To the Editor:
We read with interest the recent article by Kapadia et al.1 suggesting that “bleach disinfection of syringes may help to prevent HCV [hepatitis C] infection among injection drug users.” In that multi-site study, the risk of HCV seroconversion was 0.4 (95% confidence interval = 0.1-1.6) in drug injectors who always used bleach compared with those who used bleach less than all the time. In contrast, we found among injection drug users (IDUs) in Seattle that the use of bleach to disinfect syringes “usually or always” did not appear to influence the risk of HCV seroconversion.2
Because HCV is a frequent and serious blood-borne viral infection in IDUs, and bleach may be an inexpensive and simple prevention tool, we sought to reproduce the analysis by Kapadia et al., to determine whether we could detect a similar pattern of association. Details of the methods used in the Seattle Risk Activity Variables, Epidemiology, and Network Study (RAVEN) Study—a longitudinal cohort study of nearly 3,000 IDUs—have been described elsewhere.3 Following the sample restrictions and analytic approach described in the paper by Kapadia et al, we examined the relationship between bleach use (always vs. less than always) and HCV seroconversion 12 months after study enrollment in 195 HCV-seronegative IDUs who had shared syringes or other injection equipment during the follow-up period. Because we had fewer total subjects, we did not match seroconverters to seronegative controls, but all matching variables were included as adjustment terms in the multivariate analysis. Among the 53 IDUs who reported “always” using bleach to disinfect syringes, 14 seroconverted (26%), compared with 31 (22%) of the 142 IDUs who reported using bleach “less than always.”
We conducted multiple logistic regression analysis of the association between always using bleach to disinfect syringes and HCV seroconversion, adjusting one at a time for potential confounders (similar to Table 2 in the Kapadia et al article). As shown in our table, the risk of HCV seroconversion was 1.4 times higher for those who always used bleach to disinfect syringes compared to others, although the confidence interval was broad. Adjustment for potential confounders did not change this estimate to an important degree, and all our odds ratios were in the opposite direction from those reported by Kapadia et al.
We considered several potential explanations for the discrepancy between our results and those of Kapadia et al, including differences in study methods. The multi-site study included IDUs less than 30 years of age, whereas RAVEN subjects were 15-65 years of age, but it is unlikely that the effect of bleach would vary in relation to the age of the user. Higher reporting of bleach use every time a syringe was shared in Seattle (25% vs. <10% in the multi-site study) suggested the possibility of over-reporting in Seattle due to social desirability bias, but the same data-collection method (interviewer-administered questionnaires) was used in both sets of studies. It is also conceivable that the underlying prevalence of HCV may modify the effect estimate; in Seattle, prevalence in IDUs was 83%,3 whereas in the multi-site study, mean prevalence was 36%.1
One other possibility is that there is no association between bleach use and transmission of either HCV or human immunodeficiency virus (HIV), and that studies published to date represent a distribution of point estimates around a true relative risk of approximately 1.0. For the association of bleach use with HIV, published point estimates include 0.84 and 1.05.5 Stronger evidence is needed to support the use of bleach disinfection as a way to prevent transmission of blood-borne viruses.
Center for Drug Use and HIV Research
National Development and Research Institutes, Inc.
71 West 23rd St., 8th Floor
New York, NY 10010
Public Health—Seattle and King County
1.Kapadia F, Vlahov D, Des Jarlais DC, et al. Does bleach disinfection of syringes protect against hepatitis C infection among young adult injection drug users? Epidemiology
. 2002;13: 738–741.
2.Hagan H, Thiede H, Weiss NS, et al. Sharing of drug preparation equipment associated with hepatitis C virus seroconversion in drug injectors. Am J Public Health
3.Hagan H, McGough JP, Thiede H, Weiss NS, Hopkins S, Alexander ER. Syringe exchange and risk of HBV and HCV in Seattle IDUs. Am J Epidemiol
4.Vlahov D, Munoz A, Celentano DD, et al. HIV seroconversion and disinfection of injection equipment among intravenous drug users, Baltimore, Maryland. Epidemiology
5.Titus S, Marmor M, Des Jarlais DC, Kim M, Wolfe H, Beatrice S. Bleach use and HIV seroconversion among New York City injection drug users. J Acq Immun Defic Synd