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      Estimating the force of infection for HCV in injecting drug users using interval-censored data

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          SUMMARY

          Injecting drug users (IDUs) account for most new HCV infections. The objectives of this study were: to estimate the force of infection for hepatitis C virus in IDUs within the interval-censoring framework and to determine the impact of risk factors such as frequency of injection, drug injected, sharing of syringes and time of first injection on the time to HCV infection. We used data from the Amsterdam Cohort Study collected in The Netherlands and focused on those individuals who were HCV negative upon entry into the study. Based on the results, the force of infection was found to vary with time of first injection. The risk of infection was higher in the first 3 years of an IDU's career, implying estimates based on single cross-sectional studies could be biased. Frequency of injection and type of drug injected were found to be highly significant predictors, whereas sharing syringes was not.

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          Opportunities for prevention: hepatitis C prevalence and incidence in a cohort of young injection drug users.

          The objective of this study was to compare sociodemographic, drug, and sexual risk characteristics between hepatitis C virus (HCV) baseline positive and negative young (13-24 years) injection drug users (IDUs) and to determine prospective risk factors for HCV seroconversion among the youth. Data were collected through the Vancouver Injection Drug Users Study (VIDUS). To date, more than 1,400 Vancouver-area IDUs have been enrolled and followed up; 234 were aged 24 years and younger. Semiannually, participants have completed an interviewer-administered questionnaire and have undergone serologic testing for human immunodeficiency virus (HIV) and HCV. Univariate and multivariate logistic regression analyses were undertaken to investigate predictors of baseline HCV positivity. In the multivariate analyses, Cox regression models with time-dependent covariates were used to identify predictors of HCV seroconversion. Of the 232 young injectors, 107 (46%) were HCV positive at baseline and a further 37 HCV seroconverted during the study period for an incidence rate of 37.3 per 100 person-years. Baseline positivity was associated with Aboriginal ancestry, older age, greater number of years injecting drugs, recent incarceration, sex trade work, more than 100 lifetime sexual partners, a previous sexually transmitted disease, living in the IDU epicenter, and injection more than once per day of heroin, cocaine, and speedball. Factors independently associated with HCV seroconversion were having a partner who uses injection drugs, requiring help to inject, and injection of cocaine more than once daily. In conclusion, unlike older IDUs, more than one half of young injectors were HCV negative at recruitment. Thus, there is a window of opportunity for prevention. However, the incidence rate of HCV among these young IDUs is alarming, suggesting that the opportunity to intervene is exceedingly small.
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            Methods for interval-censored data

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              Hepatitis C virus infection and needle exchange use among young injection drug users in San Francisco.

              Young injection drug users (IDUs) in San Francisco may be at high risk for hepatitis C virus (HCV) infection despite access to several needle exchange venues. The authors conducted a cross-sectional study from 1997 to 1999 in San Francisco to estimate the prevalence and incidence of antibody to HCV (anti-HCV) among street-recruited IDUs under age 30, and to examine risk behaviors and sources of sterile needles. Among 308 participants, the prevalence of anti-HCV was 45%. Using statistical modeling, incidence of HCV infection was estimated to be 11 per 100 person years. Independent risk factors for anti-HCV included age (odds ratio [OR], 1.17 per year; 95% confidence interval [CI], 1.05-1.30), years injecting (OR, 1.21 per year; 95% CI, 1.10-1.34), years in San Francisco (OR, 1.06 per year; 95% CI, 1.00-1.14), first injected by a sex partner (OR, 4.06; 95% CI, 1.74-9.52), injected daily (OR, 3.85; 95% CI, 2.07-7.17), ever borrowed a needle (OR, 2.56; 95% CI, 1.18-5.53), bleached last time a needle was borrowed (OR, 0.50; 95% CI, 0.24-1.02), snorted or smoked drugs in the prior year (OR, 0.48; 95% CI, 0.26-0.89), and injected by someone else in the prior month (OR, 0.50; 95% CI, 0.25-0.99). In the prior month, 88% used at least 1 of several needle exchange venues, and 32% borrowed a needle. We conclude that anti-HCV prevalence is lower than in previous studies of older IDUs, but 11% incidence implies high risk of HCV infection in a long injecting career. Despite access to sterile needles, borrowing of needles persisted.
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                Author and article information

                Journal
                Epidemiology and Infection
                Epidemiol. Infect.
                Cambridge University Press (CUP)
                0950-2688
                1469-4409
                June 2012
                September 12 2011
                June 2012
                : 140
                : 6
                : 1064-1074
                Article
                10.1017/S0950268811001750
                4a9edfae-cae5-4143-bc48-e164c89701d1
                © 2012

                https://www.cambridge.org/core/terms

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