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Injection drug users are at an increased risk for hepatitis C virus (HCV) infection, with incidence ranging from 15% to 40% per year. 1,2 Among recently initiated injection drug users, anti-HCV prevalence approaches 30–50%, and both anti-HCV prevalence and incidence exceed corresponding measures for HIV infection. 3 Strategies to prevent transmission of these blood-borne infections include syringe disinfection with bleach because it is both inexpensive and well accepted by injection drug users. 4–8 However, bleach use has been evaluated primarily for HIV prevention with findings yielding negligible effects. 9,10 The fact that these findings are inconclusive has been attributed to improper bleaching techniques rather than lack of effect, given that many blood-borne pathogens are susceptible to bleach. 11,12 The larger reservoir of HCV-infected persons and higher efficiency of HCV transmission compared with HIV suggest that bleach disinfection of syringes might reduce HCV infection risk, a hypothesis we evaluate in this report.
Study Design and Data Collection
We performed a matched case-control analysis, nested within the Second Collaborative Injection Drug Users Study (CIDUS-II), which is described in detail elsewhere. 13,14 Briefly, the objectives of the original study were to estimate prevalence and incidence of blood-borne infections among young or recently initiated injection drug users and to identify risk factors for these infections. From 1997 through 1999, injection drug users were enrolled in a prospective cohort study at six sites in five U.S. cities: Baltimore, Chicago, Los Angeles, New Orleans and New York City (two distinct neighborhoods of the latter). A uniform protocol was followed with respect to community-based recruitment, eligibility criteria and interview and venipuncture of all participants at baseline and at 6 and 12 months. To be eligible for enrollment, injection drug users had to be 18–30 years old or recent initiates into drug injecting (injecting ≤5 years). To be included in this analysis, participants had to be between 18 and 30 years old and be current injection drug users (defined as having injected drugs within the 6 months preceding an interview). This study was approved by institutional review boards at the Centers for Disease Control and Prevention (CDC) and at each participating institution.
All interviews were administered by trained study staff and conducted before pretest counseling and venipuncture. Questions on current drug use and sexual practices referred to the 6 months preceding the interview date; they assessed frequency and duration of drug injection, injecting practices, and number of sexual partners. Injecting practices examined in this analysis include sharing cookers used to melt drugs into a liquid, sharing cottons used to filter out particles as drugs are drawn into a syringe, sharing rinse water to clean syringes, and backloading (a practice in which one syringe is used to distribute drugs into multiple syringes). Additionally, participants reporting syringe sharing were asked to report on syringe disinfection with substances such as bleach, water, rubbing alcohol or peroxide.
Blood specimens were sent to the CDC for serologic testing of anti-HCV infection. Samples were tested for antibody to HCV using commercial enzyme immunoassays. HCV seroconversion, defined as a positive anti-HCV test result after a negative result from a prior visit, was confirmed using recombinant immunoblot assay (RIBA™ 3.0, Chiron Corp, Emeryville, CA).
Case participants were individuals who seroconverted at either follow-up visit, whereas control participants were those who remained persistently anti-HCV seronegative. Up to five randomly selected controls were matched to each case on potential confounders of bleach disinfection and anti-HCV seroconversion such as gender, race, date of entry into the study (±3 months), and duration of follow-up. Because matching on date of study entry and duration of follow-up was done to control for the effects of calendar time and possible maturation of the epidemic, we used control interviews that were closest in calendar time and length of follow-up to each respective case’s first seropositive visit. Thus, informa- tion on current drug injection and sexual practices re-ported here refers to the 6 months preceding the first follow-up visit at which a case participant seroconverted and to the 6 months preceding the matched control visit.
We also included in this analysis case and control participants who did not report syringe sharing because indirect sharing activities—sharing of cookers, cottons and rinse water—have all been associated with an increased risk for HCV seroconversion. 15 Odds ratios were estimated from conditional logistic regression to examine the effect of syringe disinfection with bleach (categorized as “all the time,” “less than all the time,” and “never”). Limited sample size required us to collapse bleach users into two categories (“all the time” and “less than all the time”) when adjusting for potential confounding factors (which were entered one at a time).
Prevalence of anti-HCV among the 2,198 participants enrolled in the original cohort was 36%. Follow-up and screening of participants who were seronegative at baseline (N = 1,324) identified 78 RIBA-confirmed anti-HCV seroconverters. We matched 390 controls to the 78 case participants identified. Males comprised 62% of the participants included in this analysis. Forty-six percent of participants were white, 19% were Hispanic/Latino, 27% were black, and 8% were of another race/ethnicity. Twenty-seven percent of participants reported injecting drugs with syringes previously used by another person, 41% reported sharing cookers, 33% sharing cottons, and 30% sharing rinse water.
Results from univariate analysis (Table 1) showed that anti-HCV seroconversion was more com-mon among those reporting injecting drugs with other people (odds ratio [OR] = 2.2); injecting in a public place (OR = 2.4); and sharing cottons (OR = 1.7), cookers (OR = 1.8) and rinse water (OR = 1.7). Bleaching frequency showed a trend toward a protective effect on anti-HCV seroconversion. Compared with those reporting “never” using bleach, odds ratios for seroconversion were 0.76 (95% confidence interval = 0.21–2.70) for participants reporting bleach use “less than all the time” and 0.35 (0.08–2.31) for those reporting using bleach “all the time.”
The unadjusted odds ratio for anti-HCV seroconversion comparing bleach use all the time with use less than all the time was 0.45 (0.11–1.55). When we individually adjusted for several possible confounding variables, the point estimate changed appreciably only when “injecting in public” was added to the model (OR = 0.14 [0.02–1.21]) (Table 2).
This analysis suggests that there is an inverse association between frequency of bleach disinfection of syringes and risk of anti-HCV seroconversion. The relation between bleach use and anti-HCV seroconversion was not weakened by individual adjustment for factors associated with HCV seroconversion. There was a stronger relation after adjusting for injecting in public, which suggests that the setting may modify the protective effect of syringe disinfection with bleach. These results are consistent with previous findings, and if true may have important implications. First, few interventions are currently available to curb the high rates (>10 per 100 person-years) of anti-HCV seroconversion among young or newly initiated injection drug users. 8 Second, conventional interventions such as syringe exchange and drug treatment programs may have less impact on HCV incidence because younger injection drug users, those more likely to seroconvert, are less likely than older users to seek services from such agencies. 16
Several methodologic limitations must be considered in interpreting these findings. First, although the initial cohort was large, we had only 78 eligible seroconverters, limiting our ability to detect an association between bleach use and anti-HCV seroconversion. A sample of 108 anti-HCV seroconverters would have been necessary to detect an odds ratio of 0.5 with an alpha level of 0.05 and 80% power. Second, underreporting of syringe sharing or overreporting of bleach use attributable to socially desirable responding could attenuate the association of anti-HCV seroconversion with syringe sharing and with bleach use. However, earlier reports suggest veracity of self-reports among injection drug users. 17 Third, assessment of the bleaching process focused only on frequency of disinfection use; contact time between the syringe and bleach, which is also important, was not ascertained.
Finally, given the structure of the interview, bleach use was assessed only among individuals reporting syringe sharing. Although it may seem unnecessary to ascertain bleach use among those who do not report syringe sharing, this is an important limitation for this analysis as recent studies have shown an increased risk of HCV seroconversion among those who share cookers, cottons and rinse water and among those who may inject (knowingly or unknowingly) with previously contaminated syringes. 13,15 On the basis of this rationale, case and control participants not reporting syringe sharing were also included in this analysis to account for the risk of HCV seroconversion from indirect sharing practices; they were grouped with those who did not disinfect with bleach. With consistency of results across categorizations of bleach use (Table 2), this conservative regrouping might underestimate the exposure, possibly biasing the association toward the null.
Given the efficiency of HCV transmission and the reluctance of newer, younger injectors to self-identify their needs or to utilize available services, risk-reduction options such as syringe disinfection using bleach should not be discounted. 16 Disinfecting syringes with bleach, which is inexpensive and readily available, merits consideration for further investigation in prevention studies of HCV infection, in both laboratory and field trials.
The CIDUS group comprises the following investigators: in Baltimore, Crystal Fuller, Steffanie Strathdee and David Vlahov (Johns Hopkins University); in Chicago, Susan Bailey, Steve Diaz, Lawrence Ouellet and Lorna Thorpe (University of Illinois at Chicago); in Los Angeles, Peter Kerndt, Javier Lopez-Zatina, David Norton and Terry Woehlre (Los Angeles Department of Health Services); in New Orleans, Edward Morse (Tulane University) and Patricia Morse (Louisiana State Medical Center); and in New York, Don Des Jarlais, Sam Friedman and Theresa Perlis (National Research and Development Institute) and Theresa Diaz, Ezra Susser and David Vlahov (New York Academy of Medicine). We also acknowledge the following people from the CDC: Edgar Monterroso, Project Officer for study development and implementation and Andrea Swartzendruber and Roberto Valverde, for preparing and assuring the quality of the data.
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