however, we suggest that this may be a consequence of a higher rate of prophylactic administration and also vaccination in , which historically has been much higher (49% to 93%) than the global average (30% to 85%) since 2000 (World Health Organization, 2019a) . 90,00089,000196,000 149,00085,000316,000354,000 76,800186,000304,000 192,000987,000 227,000 35,5002,37022,320 28,600 11,070 0100,000200,000300,000400,000500,000600,000700,000800,000900,0001,000,000 Africa Americas E Med. Europe SE Asia W pacificNumber of healthcare workers potentially exposedHCV HBV HIV 27 Figure 13: Number of healthcare workers infected with hepatitis C (HCV), hepatitis B (HBV) and human immun odeficiency virus (HIV ) through needlestick injuries in World Health Organization Regions (see Section S.4 ); data after Prüss‐Üstün et al. (2005) . Although exposu re to HBV is highest in Western Pacific ( Figure 12), numbers of infected individuals are ve ry small, possibly reflecting the high rate of historical immunisations compared to the global average (World Health Organization, 2019a) . Overall, Prüss‐Üstün et al. (2005) estimated that between 2 ,000 and 2 ,030 infections from needlestick and sharps injuries to healthcare workers will result in approxim ately 1,142 (268 to 5,267) early deaths as follows: HCV 145 (53 to 766); HBV 261 (86 to 923) and HIV 736 (129 to 3,578). Their research highlights several uncertainties, particularly with the transmission potential of the viruses, and acknowledges the abse nce of data in some regions, which has been approximated using data from similar countries. Importantly, Prüss‐Üstün et al. (2005) highlighted the fact that needlestick i nfections are largely preventable through a range of measures. For instance, immunisatio n of workers from HBV has an efficacy of 80% to 95% (Cheng e t al., 2017) , which if implemented at scale could be effective against infections contracted by approximately 40,000 per year. 1,580 1,5703,510 2,680 1,5005,5309,800 6,8009,10014,810 8,800 11072089 8 47 90 30 02,0004,0006,0008,00010,00012,00014,00016,000 Africa Americas E Med. Europe SE Asia W pacificNumber of healthcare workers infected through needlestick injuriesHCV HBV HIV 28 4.3. Activity context: where healthcare workers experience sharps and needlestick injuries Targeting interventions to reduce the incidences of needlestick and sharps injuries requires greater understanding of the context in which they occur. Two papers (Mercier, 1994; Nagao et al., 2007) reported the location in which sharps and needlestick injuries occurred among hospital healthcare workers ( Figure 14). Unsurprisingly, they were most prevalent in cl inical areas, with more than 50% reported on hospital wards. While these provide a useful indication of where to focus efforts to mitigate the likelihood of future injury, the data appear to reflect the level of activity. We suggest that further studies co uld focus efforts to determine the rate of injury per procedure, which might help to identify the circumstances in which the highest rates of injury occur. Figure 14: Location of sharps injuries reported ( A)*: in Japan by Nagao et al. (2007) ; and (B) in the UK by Mercier (1994) . *Sharps injuries were recorded over seven years at a hospital employi ng 1,346 healthcare workers and with 1,051 beds . Three studies (Cullen et al., 2006; Nagao et al., 2007; World Health Organization, 2017a) reported the type of activity being carried out when needlestick and sharps injuries took place (Figure 15). The lack of compatibility between the categories makes comparisons challenging, although several patterns can be observed. For instance, World Health Organization (2017a) , Cullen et al. (2006) and Nagao et al. (2007) (doctors ) observed that approximately 50% to 73% of injuries occurred during a procedure. For nurses in Japan, the Hospital ward 54%Operating room 25%Outpatient clinic 12%Clinical laboratories 4%Others 5%A: Nagao et al. Ward / clinic 59%Operating theatre 22%Accident and emergency 5%Clinical laboratories 4%Other 10%B: Mercia et al. 29 proportion of injuries during a procedure was much lower and the proportion sustaine d during clearing up was higher. No reason was su ggested by Nagao et al. (2007) for the disparity between doctors and nurses however we speculate that either doctors carry out more procedures than nurses or that do ctors are more careless. Both World Health Organization (2017a) and Cullen et al. (2006) observed 11% and 4% of injuries taking place after sharps had been discarded, but it is noteworthy that the studies did not explicitly include medical waste handlers, which may mean that downstream injuries were not captured in th e research. Figure 15: Proportion of needlestick and sharps injuries occurring by activity (Cullen et al., 2006; Nagao et al., 2007; World Health Organization, 2017a) . Some categories reported were merged for comparability . Cullen et al. (2006) does not sum to 100% due to rounding. Needlestick injuries were most prevalent during a procedure across all studies. In the hospital in Japan studied by Nagao et al. (2007) , more injuries took place during procedures for doctors compared to nurses, which we speculate may be a result of different roles or differing levels of diligence. We compare four studies (Cullen et al., 2006; Nagao et al., 2007; Woode et al., 2014; World Health Organization, 2017a) report ing the procedural phase at which needlestick and sha rps injuries occur ( Figure 16). Two of these (Cullen et al., 2006; Nagao et al., 2007) show data already presented in Table 5 that is harmonised by procedural phase . World Health 72% 52%73% 39%3%22% 14%8%2% 35%11% 4%14% 35%4% 11% 0%10%20%30%40%50%60%70%80%90%100% All All Doctors Nurses WHO 2017Cullen et al. 2006Nagao et al. 2007Proportion of injuriesAfter discarded After procedure, before discard Clearing work area During recapping During procedure 30 Organization (2017a) shows broad alignment with the other two, showing ca 45% of injuries occurring during procedures , however the a ge of the study . The exception is suture needle injuries reported by Nagao et al. (2007) , which took place during use in more than 75% of all cases on average (data not shown) . A comparatively recent study by Woode et al. (2014) reported a broadl y similar pattern to the other three studies in that the procedural phase showed the highest prevalence of needlestick injuries. The higher rate of prevalence amongst dental health professionals during the period just after use but before disposal indicate s a lack of procedural adherence during that phase, specific to dentistry. Figure 16: Procedural phase during which injury occurred reported by Cullen et al. (2006) , Nagao et al. (2007) , World Health Organization (2017a) and Woode et al. (2014) . The majority of injuries with suture needles appear to occur during use in comparison to hollow needles which show a higher proportion post -use. Both fixed syringe and winged (butterfly) needles resulted in considerably higher prevalence of injury after procedures had taken place (data not shown) , but before the devices were discarded (Figure 16). We speculate that this difference could highlight an opportunity for a reduction in injury rate by providing portable rigid sharps containers and enforcing adherence to guidance to deposit s harps immediately following a procedure. The number of injuries 0%10%20%30%40%50%60%70%80%90%100% All All Doctors Nurses Doctor Midwife Allied prof.Nurse / HCADentist/ d. nurseUnknown WHO 2017Cullen et al. 2006Nagao et al. 2007Woode et al. 2014Proportion of injuries During procedure During recapping Clearing work area After procedure, before discard After discarded Other 31 taking place after being discarded was low , 6% (Cullen et al., 2006) to 11 % (World Health Organization, 2017a) , in comparison to other procedural phases. 4.4. Risk characterisation for medical waste hazards at the point of generation The semi-quantitative risk assessment for medical waste during the waste generation phase focused solely on infection from HIV, HBV and HCV from used medical sharps : rationale and justification for scoring is detailed in Table 6. The risk assessment is based largely o n data already modelled by Prüss -Üstün et al. (2 016) that estimated global exposure, infection and death rate in HCWs for HIV, HBV and HCV through needlestick and sharps injury. We assess that t he risks to workers in HICs are comparatively low , because they are less likely to experience injury, the population level of infection is much lower, access to prophylactic treatment is more likely, and treatment of infection results in better outcomes. The highest risk of contracting HBV is scored very high , because of greater prevalence of the disease among the LIMIC populations and higher likelihood of infection in LIMIC hospitals where safe systems of work are often not comprehensively implemented. 32 Table 6: Risk characterisation sum mary for medical waste hazards during the waste generation phase . Haz. Pathway Receptor Geog. Evidence and justification for risk assessment Uncertainty (aleatoric and epistemic) Receptor vulnerability L S R Global receptor context HIV Medical sharps HCW LKA, TUR, NGA, GBR, all Africa global  Prevalence of sharps and needlestick injuries strongly evidenced in HICs and LIMICs (Astbury and Baxter, 1990; Auta et al., 2017; Cossart and deVries, 1994; Elder and Paterson, 2006; Elmiyeh et al., 2004; Enwere and Diwe, 2014; Kosgeroglu et al., 2004; Mercier, 1994; World Health Organization, 2017a) .  Exposure and infection rate modelled for HIV, HBV and HCV (Prüss -Üstün et al., 2016) .  Death rate between 2000 and 2030: 1,142 (268 to 5,267) and early deaths as follows: HCV 145 (53 to 766); HBV 261 (86 to 923) and HIV 736 (129 to 3,578) (Prüss -Üstün et al., 2016) .  The prevalence of blood -borne viruses is unacceptable, but the rate of infection and deaths in HICs is low compared to LIMICs where rates are co mmensurate with general population levels of infection .  HIV has a very low risk of transmission (0.3%) compared to HCV (3%) and HBV (33%) (Cheng et al., 2017) .  Evidence that many reported needlestick exposure events are underestimated (Cossart and deVries, 1994; Elmiyeh et al., 2004; Mercier, 1994) .  Lack of procedural adherence common in HICs and LIMICs (Akpieyi et al., 2015; Cullen et al., 2006; Rice et al., 2015) .  Many workers carrying out procedures without PPE, particularly in LIMICs (Kosgeroglu et al., 2004) but also in HICs. 1 4 4 HIC 2 5 10 LIMIC HBV 2 3 6 HIC 4 4 16 LIMIC HCV 2 3 6 HIC 3 4 12 LIMIC Abbreviations: Geographical research context (geog.); likelihood (L); severity (S); risk (R); hazard being assessed (Haz.); personal protective equipment (PPE) ; high income country (HIC); low income and middle income countries (LIMIC); hepatitis C virus (HCV); hepatitis B virus (HBV); human immunodeficiency virus (HIV) . 33 5. Challenge 2: Storage, collection and handling phase 5.1. Context As with the point of waste generation phase, the hazards associated with medical waste at the storage, collection and handling phase stem from pathogens that exist within the bodies of those receiving healthcare ( Figure 17). Again, the pathways through which those pathogens may reach other people involve them being carried through medical devices, which can pierce the skin of those who come in to con tact with them or enter mucous memb ranes through direct handling. Figure 17: Hazard exposure conceptual model (source –pathway –receptor) associated with medical waste during the storage, collection and handling phase . Abbreviations: hepatitis C virus (HCV); hepatitis B virus (HBV); human immunodeficiency virus (HIV). As with the medical waste generation phase, health care workers (HCWs) are also at risk of infection during the storage, collection and handling phase , if they become involved with the handling of contained or uncontained discarded medical waste. However, it is the medical waste handlers (MWHs) who are most exposed to infection during this phase , because they Sources Pathways Receptors Receptor Route of human exposure Compartment Substance or material Transfer process Legend Used hollow needle Used suture needles HBV HCV HIV Other pathogens Healthcare workers Medical waste handlers Venepuncture Administering medication Stitching Glass fragments Percutaneous puncture Trauma Mucous membranes Waste container collection Secure container Insecure container Waste container storage Uncontained Informal medical waste collectors Laundry workers Infectious soft waste 34 are inherently more likely to come into contact with it. Informal waste workers are also at risk of infection during this phase, whether through deliberate contact because of involvement with the illicit trade in reused medical equipment whe n collecting it for reprocessing, or indirectly when they are exposed to medical waste whilst they hunt for other valuable materials. 5.2. Sharps and needlestick injuries to medical waste handlers (MWH) We identified six papers (Amsalu et al., 2016; Anagaw et al., 2012; Mol et al., 2016; Shiferaw et al., 2012; Yizengaw et al., 2018) that reported on the prevalence of pathogen exposure to medical waste handlers (MWHs) through sharps and needlestick injuries ( Table 7). Three of these papers surveyed MWHs working in hospitals in Ethiopia, one in Sudan, and one in Brazil, finding a 12 month prevalence of between 33.3% and 75% in workers and a lifetime prevalence of 27 % to 47.4%. The ranges were broadly in line with those reported for injury prevalence to HCWs at the point of generation ( Table 4 and Table 5), with the exception of one further study (Yizengaw et al., 2018) of MWHs wor king in Ethiopian hospitals for whom an 18.6% prevalence was observed. Table 7: Needlestick injury rate and prevalence among medical waste handlers (MWH). Ref. Context Exposed workers Location Type of injury 12 month prevalence* Lifetime prevalence* Shiferaw et al. (2012) ETH MWHb Inpatients Sharps 34.2% Emergency 33.3% Operating rooms 45% Laboratory 50% Delivery 50% Laundry 46.7% On-site storage 53.3% Total 42.1% Inpatients Bloodstained bodily fluid exposure to mucous membranes 71.1% Emergency 55.6% Operating rooms 75% Laboratory 75% Delivery 75% Laundry 60% On-site storage 60% Total 67.5% Amsalu et al. (2016) ETH MWH (n=152) Sharps 47.4% Anagaw et al. (2012) ETH MWH (n=100) 43% Yizengaw et al. (2018) ETH HCW (n=268) MWH (n=130) Needlestick 18.6% Mol et al. (2016) BRA DWW (n=461) Needlestick/cuts 53.9%a MWH (n=61) Needlestick/cuts 75%a 35 Ref. Context Exposed workers Location Type of injury 12 month prevalence* Lifetime prevalence* Elya and Babiker (2015) SDN MWH (n=52) Injury (assumed needlestick) 27% * Unless specified, is the mean proportion of workers who have experienced one exposure over the time period; a participants were asked to respond with the type of accident they last had; b medical waste handlers (n=126) surveyed three hospitals in 2010 to assess injury rates and attitudes to personal protective equipment ( PPE); abbreviations: medical waste handler (MWH); healthcare worker (HCW); domestic waste handler (DWH). The high prevalence of needlestick injuries experienced by waste workers surveyed in Ethiopia is concerning, given the higher than average rates of blood -borne virus infection among the Ethiopian population ( . Table 8). Brazil has more comparable HIV and H CV prevalence with many HIC countries, but the prevalence of H BV is similar to Ethiopia and many other African countries (Benzaken et al., 2019) . Table 8: Individuals infected as a proportion of population (data for most recent reported year shown); selected countri es shown for comparison . Country/ region HIV HCV HBV Proportion Ref. Proportion Ref. Proportion Ref. Ethiopia 5.2% Bely hun et al. (2016) 3.1% -11% Bely hun et al. (2016) 7.4% Belyhun et al. (2016) Brazil 0.5% UNAIDS (2018a) 0.53% Benzaken et al. (2019) 2-8% Souto (2016) Western Europe ≤0.5% Kretzer et al. (2014) United States 0.4% UNAIDS (2018b) 1.7% Hofmeister et al. (2019) 0.4% Kim (2009) France 0.3% UNAIDS (2018b) 1.4% European Centre for Disease Prevention and Control (2016) United Kingdom 0.0% European Centre for Disease Prevention and Control (2016) Abbreviations: hepatitis C virus (HCV); hepatitis B virus (HBV); human immunodeficiency virus (HIV) Only one HIC context study (Blenkharn and Odd, 2008) was identified which analysed accident and injury records over three and a half years at three medical waste collection and storage premises, employing 85 waste handlers collectively. The study reported needlestick and sharps injury frequency of 1 per 29,000 man -hours or 6.45 injuries per 100 person years. Interestingly, the paper also reported the site of injury, finding injuries not only occurred to hands (n=24), but also the legs (n=11) and bodies of M WHs (Figure 18). The contractors who participated in the study were responsible for collecting waste from hospitals and ‘surgeries’ 36 (local doctor’s practice), which is where the 90% (36/40) of reported injuries occurred. Of the 40 injuries reported over th e study period, the research found that 15% were caused by incorrect or inadequate closure of sharps containers and 85% were the result of sharps being discarded in sacks intended for soft waste. Figure 18: Sharps injuries to medical waste handlers, by position on the body; after Blenkharn and Odd (2008) (permission sought for reproduction). Shiferaw et al. (2012) also reported the causes of sharps injuries among MWHs in hospitals in Ethiopia, finding that 19% of survey respondents reported that incidents of sharps and needlestick injury were due to inadequately closed sharps containers (insufficient containment ) and approximately 81% reported that sharps were placed in bags or sacks intended for soft waste. ( Figure 18). As the study by Shiferaw et al. (2012) was a cross - sectional self -reported survey, and Blenkharn and Odd (2008) was a longitudinal study based on incident reports, caution should be taken when directly comparing the two datasets, as they were not collected and reported on the same basis. 37 Figure 18: Self -reported incidents of causes of inju ries among medical waste handlers (MWHs ) in hospitals in Ethiopia; data after Shiferaw et al. (2012) . Further ev idence of sharps being discarded in flexible sacks rather than rigid sharps boxes was reported by Kanisek et al. (2018) who carried out compositional analysis of infective medical waste discarded in sacks (n=50) in Croatia. The study found sharps content at a rate of 30 g per five days (14.5 -74.5) at ‘family practices ’ (local doctor’s practice ) and 11 g per five days (1 -18) at dental practices. The inclusion of these items in soft waste, indicates almost routine non -adherence to safe working practices ; threaten ing the safety and li ves of MWHs. Speculatively, MWHs may have an expectation that sharps will be present in some bags designed for soft wastes and therefore have the opportunity to modify their own practices to avoid exposure. However, this expectation may be less prevalent in hospital laundry sorters, 13% of whom reported sharps injuries during their work in the study by Shiferaw et al. (2012) (Figure 18). Injuries from sharps arising in laundry is particularly worrying, as it indicates that sharps had either been discarded with the l aundry in error or had not been discarded at all and ended up there accidentally. Despite the obvious risk of exposure to MWHs from needlestick and sharps injuries, Blenkharn and Odd (2008) found that ballistic protection gloves were not worn in 55% (22/40) of the incidents reported at the three medical waste handling facilities studied , including two incidents where no gloves were worn at all. While Blenkharn and Odd (2008) reported lack of ballistic glove use in reported sharps inj uries, Shiferaw et al. (2012) reported ballistic glove use rate for exposed and no n-exposed MWHs, finding gloves w ere not use d by 20.6% of MWHs. Both Franka et al. (2009) and Shiferaw et al. (2012) also noted differences between prevalence of glove use between male and female MWHs, finding men less likely to 19%81%13% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90%Incorrect & inadequate closure of sharps containersSharps collected in plastic bags/sacksSorting of soiled laundrySharps and needlestick injuries (42.1%) 38 wear gloves than women in both studies ( Table 9). While the data are scarce, if this pattern is observed elsewhere it would indicate that men may be at considerably greater risk of exposure due to their non -adherence to safe working practices. Table 9: Comparison of the rate of use of ballistic protective gloves by sex. Ref Context Male Female Total Odds ratio P Shiferaw et al. (2012) ETH 75% 81.4% 79.4% 0.921 0.410 Franka et al. (2009) LBY 50.2% 88.1% 57.7% 7.37 <0.0000001 Exposure to blood -borne viruses is not limited to percutaneous injury, but can also occur through exposure of blood to mucous membranes. Shiferaw et al. ( 2012) reported the prevalence of this type of exposure to be higher (67.5%) than needlestick injuries (42.1%) among MWHs , although the statistical significance of this difference was not calculated (Figure 19). Figure 19: Self -reported incidents of exposure to mucous membranes by blood and bodily fluids by activity among medical waste handlers ( MWHs ) in hospitals in Ethiopia, after Shiferaw et al. (2012) . Overfilled or poorly handled bags were a factor in the majority of mucous membrane exposures. 59%41%35%7%11% 0% 10% 20% 30% 40% 50% 60% 70%Carrying of overfilled waste bags/sacksCompression of overfilled waste bags/sacksSharp-edged items tearing waste bags/sacksDisposal of placentaeSorting of soiled laundryBlood and bloodstained body fluid exposure to mucous membranes (67.5%) 39 Whereas sharps and needlestick injuries were the most prevalent injury to MWHs reported by seven of the authors reviewed here , there are several injury categories in which MHWs may experience lower prevalence compared to other waste workers. For instance, Mol et al. (2016) compared injuries experienced by MWHs with domestic waste collection workers finding that the latter experienced a lower prevalence of shar ps and needlestick injury but higher prevalence of traffic related injury, fracture or lesion ( Figure 20). Speculatively , these differences are unsurpris ing given that domestic waste collection workers spend more of their working day interacting with traffic, and less time handling waste with a high medical sharps concentration. However, the data are limited and further research is needed to understand the differences between these two exposure -resulting activities in different contexts ; socio - economic, cultural or otherwise . Figure 20: Comparison of injury types experienced by waste workers in Brazil, after Mol et al. (2016) . Although needlestick injuries are highest amongst MWH in comparison to other waste workers, MHWs experience fewer road traffic accidents and muscular lesions or fractures. 5.3. Risk of infection to medical waste handlers (MHWs) from contaminated sharps Two studies investigated the prevalence of blood borne virus infection among MHWs specifically. Franka et al. (2009) compared the rate of infection of MWHs with non -MWHs in Tripoli, Libya, finding the prevalence of HBV and HIV 7.14 ( p <0.04) and 15.74 ( p 0%10%20%30%40%50%60%70%80% Muscular lesion/fracture Needlestick/cuts TrafficProportion of workers who reported injury Domestic waste workers (n=461) Medical waste workers (n=61) 40 <0.0004) times greater in MHWs compared to non -MWHs and significantly ( p <0.005) higher incidents of HCV albeit at a very low rate of infection (0.3%). Arafa and Eshak (2020) included the results from the study by Franka et al. (2009) in a meta - analysis of HBV prevalence among MWHs in different contexts between 1992 and 2018, finding a significantly ( p=0.008) higher prevalence of HBV infection among MHWs ( Figure 21). The study highlighted considerable heterogeneity between the results modelled by each author and suggested that small samples sizes, variation in sociodemographic characteristics, and cross -sectional study design may have been factors which contributed to this variation. OverallDonchin (1992)Ferreira (1999)Franka (2009)Shiferaw (2011)Anagaw (2012)Mol (2016)Amsalu (2016)Yusuf (2018)Yizengaw (2018)Pooled OR 4.4914.93 (2.51, 9.68)0.9 (0.29, 2.8)7.14 (0.83, 61.79)8 (1.02, 62.88)6.32 (0.75, 53.37)1.77 (0.6, 5.25)0.53 (0.07, 3.94)11.48 (3.94, 33.45)0.96 (0.24, 3.8)2.88 (1.4, 5.93) 0.1 1 10 100Odds Ratio Study Figure 21: Studies that determined correlation between medical waste handling and hepatitis B (HBV ), adapted from Arafa and Eshak (2020) (95% CI I2=61.36%, p=0.008). Abbreviations: odds ratio (OR) (permission sought for reproduction) . Analysis of sub -groups by Arafa and Eshak (2020) identified a greater probability of African MWHs being infected by HBV. Arafa and Eshak (2020) highlight that workers are at particular risk compared to their counterparts in HICs as they are less likely to be vaccinated against HBV; unlikely to have health insurance; and have limited knowledge about the use of PPE or the risks associated with in jury from blo od-borne viruses. 5.4. Risk characterisation during the storage, collection and handling phase The semi -quantitative risk assessment shown in Table 10 is a reflection of the number of 41 MWHs who may suffer infection from blood -borne viruses as a consequence of injuries from medical sharps sustained at work. The risk in HICs is estimated to be low for all viruses, partial ly as a consequence of the low infection rates among the population. The risk of HIV infection in HICs is the lowest risk compounded by the low transmission risk of 0.3% from needlestick injuries. HBV risk is estimated to be very high in LIMICs, as a conse quence of the high rate of infection throughout the populations and also the strong likelihood of exposure through poor practices , equipment and training , which is endemic in many LIMICs. 42 Table 10: Risk characterisation summary for medical waste hazards during the collection, storage and handling phase. Haz. Pathway Receptor Geog. Evidence and justification for risk assessment Uncertainty (aleatoric and epistemic) Receptor vulnerability L S R Global receptor context HIV Medical sharps MWH ETH, BRA, SDN, GBR, LBY, Global  Prevalence of sharps and needlestick injuries among MWHs evidenced in LIMICs (Amsalu et al., 2016; Anagaw et al., 2012; Mol et al., 2016; Shiferaw et al., 2012; Yizengaw et al., 2018) but less so in HICs (Blenkharn and Odd, 2008) .  Speculatively, risk of exposure is lower in HICs as more stringent guidance, equipment and practices are in place to mitigate exposure.  Specific concern that laundry workers suffer unexpected exposure to needles which have been discarded with bedding (Shiferaw et al., 2012) .  Speculatively, disposal of sharps in soft waste bags may be commonplace in some contexts, though only limited evidence was revealed (Kanisek et al., 2018) .  Risk of HBV infection compared in meta -analysis (Arafa and Eshak, 2020) indicated odds ratio of 2.88 f or MWHs compared to general population.  Risk of HIV and HCV was not calculated but it may be reasonable to assume it is on the same ratio as for HCWs.  Evidence that many reported needlestick exposure events are underestimated (Cossart and deVries, 1994; Elmiyeh et al., 2004; Mercier, 1994)  Lack of procedural adherence common in HICs and LIMICs (Kanisek et al., 2018)  Some evidence of worker s carrying out procedures without gloves, particularly in LIMICs (Franka et al., 2009; Shiferaw et al., 2012) but also in HICs (Shiferaw et al., 2012) 1 4 4 HIC 2 5 10 LIMIC HBV 2 3 6 HIC 4 4 16 LIMIC HCV 2 3 6 HIC 3 4 12 LIMIC Blood - borne viruses Infectious soft waste MWH ETH  Limited evidence as most studies focus on needlestick and sharps, though greater prevalence of exposure to mucous membranes compared to sharps in one study (Shiferaw et al., 2012) .  na na na HIC 3 4 12 LIMIC Abbreviations: Geographical research context (geog.); likelihood (L); severity (S); risk (R); hazard being assessed (Haz.); high income country (HIC); low income and middle income countries (LIMIC); hepatitis C virus (HCV); hepatitis B virus (HBV); human immunodeficiency virus (HIV); medical waste handlers (MWH); healthcare workers (HCW). 43 6. Challenge 3: Reuse, recovery and disposal phase 6.1. Context Medical waste treatment and disposal is a critical component of any waste and resources recovery management system. It should involve sufficient controls to ensure that pathogens and potentially hazardous substances are either treated to reduce or eliminat e their hazardousness or contained and stored to prevent them interacting with human or environmental receptors ( Figure 22). The reuse, recovery and disp osal phase of medical waste represents the point in time where waste is no longer undergoing intermediate storage, has ceased being transported, and is being handled. However , Sections 6.2-6.5 describe how several activities that take place during the collection, processing and handling of waste can result in serious potential hazard exposur e to certain groups of people. 44 Figure 22: Hazard exposure conceptual model (source –pathway –receptor) associated with medical waste during the reuse, recovery and disposal phase . Abbreviations: hepatitis C virus (HCV); hepatitis B virus (HBV); human immunodeficiency virus (HIV). 6.2. Combustion of medical waste Combustion ( delimited here as complete oxidation under controlled engine ered conditions) is an effective method for the destruction of pathogens in medical waste ; and is, therefore, widely implemented in Europe, the US, and many other HICs (World Health Organization, nd). On-site incinerator units are common in Europe, but less so in the UK, reducing the risk Sources Pathways Receptor Route of human exposure Compartment Substance or material Transfer process Legend Used hollow needle Used suture needles HBV HCV HIV Other pathogens Adult citizens Materials used in devices & consumables Accidental percutaneous puncture Trauma Mucous membranes Open burning Occupational (informal) Infectious soft waste Substances in materials Landfill Atmosphere Dumpsite Centralised incineration Ash Reclamation for reuse On-site incineration Reuse Occupational (formal) Deliberate percutaneous puncture Inhalation Dust Soil Deposition Ingestion Food Uptake in crops Mouthing Child citizens Patients Recreational drug users Receptors 45 of transporting infectious waste to another facility and associated costs. Historically, three broad types of localised incinerator technologies have been used: dual -chamber; multiple - chamber; and rotary kilns (Nationa l Research Council (US) Committee on Health Effects of Waste Incineration, 2000) . In contrast to large -scale municipal or commercially run solid waste incinerators / energy form waste plants , smaller site -based facilities may be used infrequently or have a low throughput. This results in a requirement for significant auxiliary fuel to maintain the required combustion temperature as well as the temperature of the off - gasses (Batterman, 2004; National Research Council (US) Committee on Health Effects of Waste Incineration, 2000) . Medical waste itself has a markedly different composition to MSW. For instance, medical waste typically contains 30% wt. plastic (Pandelova et al., 2009) compared with approximately 11.5% wt. (Kaza et al., 2018) content in MSW worldwide. In particular, medical waste often has a high polyvinyl chloride ( PVC ) content through the inclusion of items such as: colostomy bags; blood bags; intravenous tubes; catheters; urine bags; plasma collection bags; infusion sets; draw sheets; and gloves (3R South Asia Expert Workshop, 2006) . Thus, when medical waste is combusted, significantly higher concentrations of dioxins and related compounds (DRCs) could be released into the air and ash (Table 11). Table 11: Comparison of dioxin related compounds (DRC) emissions from medical and MSW incinerators without emissions cleaning; after Hagenmaier et al. (1987) . Substance MSW incinerator (ng g-1 fly ash) Hospital waste incinerator (ng g-1 fly ash) Total dioxins 6.9-80.3 1,155 -1,737 Total furans 31.3-119.5 895-2,140 Modern incinerator plant designs incorporate air pollution control (APC) units that mitigate the emissions to meet strict limits imposed by the relevant authorities, some examples of which are shown in Table 12. Importantly, many small scale incinerators exist across LIMICs that feature no APC at all (Azage and Kumie, 2010; Bassey et al., 2006; Bazrafshan and Kord Mostafapoor, 2010; Manyele and Tanzania, 2004; Mesdaghinia et al., 2009; Musa et al., 2006; Phengxay et al., 2005; U nicomb et al., 2018) . 46 Table 12: Example emission thresholds; after World Health Organization (nd) . Pollutant Units US EPA emission limits EU emission limits Small Medium Large Daily average 0.5-hour average 0.5-8 hour average Particulates mg m-3 50 17 14 10 10, 30 CO mg m-3 18 1.6 9.8 50 100, 100 Dioxins/furans ng TEQ m-3 0.0099 0.011 0.027 0.1 HCl mg m-3 17 8.9 5.9 10 10, 60 SO 2 mg m-3 2.8 2.8 16 50 50, 200 Mercury (Hg) mg m-3 0.011 0.0027 0.00099 0.05 Lead (Pb) mg m-3 0.24 0.014 0.00053 All reference conditions: 273°K, 101.3kPa, 11% O 2, dry; small ≤ 91 kg hr-1, medium > 91 to 227 kg hr-1, and large > 227 kg hr-1; for half hour averages, at least 97% of concentrations must meet the first value and 100% must meet the second value. Abbreviations: carbon monoxide (CO); hydrochloric acid (HCl); mercury (Hg); lead (Pb); sulphur dioxide ( SO 2); United States Environmenta l Protection Agency (USEPA); European Union (EU). To provide an indication of the potential emissions from medical waste combustion, a selection of factors are presented in Table 13. The concentrations reported by Walker and Cooper (1992) are nearly 30 years old and it is conceivable that medical waste composition may have changed since then. Nonetheless, the Walker and Cooper data provide a useful comparison with the more contemporary concentrations reported by Trozzi et al. (2016) , because they indicate the characteris tics and quantity of substances emitted in incinerators currently operated in LIMICs. 47 Table 13: Typical emission factors for medical waste incinerators without emissions controls. Substance Units Walker and Cooper (1992) Trozzi et al. (2016) Red bag wastee General hospital wastef Pathologicalg Clinical waste Uncontrolled emissions incineration Uncontrolled rotary kiln incinerator Controlled air incinerator NO X mg kg-1 waste 1,450 c 1,350 c 4,290 c 2,300 1,800 CO b mg kg-1 waste 13,300 2,500 750 190 1,500 NMVOC mg kg-1 waste 700 700 SO X mg kg-1 waste 1,050 d 566 d 2,940 d 540 1,100 TSP mg kg-1 waste 17,000 2,300 BCa mg kg-1 waste 2,300 2,300 Pb µg kg-1 waste 50,800 28,600 4,310 62,000 36,000 Cd µg kg-1 waste 1,680 2,020 6,150 8,000 3,000 Hg µg kg-1 waste 110,000 25,500 637 43,000 54,000 As µg kg-1 waste 57.3 118 339 200 100 Cr (Total) µg kg-1 waste 202 422 3,900 2,000 400 Cr (VI) µg kg-1 waste NA 31.7 680 Fe µg kg-1 waste 10,300 4,780 NA Mn µg kg-1 waste 98.7 245 5,500 PM mg kg-1 waste 6,580 3,090 4,240 98,000 6,000 Ni µg kg-1 waste <208 <124 440 2,000 300 Benzene µg kg-1 waste 33.1 1,320 4,500 20 20 Dioxin/furan µg kg-1 waste 62.1 31.6 7.17 mg I -TEQ Mg-1 waste 40 40 Total 4 PAHs µg kg-1 waste 0.0400 0.0400 HCB mg kg-1 waste 100 100 HCl mg kg-1 waste 23,000 11,200 1,060 a Black carbon (BC) emission factors are assumed to equal those for elemental carbon (EC); b CO EF is high for red bag waste due to a large number of data points from one older, single chamber incinerator operating in batch mode. CO one for four multi -chamber incinerators averaged 5 ,860 mg kg-1; c as NO; d As SO; e red bag waste: includes any was te generated in the diagnosis, treatment, or immunisation of humans or animals, in research pertaining thereto, or in the production or testi ng of biologicals. For example, contaminated sharps, cultures and stocks of infectious agents, pathological waste, contaminated wastes from patient care, and discarded biologicals; f general hospital waste: includes a mixture of red bag waste and municipal waste generated by the hospital (for example, food waste, administrative waste, yard trash); g pathological waste: includes human and animal remains, tissues, body fluids, and cultures. Abbreviations: international toxic equivalent (I - TEQ); n on-methane volatile organic compounds (NMVOCs); total suspended particles (TSP); nitrogen oxides (NO X); carbon monoxide (CO); sulphur dioxides (SO X); total suspended particles (TSP); black carbon (BC); lead (Pb); cadmium (Cd); mercury (Hg); arsenic (As); chromium (Cr); iron (Fe); manganese (Mn); particulate matter (PM); nickel (Ni); hexachlorobenzene (HCB); hydrochloric acid (HCl) . Healthcare facility scale incinerators operating in LIMICs include sophisticated models with emission abatement (APC) , but more commonly, older, smaller types of installation, which range from industrial engineered facilities (Khan et al., 2019) through to locally constructed brick -built furnaces (Musa et al., 2006) . Open burning is also widely practiced, as shown in Table 14, which indic ates the proportion of medical waste treated by different methods in seven studies, ranging from 26% -100% of healthcare facilities reporting that open burning was used to treat medical waste. The proportions of medical waste open burned worldwide 48 are unknown, and the evidence presented in Table 13 does not constitute a representative global sample. However , it is estimated that MSW is open burned at a rate of between 13% and 50% across LIMICs (Bundhoo, 2018; Chanchampee, 201 0; Christian et al., 2010; Cogut, 2016; Nagpure et al., 2015; Pansuk et al., 2018; Reyna -Bensusan et al., 2018; US Environmental Protection Agency, 2001) , which may provide an indicator of how medical waste is treated in these socio -economic regions. Table 14: Proportion of waste or establishments reporting treatment of waste by different methods of medical waste. Ref. Context Sample Waste type Treatment type Proportion treated or no. of healthcare facilities reported Bazrafshan a nd Kord Mostafapoor (2010) IRN Hospitals (n=14) Healthcare waste Open burning Most common method Dumpsite Second most common method Incineration 21.4%a Mesdaghinia et al. (2009) IRN Primary care hospitals (n=120) Hazardous solid waste Incineration 32.5% Temp. incineration 8.3% Open burning 42.5% No treatment 16.7% Musa et al. (2006) NGA Static immunisation centres (n=13) Injection equipment Open burning 100% Azage and Kumie (2010) ETH Health centres (n=10) Healthcare waste Brick incinerator b 40% Open burning (pit) 60% Bassey et al. (2006) NGA Hospitals (n=2) Healthcare waste Brick incinerator b 18.3% Open burning (pit) 36.3% Burying 9.1% Municipal dumpsite 36.3% Phengxay et al. (2005) LAO Urban hospitals (n=11) Healthcare waste Open burning 73% Urban/rural hospitals (n=10) Open burning 90% Unicomb et al. (2018) BGD All Healthcare waste Burying 16% Open burning 35% Incineration 4% Dismantle/reuse 2% Nothing 43% Urban Burying 8% Open burning 26% Incineration 4% Dismantle/reuse 2% Nothing 58% Rural Burying 17% Open burning 36% Incineration 4% Dismantle/reuse 1% Nothing 41% a 35.7% of hospitals had incinerators; however, only 21.4% were in use; b local brick incinerator design. 49 No specific data were available to quantify emissions from open burning of medical waste ; however , the data for uncontrolled incineration ( Table 13) of medical wa ste can serve as an indicator. Even if an open fire re aches a high temperature at its peak combustion point, there will be periods at the start and end , and also areas on the periphery of the fire where incomplete combustion takes place (Secretariat of the Stockholm Convention on Persistent Organic Pollutants, 2008) . Though assisted by chimney effect, which draws air through the combustion chamber, even small scale, low technology incinerators may have a similar emission profile to waste that is openly burned (Mitchell et al., 20 19), as they lack auxiliary fuel that is often supplied through the addition of gas or oil to the process (Jiang et al., 2012) . Furthermore, when auxi liary heat is provided, poor quality fuel such as coal may be used which can result in combustion temperature of below 800 °C, 50 °C below the temperature recommended for medical waste combustion (Cogut, 2016) . Despite the shortcomings of open burning as a method for treating medical waste, the World Health Organization (2019c) apparently recommends it as a last resort treatment option where there are no alternatives, recommending it as a ‘safe final disposal’ method for sharps and infectious waste (World Health Organization, 2015) . It is not clear whether or not th e WHO has quantitatively assessed the relative risk of emissions from open burning in comparison to the risk of infection from medical waste that has been buried or open dumped, and no published evidence was found to substantiate the advice. The fact that medical waste incinerators are reported to be a source of DRC emissions broadly equivalent to MSW incinerators worldwide (Fiedler, 2007; Quaß et al., 2004) , but with considerably less throughput, it is likely that open burning is also a significant source. It is therefore recommended that further research is conducted to assess the evidence for the WHO’s advice in more detail to ascertain whether it is still up to date given the current state of knowledge in this area. 6.3. Reuse or recycling of medical waste The recovery of medical waste for reuse or recycling is a deeply con cerning practice, not only because of the risk of exposure to infection of patients, but also for the participants in the activity who are at significant risk of being infected by the devices they handle. The legality of reclaiming waste medical equipment for reuse is not reviewed here, but it is unlikely that syringe reuse is considered publicly acceptable in most, if not all countries (Patwary et al., 2011a; Patwary et al., 2011b; Stringer, 2011) . This creates a challenge for researchers when 50 gathering data to estimate the nature and magnitude of th e practice. Over 16 billion injections are administered every year (Hauri et al., 2004) and the World Health Organization (2016) estimates that approximately 40% of them are given reused injection equipment based on modelling by Hauri et al. (2004) and Simonsen et al. (1999) . It should be noted that reuse of medical devices is not inherently unsafe ; however , where equipment has been exposed to pathogens during its first use, there is a risk that they may be transmitted to a subsequent user. In this review, six articles were identified which evidence the reclamation of waste medical devices for reuse or recovery after they have been discarded ( Table 15). The most comprehensive study is by Patwary et al. (2011a) who observed informal recycling sector workers in Dhaka, Bangladesh, involved with the reclamation of medical equipment. The researchers estimated that a small number of waste pickers were involved with the activity, possibly only around 75 in Dhaka; suggesting that this is a highly specialist field of ‘entrepreneurs’, however it is impossible to accurately estimate the numbers due to the informal and illicit nature of the business. Table 15: Evidence of reclamation of medical waste by the informal recycling sector for reuse or recycling . Ref. Context Survey sample Observed reclamation practice Taghipour and Mosaferi (2009) IRN Review of waste management practices at healthcare facilities (n=875)  Survey team observed medical waste being collected for recycling at one hospital.  Recorded reports from hospital staff that used injection equipment is occasionally sto len for injection of illegal drugs. Yusuf et al. (2018) NGA Survey of waste pickers (n=236)  52.5% of waste pickers have been engaged in medical waste scavenging at least once. Patwary et al. (2011a) BGD Survey (n=45) of waste pickers specialising in medical waste recovery  Identified members of the informal recycling sector engaged in medical waste recovery for reuse and recyclin g and interviewed them about their practices. Unicomb et al. (2018) BGD Review of waste management practices at healthcare facilities (n=875)  2% of healthcare facilities admitted selling single use medical equipment for reuse Syed et al. (2012) BGD Review of medical waste management (n=36)  Indication that medical waste is recovered for reuse and recycling by informal recycling sector Stringer (2011) BGD; TZA Review of healthcare waste management and human rights  Includes photographic and personal observation evidence of collection, separation and processing of waste medical devices for recycling and reuse in Bangladesh and Tanzania Patwary et al. (2011a) found evidence that a wide range of medical equipment was being recovered for reuse, including: scalpels, knives, saline drip bags, cotton, and injection 51 equipment. This clearly indica tes that, at least in Dhaka, there are buyers for used medical equipment within or on the periphery of the healthcare sector. The existence of this market in Bangladesh is supported by evidence from Unicomb et al. (2018) who carried out a nationwide survey of medical facilities acros s Bangladesh, finding that 2% of facilities admitted selling single use medical devices for reuse. Strin ger (2011) also provided multiple photographic examples and personal observation data that evidence medical waste collection, sorting and recovery for reuse in Tanzania and Bangladesh. Similarly limited evidence exists for the reclamation of material f or recycling from medical waste. The cohort studied by Patwary et al. (2011a) consiste d of 20 waste pickers who collected medical waste plastics metal and glass , which were sold to reprocessors or dealers (‘junk shops’). In the case of metals, plastics and glass, the temperatures reached in reprocessing are likely to be high enough to limit the risk of exposure to product users. However, the risks to the collectors, sorters, and reprocessors are likely to be considerable. Almost no further evidence was identified in this review except a single BBC television news article (BBC Urdu, 2013) that reported on the practice in Lahore, Pakistan. The article showed video evidence of material being collected and passed to plastics r ecyclers for reprocessing. It also indicated that they might be used in the production of drinking straws : however, the direct link between the two streams was not directly stated and remains ambiguous. 6.4. Infections from reuse of injection equipment The re capping of needles on injection equipment is a common practice across many LIMICs (Enwere and Diwe, 2014; Macaulay and Odiase, 2016; World Health Organization, 2014) and some HICs (NHS Scotland, nd; Watterson, 2004) , enabling healthcare providers to reduce the cost of replacing equip ment. This practice not only exposes HCWs to the risk of infection, but also patients who are seeking to improve their health rather than endanger it further. The worldwide prevalence of injection equipment reuse was investigated by Hauri et al. (2004) who estimated that approximately 41% of injections are carried out with reused equipment ( Figure 23). The study found that rates of injection equipment reuse were extremely low in Western Europe and North America, and high in parts of Eastern 52 Mediterranean and Western Pacific Regions, which showed rates of 70 –75% respectively (details of World Bank sub -regions are provided in Table S 4 ). Figure 23: Reuse of injection equipment in World Health Organization ( WHO ) Global Burden of Disease regions (detailed in Table S 4 ); after Hauri et al. (2004) . The rates of blood borne virus infection from reused injection equipment were also modelled by Hauri et al. (2004) , who found the infection profile dominated by HBV infections across all regions, with comparatively large numbers of infections across Western Pacific and South East Asia regions ( Figure 24). As with the global burden of disease modelling of risks to HCWs carried out by (Prüss‐Üstün et al. , 2005) , the modelled exposure presented by Hauri et al. (2004) (Figure 24) is not always proportional to the recapping prevalence ( Figure 23); as in the case of the Western Pacific Region. 0.40.30.00.23.00.00.40.63.00.71.4 1.81.71.71.71.32.53.11.51.01.72.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5AfricaAfrica EAmericas BAmericas DEastern Mediterranean DEurope BEurope CSouth East Asia BSouth East Asia DWestern Pacific Region BWorld Injections per person per annumInjections with reused needle Injections with unused needle 53 Figure 24: Infections due to reuse of injection equipment in World Health Organization (WHO ) Global Burden of Disease regions (detailed Section S.4 ); after Hauri et al. (2004) . The rate of infection from HIV was comparatively low in all regions according to Hauri et al. (2004) , with the highest prevalence of infection in South East Asia with 200,000 new cases per a nnum. In the African regions, the rate of HIV infection from used injection equipment was modelled to be low, despite the high numbers of people living with HIV which is up to 20% of the population in some areas (UNAIDS, 2018b) . This is partly a result of the low reuse rate (15 -18%) reported. But, also the fact that HIV transmission risk is just 0.3% compared with HCV which is 3% , and with HBV which is 33% (Cheng et al., 2017) . 6.5. Sharps and needlestick injuries to informal waste collectors Whereas small numbers of informal waste workers are known to purposefully seek medi cal waste as a valuable resource to be reused or recycled, waste pickers also encounter medical waste accidentally while searching for other valuable materials (Zolnikov et al., 2019) . Consequently, informal waste workers are exposed to infection from blood -borne viruses and 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0AfricaAfrica EAmericas BAmericas DEastern Mediterranean DEurope BEurope CSouth East Asia BSouth East Asia DWestern Pacific Region B Number of infections (millions people per annum)Number of HBV infections Number of HCV infections Number of HIV infections 54 other pathogens, often unexpectedly, as medical waste is collected, processed and co - disposed along with MSW. Pathogens from medical waste may enter the body through the skin or mucous membranes. Here we compare six studies report ing the prevalence of percutaneous exposure to pathogens among informal waste collectors, rang ing 3.4 -61.6% (Table 16). The studies were carried out in South Asia, South America and West Africa, indicating that the risk of injury to informal waste workers may be g eographically widespread. Table 16: Prevalence of sharps and needlestick injuries among waste pickers from cross - sectional surveys. Ref. Year Context Survey sample Work site Injury Period Prevalence Black et al. (2019) 2019 NPL 1,278 Not reported Medical sharps 12 month 3.4% Cunningham et al. (2012) 2012 PRY 102 Landfill Needlestick Lifetime 23% Exposed to blood other than own 13% Parizeau (2015) 2015 ARG 397 Streets Needlestick Lifetime 10% Chokhandre et al. (2017) 2017 IND 200 Dumpsite b Needles and glass 6 month 35%a Patwary e t al. (2011a) 2011 BGD 45c Streets, treatment plants, dumpsites Medical sharps Lifetime 56% Afon (2012) 2012 NGA 112 Dumpsite Sharp objects Lifetime 61.6% a Laceration (ne edles and glass) 35% (70/200) compared to control group 11% (11.7/103) (Chi squared = 92.58; p = 0.000); b the method reports that the waste pickers lived near the dumpsite so it is assumed that they work there too, however this was not explicitly clarifie d; c all interviewees were medical waste specialists. The lowest lifetime prevalence of 3.4% reported by Black et al. (2019) was observed in a comparatively large sample of waste pickers in Nepal and the highest lifetime prevalence (61.6%) was reported by Afon (2012) in a study of waste pickers working in Nigeria. The large range could be a result of differing medical waste disposal practices in each country whereby infectious medical waste is separated and disposed of separa tely in one country, reducing exposure to informal collectors, and frequently co -disposed in another. The large differences may also be related to the sample selection. For instance, Black et al. (2019) did not report the location where the survey respondents carried out their activities. It is therefore feasible that the workers interviewed worked in locations where medical waste was not disposed of, such as on urban streets or door -to-door. Conversely, the subjects surve yed by Afon (2012) , worked exclusively on dumpsites, which speculatively, are mor e 55 likely to contain medical waste that has been co -disposed with MSW . Moreover, the categories reported by researchers were similar, but not fully aligned. For instance, the category reported by Afon (2012) was ‘wound from sharp objects’ which could include non - medical sharps and inflate the reported prevalence. Similarly, the categor y reported by Chokhandre et al. (2017 ) included injuries from glass. In summary, there is little doubt that informal waste collectors are occupationally exposed to pathogens from medical waste in several global locations. However, there is significant uncertainty over the prevalence of thi s exposure, and it is therefore challenging to determine the risk to their health. There are possibly 10 to 20 million informal waste workers globally collecting virtually all of the post -consumer recyclate in LIMICs (Lau et al., 2020; Wilson et al., 2015) . The continued co -disposal of medical waste within their feedstock represents a serious and unacceptable ris k that would not be tolerated in the formal economy, highlighting continued inequ ality between the two sectors. 6.6. Risk characterisation for medical waste during the reuse recovery, treatment and disposal phase Despite the comparatively high levels of chlorin e in medical waste, the qualitative risk assessment shown in Table 17 indicates a very low level of risk from medical waste incineration in HICs. This is because facilities in these countries are subject to strict regulation and enforcement to ensure that emissions are restricted to very low levels. In contrast, incineratio n of medical waste in LIMICs is categorised as medium high risk as facilities in countries in these income group categories are less likely to incorporate emissions cleaning in to their facilities. Evidence suggests that open burning or rudimentary incine ration is widely practiced in LIMICs (Azage and Kumie, 2010; Bassey et al., 2006; Bazrafshan and Kord Mostafapoor, 2010; Manyele and Tanzania, 2004; Mesdaghinia et al., 2009; Musa et al., 2006; Phengxay et al., 2005; Unicomb et al., 2018) . Given the high content of plastics, particularly chlorinated plastics, the emissions are likely to be extremely hazardous to those in close proximity and beyond. Therefore , this is scored here as representing a very high risk to human health due to significant emissions of potentially hazardous substances highlighted in our research. Open burning is not assessed in HICs , because the practice is considered to be unlikely to occur . 56 The population risk from reused injection equipment qualitatively assessed in Table 18, shows a very high risk for HBV, and a medium high risk of HCV in LIMICs. The risk in HICs is scored very low for HIV and HBV, partly because of the low prevalence among the population but also the low rate of injection equipmen t reuse in countries under this income category. The risk of infection from sharps injury to members of the informal waste collection sector is assessed to be very high for workers who specialise in medical waste recovery. The risk is medium -high for thos e who recover other materials as their encounters with injection equipment are considered to be less frequent than the medical waste specialists. Both sets of workers have been shown to have a low rate of personal protective equipment (PPE) use, which increases their chances of viral transmission. 57 Table 17: Risk characterisation summary for medical waste hazards during the recovery, treatment and disposal phase: combustion of me dical waste . Activity Haz. Pathway Receptor Geog. Evidence and justification for risk assessment Uncertainty (aleatoric and epistemic) Receptor vulnerability L S R Global receptor context Medical waste incineration Potentially hazardous substances (particularly DRCs) Atmosphere/ inhalation Population IRN, NGA, ETH, LAO, BGD  Medical waste typically contains 30% plastic (Pandelova et al., 2009) compared to approximately 11.5% (Kaza et al., 2018) content in MSW worldwide.  PVC is used extensively in single use medical products (3R South Asia Expert Workshop, 2006) which results in a high chlorine content and thus higher DRC emissions when it is combusted (Fiedler, 2007; Hagenmaier et al., 1987; Quaß et al., 2004) .  Modern incinerator designs, which are prevalent in HICs, incorporate components that effectively mitigate emissions of potentially hazardous substances, however many small scale incinerators exist across LIMICs that have no emission cleaning at all (Azage and Kumie, 2010; B assey et al., 2006; Bazrafshan and Kord Mostafapoor, 2010; Manyele and Tanzania, 2004; Mesdaghinia et al., 2009; Musa et al., 2006; Phengxay et al., 2005; Unicomb et al., 2018) .  Evidence for potential emissions from medical waste incinerators which have no pollution control devices indicate emissions of p otentially hazardous substances (Trozzi et al., 2016; Walker and Cooper, 1992) which are far greater than the emissio ns thresholds in Europe and the US (World Health Organization, nd) .  No specific data available to quantify emissions from open burning of medical waste, however data for uncontrolled incineration of medical waste are indicative.  A priori data suggests even if open fires reach high temperatures at peak combustion, periods at the start and end and also areas on the fire periphery where incomplete combustion takes place.  Emissions cleaning likely to be implemented in most cases to comply with stringent legal thresholds (World Health Organiza tion, nd). 1 2 2 HIC  Lack of emissions cleaning in medical waste incinerators in LIMICs (Azage and Kumie, 2010; Bassey et al., 2006; Bazrafshan and Kord Mostafapoor, 2010; Manyele and Tanzania, 2004; Mesdaghinia et al., 2009; Musa et al., 2006; Phengxay et al., 2005; Unicomb et al., 2018) .  Residents living nearby have no choice but to inhale pollutants from these activities. 3 4 12 LIMIC Waste workers (formal and informal)  Informal waste workers unlikely to wear respiratory protective equipment 3 4 12 Medical waste open burning Potentially hazardous substances (particularly DRCs) Atmosphere/i nhalation Population IRN, NGA, ETH, LAO, BGD  Open burning is practiced as a method of medical waste disposal throughout LIMICs (Azage and Kumie, 2010; Bassey et al., 2006; Bazrafshan and Kord Mostafapoor, 2010; Mesdaghinia et al., 2009;  No evidence was found to compare the relative risk of pathogen infection from medical waste with exposure to  Lack of emissions cleaning in medica l waste incinerators in LIMICs (Azage and Kumie, 2010; Bassey et 4 5 20 LIMIC 58 Activity Haz. Pathway Receptor Geog. Evidence and justification for risk assessment Uncertainty (aleatoric and epistemic) Receptor vulnerability L S R Global receptor context Musa et al., 2006; Phengxay et al., 2005; Unicomb et al., 2018) .  The World Health Organization (2019c) , (WHO) still recommends pen burning as a last resort treatment option where there are no alternatives citing it as a ‘safe final disposal’ method for sharps and infectious waste (World Health Organization, 2015) .  The fact that medical waste incinerators are reported to be a source of DRC emissions broadly equivalent to MSW incinerators worldwide (Fiedler, 2007; Quaß et al., 2004) , but with considerably less throughput, it is li kely that open burning is also a significant source. hazardous substances from open burning of medical waste. al., 2006; Bazrafshan and Kord Mostafapoor, 2010; Manyele and Tanzania, 2004; Mesdaghinia et al., 2009; Musa et al., 2006; Phengxay et al., 2005; Unicomb et al., 2018) .  Residents living nearby have no choice but to inhale pollutants from these activities. Waste workers (informal)  Informal waste workers unlikely to wear respiratory protective equipment 4 5 20 Abbreviations: Geographical research context (geog.); likelihood (L); severity (S); risk (R); hazard being assessed (Haz.); high income country (HIC); low income and middle income countries (LIMIC); hepatitis C virus (HCV); hepatitis B virus (HBV); human immunodeficiency virus (HIV); medical waste handlers (MWH) ; healthcare workers (HCW); dioxins and related compounds (DRC); polyvinyl chloride (PVC). 59 Table 18: Risk characterisation summary for medical waste hazards during the reco very, treatment and disposal phase: exposure to pathogens . Haz. Pathway Receptor Geog. Evidence and justification for risk assessment Uncertainty (aleatoric and epistemic) Receptor vulnerability L S R Global receptor context HIV Medical sharps Population Global  Recapping of needles on injection equipment is a common practice across many LIMICs (Enwere and Diwe, 2014; Macaulay and Odiase, 2016; World Health Organization, 2014) .  41% of injections are carried out with reused equipment (Hauri et al., 2004) .  The rate of infection from HIV is comparatively low in all regions (Hauri et al., 2004) , with the highest prevalence of infection in South East Asia with 200,000 new cases per annum.  In African regions, the rate of HIV infection from used injection equipm ent is low (Hauri et al., 2 004) , despite the high numbers of people living with HIV which are up to 20% of the population in some areas (UNAIDS, 2018b) . This is partly a result of the low reuse rate (15% to 18%) reported. But, also the fact that HIV transmission risk is just 0.3% compare d to HCV which is 3% and HBV which is 33% (Cheng et al., 201 7).   Those in receipt of healthcare are unlikely to be aware that injection equipment may have been reused 1 4 4 HIC 2 5 10 LIMIC HBV 1 3 3 HIC 4 4 16 LIMIC HCV 2 3 6 HIC 3 4 12 LIMIC Blood - borne viruses Medical sharps Informal waste collectors NPL, PRY, ARG, IND, BGD, NGA  Strong evidence of sharps injury prevalence (3.4% to 61.6%) to informal waste collectors (Afon, 2012; Black et al., 2019; Chokhandre et al., 2017; Cunningham et al., 2012; Parizeau, 2015; Patwary et al., 201 1a).  Particular risk to medical waste handling specialists in the informal recycling sector with four sources indic ating the practice (Patwary et al., 2011a; Stringer, 2011; Taghipour and Mosaferi, 2009; Unicomb et al., 2018) .  Various methodological issues, such as lack of reporting on sample selection, and differing terminology over the cau se of injury.  Risk of virus contraction not calculated.  Limited knowledge about specialists in medical waste reclamation for reuse as the practice is considered illicit in most countries and institutions (Patwary et al., 2011a; Patwary et al., 2011b; Stringer, 2011) .  Informal waste workers are rarel y equipped with ballistic protective clothing to mitigate the risk of injury from used injection equipment. 3 5 15 LIMIC Informal medical waste collectors BGD  While medical waste specialist informal waste workers anticipate percutaneous injury, they seldom wear PPE. 4 5 20 Abbreviations: Geographical research context (geog.); likelihood (L); severity (S); risk (R); hazard being assessed (Haz.); high income country (HIC); low income and middle income countries (LIMIC); hepatitis C virus (HCV); hepatitis B virus (HBV); human immunodeficiency virus (HIV); medical waste handlers (MWH); healthcare workers (HCW). 60 7. Conclusions This sy stematic review brings together and organises , for the first time in one place, the extensive array of research that exists on the safe management of medical devices and consumables (medical waste) at the end of their engineered life (waste , after-use phase). We summarise the evidence through the conceptualisation of haz ard-pathway -receptor combinations ; which were subsequently semi -quantitatively assessed and ranked to indicate and enable prioritisation of mitigating actions. These mapped pathways were presented in a series of conceptual flow diagrams based on the phase of waste management / mismanagement, a combination of which is shown in Figure 25. Figure 25: Hazard exposure conceptual model (source –pathwa y–receptor) for medical waste . Predominantly, risks were greater in LIMICs where the resource reduces the capability of actors in the system to develop, implement and maintain safe systems of work. Risk to human 61 health during the waste generation phase was almost entirely cantered around the infection of healthcare workers (HCWs) with blood -borne pathogens such as HIV, HBV, and HCV via percutaneous puncture with used injection, suture, or phlebotomy equipment. Several studies exist that determine prevale nce, particularly by authors examining the African continent, and these are supported by high quality global burned of disease studies (Prüss -Üstün et al., 2016) that model the potential harm from these types of injury across World Health Organizations regions. The higher rate of transmission for HBV resulted in a high indicative risk according to our semi -quantitative process, particularly, and overwhelmingly centred on LIMICs, but also in Europe. However , in the case of the latter, the cause for concern is lower as the capability to treat patients contracting the disease is greater. A similar picture is evident for medical waste handlers ( MWHs) who, especially in LIMICs , are at considerable risk of contracting HBV as well as other blood borne infections as a result of accidental puncture with sharps that have been stored in non -protective containers. Even in HICs, the rate of percutaneous p uncture with used needles was significant amongst MWHs, despite the generally higher standards of waste handling and storage practices. A deeply concerning practice amongst a specialist group of waste pickers involves the reclamation of used medical equip ment to be cleaned and sold for reuse by substance abusers and medical waste providers. Its highlight illicit nature means that the scale of this activity is inherently challenging to quantify, with the few sources of evidence indicating that it is a compa ratively small industry. However , the risk to the workers themselves and the potential prevalence of the many materials that might be collected is a serious cause for concern that warrants fu rther research and investigation to establish and quantify the le vel of risk. Even for those waste pickers who are not engaged in this activity, the risks posed by medical waste are high in countries where it is frequently co -disposed with MSW ; both in unprotected, unlocked containers, and also on the dumpsites, landf ills and open terrestrial dumps. An inexorable dilemma is often faced by HCWs and MWHs in some LIMICs in that they must decide between managing potentially infected waste by sending for unprotected land disposal (open dumping or co -disposal with MSW) and ope n burning or rudimentary incineration. Even the World Health Organization (2015) and (2019c) recommend open burning as a last resort, but the evidence for making such a decision was not revealed in our research. The h igh content of plastics, particularly PVC, will undoubtedly result in the release of DRCs , which will persist in soil, and enter the atmosphere where they will expose the 62 people tending the combustion process as well as those living within the local area a nd beyond. A recommendation of this study is that the relative risk of each of these approaches to disposal is urgently quantified to determine the risk and prioritise the activities that mitigate the most potential harm. Although some methodologically robust studies of specific aspects of medical waste management were revealed in this review, the majority, especially in the parts of the world where harm is most evident, were insufficiently detailed to properly assess and derive a quantitative risk to hu man health. As with the waste sector as a whole, medical waste management appears not to have received sufficient research attention, being on the margins of an already unde rfunded sector. The mismanagement of medical waste is somewhat ironic in the contex t that the waste has been generated, where the imperative is to prevent cure and rehabilitate those who have experienced ill health. When waste is not passed through a system of protective stewardship and ultimately rendered harmless, it poses an ongoing a nd obvious risk to human health, either through the pathogens contained within or through the emissions released when it is combusted in an uncontrolled fire. Whilst these risks have been considered and demonstrated as being unacceptable to both workers an d the society at large, the lack in sufficiently well-resourced research in this field and its low volume unlikely to result in timely and significant reduction in harm. 63 CRediT author statement Ed Cook: Conceptualization; Data curation; Formal Analysis; Investigation; Methodology; Project administration; Resources; Validation; Visualization; Writing – original draft; Writing – review & editing. Costas A. Velis: Conceptualization; Data curation; Formal Analysis; Funding acquisition; Investigation; Methodo logy; Project administration; Resources; Software; Supervision; Validation; Visualization; Writing – original draft; Writing – review & editing. Anne Woolridge : Formal Analysis; Funding acquisition; Project administration; Resources; Supervision; Visualiza tion; Writing – original draft; Writing – review & editing. Petra Stapp: Data curation; Investigation; Writing – original draft. Sarah Edmondson : Data curation; Investigation. Acknowledgements We are grateful to the Technical Advisory Board of the Engineering X Safer End of Engineered Life programme , of the Royal Academy of Engineering for their steering and insightful feedback, especially on early versions of this research and manuscript. We thank the Programme Board, chaired by Professor William P owrie FREng & the Academy staff, especially Hazel Ingham and Shaarad Sharma who provided support throughout the process. Ad hoc advice, guidance and criticism was provided by multiple stakeholder representatives, as listed in the relevant Engineering X rep ort. We are grateful to Nick Rigas, (D -Waste) for the presentation of infographics. The research communicated and opi nions expressed here are author s’ alone. Financial This work was made possible by the Engineering X Safer End of Engineered Life program me which is funded by Lloyd’s Register Foundation. Engineering X is an international collaboration, founded by the Royal Academy of Engineering and Lloyd’s Register Foundation, that brings together some of the world’s leading problem -solvers to address the great challenges of our age. The Engineering X Safer End of Engineered Life programme which seeks to improve safety and reduce harm caused by the decommissioning, dismantling and disposal of engineered products, artefacts, and structures at the end of the ir life. 64 8.