1 Division of Epidemiology and Biostatistics, School of Public Health, University of Illinois at Chicago, Chicago, IL 60612.
2 Division of Viral Hepatitis, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333.
3 National Center for HIV, STD, and TB Prevention, Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, Atlanta, GA 30333.
4 Current affiliation: Division of Epidemiology, New York City Department of Health and Mental Hygiene, New York, NY 10013.
We thank Koester et al. (1) for their observations on the potential risk of hepatitis C virus (HCV) transmission associated with using a common syringe to divide drug solutions ("drug-splitting"). The authors correctly point out that, among injection drug users (IDUs), nonsyringe paraphernalia (cookers, cotton, and rinse water) are often shared after a single syringe has been used to prepare and measure the drug solution. The solution is squirted either directly into another syringe or into a cooker for other drug users to then draw into their own syringes. The authors suggest that we do not adequately attribute our observed statistical association between HCV transmission and sharing of nonsyringe equipment (2) to what may be the "true" cause of exposure to contaminated blood: sharing solutions that were first prepared in blood-contaminated syringes.
We fully agree with Koester et al. that sharing paraphernalia cannot result in HCV transmission without the introduction of infected blood. Although we provided some description and several citations of ethnographic works describing the injection process, perhaps we should have more thoroughly reviewed the various mechanisms by which cookers, cotton, and water can become contaminated with blood. The authors letter gives a clear description of one practice that may often be responsible for contaminating nonsyringe injection paraphernalia with HCV. However, splitting drugs "wet" is not the only scenario in which cookers, cotton, and water are shared, nor is this the only means by which these paraphernalia can become contaminated.
The serial reuse of paraphernalia by individual and multiple IDUs is common and has been described in observational studies (36). For example, IDUs injecting in abandoned buildings, "shooting galleries," and semipublic venues often use injection paraphernalia left behind by others. Friends make their cookers available to one another, and "cotton hounds" collect used cotton filters to retrieve available drug residue. Contact between contaminated syringes and other injection paraphernalia, whether through drug-splitting or another means, could result in HCV transmission when equipment is later used by other persons (7, 8). Contamination may also occur through more direct contact with blood. We have observed IDUs using their fingers to wipe blood from injection sites and then handling cookers and cotton, a possible scenario for contamination.
In our study (2), we asked participants (IDUs between the ages of 18 and 30 years) at baseline whether they had split drugs using a needle during the past 6 months. Thirty-two percent of all respondents said that they had; this was substantially fewer than those who reported sharing cookers (62 percent), cotton (45 percent), or rinse water (54 percent). In response to Koester et al.s letter, we generated specific interval-censored Cox proportional hazards models similar to the ones described in our article (both univariate and multivariate) to examine whether the practice in questiondrug-splittingwas associated with HCV transmission. We found no significant association in either model (univariate relative hazard = 1.69, 95 percent confidence interval: 0.79, 3.61; multivariate relative hazard = 1.78, 95 percent confidence interval: 0.84, 3.81).
Because of the multiple ways that blood can be introduced into nonsyringe equipment, we emphasized in our Discussion section that the sharing of any type of nonsyringe equipment should not be singled out as the sole source of transmission. We also suggested that HCV prevention messages need to discourage "all equipment-sharing practices" (2, p. 652).
We thank Koester et al. (1) for calling specific attention to the practice of splitting drugs, and we wholeheartedly agree that prevention education should facilitate a full understanding of the contamination process. In particular, if the circumstances of injection drug use make it impossible for many IDUs to avoid splitting drugs wet, then risk reduction messages should identify steps that minimize the risks inherent in this practice (9).
We do believe that sharing syringes is still the most efficient and biologically plausible means of transmitting HCV when injecting drugs. However, substantial epidemiologic evidence is beginning to accumulate which suggests that HCV transmission can occur via cross-contamination of nonsyringe equipment in a number of different settings. For example, cross-contamination of equipment has been implicated as a source of HCV transmission among patients on chronic hemodialysis (10). In our paper (2), we suggested that our observation of a greater association between HCV infection and sharing of nonsyringe equipment as compared with syringes themselves (a finding consistent with that of Hagan et al. (11)) may have been partially due to differences in the type and number of people with whom IDUs shared each type of equipment. In our study and elsewhere, IDUs have reported sharing syringes less frequently than other equipment (4), and it is likely that sharing of nonsyringe paraphernalia involves more partners and wider social networks, increasing the risk of contact with HCV-infected persons. Therefore, interventions to prevent HCV infection should instill a more thorough understanding of contamination processes and assist IDUs to develop and implement strategies that minimize these risks, including always using a new syringe when splitting drugs.
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