Gordon Hay

Monitoring hepatitis C virus infection among injecting drug users in the European Union: a review of the literature

Hepatitis C virus (HCV) among injecting drug users (IDUs) is one of the European Unions (EU) major public health problems. This review examines the current state of knowledge regarding HCV among IDUs in EU countries. Studies published between January 1990 and December 2000, were identified through a computerized search (MEDLINE and EMBASE). Ninety-eight studies have reported prevalence for HCV among groups of IDUs in all EU countries except Luxembourg. The prevalence of anti-HCV ranged from 30 to 98%. Incidence rates ranged from 6.2 to 39.3 per 100 person years. This review provides a comprehensive examination of HCV infection among IDUs in the countries of the EU, and quite clearly demonstrates that the quality and epidemiological relevance of the studies published varies widely. Thus, the reported data may not reflect accurately the current or recent past prevalence of HCV among IDUs in the EU. A strategic approach to the surveillance of HCV among IDUs in the EU, utilizing robust and consistent methods, is required urgently.

Estimating the prevalence of drug misuse in Dundee, Scotland: an application of capture-recapture methods.

STUDY OBJECTIVES: To apply capture-recapture methods to provide an estimate of the prevalence of opiate and benzodiazepine misuse in Dundee, Scotland. DESIGN: A four sample capture-recapture method using data from both statutory and non-statutory data sources to estimate drug misuse prevalence in Dundee between January 1990 and December 1994. PARTICIPANTS: Users of benzodiazepines or opiates residing within Dundee. RESULTS: Altogether 855 drug misusers were identified from various sources within Dundee; many were identified from more than one source. Using this data, the estimated unknown population was 1702, giving a total population of 2557 (95% confidence interval (CI) 1974, 3458) who misuse benzodiazepines or opiates. This represents a prevalence of 28.8 (95% CI 22.3, 39.0) per thousand. CONCLUSIONS: Capture-recapture techniques can be applied to statutory and non-statutory agency data to produce an estimate of at least certain sections of the drug misusing population. However, it is important to recognise the limitations of this methodology and in future to seek to combine a range of approaches to the problem of estimating prevalence rather than sticking rigidly to any single approach.

Contribution of problem drug users' deaths to excess mortality in Scotland: secondary analysis of cohort study

Objectives To examine the “Scottish effect”—namely, the growing divergence between mortality in Scotland and England that is not explained by national differences in levels of deprivation—and, more specifically, to examine the extent to which the Scottish effect is explained by cross national differences in the prevalence of problem drug use. Design Secondary analysis of cohort study (the DORIS study). Participants 1033 Scottish drug users recruited to the cohort study in 33 drug treatment facilities across Scotland in 2001-2 and followed up 33 months later in 2004-5. Results 38 deaths occurred in the cohort, giving a standardised mortality ratio for the cohort of 1244 (95% credible interval 876 to 1678). Only 22 of the 38 deaths in drug users were classified as drug related deaths. From estimates of the size of the problem drug using populations in both England and Scotland, the contribution of deaths in drug users to national death rates can be estimated: the attributable risk fraction for Scotland is 17.3% (12.3% to 22.8%) and that for England is 11.1% (7.8% to 14.8%). Excluding estimated numbers of deaths in drug users would bring down age standardised mortality at ages 15-54 years from 196 to 162 per 100 000 in Scotland and from 138 to 122 per 100 000 in England; 32.0% (22.3% to 43.0%) of the excess mortality in Scotland is due to drug use. Conclusion Although problem drug use is a low prevalence risk behaviour, it carries a high mortality; the standardised mortality ratio for Scottish drug users is 12 times as high as for the general population. The higher prevalence of problem drug use in Scotland than in England accounts for a third of Scotland’s excess mortality over England. Successful public health efforts to reduce the prevalence of problem drug use in Scotland or deaths in Scottish drug users would have a dramatic impact on overall mortality in Scotland.

Estimating injection drug use prevalence using state wide administrative data sources: Estonia, 2004

Estonia has rapidly expanding injection drug use (IDU) driven HIV/AIDS epidemic with the highest reported incidence rate and prevalence (1.3%) of HIV in the European region. To evaluate the feasibility of IDU prevalence estimations based on routine nationwide data sources using capture-recapture methodology, and provide estimates of IDU prevalence. IDUs were identified from the Police, Health insurance fund, State HIV reference laboratory data sources. Poisson regression models were fitted to the observed data, with interactions between data sources fitted to replicate ‘dependencies’ between the data sources. There were 13,886 (95% CI 8132–34,443) IDUs in Estonia in 2004, which translates into a prevalence of 2.4% (95% CI 1.4–5.9%) among people aged 15–44 years. The estimate is in line with the estimate provided by the panel of experts and estimates from the neighbouring countries experiencing similar societal and economic challenges.

Hepatitis C prevalence in Denmark -an estimate based on multiple national registers

BackgroundA national survey for chronic hepatitis C has not been performed in Denmark and the prevalence is unknown. Our aim was to estimate the prevalence of chronic hepatitis C from public registers and the proportion of these patients who received specialized healthcare.MethodsPatients with a diagnosis of chronic hepatitis C were identified from four national registers: a laboratory register, the Hospital Discharge Register, a clinical database of chronic viral hepatitis and the Register of Communicable Diseases. The total population diagnosed with hepatitis C was estimated by capture-recapture analysis. The population with undiagnosed hepatitis C was derived from the national register of drug users by comparing diagnosed and tested persons.ResultsA total of 6,935 patients diagnosed with chronic hepatitis C were identified in the four registers and the estimated population diagnosed with the disease was 9,166 persons (95% C.I. interval 8,973 – 9,877), corresponding to 0.21% (95% CI 0.21%-0.23%) of the Danish population over 15years of age. The prevalence was highest among persons 40–49years old (0.39%) and males (0.28%). It was estimated that 40% of the diagnosed patients lived in the capital region, and 33.5% had attended specialised healthcare. It was estimated that 46% of hepatitis C patients had not been diagnosed and the total population with chronic hepatitis C in Denmark was 16,888 (95% C.I. 16,474-18,287), corresponding to 0.38% (95% CI 0.37-0.42) of the population over 15years of age.ConclusionsThe estimated prevalence of chronic hepatitis C in Denmark was 0.38%. Less than half of the patients with chronic hepatitis C in Denmark have been identified and among these patients, one in three has attended specialised care.

Estimating the Number of Drug Injectors from Needle Exchange Data

Background. Information on the size of a drug injecting population is required for resource allocation and health service evaluation. The truncated Poisson (tP) estimator is a method of prevalence estimation which, in contrast to the capture-recapture method, can be used when only a single data source is available. Objective. We present a study on the size of a drug injecting population to illustrate how the tP estimator can be calculated and how some of its underlying assumptions can be checked. Results. Although 647 individuals attended the needle exchange in 1997, the total number of drug injectors was estimated to be 1041 within a 95% confidence interval of 960 ∼ 1137. Discussion. The truncated Poisson estimator can be an easy and quick method of providing a prevalence estimate of drug injecting and may produce valid estimates of relative changes in prevalence rates over time.

Capture-recapture estimates of problem drug use and the use of simulation based confidence intervals in a stratified analysis.

STUDY OBJECTIVE To establish the prevalence of problem drug use in the 10 local authorities within the Metropolitan County of Greater Manchester between April 2000 and March 2001. SETTING AND PARTICIPANTS Problem drug users aged 16-54 resident within Greater Manchester who attended community based statutory drug treatment agencies, were in contact with general practitioners, were assessed by arrest referral workers, were in contact with the probation service, or arrested under the Misuse of Drugs Act for offences involving possession of opioids, cocaine, or benzodiazepines. DESIGN Multi-sample stratified capture-recapture analysis. Patterns of overlaps between data sources were modelled in a log-linear regression to estimate the hidden number of drug users within each of 60 area, age group, and gender strata. Simulation methods were used to generate 95% confidence intervals for the sums of the stratified estimates. MAIN RESULTS The total number of problem drug users in Greater Manchester was estimated to be 19 255 giving a prevalence of problem drug use of 13.7 (95% CI 13.4 to 15.7) per 1000 population aged 16-54. The ratio of men to women was 3.5:1. The distribution of problem drug users varied across three age groups (16-24, 25-34, and 35-54) and varied between the 10 areas. CONCLUSIONS Areas in close geographical proximity display different patterns of drug use in terms of prevalence rates and age and gender patterns. This has important implications, both for future planning of service provision and for the way in which the impact of drug misuse interventions are evaluated.

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

Capture—recapture (C—RC) using four data sources, one of which accounted for 81% of captured injectors, and multiple indicator methods (MIM) were used to obtain national, regional and local estimates of the prevalence of injecting drug use among opiate and/or crack cocaine users in England. Persons aged 15 to 64 years, in contact with health and/or criminal justice services during 2005/2006, and known to be using opiates and/or crack cocaine and injecting drugs were included in the C—RC analysis. The MIM analysis included indicators relating to drug treatment, drug-related deaths, population density and drug offences. There were an estimated 130,000 opiate and/or crack cocaine users who injected drugs in 2005/06 (95% confidence interval 125,800 to 137,000), corresponding to 3.9 per thousand of the population aged 15 to 64 years (95% confidence interval 3.8—4.1). Regional variation in the prevalence of injecting was evident, ranging from 6.1 per thousand of the population aged 15 to 64 years in Yorkshire and the Humber (95% confidence interval 5.6 to 6.6) to 2.3 per thousand in the East of England (95% confidence interval 1.8 to 2.9). Application of gender and age-group distributions for treated injecting drug users (IDUs) to the prevalence estimates suggested that there were 97,200 male injectors (95% confidence interval 94,000 to 102,500) and 63,600 female injectors aged 25 to 34 years (95% confidence interval 61,500 to 67,000). The prevalence estimates provide a basis from which numbers of current IDUs infected with hepatitis C virus (HCV) can be approximated.

Incomplete contingency tables with censored cells with application to estimating the number of people who inject drugs in Scotland

Estimating the size of hidden or difficult to reach populations is often of interest for economic, sociological or public health reasons. In order to estimate such populations, administrative data lists are often collated to form multi-list cross-counts and displayed in the form of an incomplete contingency table. Log-linear models are typically fitted to such data to obtain an estimate of the total population size by estimating the number of individuals not observed by any of the data-sources. This approach has been taken to estimate the current number of people who inject drugs (PWID) in Scotland, with the Hepatitis C virus diagnosis database used as one of the data-sources to identify PWID. However, the Hepatitis C virus diagnosis data-source does not distinguish between current and former PWID, which, if ignored, will lead to overestimation of the total population size of current PWID. We extend the standard model-fitting approach to allow for a data-source, which contains a mixture of target and non-target individuals (i.e. in this case, current and former PWID). We apply the proposed approach to data for PWID in Scotland in 2003, 2006 and 2009 and compare with the results from standard log-linear models.

The selection from multiple data sources in epidemiological capture–recapture studies

Capture–recapture methods are becoming more commonly used in estimating the size of hidden human populations such as drug users. The available literature appears polarized between those who totally reject the usage of these methods and those who promote the methodology as a simple and concise method of population size estimation. In this paper we demonstrate the differences that occur when employing different combinations of data sets in estimating the prevalence of drug use. We show that using three data sources often results in unreliable estimates and suggest that the use of four data sources should be critically assessed.