Query: contact tracing and isolation on COVID-19

title: COVID 19 epidemic in Switzerland: on the importance of testing, contact tracing and isolation.
abstract: Switzerland is among the countries with the highest number of coronavirus disease 2019 (COVID 19) cases per capita in the world. There are likely many people with undetected SARS CoV 2 infection because testing efforts are currently not detecting all infected people, including some with clinical disease compatible with COVID 19. Testing on its own will not stop the spread of SARS CoV 2. Testing is part of a strategy. The World Health Organization recommends a combination of measures: rapid diagnosis and immediate isolation of cases, rigorous tracking and precautionary self isolation of close contacts. In this article, we explain why the testing strategy in Switzerland should be strengthened urgently, as a core component of a combination approach to control COVID 19.

title: Contact tracing and isolation of asymptomatic spreaders to successfully control the COVID 19 epidemic among healthcare workers in Milan (Italy)
abstract: To study the source, symptoms, and duration of infection, preventive measures, contact tracing and their effects on SARS CoV 2 epidemic among healthcare workers (HCW) in 2 large hospitals and 40 external healthcare services in Milan (Italy) to propose effective measures to control the COVID 19 epidemic among healthcare workers.  Epidemiological observational study.  Two large hospitals and 40 territorial healthcare units, with a total of 5700 workers. Participants 143 HCWs with a SARS CoV 2 positive nasopharyngeal (NF) swab in a population made of 5,700 HCWs.  Clinical data on the history of exposure, contacts inside and outside of the hospital, NF swab dates and results. A daily online self reported case report form consisting of the morning and evening body temperature and 11 other symptoms (cough, dyspnoea, discomfort, muscle pain, headache, sore throat, vomiting, diarrhoea, anosmia, dysgeusia, conjunctival hyperaemia)  Most workers were tested and found positive due to a close contact with a positive colleague (49% followed by worker initiated testing due to symptoms (and unknown contact, 28% and a SARS CoV 2 positive member of the family (9.8% 10% of NF swabs performed in the framework of contact tracing resulted positive, compared to only 2.6% through random testing. The first (index) case caused a cluster of 7 positive HCWs discovered through contact tracing and testing of 250 asymptomatic HCWs. HCWs rarely reported symptoms of a respiratory infection, and up to 90% were asymptomatic or with mild symptoms in the days surrounding the positive NF swab. During the 15 day follow up period, up to 40% of HCWs reported anosmia and dysgeusia/ageusia as moderate or heavy, more frequently than any other symptom. The time necessary for 95% of HCWs to be considered cured (between the positive and two negative NF swabs) was 30 days.  HCWs represent the main source of infection in healthcare institutions, 90% are asymptomatic or with symptoms not common in a respiratory infection. The time needed to overcome the infection in 95% of workers was 30 days. Contact tracing allows identifying asymptomatic workers which would spread SARS CoV 2 in the hospital and is a more successful strategy than random testing.

title: Using real world contact networks to quantify theeffectiveness of digital contact tracing and isolation strategies for Covid 19 pandemic
abstract: Contact tracing, both manual and potentially with digital apps, is considered a key ingredient in the control of infectious disease outbreaks, and in the strategies making it possible to alleviate the lock down and to return to a quasi normal functioning of society in the COVID 19 crisis. However, the current leading modeling framework for evaluating contact tracing is highly stylized, lacking important features and heterogeneities present in real world contact patterns that are relevant for epidemic dynamics. Here, we fill this gap by considering a modeling framework extensively informed by real world, high resolution contact data to analyze the impact of digital (app based) containment strategies for the COVID 19 pandemic. More specifically, we investigate how well contact tracing apps, coupled with the quarantine of identified contacts, can mitigate a spread in realistic scenarios such as a university campus, a workplace, or a high school. We find that restrictive policies are more effective in confining the epidemics but come at the cost of quarantining a large part of the population with a consequent social cost. It is possible to design less limiting policies, considering at risk only contacts with longer exposure and at shorter distance, in order to avoid this effect. Our results also show that isolation and tracing alone are unlikely to be sufficient to keep an outbreak under control, and additional measures need to be implemented simultaneously. Moreover, we confirm that a high level of app adoption is crucial to make digital contact tracing an effective measure. Finally, given the currently implemented infectiousness, we find that strategies focusing on long exposure times, even for weak links, perform better than approaches that emphasize close range contacts for shorter time periods. Our results have implications for the app based contact tracing efforts currently being implemented across several countries worldwide.

title: Modelling the Health and Economic Impacts of Population Wide Testing, Contact Tracing and Isolation (PTTI) Strategies for COVID 19 in the UK
abstract: The COVID 19 epidemic in the UK has resulted in over 280,000 reported cases and over 40,000 deaths as of 5th June 2020 In the context of a slower i

title: Contact tracing and isolation reduces Covid 19 incidence in a structured agent based model
abstract: The World Health Organization has identified contact tracing and isolation (CTI) as a key strategy to slow transmission of SARS CoV 2. Structured agent based models (ABMs) provide a means to investigate the efficacy of such strategies in heterogeneous populations and to explore the impact of factors such as changes in test turnaround times (TaT)  We developed a structured ABM to simulate key SARS CoV 2 transmission and Covid 19 disease progression dynamics in populations of 10,000 agents. We ran 10,000 simulations of each of three scenarios: (1) No CTI with a TaT of two days, (2) CTI with a TaT of two days, and (3) CTI with a TaT of eight days. We conducted a secondary analysis in which TaT values were varied from two to 11. The primary outcome for all analyses was mean total infections.  CTI reduced the mean number of infections from 5,577 to 4,157 (a relative reduction of 25.5% when TaT was held steady at two days. CTI with a TaT of eight days resulted in a mean of 5,163 infections (a relative reduction of 7.4% compared to no CTI and a TaT of two days) In the secondary analysis, every additional day added to the TaT increased the total number of infections with the greatest increase in infections between four and five days, and the smallest increase between ten and eleven days.  In a structured ABM that simulates key dynamics of Covid 19 transmission and disease progression, CTI results in a substantial reduction in the mean number of total infections. The benefit is greater with shorter TaT times, but remained substantial even with TaTs of eight days. The results suggest that CTI may play a critical role in reducing the size of outbreaks and that TaTs should be kept as short as possible in order to maximise this benefit.

title: Dysgeusia and dysosmia in asymptomatic COVID 19 patients for contact tracing and isolation
abstract: We read with interest a case report in this journal regarding PCR positive urinary sample in an asymptomatic COVID 19 patient, indicating a possible usefulness for screening  Sim.

title: Modelling the Dynamics of COVID 19 Disease with Contact Tracing and Isolation in Ghana
abstract: We have formulated a mathematical model to investigate the transmission dynamics of the current novel COVID 19 disease outbreak in Ghana. The coronavirus originated from Wuhan, China. Majority of people who contact the disease experience mild to moderate respiratory illness and recover. The elderly and people with underlying health issues experience severe complications. A plethora of measures have been taken by the government of Ghana to curtail the disease. The model considers, among other things, quarantining and testing of immigrants, contact tracing and isolation in the form of quarantining or hospitalization, as control measures in mitigating the spread of the pandemic. Our model considers the following classes: susceptible, exposed, infectious, quarantine, treatment and recovery class. The steady state solution was calculated and the basic reproduction number for this model calculated and used as a threshold to determine the asymptotic behaviour of the model. Our analytical and numerical results show a close dependence of the basic reproductive number on epidemic parameters. The aim of this paper was to incorporate the various intervention strategies into the model and ascertain their impact on COVID 19. Some of the methods employed in the analysis include the Next Generation Matrix and the Jacobian Matrix. Our simulations results correlate well with data and indicate that early quarantine and a high quarantine rate are crucial to the control of COVID 19. Thus, current preventative measures, such as isolation, contact tracing and treatment are, indeed, critical components in the control of COVID 19 until appropriate cure or vaccine is found.

title: Isolation and contact tracing can tip the scale to containment of COVID 19 in populations with social distancing
abstract: Novel coronavirus (SARS CoV 2) has extended its range of transmission in all parts of the world, with substantial variation in rates of transmission and severity of associated disease. Many countries have implemented social distancing as a measure to control further spread.  We evaluate whether and under which conditions containment or slowing down COVID 19 epidemics are possible by isolation and contact tracing in settings with various levels of social distancing. We use a stochastic transmission model in which every person generates novel infections according to a probability distribution that is affected by the incubation period distribution (time from infection to symptoms) distribution of the latent period (time from infection to onset of infectiousness) and overall transmissibility. The model distinguishes between close contacts (e.g. within a household) and other contacts in the population. Social distancing affects the number of contacts outside but not within the household.  The proportion of asymptomatic or unascertained cases has a strong impact on the controllability of the disease. If the proportion of asymptomatic infections is larger than 30% contact tracing and isolation cannot achieve containment for an R0 of 2.5. Achieving containment by social distancing requires a reduction of numbers of non household contacts by around 90% Depending on the realized level of contact reduction, tracing and isolation of only household contacts, or of household and non household contacts are necessary to reduce the effective reproduction number to below 1. A combination of social distancing with isolation and contact tracing leads to synergistic effects that increase the prospect of containment.  Isolation and contact tracing can be an effective means to slow down epidemics, but only if the majority of cases are ascertained. In a situation with social distancing, contact tracing can act synergistically and tip the scale towards containment, and can therefore be a tool for controlling COVID 19 epidemics as part of an exit strategy from current lockdown measures.

title: Global strategies and effectiveness for COVID 19 prevention through contact tracing, screening, quarantine, and isolation: a systematic review
abstract: COVID 19 is an emerging disease caused by highly contagious virus called SARS CoV 2. It caused an extensive health and economic burden around the globe. There is no proven effective treatment yet, except certain preventive mechanisms. Some studies assessing the effects of different preventive strategies have been published. However, there is no conclusive evidence. Therefore, this study aimed to review evidences related to COVID 19 prevention strategies achieved through contact tracing, screening, quarantine, and isolation to determine best practices.  We conducted a systematic review in accordance with the PRISMA and Cochrane guidelines by searching articles from major medical databases such as PubMed/Medline, Global Health Database, Embase, CINAHL, Google Scholar, and clinical trial registries. Non randomized and modeling articles published to date in areas of COVID prevention with contact tracing, screening, quarantine, and isolation were included. Two experts screened the articles and assessed risk of bias with ROBINS I tool and certainty of evidence with GRADE approach. The findings were presented narratively and in tabular form.  We included 22 (9 observational and 13 modeling) studies. The studies consistently reported the benefit of quarantine, contact tracing, screening, and isolation in different settings. Model estimates indicated that quarantine of exposed people averted 44 to 81% of incident cases and 31 to 63% of deaths. Quarantine along with others can also halve the reproductive number and reduce the incidence, thus, shortening the epidemic period effectively. Early initiation of quarantine, operating large scale screenings, strong contact tracing systems, and isolation of cases can effectively reduce the epidemic. However, adhering only to screening and isolation with lower coverage can miss more than 75% of asymptomatic cases; hence, it is not effective.  Quarantine, contact tracing, screening, and isolation are effective measures of COVID 19 prevention, particularly when integrated together. In order to be more effective, quarantine should be implemented early and should cover a larger community.

title: De Escalation by Reversing the Escalation with a Stronger Synergistic Package of Contact Tracing, Quarantine, Isolation and Personal Protection: Feasibility of Preventing a COVID 19 Rebound in Ontario, Canada, as a Case Study
abstract: Since the beginning of the COVID 19 pandemic, most Canadian provinces have gone through four distinct phases of social distancing and enhanced testing. A transmission dynamics model fitted to the cumulative case time series data permits us to estimate the effectiveness of interventions implemented in terms of the contact rate, probability of transmission per contact, proportion of isolated contacts, and detection rate. This allows us to calculate the control reproduction number during different phases (which gradually decreased to less than one) From this, we derive the necessary conditions in terms of enhanced social distancing, personal protection, contact tracing, quarantine/isolation strength at each escalation phase for the disease control to avoid a rebound. From this, we quantify the conditions needed to prevent epidemic rebound during de escalation by simply reversing the escalation process.