Capture—recapture and anchored prevalence estimation of injecting drug users in England: national and regional estimates

Hay, Gordon; Gannon, Martin J.; MacDougall, Jane; Eastwood, Catherine; Williams, Kate; Millar, Tim

doi:10.1177/0962280208094687

Cited by 26 publications

(26 citation statements)

References 39 publications

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“…Instead, indirect methods such as capture–recapture (CRC) estimation have been recommended 12, 13, 14, 15. CRC is used extensively to estimate the prevalence of problem drug use 11, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25.…”

Section: Introductionmentioning

confidence: 99%

Problem drug use prevalence estimation revisited: heterogeneity in capture–recapture and the role of external evidence

et al. 2015

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Background and AimsCapture–recapture (CRC) analysis is recommended for estimating the prevalence of problem drug use or people who inject drugs (PWID). We aim to demonstrate how naive application of CRC can lead to highly misleading results, and to suggest how the problems might be overcome.MethodsWe present a case study of estimating the prevalence of PWID in Bristol, UK, applying CRC to lists in contact with three services. We assess: (i) sensitivity of results to different versions of the dominant (treatment) list: specifically, to inclusion of non‐incident cases and of those who were referred directly from one of the other services; (ii) the impact of accounting for a novel covariate, housing instability; and (iii) consistency of CRC estimates with drug‐related mortality data. We then incorporate formally the drug‐related mortality data and lower bounds for prevalence alongside the CRC into a single coherent model.ResultsFive of 11 models fitted the full data equally well but generated widely varying prevalence estimates, from 2740 [95% confidence interval (CI) = 2670, 2840] to 6890 (95% CI = 3740, 17680). Results were highly sensitive to inclusion of non‐incident cases, demonstrating the presence of considerable heterogeneity, and were sensitive to a lesser extent to inclusion of direct referrals. A reduced data set including only incident cases and excluding referrals could be fitted by simpler models, and led to much greater consistency in estimates. Accounting for housing stability improved model fit considerably more than did the standard covariates of age and gender. External data provided validation of results and aided model selection, generating a final estimate of the number of PWID in Bristol in 2011 of 2770 [95% credible interval (Cr‐I) = 2570, 3110] or 0.9% (95% Cr‐I = 0.9, 1.0%) of the population aged 15–64 years.ConclusionsSteps can be taken to reduce bias in capture–recapture analysis, including: careful consideration of data sources, reduction of lists to less heterogeneous subsamples, use of covariates and formal incorporation of external data.

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Section: Introductionmentioning

confidence: 99%

Problem drug use prevalence estimation revisited: heterogeneity in capture–recapture and the role of external evidence

et al. 2015

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“…By contrast, Bird, Hutchinson, and Goldberg (2003), King, Bird, Brooks, Hutchinson, and Hay (2005), King et al. (2009), and King, Bird, Overstall, Hay, and Hutchinson (submitted) have drawn attention not only to higher DRD rates per 100 IDUs in older IDUs but also to higher numbers of DRDs at older ages consequent upon the ageing (to 35+ years) in the twenty-first century of epidemic waves of IDUs who had commenced injecting in the 1980s – earlier in Scotland, for example, than in England.…”

Section: Introductionmentioning

confidence: 97%

“…Covariate-adjusted, Bayesian, and even single-list (Mascioli & Rossi, 2008; Hay & Smit, 2003) CRC methods have been variously deployed to estimate the number of IDUs. There has been serial use of CRC methods in Scotland and England (Hay et al., 2009; King et al., 2009; Surveys, Design and Statistics Subcommittee, 2008); use in resource-poor countries, as reviewed by van Hest, Grant, and Abubakar (2011), in Eastern Europe (Uuskula et al., 2007), in multiple cities of England or France (Hickman et al., 2004; Vaissade and Legleye, 2009); and within a primary care trust where CRC analysis focused additionally on IDUs who were matchable to the primary care register (“registered”) and for whom two-year mortality could therefore be ascertained directly (Hickman et al., 2009). Hickman et al.…”

Section: Introductionmentioning

confidence: 99%

Injecting drug users in Scotland, 2006: Listing, number, demography, and opiate-related death-rates

King

Bird

Overstall

et al. 2012

Addiction Research & Theory

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Using Bayesian capture–recapture analysis, we estimated the number of current injecting drug users (IDUs) in Scotland in 2006 from the cross-counts of 5670 IDUs listed on four data-sources: social enquiry reports (901 IDUs listed), hospital records (953), drug treatment agencies (3504), and recent Hepatitis C virus (HCV) diagnoses (827 listed as IDU-risk). Further, we accessed exact numbers of opiate-related drugs-related deaths (DRDs) in 2006 and 2007 to improve estimation of Scotland's DRD rates per 100 current IDUs. Using all four data-sources, and model-averaging of standard hierarchical log-linear models to allow for pairwise interactions between data-sources and/or demographic classifications, Scotland had an estimated 31700 IDUs in 2006 (95% credible interval: 24900–38700); but 25000 IDUs (95% CI: 20700–35000) by excluding recent HCV diagnoses whose IDU-risk can refer to past injecting. Only in the younger age-group (15–34 years) were Scotland's opiate-related DRD rates significantly lower for females than males. Older males’ opiate-related DRD rate was 1.9 (1.24–2.40) per 100 current IDUs without or 1.3 (0.94–1.64) with inclusion of recent HCV diagnoses. If, indeed, Scotland had only 25000 current IDUs in 2006, with only 8200 of them aged 35+ years, the opiate-related DRD rate is higher among this older age group than has been appreciated hitherto. There is counter-balancing good news for the public health: the hitherto sharp increase in older current IDUs had stalled by 2006.

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“…PWID estimates for many countries and cities in Europe and elsewhere are out of date, missing, or inconsistent. For instance, in Scotland the estimated number of currently active PWID for has varied from 19,000 to 27,000 (60); and the number of PWID in England varies from 130,000 to 200,000 (1, 61, 62). …”

Section: Introductionmentioning

confidence: 99%

Hepatitis C virus treatment as prevention in people who inject drugs

Hickman

Angelis

Vickerman

et al. 2015

Current Opinion in Infectious Diseases

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Purpose of Review The majority of HCV infections in UK and many developing countries were acquired through injecting. New clinical guidance suggests that HCV treatment should be offered to people with a transmission risk – such as people who inject drugs (PWID) – irrespective of severity of liver disease. We consider the strength of the evidence base and potential problems in evaluating HCV treatment as prevention among PWID. Recent Findings There is good theoretical evidence from dynamic models that HCV treatment for PWID could reduce HCV chronic prevalence and incidence among PWID. Economic evaluations from high-income settings have suggested HCV treatment for PWID is cost-effective, and that in many settings HCV treatment of PWID could be more cost-effective than treating those at an equivalent stage with no ongoing transmission risk. Epidemiological studies of older interferon treatments have suggested that PWID can achieve similar treatment outcomes to other patient groups treated for chronic HCV. Impact and cost-effectiveness of HCV treatment is driven by the potential “prevention benefit” of treating PWID. Model projections suggest that more future infections, End Stage Liver Disease, and HCV related deaths will be averted than lost through re-infection of PWID treated successfully for HCV. However, there is to date no empirical evidence from trials or observational studies that test the model projections and “prevention benefit” hypothesis. In part this also is because of uncertainty in the evidence base but also because PWID HCV treatment rates historically in most sites have been low, and any scale-up and switch to the new DAA has not yet occurred. There are a number of key uncertainties in the data available on PWID that need to be improved and addressed in order to evaluate treatment as prevention. These include estimates of the prevalence of PWID, measurements of HCV chronic prevalence and incidence among PWID, and how to interpret re-infection rates as potential outcome measures. Summary Eliminating HCV through scaling up treatment is a theoretical possibility. But empirical data are required to demonstrate that HCV treatment can reduce HCV transmission which will require an improved evidence base and analytic framework for measuring PWID and HCV prevalence.

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Capture—recapture and anchored prevalence estimation of injecting drug users in England: national and regional estimates

Cited by 26 publications

References 39 publications

Problem drug use prevalence estimation revisited: heterogeneity in capture–recapture and the role of external evidence

Problem drug use prevalence estimation revisited: heterogeneity in capture–recapture and the role of external evidence

Injecting drug users in Scotland, 2006: Listing, number, demography, and opiate-related death-rates

Hepatitis C virus treatment as prevention in people who inject drugs

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