Methods to Recruit Hard-to-Reach Groups: Comparing Two Chain Referral Sampling Methods of Recruiting Injecting Drug Users Across Nine Studies in Russia and Estonia

Evidence suggests rapid diffusion of injecting drug use and associated outbreaks of HIV among injecting drug users (IDUs) in the Russian Federation and Eastern Europe. There remains a need for research among non-treatment and community-recruited samples of IDUs to better estimate the dynamics of HIV transmission and to improve treatment and health services access. We compare two sampling methodologies “respondent-driven sampling” (RDS) and chain referral sampling using “indigenous field workers” (IFS) to investigate the relative effectiveness of RDS to reach more marginal and hard-to-reach groups and perhaps to include those with the riskiest behaviour around HIV transmission. We evaluate the relative efficiency of RDS to recruit a lower cost sample in comparison to IFS. We also provide a theoretical comparison of the two approaches. We draw upon nine community-recruited surveys of IDUs undertaken in the Russian Federation and Estonia between 2001 and 2005 that used either IFS or RDS. Sampling effects on the demographic composition and injecting risk behaviours of the samples generated are compared using multivariate analysis. Our findings suggest that RDS does not appear to recruit more marginalised sections of the IDU community nor those engaging in riskier injecting behaviours in comparison with IFS. RDS appears to have practical advantages over IFS in the implementation of fieldwork in terms of greater recruitment efficiency and safety of field workers, but at a greater cost. Further research is needed to assess how the practicalities of implementing RDS in the field compromises the requirements mandated by the theoretical guidelines of RDS for adjusting the sample estimates to obtain estimates of the wider IDU population.
Introduction
Evidence suggests recent diffusion of injecting drug use and associated HIV infection in the Russian Federation since 1996.1,2 Approximately 60% of HIV case reports have been associated with injecting drug use,1,3 with recent estimates indicative of increased sexual HIV transmission.4 According to UNAIDS classifications, HIV in much of the Russian Federation and former Soviet Union is a concentrated epidemic, with prevalence consistently above 5% in a single risk group (i.e., IDUs) but less than 1% in the general population.5 Concentrated epidemics require targeted surveillance of the population group most at risk in order to track the spread within that group as well as potential transmission to others.
Surveillance among IDUs is problematic, and there has been much discussion on the merits of different methods to recruit marginalized and hidden groups for these purposes.6–8 We know that surveying drug users in treatment settings misses an important segment of the drug using population. Evidence suggests that behaviours, characteristics and HIV prevalence amongst IDUs in treatment often systematically differ to IDUs not in treatment.9–13
Many surveillance studies of IDUs conducted in the 1990s relied on non-probability sampling such as convenience, snowball sampling or chain referral sampling to recruit members of the target group.12,14 These methods work on the assumption that peers are better able to recruit members of a hidden population than researchers.15 Typically studies employed ‘privileged access interviewers’ or ‘indigenous field workers’ to recruit IDUs from community settings. Indigenous field workers are interviewers who are either current or former drug users or individuals who have experience working with drug users and have privileged access to IDU networks. Over the last 15 years, this has become the established sampling method for recruiting hidden populations of IDUs and sex workers both in the UK and internationally.16–21
A refinement of the chain referral methodology called respondent-driven sampling (RDS), has recently been developed.22 RDS is inspired by the insight of “small world theory” that suggests that every person is indirectly associated with every other person through approximately six intermediaries,23 and therefore that everyone in a defined population could be potentially reached through several waves of recruitment in a chain-referral sample.24 This implies that there is a probability greater than zero that everyone in that population will be sampled.
The unique selling point of RDS is that the collection of data on participants’ social networks allow for adjustment for non-random recruitment. RDS uses social network data to make inferences about the wider target population from which the sample is drawn to provide proportional population estimates of characteristics and behaviours.24,25 In this paper, we do not attempt to test the statistical superiority of RDS in providing ‘population’ estimates over other sampling strategies but instead focus on RDS as a recruitment strategy examining the unadjusted RDS sample characteristics.
This paper compares two sampling methodologies, RDS and chain referral sampling using indigenous field workers (IFS), in terms of cost effectiveness, duration of fieldwork and effects on the demographic composition of the sample. First we offer a theoretical descriptive comparison of the two approaches.
Theoretical Comparison of the Sampling Methods
Indigenous Field Worker Sampling
The IFS recruitment method uses a standard chain referral approach. Indigenous field workers undergo training covering aims of the study, fieldwork protocols, ethics, informed consent, interview skills and safety procedures. Field workers (FWs) identify individuals known to them from IDU networks, recruit; and then interview them in community settings, separate from the rest of the research team. Eligible participants are given an incentive to take part and also asked to introduce their peers to the FW. The use of multiple site and network recruitment ensures a wide coverage of the population, providing as representative a sample as possible. There is some evidence that the use of FWs with direct access to IDU social networks facilitates recruitment and reduces masking (undersampling reclusive respondents), volunteer bias (oversampling cooperative respondents) and underreporting of socially undesirable behaviours.10,26
Respondent-driven Sampling
In RDS, a fixed site or “store front” is established where all interviewing takes place, providing the research team with greater control over the fieldwork. Unlike IFS and other chain referral samples, RDS uses a dual incentive system, a primary incentive for participating in the study and a secondary incentive for recruiting others into the study.22 Sampling begins with a set of initial subjects who serve as ‘seeds’ for an expanding chain of referrals, with respondents from each link in the chain or ‘wave’ referring respondents who form subsequent waves. Rather than being asked to identify their peers to interviewers, respondents inform their peers about the study and allow them to decide independently whether they want to participate or not. This theoretically reduces masking since recruiters are part of the target group with direct access to other IDUs, and it reduces volunteer bias since recruitees decide themselves whether to participate.
Information on the relationships between recruiters and recruited and their estimated network size is collected during the interview to allow for the calculation of selection probabilities.27 This information is used to assess homophily, the extent to which recruiters are likely to recruit individuals similar to themselves, and to weight the sample to compensate or control for differences in network size, homophily and recruitment success.24
Materials and Methods
Data Collection
Between 2001 and 2005, we undertook nine community surveys of IDUs in the Russian Federation and Estonia (Table 1). Four studies used IFS to recruit IDUs, and five used RDS. All IDUs were recruited from community settings. Seven of the studies had an epidemiological focus and measured the prevalence of HIV, HCV and associated injecting and sexual risk behaviours in IDUs.13,28,29 Two of the studies collected data on the social and economic characteristics of IDUs.30 All studies collected some standardised indicators and defined current IDUs as individuals who injected drugs for non-medical purposes in the last 4 weeks.
Table 1.Research amongst hard to reach populations recruited via respondent-driven sampling (RDS) and indigenous field workers (IFS) in Estonia and the Russian Federation, 2001–2005 PlacePopulation  sizeDates of field work  (days)Average number  of interviews  conducted  per daySample  sizeAim of studyRecruitment  methodReference1Togliatti,Russia740,6361/10/2001–18/10/2001 (18)23426HIV prevalence  and risk behaviourIFS292Moscow, Russia13,251,40127/09/2003–21/10/2003 (27)18514HIV prevalence  and risk behaviourIFS133Volgograd, Russia∼1,012,00026/09/2003–23/10/2003 (21)21597HIV prevalence  and risk behaviourIFS134Barnaul, Russia∼750,00026/09/2003–30/10/2003 (21)24512HIV prevalence  and risk behaviourIFS135Volgograd, Russia∼1,012,00019/8/2004–7/9/2004 (20)20400Social and economic  studyRDS306Barnaul, Russia ∼750,00026/8/2004–16/9/2004 (22)18400Social and economic  studyRDS307Togliatti, Russia740,63621/05/2004–09/06/2004 (20)24472HIV prevalence  and risk behaviourRDS348Tallinn, Estonia 396,37502/05/2005 (34)10350HIV prevalence  and risk behaviourRDS289Kohtla Jarve, Estonia46,34602/05/2005 (16)6100HIV prevalence  and risk behaviourRDS28
For each of the IFS studies, IDUs were recruited using a team of 10–12 FWs at each site. Settings included street locations and respondents’ homes but excluded drug treatment centres and STI clinics. Volunteers and outreach workers at local harm reduction non-governmental organizations (NGOs) were employed as FWs, as well as two researchers at a local university in each site. In all IFS studies, two experienced supervisors from Moscow and a researcher from the UK provided technical expertise and management for all studies. Measures to ensure data quality and to minimise network bias included limiting the number of interviews per FW, random spot-checks in the field, and follow-up validation interviews with 10% of participants. Primary incentives included HIV prevention materials (including needles/syringes), chocolates and cigarettes.
In each RDS study, recruitment was undertaken by a team of seven to eight FWs at each site. The interview team comprised trained research staff from a local university, two FWs recruited from local harm reduction NGOs, two to three trained research staff from a local university, and two supervisors from Moscow. A researcher from the UK was also present at the studies, with the exception of the two socio-economic studies in Volgograd and Barnaul, Russia. In each study, a pre-fieldwork focus group was held with outreach workers from the local harm reduction NGOs to obtain information about the drug scene and to identify seeds to begin recruitment. Respondents received the same primary incentives for participating in the RDS study as in the IFS study and also an additional secondary incentive for each respondent they recruited into the study.22,24
In all studies FWs recorded their observations on the drug scene, progress of the fieldwork and any difficulties arising from the research in detailed notes. These observations provide a useful additional comparison between the two sampling methods.
Duration and Cost of Fieldwork
We compared the duration of fieldwork for the IFS and RDS methods by calculating the mean number of days of fieldwork for each method and the proportion of the sample recruited on each day as the studies progressed. Means were compared using t-tests.
Costs were estimated for five of the seven surveys conducted in Russia and analysis focused on examining the cost effectiveness of recruiting a given sample for each of the sampling methodologies from a programmatic point of view as opposed to examining societal or health system costs. The IFS studies in Moscow, Barnaul and Volgograd were conducted in 2003 and the RDS studies in Togliatti, Barnaul and Volgograd were conducted in 2004. Costs were calculated as: (1) ‘outside’ costs including salary, accommodation and travel of field work consultants; (2) local salary costs of FWs and researchers; (3) recruitment costs including the packages of goods valued at 140 roubles and 300 roubles, respectively, for primary and secondary incentives; and (4) other costs including local transport, telephone calls and logistical costs of training FWs. For the RDS study the cost of the fixed site used for interviews is not included as an explicit cost, rather it is subsumed into the local salary costs since local staff contracted to undertake the work were employed from syringe exchange programmes. Costs are presented assuming that there are elements of fixed and variable costs at each sample size and that an extra 20 respondents will require keeping the entire survey team in the field for one extra day.
Demographic and Injecting Risk Behaviours of Sample
Demographic and injecting risk behaviours of IDUs recruited through IFS and RDS were compared in the two sites (Volgograd and Barnaul) where both survey methodologies were used to ensure a cleaner comparison between survey methods. Demographic and injecting characteristics were used as the outcome variables with recruitment method included as an independent variable. In the univariate analysis, chi-squared tests were used to compare outcomes for categorical variables and Bartlett’s test for equal variance to compare continuous variables. For the multivariate analysis, logistic regression models were used to explore associations between explanatory variables and a binary outcome, multinomial logit models were used for categorical variables with multiple values and ordinary least squares for continuous variables. The multivariate analysis includes all common independent variables and a categorical variable indicating survey method used. This allows outcomes to be compared controlling for all independent variables and to identify impacts associated with only survey methodology. All statistical analyses were conducted using Stata 7 with significance set at 5% (Stata Corporation, College Station, Texas).
Results
The Surveys
A total of 3,771 IDUs were recruited into nine surveys across four cities in the Russian Federation and two cities in Estonia (Table 1). A total of 2,049 (54%) participants were recruited through IFS and 1,722 (46%) through RDS. Only IDUs are included in the analyses we present here.
Duration of Field Work
The mean (standard deviation) duration of fieldwork for IFS surveys was 23.8 (4.1) days and for RDS 20.6 (0.9) days (t  =  27.9, p < 0.001). Figure 1 depicts the number of respondents recruited by each successive day of fieldwork by city and recruitment method. The RDS studies appear to follow a pattern of recruitment that we might expect: the number of respondents increases steadily as the number of waves increase and then declines towards the end of the study as completion of the target sample size approaches and respondents are asked to refer fewer contacts to the study. Kohtla Jarve, Estonia, appears to be an exception to this as recruitment peaks more sharply then abruptly finishes. The recruitment for the IFS studies does not appear to follow any set pattern across the cities. In Moscow the highest number of respondents in any 1 day occurs at the start of the study. In Barnaul, and to a less extent Volgograd, the number of participants recruited per day is more even across the duration of the study.
Figure 1Frequency of recruitment per day amongst studies of injecting drug users in Russia and Estonia (2001–2005), by city and recruitment method.
Sample Characteristics
Table 2 summarizes the characteristics of IDUs by recruitment method from the four surveys conducted in Volgograd and Barnaul. In both cities, RDS participants were younger, more likely to be male, to have attended higher education and to have official residency permits for the city. RDS participants were more likely to report injecting heroin in both sites and less likely to report injecting vint or mak1 than IFS participants. Frequency of injecting did not differ by recruitment method in either city. Regarding injecting risk behaviour, there was no difference between recruitment methods in the proportion of IDUs reporting injecting with a used needle/syringe in the last 4 weeks in Volgograd but in Barnaul a higher proportion of RDS respondents reported this behaviour (21 vs. 15%, p  =  0.02). In Volgograd IFS respondents were more likely to report ever having injected with a used needle/syringe than RDS respondents (61 vs. 40%, p  <  0.001). The opposite was found in Barnaul (53 vs. 63%, respectively, p  <  0.003). In both cities and with both methods, the main source of new needles/syringes was pharmacies. A higher proportion of IFS respondents reported using needle/syringe exchanges or treatment centres in both cities and in Barnaul a higher proportion of RDS respondents reported using a source other than needle/syringe exchange (defined as friend, dealer, family or on the street) as their main source of needles/syringes.
Table 2.Comparison of characteristics and injecting risk behaviours among injecting drug users in Volgograd and Barnaul (2003–2004) by recruitment method CharacteristicBarnaulVolgogradIFRDSaIFRDSan/total%/mean  (SD)n/total%/mean  (SD)χ2P valuen/total%/mean  (SD)n/total%/mean  (SD)χ2P valueTotal† age (years)25.8 (8.2)24.8 (6.1)2.20.0324.5 (3.9)23.8 (5.4)2.30.022Male348/50469%293/36580%13.8<0.001388/51276%317/34692%35.3<0.001Attended higher education 67/50413%136/35339%73.1<0.001140/50928%150/33445%27.1<0.001Duration of injection (years)7.1 (6.9)6.7 (4.3)1.10.295.4 (3.4)6.1 (4.3)−2.60.009No official residency permit34/4957%7/3562%11.20.00119/4714%8/3382%1.90.174Injecting risk behaviours  in the last 4 weeksMain drug injected  Heroin280/50456%263/35774%424/50883%328/34595%  Vint135/50427%38/35711%37/5087%7/3452%  Mak84/50417%51/35714%21/5084%6/3452%  Other5/5041%5/3571%39<0.00126/5085%4/3451%27<0.001 Daily injection 100/50020%69/35619%0.050.82386/51217%63/34118%0.40.53 Injected with used  needles/syringes 75/50015%75/35321%5.60.01863/51012%37/33611%0.350.55Main source of new  needles/syringes  Pharmacy466/49894%325/36589%463/50891%327/34196%  Treatment21/4984%12/3653%33/5086%6/3412%  Other**11/4982%28/3658%14.90.00112/5082%8/3412%10.50.005 Ever injected with used  needles/syringes255/48153%225/35663%8.70.003301/49361%137/34540%37.1<0.001aThe RDS data are not adjusted for homophily and network effects.†Numbers do not always add up to total because not all respondents answered each question.**Other refers to friends, family, found on the street, drug dealers.
Multivariate Analysis
Table 3 summarizes the multivariate analysis for the categorical and continuous variables for Barnaul and Volgograd. After controlling for all independent variables, our findings indicate that RDS recruited a population 0.07 years younger in both cities. In both cities RDS participants had been injecting slightly longer than IFS participants. In Barnaul, RDS participants were less likely to report obtaining their new needles/syringes from pharmacies (−5%) but there was no evidence to suggest a difference in Volgograd. In Volgograd RDS participants were less likely to report using needle/syringe exchanges (−3%) but there was no difference in Barnaul. RDS participants in Barnaul were 4% more likely to report using another source for their new needles/syringes (Table 3).
Table 3.Effect of recruitment method on demographic indicators and injecting risk behaviours amongst injecting drug users in Barnaul and Volgograd (2003–2004)OutcomesRDSaType of analysisBarnaulVolgogradCoefficient95% CIStd. err.Coefficient95% CIStd. err.log AGE−0.07−0.1–(−0.04)0.01−0.07−.0.9–(−0.05)0.01Ordinary least squaresYears of injecting0.1 0.04–0.20.040.20.1–0.20.04Negative binomial regressionIncrease in probability  of using pharmacies−5%−8–(−1%)0.023%0.1%–5%)0.1Multinomial logitIncrease in probability  of using needle/syringes  exchanges0.5%−1–3%0.01−3%−5%–(−0.2%)0.01Multinomial logitIncrease in probability  of using another source  for needles/syringes4%1–7%0.01n/an/an/aMultinomial logitaThe RDS data are not adjusted for homophily and network effects.n/a = not applicable.
In the logistic regression analysis (Table 4), RDS was more likely to result in a higher proportion of male IDUs (Barnaul OR  =  2.0, Volgograd OR  =  3.8) and participants who had attended higher education (Barnaul OR  =  5.2, Volgograd OR  =  3.0). In Barnaul RDS participants were more likely to have official residency permits (OR  =  4.6) but not in Volgograd. In both cities, RDS participants were more likely to inject heroin over mak or vint than IFS participants (Barnaul OR  =  2.5 and Volgograd OR  =  3.4). In Volgograd RDS participants had almost twice the odds of reporting daily injection (OR  =  1.7) than IFS participants and had reduced odds of ever injecting with used needles/syringes (OR  =  0.3). In Barnaul, RDS participants were more likely to report injecting with used needles/syringes in the last 4 weeks and ever (OR  =  1.6 and OR  =  1.4, respectively).
Table 4.Effect of recruitment method on demographic indicators and injecting risk behaviours amongst injecting drug users in Barnaul and Volgograd (2003–2004)OutcomesRDSaType of analysisBarnaulVolgogradOdds ratio95% CIStd. err.Odds ratio95% CIStd. err.Male2.01.3–3.10.43.82.1–6.91.2Logistic regressionAttended higher education5.23.5–7.61.03.02.1–4.30.5Logistic regressionOfficial residency permit 4.61.8–12.12.31.40.5–4.30.8Logistic regression Injected heroin as primary drug in the last 4 weeks versus mak/vint2.51.7–3.50.43.41.7–7.01.2Logistic regressionDaily injected0.80.5–1.20.21.71.04–2.60.4Logistic regression Injected with used needles/syringes in the last 4 weeks1.61.0–2.10.41.00.6–1.80.3Logistic regression Ever injected with used needles/syringes1.41.0–1.90.20.30.2–0.50.1Logistic regression Sold sex in the last 4 weeks1.40.6–3.00.51.80.6–5.41.0Logistic regressionaThe RDS data are not adjusted homophily and network effects.
Costs
The total cost of conducting an IFS survey recruiting 400 respondents was estimated to be $14,651 (USD) but $16,100 for the RDS survey (Table 5). This translates to $43 per respondent using RDS and $37 using the IFS method. Increasing the sample from 400 to 500 reduced the average cost per respondent by $1 for the RDS method and by $3 for the IFS method. Reducing the sample from 400 to 300 respondents increased the cost per respondent by $2 for the RDS method and $5 for the IFS method. These results are presented in Table 5.
Table 5.Analysis of costs of recruiting IDUs and sex workers from five surveys in Moscow, Volgograd and Barnaul, Russian Federation (2003–2004) by recruitment method and sample size Recruitment methodIndigenous field workersRespondent-driven samplingSample size300400500300400500Outside costsa−15.40$20.3011.40−0.18$19.620.18Local costsb−13.20$7.9310.40−0.25$5.500.25Recruitment of respondentsc−33.30$7.0020.00−0.25$9.950.25Other0.00$1.400.00−0.25$5.250.25Total−17.20$14,651.0012.60−0.21$16,1000.21Cost per respondent$42.00$37.00$34.00$43.00$41.00$40.00At the time of writing 28 rubles was equivalent to one US Dollar. The 2003 costs are adjusted for inflation that occurred between August 2003 and 2004 based on price indices taken from the Bank of Russia.aCosts are presented assuming that there are elements of fixed and variable costs in each sample size and that an extra 20 respondents will take one extra day necessitating employing the entire fieldwork team for that extra day.bIn order to protect the confidentiality of staff we report only the total amount of all salaries and fees paid to project staff.cThe costs for the RDS surveys are also based on providing a package of goods valued at 140 rubles for each survey participant and a secondary reward of 300 rubles for each participant recruited. Costs for the IFS surveys are based on providing a package of goods valued 140 rubles for each participant and no secondary reward.
Discussion
Our findings suggest that RDS does appear to be a faster recruitment method and that there are significant differences in the demographic characteristics of IDUs recruited via RDS in comparison with those recruited via IFS. However, evidence from the two cities is conflicting with regard to whether RDS recruits IDUs who engage in riskier injecting practices.
One of the suggested benefits of RDS is its apparent ability to recruit the hardest to reach sections of hidden populations.22 We found some differences in measures of marginalization and risk behaviours between the two recruitment methods, RDS participants tend to be slightly younger and are less likely to use needle/syringe exchange programs. Some evidence in Russia suggests that IDUs whose primary source of needles/syringes is informal are at more risk of engaging in high-risk behaviours.31 However, IFS participants were less likely to have attended higher education and have official residency permits to live in the city and more likely to be female. Lack of residency permit is an indicator of marginalization as it will affect an individual’s ability to use health services or obtain employment.32,33
As no consistent trend emerges from the analysis of the effect of recruitment method on sample characteristics, then choice of method might be made on the basis of methodology and cost.
Inclusion Criteria and Data Validity
With IFS the responsibility for selecting the right target group is placed with the FWs, and its success depends on establishing a trusting relationship between the researchers and the fieldwork team. With RDS, issues of trust are less important, as researchers undertake the interviews themselves. The problems of establishing whether respondents are genuine members of the target group remain. Although measures can be put in place which might reduce this from happening, such as using indigenous field workers to screen participants or recording biometric measurements to avoid the same respondent being interviewed twice, it is very difficult to measure to what extent fabricated data may enter a survey.
A disadvantage of both methods is that study participants who are not members of the target group may lie about their membership in order to receive a reward. This was the case in two of the IFS sites where 9 and 14% of questionnaires were subsequently found to be fakes. This was discovered because strict validation processes had been set up and there was a good relationship between the FW supervisor and indigenous field workers. In the Togliatti RDS study 15 people were refused entry into the study, as they were suspected of not being current injectors. However these may be considered a minimum estimate as one cannot rule out that additional fabrication might have occurred and gone undetected. Having a modest primary and secondary incentive can minimize the chances that participants who are not members of the target population will be recruited.
Determining the best incentive size is difficult and has many implications for the study, especially for RDS studies where the secondary incentive is so crucial to recruitment success. The networks recruited through RDS are largely artificial, created as a result of the study and since their composition is dependent on the incentive, changes to the amount of incentive offered would change the composition of the network. This is illustrated with the case of sex workers in Eastern Europe, who have been found to be harder to recruit through RDS in part due to the small incentive and social network properties; this is discussed in more detail in a paper in this issue by Simic et al.
Adjusting the RDS sample to obtain ‘population’ estimates depends on the ability to recruit a random population within a subject’s social networks and a positive probability of recruiting everyone in that network. The possibility that the network is highly dependant on the incentive raises the question whether the latter condition obtains. This is particularly relevant when the definition of the population of study is fluid or artificially constructed by the research as with IDUs and sex workers. It should also be noted that the collection of information describing network characteristics which allows RDS analysis to produce ‘population’ estimates requires the respondent to recall detailed information on the composition of their network, including its size and each member’s relationship with the recruiter. This process carries a large potential for error.
Personal Safety and Capacity Building
There are safety considerations that favour RDS as respondents attend a fixed site for an interview in which a minimum number of staff is always present. In the IFS method, interviewers may find themselves travelling to an area in which they are unfamiliar, and unintentionally put themselves in danger, especially if it becomes known that they are carrying financial rewards or gift packs.
Limitations
Whilst we have tried to limit confounding in our analysis by comparing RDS and IFS studies conducted in the same cities, the studies were conducted in different years, and the findings may be confounded by time. Time may be important in relation to behaviour, but is likely to be less important in relation to socio demographic characteristics of the target group. None of the studies were set up specifically with the aim of comparing sampling methodologies, and this limited the number of characteristics that could be compared between study methodologies. A study set up specifically with the aim of comparing the methodologies might produce different results and facilitate more detailed comparison of characteristics. Additionally the starting point for both the IFS and RDS studies in all sites was the local outreach team. This may have led to more similarities in the sample composition than would have occurred if seeds had been selected through other methods. However, according to the principles of RDS, the selection of seeds does not ultimately influence the composition of the sample, since after several waves of recruitment the sample should be independent of the non-randomly selected seeds.24
Conclusion
The HIV epidemic is driven by populations engaging in high-risk behaviours mixing with those engaging in lower risk behaviours. It is important to identify the parameters of risk behaviour in order to model these epidemics and to design appropriate interventions. If we assume that, after adjusting for network sizes and homophily, RDS is more successful at estimating risk behaviours across a more representative population than IFS, then it could lead to more effective modelling and prediction of such epidemics; however to date there is no evidence to suggest that this is the case. Our findings indicate that as a recruitment strategy, RDS is no better than IFS in identifying populations with highest risk behaviours. It does have practical advantages in terms of safety of the FW team, with faster recruitment at only additional costs. In the meantime, until the statistical superiority of RDS can be proven, a preferred approach may be to adopt the best aspects of both methodologies, depending on the resources available. A combination could include the use of coupons for recruitment, but also training indigenous field workers to work alongside researchers to undertake interviews, serving to increase their capacity in research skills whilst ensuring that the correct target group is being reached.

injecting drug users
estonia
hiv
respondent-driven sampling
indigenous field workers
russia.


Are radiographs needed when MR imaging is performed for non-acute knee symptoms in patients younger than 45 years of age?

Objective The objective was to determine the value of radiographs in young adults with non-acute knee symptoms who are scheduled for magnetic resonance imaging (MRI).
Introduction
Radiographs in patients with acute knee problems that are obtained at, or close to, the time of trauma serve mainly to exclude fractures and most of these radiographs are normal. To reduce the total number, and especially the number of normal radiographs, clinical decision rules that identify patients with a high risk of fracture have been developed and validated [2–4]. In patients with non-acute knee symptoms radiographs are the mandatory minimal initial exam in patients with non-traumatic knee pain, according to ACR appropriateness criteria [5]. Magnetic resonance imaging (MRI) is frequently obtained if additional imaging is clinically needed to search for suspected intra-articular abnormalities. The value of radiographs relative to MRI in a heterogeneous group of patients was recently reported [6]. Radiographs were rated “essential” or “very important” in 46–58% of cases and added “not needed information” in 14–29% of cases. However, the value of radiographs relative to MRI in young adults presenting with non-acute knee symptoms has, to our knowledge, not been established. If in these patients radiographs could be omitted, or obtained only when needed when reading MRI, this could possibly lead to a significant reduction of the volume of knee radiographs with ensuing reduction in radiation dose and costs.
The purpose of our prospective study was to determine the value of radiographs in young patients with non-acute knee symptoms and suspected intra-articular pathology who are scheduled for MRI based on the results of a physical exam. We therefore determined the prevalence of osseous abnormalities visible on radiographs and MRI and the yield of MRI compared with that of radiographs. In addition, we measured the radiation dose of standard radiographs of the knee.
Material and methods
Over 3 years, 961 patients referred from general practitioners to the outpatient surgery or orthopedic surgery clinics of three hospitals (two general hospitals and one university hospital) because of non-acute knee symptoms agreed to participate in our prospective study. The symptoms had to have been present for at least 4 weeks. The institutional review board of each hospital approved the study. We obtained written informed consent from all patients. At study entry a standardized history, including inventory of traumatic events and other knee-related events such as morbidity and medical procedures was taken. Physical exam was performed by one of 15 (orthopedic) surgeons or by residents under their supervision. All the patients included underwent MRI and radiographs of the knee. Recent radiographs taken for the same complaints that were obtained prior to study inclusion were not repeated.
We included patients who met the following inclusion criteria: knee symptoms (pain, swelling of the joint, feeling of instability or giving way, history of locking) of at least 4 weeks’ duration and age between 16 and 45 years. To obtain a homogenous study population without co-morbidity we did not include patients who had had previous surgery of the affected knee (including arthroscopy) or previous MRI, a history of rheumatoid arthritis, and clinical diagnosis of retropatellar chondromalacia, contra-indication for MRI, or an incomplete data set. One hundred and sixty-three patients (17.0%) were eventually excluded (Table 1), leaving 798 patients as our study group. Of these excluded patients a substantial number should not have been included by the orthopedic surgeons in the first place according to our study protocol, for instance, because they were either too young, too old or had knee complaints of less than 4 weeks’ duration.
Table 1Excluded patients. Of the 961 patients referred, 163 (17.0%) were excludedExclusion criterianSymptoms of less than 4 weeks’ duration65Aged under 16 years1Aged over 45 years6Previous surgery8Retropatellar chondromalacia14Previous MRI1Radiographs unavailable or not obtained65MRI or arthroscopy prohibited2Immediate arthroscopy required30Criteria are not mutually exclusive.
One out of six musculoskeletal radiologists (all with at least 5 years’ experience) evaluated the radiographs without knowledge of the MR images and recorded their findings on a Case Record Form (CRF).
The radiation dose of standard antero-posterior and lateral radiographs was determined in two of the three hospitals using flat ionization chambers. We used PCXMC software (STUK, Finland) to convert the measured radiation doses into effective doses.
The radiologist evaluated the radiographs for articular surface lesions, using the classification developed by Bohndorf [7]. Osteoarthritis was scored using the scoring system developed by Kellgren et al. [1]. In the analysis, grades 1 to 3 were considered as one group, with osteoarthritis being present.
Radiographs were also evaluated for fractures [8–10], loose bodies, and incidental findings. A loose body was defined as a radiodense circumscriptive lesion located in the femorotibial, patellofemoral jointline or suprapatellar pouch. Incidental findings, such as non-ossifying fibromas and enchondromas were diagnosed using established criteria [11, 12]. On radiographs a lesion was considered a non-ossifying fibroma if it met the following criteria: asymptomatic, cortical metaphyseal location, and radiographically non-aggressive. A lesion was considered an enchondroma if it met the following criteria: central metaphyseal location, chondroid matrix, geographic pattern of destruction with or without sclerotic margin.
We performed the MR studies in all three hospitals on an identical 0.5-T system (Gyroscan T5, Philips Medical Systems, Best, the Netherlands), with the same software release using a dedicated transmit–receive knee coil.
The standardized scanning protocol consisted of three sequences: a sagittal and a coronal dual spin-echo (SE) sequence and a sagittal T1-weighted 3D gradient-echo (GE) sequence with frequency selective fat suppression. The following parameters were identical for both SE sequences: field of view 140–160 mm, echo time (TE) 20/80 ms. The coronal dual SE had a repetition time (TR) of 2,100 ms, a 256 × 205 matrix and a slice thickness of 5 mm with a 0.5-mm interslice gap. The sagittal dual SE had a TR of 2,350 ms, a 256 × 179 matrix and a slice thickness of 4 mm with a 0.4-mm interslice gap. The parameters for the sagittal frequency selective fat-suppressed T1-weighted 3D GE were: TR 70 ms, TE 13 ms, 45° flip angle, field of view 160 mm, 256 × 205 matrix, 4 mm slice thickness with a 2-mm overlap.
The total imaging time of the standard protocol (including the initial survey sequence) was 26 min.
After reading the radiographs one out of six radiologists evaluated MR images and reported his findings on a CRF. In accordance with usual management the observer had access to the radiographs, but not to the reports, when evaluating MR images. The CRF was similar to the one used for radiographs [8–12], except that bone marrow edema was added as an item [13]. For articular surface lesions we again used the classification developed by Bohndorf [7]. For osteoarthritis we used the scoring system developed by Recht et al. [14]. For the purpose of this study, grades 1 to 4 were considered as one group, with osteoarthritis being present.
To overcome bias in the reading of MR studies, introduced by knowledge of the results of conventional radiographs, one radiologist (JLB) re-evaluated MR studies of patients with abnormalities on conventional radiographs with the exception of osteoarthritis of Kellgren [1] grades 1–2. We used the same CRF format. At this second evaluation, MR studies of patients with osseous abnormalities on conventional radiographs were mixed with age- and gender-matched MR studies of patients without abnormalities on conventional radiographs. The radiographs and the findings on the CRF were not available at that time.
We divided the completed CRFs over two groups: group A had no history of trauma, and group B had a history of trauma of more than 4 weeks before presentation at the hospital.
We used the Chi-squared test to identify significant differences between the yield of radiographic and MR diagnoses, and between the number of findings in group A and that in group B. To look for statistically significant differences between the yield of radiographs and MRI within groups A, B and the study population as a whole, we used McNemar’s Chi-squared test.
Results
The median age of the 798 patients included was 31 years (range 16–45 years), and 261 patients (32.7%) were female. Minimal and median duration of symptoms were 4 and 20 weeks respectively (range 4–1,490 weeks). Three hundred and thirty-two patients reported no history of trauma (group A), and 466 patients reported an old (more than 4 weeks prior to consultation) history of trauma (group B).
Magnetic resonance imaging depicted arthroscopically treatable intra-articular pathology in 341 patients (42.7%). Medial and lateral meniscal tears were found in 225 (28.2%) and 111 patients (13.9%) respectively. The average radiation dose of supine antero-posterior and lateral radiographs was 0.2 and 0.3 mSv respectively. The median duration of the interval between radiographs and MRI was 8 days (95 percentile, 85 days). In 196 patients (24.6%) radiographs were obtained prior to inclusion in the study. These radiographs were not repeated since the knee complaints had not changed between the moment they were obtained and inclusion in this study.
In group A, radiographs showed 36 osseous abnormalities in 332 patients (10.8%, Table 2). All these abnormalities, except 13 Kellgren [1] grade 1 osteoarthritis cases, were also depicted on MRI. There were 23 concordant radiographic and MRI diagnoses (Fig. 3; Table 2). One incidental finding (enchondroma) was demonstrated on radiographs and MRI. The majority of the 72 diagnoses made only with MRI were osteoarthritis and bone bruising (Table 2). Most osseous lesions (osteoarthritis, articular surface lesions, loose bodies and bone marrow edema) with the exception of incidental findings (one case) and old fractures (not present in this group) were significantly more often diagnosed with MRI than with radiographs (Table 2).
Table 2Osseous abnormalities detected on radiographs only, on radiographs and MRI, and on MRI only in 332 patients with non-acute non-traumatic knee complaintsOsseous abnormalityR (%)R and MR (%)MRI (%)Total (%)McNemar test, p valueOA13 (3.9)18 (5.4)39 (11.7)70 (21.1)0.00ASL0 (0)3 (0.9)7 (2.1)10 (3.0)0.02LB0 (0)1 (0.3)6 (1.8)7 (2.1)0.03Fractures0 (0)0 (0)0 (0)0 (0)NAIncidental finding0 (0)1 (0.3)0 (0.0)1 (0.3)1.00Bone marrow edema0 (0)0 (0)20 (6.0)20 (6.0)NA Total13 (3.9)23 (6.9)72 (21.7)108 (32.5)0.00OA: osteoarthritis grade 1 or higher according to Kellgren [1] on radiographs and according to Recht [14] on MRI ; ASL: articular surface lesion with or without disrupted cartilage; LB: loose body; R: abnormality detected with radiographs only; R and MR: abnormality detected with both radiograph and MRI; MRI: abnormality detected with MRI only; NA: not applicable. Categories are not mutually exclusive.
In group B, radiographs showed 40 osseous abnormalities in 466 patients (8.6%, Table 3). All these abnormalities, except 15 Kellgren [1] grade 1 osteoarthritis cases, were also depicted on MRI. There were 25 concordant radiographic and MRI diagnoses (Figs. 1, 4, 5 and 6; Table 3). Four of the six incidental findings were diagnosed on radiographs and MRI (1 non-ossifying fibroma and 3 enchondromas, Fig. 7). Two enchondromas were depicted on MRI only (Fig. 8). The majority of the 192 diagnoses made only with MRI were bone marrow edema (Fig. 2), osteoarthritis and articular surface lesions (Table 3). These three diagnoses were significantly more often diagnosed with MRI than with radiographs (Table 3). There was no significant difference between MRI and radiographs in the diagnosis of loose bodies, old fractures and incidental findings.
Table 3Osseous abnormalities detected on radiographs only, on radiographs and MRI, and on MRI only in 466 patients with non-acute traumatic knee complaintsOsseous abnormalityR (%)R and MR (%)MRI (%)Total (%)McNemar test, p valueOA15 (3.2)13 (2.8)65 (13.9)93 (20.0)0.00ASL0 (0)3 (0.6)22 (4.7)25 (5.4)0.00LB0 (0)1 (0.2)4 (0.9)5 (1.1)0.13Fractures0 (0)4 (0.9)3 (0.6)7 (1.5)0.25Incidental finding0 (0)4 (0.9)2 (0.4)6 (1.3)0.5Bone marrow edema0 (0)0 (0)96 (20.6)96 (20.6)NA Total15 (3.2)25 (5.4)192 (41.2)232 (49.8)0.00Categories are not mutually exclusive.Fig. 1Severe osteoarthritis on both radiographs and MRI. a, b Lateral and antero-posterior radiographs showing deformation of the femoral condyles and tibia plateau with marked subchondral cyst formation and osteophyte formation in a 44-year-old female patient with a history of knee trauma (group B). c–e Coronal proton density and T2-weighted spin-echo (SE) images and of the same lesion showing, in addition to the deformities and changes already noted on the radiographs, the osteochondral defect to a better extent. e Sagittal T2-weighted SE image showing the same features, but also focal full-thickness cartilage lossFig. 2Three-month-old transchondral fracture on both radiographs and MRI. a, b Antero-posterior and lateral radiograph showing irregularity and deformation of the lateral femoral condyle consistent with a transchondral fracture of the lateral femoral condyle in a 40-year-old male with a history of knee trauma (group B). c–d Sagittal T2-weighted SE images and T1-weighted 3D gradient-echo (GE) with fat suppression showing subtle contour deformity of the lateral femoral condyle with kissing bone bruises in the lateral femoral condyle and tibial plateau
Osseous abnormalities were more frequently encountered in group B than in group A (p < 0.001). This difference is explained by a significant difference in the number of old fractures (p < 0.05, no old fractures were seen in group A), and patients with bone marrow edema (p < 0.001).
Bone marrow edema was demonstrated with MRI in 116 patients (14.5%, Table 4); 96 of these were found in group B (82.8% of patients with bone marrow edema, Table 3).
Table 4Osseous abnormalities detected on radiographs only, on radiographs and MRI, and on MRI only in 798 patients with non-acute knee complaintsOsseous abnormalityR (%)R and MRI (%)MRI (%)Total (%)McNemar test, p valueOA28 (3.5)31 (3.9)104 (13.0)163 (20.4)0.00ASL0 (0)6 (0.8)29 (3.6)35 (4.4)0.00LB0 (0)2 0.3)10 (1.3)12 (1.5)0.00Fractures0 (0)4 (0.53 (0.4)7 (0.9)0.25Incidental finding0 (0)5(0.6)2 (0.3)7 (0.9)0.5Bone marrow edema0 (0)0 (0)96 (12.0)96 (12.0)NATotal28 (3.5)48 (6.0)264 (33.1)340 (42.6)0.00Categories are not mutually exclusive.
In 6 (30%) of the 20 group A patients with bone marrow edema, it was either associated with intra-articular damage of non-osseous origin or it was an isolated finding. The associated osseous abnormalities in the other 14 patients were as follows: bone marrow edema was found in 4 of the 10 patients with articular surface lesions, in 1 of the 7 patients with a loose body, and in 9 of the 70 patients with osteoarthritis.
In 89 (92.7%) of the 96 group B patients with bone marrow edema, it was either associated with intra-articular damage of non-osseous origin or it was an isolated finding. The associated osseous abnormalities in the other 7 patients were as follows: bone marrow edema was found in 4 of the 25 patients with articular surface lesions (Fig. 2), in 1 of the 5 patients with a loose body and in 2 of the 93 patients with osteoarthritis.
In our population we did not find any other osseous lesions like osteopenia or femoropatellar disease. Also, we did not find chondrocalcinosis on radiographs.
Subsequently, all patients with radiographically detected abnormalities with the exception of Kellgren [1] grade 1 and 2 osteoarthritis were identified. MRI studies of the 17 patients with 18 radiographically detected osseous abnormalities were mixed with 17 gender- and age-matched MRI studies of patients without abnormalities on radiographs. There were 6 females in each group, and the mean age in each group was 33.1 years, SD 7.9 years). At revision, the reader (JLB) was blinded to all information and had no access to the radiographs. All 18 osseous abnormalities (1 caae of osteoarthritis Kellgren grade 3 [Fig. 1], 6 articular surface lesions [Figs. 2, 3], 2 loose bodies [Fig. 4], 4 old healed fractures [Figs. 5, 6] and 5 incidental findings [4 enchondromas and 1 non-ossifying fibroma, Figs. 7, 8]) were all diagnosed on MRI.
Fig. 3Twenty-six-month-old transchondral fracture on both radiographs and MRI. a Antero-posterior radiograph showing abnormal density, subtle irregularity and deformation of the medial femoral condyle in a 35-year-old male patient with no history of knee trauma (group A). b–d Sagittal T1-weighted 3D GE with fat suppression and coronal proton density and T2-weighted SE images of this knee showing the transchondral fractureFig. 4Loose body on both radiography and MRI. a Lateral radiograph showing a ventrally located loose body in the left femorotibial joint in an 18-year-old male professional skater with a history of knee trauma (group B). b–c Sagittal T1-weighted 3D GE with fat suppression and coronal proton density SE images of the same patient, also showing the loose body that is ventrally located in the lateral compartment of the femorotibial joint. At subsequent arthroscopy this loose body was removedFig. 5Eight-month-old healed fracture on both radiograph and MRI. a Lateral radiograph showing a healed fracture of the inferior patellar pole in an 18-year-old male patient with a history of knee trauma (group B). b Sagittal proton density SE image of the same patient, also delineating the healed fracture of the inferior pole of the patellaFig. 6Two-month-old healing fracture on both radiograph and MRI. a Lateral radiograph showing a healing fracture of the left inferior patellar pole in a 40-year-old male patient with a history of knee trauma (group B). b, c Sagittal T1-weighted 3D GE with fat suppression and T2-weighted SE images of the same patient, also delineating the healing fracture of the inferior pole of the patella without cartilaginous irregularities. Around the fracture line bone marrow edema can be appreciatedFig. 7Incidental finding depicted on both radiographs and MRI. a, b Lateral and antero-posterior radiographs showing a central, metaphyseally located lesion with chondroid matrix consistent with enchondroma in the femur in a 44-year-old female patient with a history of knee trauma (group B). c, d Sagittal proton density and T2-weighted SE images of the same lesionFig. 8Incidental finding depicted on MRI only. a Lateral radiograph showing no femoral osseous lesion in a 40-year-old female patient with a history of knee trauma (group B). b, c Sagittal proton density and T2-weighted SE images showing a metaphyseal lesion consistent with an enchondroma
Discussion
Key characteristics of our population such as age, gender, clinical suspicion of intra-articular abnormalities, intra-articular abnormalities detected with MRI, and history suggest that our conclusions can be applied to typical populations scheduled for MRI to analyze non-acute knee problems.
The yield of radiographs in patients with subacute or chronic knee symptoms who are otherwise healthy and who are scheduled for MRI based on the results of a physical exam suggesting the presence of intra-articular damage is only 9.5% (76 patients). The majority of these patients (77.6%) have osteoarthritis. We failed to confirm with MRI the radiographic diagnosis of Kellgren [1] grade 1 osteoarthritis in 28 patients, but none of the other abnormalities were diagnosed only with radiographs. This was confirmed in a second reading of MRI blinded to clinical and radiographic information. Radiographs do not, in the setting of this study, contribute to clinical decision-making or clinical management of the patient. Although the dose administered when obtaining radiographs of the knee is small, the size of the population with knee complaints make the reduction of an administered dose a relevant issue. Radiographs can therefore be omitted in this specific population when the decision to perform MRI is taken based on clinical assessment. The disadvantage of occasionally missing Kellgren [1] grade 1 osteoarthritis is limited when we realize that because of the lack of a gold standard these radiographic diagnoses may also be false-positive.
Taljanovic et al. [6] rated radiographs as “essential” or “very important” in 46–58% of cases and radiographs added “not needed information” in 14–29% of cases. They conclude in their study that radiographs are an important, and sometimes essential initial, complementary study for reading musculoskeletal MR examinations. This apparently different conclusion can be explained by the differences in study populations. Taljanovic et al. [6] analyzed a large variety of diagnosis (trauma, infection, tumors, degenerative or miscellaneous) in all anatomical locations in patients of all ages. We only analyzed patients between 16 and 45 years of age with non-acute knee symptoms lasting at least 4 weeks, excluding amongst others patients with acute knee symptoms (i.e., less than 4 weeks), history of rheumatoid arthritis, and clinical diagnosis of retropatellar chondromalacia. Other major methodological differences are mainly related to this difference.
The concordance between radiographs and MRI is not high because of the large number of diagnoses (77.6%) made only with MRI. In groups A and B osteoarthritis, articular surface lesions, and bone marrow edema were significantly more often diagnosed with MRI than with radiographs. Loose bodies were significantly more frequently diagnosed with MRI in group A only. This higher yield of MRI is no surprise, since abnormalities such as articular surface lesions and bone marrow edema are known to be better, or even exclusively appreciated on MRI. These findings have, in addition to the intra-articular abnormalities detected with MRI, potential clinical significance in view of the patients’ presenting symptoms.
The advantage and comprehensiveness of MRI is illustrated by its ability to demonstrate bone marrow edema that is associated with other abnormalities. In the patients with a history of old trauma, bone marrow edema was mainly (92.7%) associated with intra-articular damage. In the group with no history of trauma, however, bone marrow edema was mainly (70%) seen in association with osseous abnormalities, thus facilitating the diagnosis of articular surface lesions and osteoarthritis.
This prospective study has several limitations that are mainly related to the decision to follow usual care. This means that radiographs were available at the time of MRI. To overcome this limitation, one radiologist (JLB) re-evaluated MR studies of patients with abnormalities on conventional radiographs without knowledge of the radiographs, as described.
Another limitation is that we could not determine accuracy because of the absence of a reference standard. If we look at the discordant cases, there are no potentially false-negative MRI diagnoses (with the exception of Kellgren [1] grade 1 osteoarthritis), but the number of potential false-positive MRI diagnoses (abnormal finding on MRI in combination with a normal radiograph) is substantial, mainly because of the high prevalence of bone marrow edema.
Another possible limitation of this study is the selection bias introduced by including only patients between 16 and 45 years of age and excluding patients with co-morbidity. The study design was not tailored toward assessment of the value of conventional radiographs only. The overall goal of this multicenter study was to evaluate the efficacy of MRI compared with direct arthroscopy in patients with subacute knee complaints, based on clinical outcome. To this end we tried to obtain a homogenous study population without co-morbidity. This is most likely the reason we encountered only 1 patient with high-grade osteoarthritis (Kellgren [1] grade 3). However, because the majority of MR examinations performed in our institutions will be of patients in this age range without known co-morbidity, we do not think this selection bias will alter our overall conclusions.
We tried to mimic usual care as much as possible in this study. However, in our study MRI was performed within 2 weeks of inclusion in the study. Due to the limited availability of MRI compared with conventional radiographs in most hospitals, MRI often cannot be performed at such short notice. This can lead to a considerable waiting time for MR examinations and this may direct physicians to prior conventional radiographs to rule out gross pathology and reassure the patient. To prevent these unnecessary radiographs, the waiting time for MRI must be as short as possible. In the Netherlands waiting times for MRI in most institutions are down from several months a couple of years ago to several weeks nowadays.
We conclude that radiographs should not be obtained routinely when MRI is being performed in non-acute young patients with knee complaints because the number of clinically relevant lesions detected on radiographs is low. In addition, the small number of abnormalities found on radiographs is, with the exception of an occasional case of Kellgren [1] grade 1 osteoarthritis, also depicted on MRI. Reduction of costs and radiation dose is small in the individual patient, but, because of its size, substantial in the entire population with subacute and chronic complaints suspected to be knee injury.

radiographs
knee
magnetic resonance imaging


Work-related physical and psychosocial risk factors for sick leave in patients with neck or upper extremity complaints

Objectives To study work-related physical and psychosocial risk factors for sick leave among patients who have visited their general practitioner for neck or upper extremity complaints.
Introduction
Many people suffer from work-related neck and upper extremity complaints. In a population-based study in the Netherlands, the 12-month prevalence of work-related neck and upper extremity symptoms was found to be 31% (Blatter and Bongers 1999). These complaints have an important impact on loss of time from work. Sick leave has enormous cost implications, considering costs to employers, insurers, health care providers, and patients themselves. In the Netherlands, 8% of the employed population reported lost days from work in the past year because of complaints at the neck, shoulder, arm, elbow, wrist or hand (Blatter et al. 2001). The results of a British national survey in 1995 showed that musculoskeletal disorders of the neck and upper extremity were responsible for the loss of 4.2 million working days in a 12-month period (Jones et al. 1998). Borghouts et al. (1999) estimated the total number of sick days due to neck pain in 1996 in the Netherlands to be 1.4 million, with a total cost of US$ 185.4 million.
It is well recognized that neck and upper extremity complaints have a multi-factorial aetiology. Several reviews have identified individual characteristics, and (work-related) physical and psychosocial factors as risk factors for the onset of neck and upper extremity complaints (Bernard 1997; Bongers et al. 2002a, b; Malchaire et al. 2001; Muggleton et al. 1999; van der Windt et al. 2000; Zakaria et al 2002). Furthermore, these factors have also been recognized as potential prognostic factors for chronic pain and disability in patients with neck or upper extremity complaints (Ariëns et al. 2000, 2001; Cole and Hudak 1996; Eriksen et al. 1999; Feuerstein et al. 2000). However, relatively little is known about the association of work-related factors with sick leave in patients with neck or upper extremity complaints. Risk factors for the onset of neck and upper extremity complaints may differ from risk factors for sick leave due to these complaints (IJzelenberg et al. 2004). Ekberg and Wildhagen (1996) studied the impact of physical workload, work organization, psychosocial conditions and individual characteristics on days of sick leave after rehabilitation in patients with neck and shoulder disorders. They found two work-related factors (i.e., work content and uncomfortable sitting) to be independently related to sick leave days. A prospective cohort study on work-related determinants of sick leave in employees without neck pain at baseline suggested that work-related neck flexion and rotation, sitting, decision authority and skill discretion were independently related to sick leave due to neck pain (Ariëns et al. 2002). In contrast to these findings, a recent cross-sectional study on risk factors for musculoskeletal sick leave showed that physical workload nor psychosocial workload were significantly related to sick leave due to neck or upper extremity pain (IJzelenberg et al. 2004). Hansson and Jensen (2004) reviewed the literature on the causes for back and neck disorders and found that heavy physical workload, bent or twisted working position and low work satisfaction increased the risk of short-term and long-term sick leave, and self-reported pain and functional impairments were associated with a high risk for long-term sick leave.
Exposure to work-related physical risk factors may lead to pain and disability, which in turn may lead to sick leave. Psychosocial exposures at work may lead to psychological distress that may cause physiologic changes in the neck and upper extremity (e.g., increased muscle tension (Hagg and Astrom 1997; Lundberg 2002; Rissen et al. 2000), causing pain and disability, which in turn may lead to sick leave. Furthermore, psychosocial exposures at work may modify the effect of physical workload on sick leave. The objective of our study was to determine the influence of work-related physical and psychosocial risk factors on sick leave due to neck or upper extremity complaints in patients who have visited their general practitioner (GP) for these complaints.
Methods
Design and study population
This study is part of a large observational cohort study on musculoskeletal disorders conducted in 61 general practices (97 GPs) (van der Waal et al. 2003). Part of the GPs participated in the second Dutch National Survey of General Practice (NS2), carried out by the Netherlands Institute for Health Services Research in co-operation with the National Information Network of General Practice in 2001 (Schellevis et al. 2003). The Medical Ethics Committee of the VU University Medical Center approved our study. Written informed consent was obtained from all patients. Details of the study design are described elsewhere (van der Waal et al 2003).
Over a period of 1 year the GPs recruited 727 patients with a new complaint or new episode of a complaint at the neck, shoulder, elbow, arm, wrist or hand. An episode was considered to be ‘new’ if patients had not visited their GP for the same complaint during the preceding 3 months. Patients were eligible for participation if they were 18 years or older and capable of filling in Dutch questionnaires. Patients were excluded from the study if the presented symptoms were presumably caused by a fracture, malignancy, prosthesis, amputation or congenital defect or if the patient was pregnant.
At baseline a self-report questionnaire was sent to collect data on a broad range of factors (including work-related factors) that may be predictive of sick leave. In total, 643 patients (88%) returned the baseline questionnaire, of whom five patients were excluded (two were too young; three were pregnant). For our study, patients who reported to have paid work for more than 8 h per week were included (8–16 h: n = 41; 17–24 h: n = 69; 25–36 h: n = 101; >36 h: n = 172). Outcome (sick leave due to neck and/or upper extremity complaints) was assessed after 3 months using a self-report questionnaire.
Outcome measure
Sick leave was measured at 3 months after baseline by the question: “how long were you absent from work because of your complaint since the baseline questionnaire”. Response categories were (1) no sick leave; (2) less than 1 week; (3) between 1 and 2 weeks; (4) between 2 weeks and 1 month; (5) between 1 and 3 months; (6) more than 3 months. Sick leave was dichotomised into no sick leave (response category 1) and sick leave (response categories 2–6).
Determinants
At baseline, work-related physical risk factors were assessed by a questionnaire consisting of two scales “heavy physical workload” [12 items; e.g., does your work involve (a) standing for long periods of time, (b) walking for long periods of time, (c) moving loads, (d) physical hard work] and “long-lasting postures and repetitive movements” [six items; e.g., does your work involve (a) making the same movement for long periods of time; (b) bending or twisting your neck often; (c) working in the same position for long periods of time; (d) doing repetitive tasks with arms, hands or fingers many times per minute) (Bot et al. 2004). Response options varied from “seldom or never”, “sometimes”, “often”, and “(almost) always”. Scoring was done by simply adding up the response to each item, which produced a raw score from 0 to 36 for the first subscale, and 0 to 18 for the second subscale. The final scores were calculated by dividing the raw score by the maximum score, multiplied by 100, resulting in a final score ranging between 0 (no workload) and 100 (highest workload) for both subscales. The internal consistency and validity of this questionnaire were considered to be good in a population with upper extremity and lower extremity musculoskeletal disorders (Bot et al. 2004). Furthermore, two questions about “prolonged sitting” and “ working with visual display units (VDU) for long periods of time” (yes/no) were asked.
Work-related psychosocial risk factors were assessed according to the Demands–Control model of Karasek (1979). We used three subscales of the Job Content Questionnaire (JCQ): “job demands”, “decision authority” and “co-worker support” and one single item on “job security” (Karasek et al. 1998). The hypothesis of the Demands–Control model is that the most adverse reactions of psychological strain occur when demands are high and the worker’s decision latitude is low (Karasek et al. 1998). Therefore, we decided to combine the subscales high job demands and low decision authority into an additional determinant “job strain”. Both subscales were dichotomized by their median score and four categories were created: (1) high decision authority and low job demands (reference category); (2) high decision authority and high job demands; (3) low decision authority and low job demands; (4) low decision authority and high job demands.
Statistical analysis
Descriptive statistics (e.g., means and standard deviations) were used to present baseline characteristics of the study population. Differences between patients reporting sick leave and patients without sick leave were tested with the unpaired Student T-test (continuous variables) and the Chi square (χ2) test (categorical and dichotomous variables). In case a continuous variable was not normally distributed the Mann–Whitney test was used.
Instead of using logistic regression analysis, Cox regression models with equal survival time were used to investigate the association between work-related risk factors (determinants) and sick leave (outcome). Hazard ratios are more easy to interpret and provide a better estimate of relative risks than odds ratios (Barros and Hirakata 2003; Lee and Chia 1994; Skov et al. 1998; Thompson et al. 1998) Associations were expressed as hazard ratios (HR) and corresponding 95% confidence intervals (95% CI) per unit increase of the risk factor involved. For continuous factors the linearity of the relation between the risk factor and sick leave was examined. Factors that were found to be non-linearly related to sick leave were either dichotomized or divided into tertiles with equally sized groups (Table 1). The “low-category” served as the reference category in all analyses.
Table 1Potential confounders of the association between work-related risk factors and sick leave in patients with neck or upper extremity complaintsPotential confoundersCategorizationIndividual factors AgeContinuous (per year) SexMale versus female SmokingPresent versus previous smoker EducationPrimary versus secondary; college/university Pain copinga: retreating (seven items)Continuous (scale 7–28) Pain copinga: worrying (nine items)Continuous (scale 9–36) Distress (six items)Continuous (scale 1–9)General health ACSM position standcNorm not met versus norm met Norm healthy activityNorm not met versus norm met Perceived healthdContinuous (scale 1–5) Vitalityd (four items)Continuous (scale 0–100) Quality of lifeContinuous (scale 1–5)Characteristics of the complaint Kind of complaintLocalized versus generalized Duration of the complaintCategorical (<1, 1–4 weeks; 1–6 , >6 months) History of neck/upper limb complaintsHistory versus no history Musculoskeletal co-morbidityYes versus no Other co-morbidityYes versus noWork-related psychosocial factors (%) Decision authorityf (three items)Tertiles (low, medium, high) Job demandsf (five items)Tertiles (low, medium, high) Co-worker supportf (four items)Tertiles (low, medium, high) Job-securityfLow security versus high security Job as perceived cause of complaintYes versus noaPain Coping Inventory (Kraaimaat and Evers 2003; Kraaimaat et al. 1997)bFour Dimensional Symptom Questionnaire (Terluin 1998)cAmerican College of Sports Medicine Position Stand (American College of Sports Medicine Position Stand 1990)dMedical Outcomes Study 36-item Short Form Health Survey (Ware and Sherbourne 1992)ePhysical workload questionnaire (Bot et al. 2004)fJob Content Questionnaire (Karasek et al. 1998); %work-related psychosocial factors were considered as potential confounders in the relation between work-related physical factors and sick leave
To prevent multicollinearity we checked whether the psychosocial risk factors, the physical risk factors, and potential confounders were highly correlated (P > 0.5 or P < −0.5). The factor with the highest association with sick leave was retained and the other factor was removed from further analyses. This was the case for prolonged sitting and prolonged VDU work (P = 0.69), distress and worrying (P = 0.52); prolonged VDU-work and heavy physical work (P = −0.56), and prolonged sitting and heavy physical work (P = −0.65).
We performed the analyses in several stages. First, the unadjusted relationships between the work-related risk factors and sick leave were examined. Second, these relationships were adjusted for each of the potential confounders individually. Potential confounders of the relationship between work-related risk factors and sick leave included individual factors, general health, characteristics of the complaint, and other work-related risk factors (Table 1). Factors were considered as potential confounders if they had been reported as predictive of sick leave or poor prognosis in previously published scientific papers. Only those factors that led to a considerable change in the regression coefficient of the risk factor (>10%) were considered as potential confounders in the multiple regression models. Next, a manual forward selection procedure was used to sequentially include potential confounders that induced the most change in the regression coefficient of the risk factor (i.e., in order of highest change of the regression coefficient). Confounders that changed the regression coefficient of sick leave by more than 10% were retained in the model. If the unadjusted relationship between the work-related risk factor and sick leave was not statistically significant (P > 0.05) and remained not significant after controlling for all potential confounders individually, the relationship was adjusted for sick leave at baseline and sex only.
Individual factors may interact in the relation between work-related physical and psychosocial risk factors and sick leave. We considered possible effect modification by sick leave at baseline, sex, coping style worrying (dichotomized) and musculoskeletal co-morbidity. Product terms of the potential effect modifier and the work-related risk factor were added to the model (e.g., sex × risk factor). Furthermore, possible effect modification by psychosocial risk factors was investigated in the relation between the four physical risk factors and sick leave. Factors significantly interacting with determinants in the model were retained in the models. In case of significant effect modification stratified analyses were carried out presenting the effect of the work-related risk factor for relevant subgroups of workers. All analyses were performed with the use of SPSS for Windows version 10.1 (SPSS Inc., Chicago, IL, USA).
Results
In total, 342 of the 383 included patients (89%) completed the 3 months follow-up questionnaire. Fifty-eight of the patients were excluded, because data on sick leave at follow-up were missing. There were no significant differences between responders and dropouts by age, sex, and any of the determinants (P > 0.05). Baseline characteristics of patients reporting sick leave in the 3 months following baseline (n = 73) and patients without sick leave (n = 252) are shown in Table 2. The mean age of the total study population was 43 years (SD 10.3) and 54% was female. At baseline 80 patients reported sick leave in the 3 months preceding baseline due to their neck or upper extremity complaint. Half of these patients reported sick leave in the 3 months following baseline. With reference to physical and psychosocial risk factors, there was a statistically significant difference between patients reporting sick leave and patients without sick leave for decision authority, heavy physical work, static postures and repetitive movements, prolonged sitting and prolonged VDU-work.
Table 2Baseline characteristics and values of patients with neck or upper extremity complaints reporting sick leave (n = 73) and of patients reporting no sick leave (n = 252) due to their complaints in the 3 months following baseline assessmentCharacteristicSick leaveaNo sick leaveaTotalIndividual factors Age, years [mean (SD)]42.0 (11.5)43.6 (9.8)43.0 (10.3) Sex (female)75%49%**54% Sick leave in 3 months before baseline59%16%**25% Education level  Primary48%30%*34%  Secondary40%49%48%  College/university12%21%18% Number of hours work (h)  8–1611%12%11%  17–2418%25%20%  25–3626%30%27%  >3645%33%42%Married/living together63%83%*78%Smoking (now, ever)77%67%70%Pain coping: retreating [scale 7–28; median (IR)]11.0 (5.0)9.0 (4.8)**10.0 (4.5)Pain coping: worrying (scale 9–36; median (IR))18.0 (7.0)14.0 (5.0)**15.0 (6.0)Psychological distress (scale 0–12; median (IR))7.0 (5.0)4.0 (5.0)**5.0 (6.0)General health Meeting ACSM position stand4%16%*13% Meeting Norm Healthy Activity41%42%43% Perceived health [scale 1–5; mean (SD)]3.1 (0.8)3.4 (0.9)*3.3 (0.8) Quality of life [scale 1–5; mean (SD)]3.2 (0.7)3.5 (0.8)*3.4 (0.8) Vitality [scale 0–100; mean (SD)]54.3 (20.9)62.4 (17.2)**60.0 (18.5)Characteristics complaint Localized complaint40%53%*49% Complaint at both arms10%15%13% Complaint at dominant arm50%44%47%Duration of current episode <1 week5%7%7% 1week–1 month36%32%33% 1–6 months29%37%34% >6 months30%24%26%History of elbow complaints51%43%45%Musculoskeletal co-morbidity56%47%50%Pain intensity [scale 0–10; mean, (SD)]6.0 (1.9)4.4 (2.1)**4.8 (2.2)Functional disability [scale 0–100; median (IR)]36.3 (28.8)16.5 (21.3)**20.0 (25.3)Work-related factors Heavy physical work [scale 0–100; mean (SD)]36.1 (40.2)16.7 (36.1)**22.2 (42.8) Static postures and repetitive movements (scale 0–100)55.6 (47.2)44.4 (44.4)**44.4 (38.9) Sitting for a long period of time22%48%**42%VDU-work for a long period of time21%36%*31% Decision authority [scale 3–12; mean (SD)]9.0 (3.0)9.0 (3.0)*9.0 (3.0) Job demands [scale 5–20; mean (SD)]13.4 (3.6)12.8 (2.9)12.9 (3.1) Co-worker support [scale 4–16; mean (SD)]12.0 (1.0)12.0 (2.0)12.0 (2.0) Job security78%85%83% Job as perceived cause of complaint62%49%56%VDU visual display unit, SD standard deviation, IR interquartile range* P < 0.05; ** P < 0.001 (independent T-test, Mann–Whitney test, or χ2-test)avalues are percentages of patients unless indicated
Table 3 shows the effect of work-related physical and psychosocial risk factors on sick leave. After adjustment for confounders, a statistically significant effect was found for heavy physical work and prolonged sitting, but only in patients with a high score on pain coping strategy “worrying”. In patients who scored low on the pain coping subscale “worrying” the hazard ratio of sick leave was 1.05 (0.93–1.18, P = 0.46) per 10% increase in heavy physical work. In patients scoring high on “worrying” the relative risk of sick leave was 1.32 (95% CI 1.07–1.62) per 10% increase in heavy physical work. Patients who were sitting for long periods of time had a reduced risk of sick leave as compared to patients who did not spent a lot of time sitting, again only in patients who scored high on “worrying” (HR = 0.17, 95% CI 0.04–0.72). In patients who scored low on “worrying”, sitting for long periods of time did not have an effect on sick leave (P = 0.43). Sick leave at baseline, sex and musculoskeletal co-morbidity did not modify the relationship between the physical and psychosocial risk factors and sick leave. The psychosocial risk factors neither modified the relationship between heavy physical work and sick leave.
Table 3Relationship between work-related risk factors and sick leave in patients with neck or upper extremity complaints: results from the multiple Cox regression analysesDeterminantNCrude HR95% CIAdjusted HR95% CIHeavy physical work (per 10% increase)69/3201.23[1.12; 1.36]* For patients with low scores on worrying d21/1401.05[0.93; 1.18]a For patients with high scores on worryingd48/1801.32[1.07; 1.62]a,*Static postures, repetitive movements (per 10% increase)69/3201.16[1.06; 1.27]*1.04[0.94; 1.14]bSitting for long periods of time (vs. never/now and then)16/3220.40[0.23; 0.70]* For patients with low scores on worryingd2/1800.81[0.43; 1.52]a For patients with high scores on worryingd14/1420.17[0.04; 0.72]a,*VDU-work long periods of time (vs. never/now and then)15/3220.56[0.32; 1.00]*0.70[0.36; 1.36]cDecision authority Low1.00 Medium0.80[0.47; 1.35]0.94[0.55; 1.59]a High0.59[0.31; 1.13]0.87[0.45; 1.68]aJob demands Low23/1151.001.00 Medium20/1110.90[0.49; 1.64]0.91[0.50; 1.66]a High27/951.42[0.81; 2.48]1.13[0.64; 1.97]aCo-worker support Low16/861.001.00 Medium31/1401.19[0.65; 2.18]1.22[0.67; 2.23]a High23/881.40[0.74; 2.66]1.14[0.59; 2.17]aLow job security (vs high)70/3191.43[0.78; 2.60]1.47[0.80; 2.69]aJob strain High decision authority, low job demands10/771.001.00 High decision authority, high job demands11/521.63[0.69; 3.84]1.29[0.54; 3.07]b Low decision authority, low job demands25/1041.85[0.89; 3.85]1.30[0.62; 2.73]b Low decision authority, high job demands 24/862.15[1.03; 4.49]*1.15[0.54; 2.47]bN Number of patients reporting sick leave/total, HR hazard ratio* P < 0.05aAdjusted for sick leave at baseline and sexbAdjusted for sick leave at baseline, sex and worryingcAdjusted for sick leave at baseline, sex, education level, quality of life, working in static postures and with repetitive movementsdEffect modification by worrying
Discussion
We studied a population of working employees who consulted their GP with a complaint at the neck or upper extremity. The results show that heavy physical work and prolonged sitting in patients that worry a lot predicted sick leave in the three successive months after baseline. Other physical and psychosocial risk factors appeared not to be related to sick leave after adjustment for confounding variables.
Individual factors and stress may have a modifying effect on the relation between work related factors and outcome in musculoskeletal complaints. The pain coping style “worrying” appeared to be an effect modifier in the relationship between heavy physical work and sick leave. An increase of 10% of heavy physical work in patients who worried a lot increased the probability on sick leave with 1.3. A passive coping style like worrying (e.g., “focus on pain all the time”; “I think the pain will get worse”) is thought to generate a preoccupation with bodily symptoms, which may increase the perception of pain and disability (Covic et al. 2000; Evers et al. 2003) or generate a different appraisal of the work situation and musculoskeletal symptoms (Bongers et al. 2002b), which in turn may lead to sick leave. Sitting for long periods of time reduced the risk of sick leave, only in patients who scored high on the pain subscale “worrying” In the study of Ariëns et al. (2002) sitting was also related to a reduced risk of sick leave. However, uncomfortable sitting has been found to increase the number of days on sick leave due to neck and shoulder disorders (Ekberg and Wildhagen 1996). Sitting was highly negatively correlated with heavy physical work. Perhaps, people who sit for long periods of time at their work do not experience heavy physical work, and thus the absence of heavy physical work results in a reduced risk. This may explain why sitting had only a protective effect in patients that worry a lot.
In the unadjusted analyses, all the physical risk factors and two of the psychosocial risk factors (i.e., decision authority and job strain) had a statistically significant effect on sick leave. It is partly due to the underlying distribution of the exposure which physical factors are most strongly associated with sick leave in the multivariate analyses. Adjustment for sick leave at baseline had the strongest effect on the presented associations, diminishing the strength of the relations between work-related risk factors and sick leave. Sick leave may have been the result of exposure to these risk factors, but once patients were on sick leave work-related risk factors no longer seem to have an impact on continued sick leave. Half of the patients who reported sick leave within the 3 months before baseline also reported sick leave in the 3 months following baseline. The effect of sick leave in the months preceding baseline apparently outweighed the impact of work-related risk factors in the analyses. The proportion of patients reporting sickness during the 3 months follow-up was too small to be able to exclude patients reporting sick leave at baseline. Cox regression produces large estimates of the standard errors, which results in conservative estimates of the confidence intervals (Skov et al. 1998). Therefore, it may be possible that relevant associations did not reach statistical significance.
Sick leave data were collected by a self-reported questionnaire. Sick leave data collected by an objective method (i.e., sick leave records) may be more accurate than self-reported sick leave. However, in large epidemiological studies the use of questionnaires is more feasible and can be a source of reliable data on sick leave. Burdorf et al. (1996) investigated the reliability of self-reported sick leave with company records as reference. A good agreement was found between prevalence, frequency and duration of self reported sick leave and company records in patients with back pain. In our study we only examined the prevalence of sick leave and consider the reported sick leave data to be fairly reliable.
Our study population differs from an occupational cohort, consisting of workers from a wide variety of occupational settings who had visited the GP due to neck or upper extremity complaints. This makes our results more widely generalisable than a selective sample of workers from a specific company or industry. However, due to the fact that our population already had symptoms at baseline we may not be able to discriminate between factors that are a consequence of sick leave at baseline and factors that may increase the risk of sick leave. For example, patients may worry more about their pain problem because they are no longer able to work, or worrying about their pain problem may be the reason for sick leave after their visit to the doctor.
In the Netherlands the GP is often confronted with patients who are on sick leave due to musculoskeletal complaints, as patients who seek medical care usually first consult their GP. The GP acts as a gatekeeper in the health care system. At the time of our study, referrals to the second or third level of care could, in principle, only be made by the GP. This is comparable to, for instance, the British and the Canadian health care systems. As a result of their position in the Dutch health care system, GPs could play an important role in the prevention of aggravation of complaints. In this study the copying style “worrying” seemed to be an important factor in patients who have jobs involving heavy physical work. Reassuring patients might help to reduce aggravation of complaints, which might improve the chances of return to work in this group of patients with neck or upper extremity complaints. It may be interesting to investigate whether early intervention aimed at promoting particular coping styles can prevent or reduce sick leave in patients with neck or upper extremity complaints in a primary care setting.
In conclusion, heavy physical work increased the risk of sick leave and prolonged sitting reduced the risk of sick leave in a subgroup of patients who worry much. Other work-related physical risk factors and work-related psychosocial risk factors were not significantly related to sick leave. Additional large longitudinal studies of sufficiently large size among employees with neck or upper extremity complaints are needed to confirm our results.

sick leave
neck
upper extremity
workload
cohort study