December 12, 2013

Hepatitis C Virus Serosorting in People Who Inject Drugs

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The Journal of Infectious Diseases Dec 15 2013

" These complexities have the potential to result in incorrect perceptions or interpretations of HCV infectiousness. Thus, serosorting is even less likely to be effective as a preventive strategy among PWID to avoid HCV than the parallel sexual behaviors observed among MSM to avoid HIV-1......In an ideal world, all results would be at the point of care and rapidly obtained to enhance the provider's ability to counsel and refer patients. "

"Future studies should examine in more detail the consequences and potential utility of HCV testing and counseling, including the understanding that PWID and others have of their HCV testing results, and how they interpret and use these in decision making and risk assessments. Prospective studies in PWID are needed to assess the durability of counseling messages on individual behaviors and within injecting partnerships, which are often complex and vary significantly over time and arrangement (eg, cohabitating, sexual) [13]. Increasing "PWID's awareness of their HCV status will have important consequences for public health" [8] only if testing is both accurate and comprehensive, then accompanied by counseling that is truly informative of those at risk of and with infection, and finally followed by linkage to treatment."

"This article is not intended to promote injection equipment serosorting as a HCV risk-reduction strategy for PWID but to report that participants were more likely to share syringes with persons of concordant serostatus. One problem that can be expected if injection equipment serosorting is adopted by PWID is the potential effect of incomplete knowledge of infection status. If PWID know they are anti-HCV positive but mistakenly believe they are infected (when they have actually cleared the virus and are negative for HCV RNA), they could opt to serosort injection equipment with infected persons based on this misunderstanding, placing themselves at risk. This issue highlights the importance of conducting HCV RNA tests for all HCV antibody-positive persons and ensuring that they receive and understand their results.

A similar challenge that arises when PWID serosort by injection equipment is the injecting partner's knowledge of their own HCV status. This requires both accurate knowledge and understanding by the injection partner and full disclosure of their HCV status. Although there are proven effective HIV testing and counseling interventions [30], as well as effective interventions to improve disclosure skills for HIV-positive persons [31], there are no HCV-specific interventions to improve either of these factors. Much can be learned from these established interventions, but HCV test results and counseling messages and disclosure issues require more nuanced communication given the 2-step testing process to determine HCV-infection status and the knowledge needed to understand and disclose that information to injection partners."

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Hepatitis C Virus Serosorting in People Who Inject Drugs: Sorting Out the Details - Editorial Commentary

original article follows below after editorial

The Journal of Infectious Diseases Dec 15 2013

Arthur Y. Kim1,a and Kimberly Page2,a
1Division of Infectious Diseases, Massachusetts General Hospital and Harvard Medical School, Boston; and 2Department of Epidemiology and Biostatistics, University of California, San Francisco

In developed countries such as the United States, hepatitis C virus (HCV) is primarily transmitted between people who inject drugs (PWID) due to the combination of high existing prevalence in the population, HCV's high infectivity, and repeated exposures to multiple potential contaminated sources of both drug preparation and administration equipment [1-3]. Although HCV incidence has declined since the 1990s in the United States, and several studies suggest it has been stable in the past decade [4], newly detected outbreaks of HCV in multiple areas of the United States, especially in suburban and rural (or "exurban") settings, have been tied to increasing rates of opiate use in young adults [5, 6]. These new outbreaks raise serious concerns as HCV quickly reaches epidemic levels, as seen among adolescents and young adults in Massachusetts [7].

Further dissection of risk factors and behaviors that govern HCV risk related to injection practices in PWID is welcomed. In this issue of The Journal of Infectious Diseases, Smith et al present intriguing data that suggest that PWID throughout the United States are engaging in "serosorting," defined as a decision to share or not to share injection equipment based on the partner's HCV serostatus [8]. A person injecting drugs who is HCV seropositive will worry less about acquisition if the sharing partner is also HCV positive; conversely, someone who perceives himself or herself to be HCV negative will seek HCV-negative partners to avoid acquisition.

For human immunodeficiency virus type 1 (HIV-1), serosorting has been previously described in men who have sex with men, as a seroadaptive strategy aimed at preventing HIV transmission-for instance, choosing sex partners with concordant HIV status [9, 10]. For HCV, less is known about serosorting. One study among young injection drug users found that knowledge about one's own serostatus correlated with higher knowledge about transmission of HCV but not with reduced distributive or receptive syringe sharing [11]; this study did not evaluate participants' knowledge or perception of their partner's serostatus. Results from subsequent single-center studies that assessed seroadaptive behavior in PWID and examined perceived partner serostatus for HCV [12, 13] and HIV [14] do support that it influences whether to share or not share injecting equipment. In fact, in one of those studies [12], 39% of participants who reported sharing equipment said serosorting was an intentional strategy. The present study provides further evidence of seroadaptive behavior among PWID in association with HCV, and indicates that this behavior may be common on a national level. By asking about the testing history of last injection partner as a preface to participants' awareness of their partners' HCV status, the authors increase the potential for higher internal validity of this self-reported measure in their analyses. They found strong independent associations indicative of serosorting between both self-reported HCV-positive and -negative respondents: the former with higher, and the latter with lower, odds of sharing with HCV-positive partners compared to those with unknown HCV status. An additional strength of this study was the very large and well-sampled population of PWID from multiple urban centers.

As the authors point out, inference about intention is limited; this study, like others, was cross-sectional, and it cannot be determined if the participants made selective decisions about behavior or if the behavioral mixing influenced knowledge of and testing for HCV. To gain further knowledge, both prospective studies as well as measures regarding seroadaptive intention are needed. One important limitation of the current study was reliance of self-reported HCV infection status, as actual test results of the respondents and their partners were not present.

This study shows that HCV testing and counseling may influence injecting behavior of PWID. It is remarkable that up to 75% of PWID at these centers reported a perceived serostatus for themselves. Although almost half of the participants reported sharing injecting equipment, more than a third (37.7%) of those reported knowledge of their injecting partners' serostatus, based on testing history [8]. These numbers imply that testing has been widely applied in this population and that status is shared among injecting groups. What is not clear is whether testing is as widespread in nonurban settings, such as the "exurban" areas where opiate use and HCV cases may be rising.

Moreover, it remains unclear whether appropriate counseling about the meaning of a positive result and, specifically, regarding infectiousness has been communicated. PWID are infectious if they have HCV RNA in the blood compartment. Testing algorithms have suggested that all HCV antibody-positive persons receive confirmation of viremia via a nucleic acid test [15], not only because approximately 20% of those infected clear virus (and are not infectious), but also because of false-positive anti-HCV tests. Although there are alternative approaches, such as reflexive testing on a single sample (mostly for anti-HCV confirmation), in practice, 2-stage testing for HCV RNA following a positive screening enzyme-linked immunosorbent assay (ELISA) is the most widely utilized approach. For a variety of reasons, including competing priorities and the cost and time associated with multiple visits for counseling, it is not clear that nucleic acid tests have been widely applied or that knowledge regarding the nuances of HCV results have been disseminated among PWID.

For someone choosing to avoid acquisition of HIV-1, serosorting to guide choice of sexual partners makes intuitive sense, as a positive result, when combined with an idea of treatment status (being off antiretrovirals), correlates with infectiousness. In contrast, HCV serostatus alone may not correlate with infectiousness, as a positive HCV antibody result simply indicates exposure without information regarding viremia in the bloodstream. This results in potential misclassification of infectious status between partners for at least 2 major reasons: (1) During acute HCV infection, there is a relatively long period averaging 6 weeks where HCV antibody is negative but viremia is present, when exposed individuals may perceive themselves to be negative; and (2) a significant proportion of untreated individuals infected with HCV, especially more women, will spontaneously clear the virus and, thus, be noninfectious [16]. Moreover, clearing virus does not eliminate susceptibility; seropositive individuals who have spontaneously cleared the virus remain at risk for reinfection. Counseling messages that accompany routine HCV testing are, therefore, more complex than for other infections such as HIV, and are parallel to those for human papillomavirus, another infection with a possibility of clearance. These complexities have the potential to result in incorrect perceptions or interpretations of HCV infectiousness. Thus, serosorting is even less likely to be effective as a preventive strategy among PWID to avoid HCV than the parallel sexual behaviors observed among MSM to avoid HIV-1.

Recent recommendations by the Centers for Disease Control and Prevention [17], endorsed by the US Preventive Services Task Force, call for more widespread HCV testing [18]. Among PWID, regular testing that is comprehensive and includes HCV RNA to confirm a positive screening ELISA test will have the benefit of providing information about infectiousness, in addition to follow-up for clinical care to avoid long-term risks for premature death due to liver disease. The results may not only inform future behaviors, including seroadaptive ones, but also care seeking. In an ideal world, all results would be at the point of care and rapidly obtained to enhance the provider's ability to counsel and refer patients. The test would be less costly than current viral titer measurements to allow for greater implementation, especially when resources are limited. At present, the most recent-generation tests for HIV-1 combine antibody and antigen testing to capture the acute stage; parallel development of similar tests for HCV would obviate the 2-step testing algorithm currently recommended, but are currently not available.

Future studies should examine in more detail the consequences and potential utility of HCV testing and counseling, including the understanding that PWID and others have of their HCV testing results, and how they interpret and use these in decision making and risk assessments. Prospective studies in PWID are needed to assess the durability of counseling messages on individual behaviors and within injecting partnerships, which are often complex and vary significantly over time and arrangement (eg, cohabitating, sexual) [13]. Increasing "PWID's awareness of their HCV status will have important consequences for public health" [8] only if testing is both accurate and comprehensive, then accompanied by counseling that is truly informative of those at risk of and with infection, and finally followed by linkage to treatment.

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"To Share or Not to Share?" Serosorting by Hepatitis C Status in the Sharing of Drug Injection Equipment Among NHBS-IDU2 Participants\

The Journal of Infectious Diseases Dec 15 2013

Bryce D. Smith,1 Amy Jewett,2 Richard D. Burt,3 Jon E. Zibbell,1 Anthony K. Yartel,4 and Elizabeth DiNenno5 1Division of Viral Hepatitis, Centers for Disease Control and Prevention, Atlanta, Georgia; 2Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee; 3Public Health Seattle and King County, Seattle, Washington; 4Centers for Disease Control and Prevention Foundation, Atlanta, Georgia; and 5Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia

Abstract

Background. Persons who inject drugs (PWID) are at high risk for acquiring hepatitis C virus (HCV) infection. The Centers for Disease Control and Prevention estimates there are 17 000 new infections per year, mainly among PWID. This study examines injection equipment serosorting-considering HCV serostatus when deciding whether and with whom to share injection equipment. Objective. To examine whether injection equipment serosorting is occurring among PWID in selected cities.

Methods. Using data from the National HIV Behavioral Surveillance System-Injection Drug Users (NHBS-IDU2, 2009), we developed multivariate logistic regression models to examine the extent to which participants' self-reported HCV status is associated with their injection equipment serosorting behavior and knowledge of last injecting partner's HCV status. Results. Participants who knew their HCV status were more likely to know the HCV status of their last injecting partner, compared to those who did not know their status (HCV+: adjusted odds ratio [aOR] 4.1, 95% confidence interval [CI], 3.4-4.9; HCV-: aOR 2.5, 95% CI, 2.0-3.0). Participants who reported being HCV+, relative to those of unknown HCV status, were 5 times more likely to share injection equipment with a partner of HCV-positive status (aOR 4.8, 95% CI, 3.9-6.0).

Conclusions. Our analysis suggests PWID are more likely to share injection equipment with persons of concordant HCV status.

The Centers for Disease Control and Prevention (CDC) estimates that 4.1 million Americans have been infected with the hepatitis C virus (HCV) with 75%-80% of those chronically infected [1]. While CDC recommendsroutine antibody testing for persons at risk of HCV exposure [2], recent studies estimate 40%-85% of HCV-infected persons are unaware of their infection status [3-5]. This lack of awareness has important consequences for disease prevention because knowledge of HCV status is often a prerequisite to making health-promoting behavioral changes and treatment decisions.

HCV prevalence has reached epidemic proportions in the United States and is endemic among persons who inject drugs (PWID). HCV is primarily by percutaneous exposure to contaminated blood, making injection drug use (IDU) the leading cause of incidence in the United States. HCV prevalence among PWID resides between 30% and 70%, depending on frequency and duration of use, and incidence ranges from 16%-42% per year [6-8].

With such high prevalence of infection, recent attention has focused on factors that influence a person's decision to share or not to share injection equipment (IE). One such factor is serostatus, particularly the question as to whether knowing one's HCV status, and that of a prospective partner, affects a person's decision to share IE. We suggest the complex relationship between a person's serostatus and their decision to share IE can be illuminated, in part, through the concept of serosorting.

Serosorting occurs when viral serostatus serves as a determining factor in a person's choice of sex or drug-injecting partners and in the selection of behaviors stemming from that choice. The term has traditionally been used to describe men who have sex with men (MSM), who deliberately select sex partners based on their own and their prospective partner's human immunodeficiency virus (HIV) serostatus [9]. Here, serostatus is characterized as a type of measure whereby people choose a sexual partner based on their own and their partner's HIV status and then base the extent of their sexual activity on that knowledge for the specific purpose of reducing the risk of acquiring or transmitting HIV. While serosorting has been used most notably to describe the sexual choices of MSM, researchers have recently found similar trends among PWID [10-12]: one study in Seattle reported PWID were more likely to share injection equipment with the last injecting partner of concordant status [10]; an investigation in San Francisco found those who perceived their injecting partner to be HCV-positive were less likely to engage in receptive needle sharing [11]; and in Baltimore, HIV-positive participants reported being less likely to serosort than HIV-negative participants [12]. Bearing in mind these city-specific trends, this study expands their scope by examining injection equipment serosorting among PWID on a national scale. Specifically, we examine the relationships between participant's self-reported HCV status and (a) injection equipment sharing behavior, (b) knowledge of last injecting partner's HCV status (known/unknown), and (c) last injecting partner's HCV status (positive/negative).

METHODS

National HIV Behavioral Surveillance System (NHBS)

NHBS is a community-based survey that conducts interviews in triennial cycles among MSM, heterosexuals at increased risk for HIV infection, and PWID. Its purpose is to track the prevalence of and trends in HIV-related risk behaviors, including sex and injection drug use, and to record levels of HIV testing and the use of HIV prevention services among persons at high risk for HIV transmission such as PWID [13]. The second IDU cycle (NHBS-IDU2) was conducted between September and December 2009 and employed respondent-driven sampling (RDS) [14] to target individuals from social networks that can serve as seeds to recruit their peers into the study. Participating sites included in this analysis were located in Atlanta, Baltimore, Boston, Chicago, Dallas, Denver, Detroit, Houston, Los Angeles, Miami, Nassau, Newark, New Orleans, New York, Philadelphia, San Diego, San Francisco, San Juan, Seattle, and Washington, DC. Across the 20 sites, 10 352 respondents were eligible for NHBS-IDU2 and participated in the study. The current study was restricted to 9690 participants with valid responses to questions concerning their HCV status and the HCV status of their last injection equipment sharing partner within the previous 12 months.

Outcome Measures

The outcomes of interest were (a) injection equipment sharing behavior, (b) knowledge of last injecting partner's HCV status (known/unknown), and (c) last injecting partner's HCV status (positive/negative). The HCV status of respondent and respondent's last injecting partner were both self-reported by the respondent. The HCV status of respondent's last injection partner was derived from the following questions: "The last time you injected with this person (last sharing partner in past 12 months), did you know if they had been tested for hepatitis C?" and if yes, "What was the result of their hepatitis C test?" Respondents were also asked a series of questions with respect to their injection equipment sharing behaviors over the previous 12 months. Equipment sharing was defined to include the reuse of syringes, filters, cookers, water, and the practice of dividing drugs with a syringe (eg, backloading or frontloading). We categorized equipment sharing behavior in 2 different ways. For exploratory bivariate analysis, we dichotomized this variable as shared vs did not share. We also categorized the same outcome as a 4-level multinomial response variable for subsequent advanced analysis: shared with HCV-negative partner, shared with HCV-positive partner, shared with partner of unknown HCV status, or shared no injection equipment.

Independent Variables

\The primary independent variable was respondent's HCV status. Based on a review of the literature regarding HCV and injection equipment sharing, we also included the following variables as confounders and/or independent predictors: respondent's gender, race/ethnicity, birth year (as proxy for age), education, homelessness, employment status, annual income, age at first injection, and duration of injection.

Data Analysis

We calculated unweighted proportions to describe the characteristics of the study population. Pearson χ2 tests were used to explore bivariate associations between all independent variables and outcome variables. Consistent with the stated objectives of this study, we developed 3 separate multivariate logistic regression models to evaluate the associations between the respondent's HCV status and the 3 outcome measures, adjusting for all plausible confounders.

First, we modeled equipment sharing (4-level response category) as the dependent variable in a multinomial logistic regression; participants who shared equipment with their last injecting partner of negative, positive, or unknown HCV status were compared to those who did not share. This model was based on the full analytic population (n = 9690). In the second model, we restricted our analysis to respondents who reported sharing equipment (n = 4542) and modeled respondent's knowledge of last injecting partner's HCV status (known/unknown) as the dependent variable. In the third model, we further restricted the analysis to respondents who reported awareness of their last injecting partner's HCV status (n = 1712), and modeled last injection partner's HCV status (positive/negative) as the dependent variable. In all 3 models, respondent's HCV status was the primary explanatory variable. Data were analyzed using SPSS v.18 (IBM, Chicago, IL). We did not account for potential variance inflation induced by the RDS design, due to the limitation of the statistical software used; RDS is a relatively new methodology and is not currently incorporated into multivariate procedures available in standard statistical software.

RESULTS

Of the NHBS-IDU2 participants, 9690 respondents self-reported both their HCV status and the HCV status of their last injecting partner. Of all participants, 7270 (75.0%) reported knowing their HCV status and 4128 (56.8%) of those reported HCV positivity. Nearly 47 percent of all participants (n = 4542) reported sharing equipment with their last injecting partner in the previous 12 months, and of those 37.7% (n = 1712) said they were aware of the HCV status of their last sharing partner. The demographic characteristics of participants are shown in Table 1. Approximately 71.8% were male, 21.6% Hispanic, 46.8% non-Hispanic black, and 27.1% non-Hispanic white. Respondents were born between 1930 and 1991, with a mean of 1963 (ie, approximately 46 years of age). About 13.3% of respondents were employed, 57.3% were unemployed, and 24.1% were disabled for work. More than 61% of respondents reported ever being homeless, and 32.1% reported injecting before the age of 18 years.

Association Between Participant's HCV Status and Sharing Equipment With Last Injection Partner

In bivariate analysis, all independent variables, with the exception of injection duration, were significantly associated with participant's equipment sharing behavior (Table 1). Following multivariate adjustment in a multinomial logistic regression, HCV-negative participants, compared to those of unknown HCV status, were more likely to share equipment with an HCV-negative injecting partner vs not sharing (adjusted odds ratio [aOR] 2.0, 95% confidence interval [CI], 1.6-2.6) (Table 2). Similarly, the odds of sharing with an HCV-positive partner, vs not sharing, is increased nearly 5-fold (aOR 4.8, 95% CI, 3.9-6.0) for HCV-positive participants relative to those of unknown HCV status. In contrast, respondents with known HCV status, compared to those of unknown HCV status, were less likely to share with a partner of unknown HCV status vs not sharing (HCV-positive: aOR .8, 95% CI, .7-.9; HCV-negative: aOR .6, 95% CI, .5-.7). Other variables found to be significantly related to injection equipment sharing behavior after multivariate adjustment were gender, race/ethnicity, birth year, education, history of homelessness, employment, and age at first injection (Table 2).

Association Between Participant's HCV Status and Knowledge of Sharing Partner's HCV Status

The results of multivariate logistic regression analysis examining the relationship between participant's self-reported HCV status and knowledge of last injecting partner's HCV status are presented in Table 3. Among respondents who shared injection equipment, those who knew their HCV status were more likely to know their last injecting partner's HCV status compared to those with unknown HCV status: HCV-negative participants (aOR 2.5, 95% CI, 2.0-3.0) were more than 2 times and HCV-positive participants (aOR 4.1, 95%CI, 3.4-4.9) were more than 4 times more likely to have knowledge of their last partner's HCV status compared to respondents who reported an unknown HCV status. Female gender, non-Hispanic white race/ethnicity, educational attainment of high school or more, disabled status, and higher annual income were also positively associated with knowledge of last partner's HCV status. Non-Hispanic black race/ethnicity and history of homelessness were associated with lack of knowledge of last partner's HCV status.

Association Between Participant's HCV Status and Sharing Partner's HCV Status Table 4 shows the results of a multivariate logistic regression model examining the association between participant's self-reported HCV status and last injecting partner's HCV status. Among the respondents who shared injection equipment and reported knowing their last injecting partner's HCV status, HCV-positive persons (aOR 4.6, 95% CI, 3.2-6.4) were nearly 5 times more likely to report their last injecting partner's HCV status as positive relative to persons with an unknown HCV status. By comparison, HCV-negative persons (aOR .4, 95% CI, .3-.6) were 60% less likely to report their last injecting partner's HCV status as positive relative to persons with an unknown HCV status. Non-Hispanic black participants were less likely to report their injecting partner's HCV status as positive compared to Hispanics. Participants with a history of homelessness and those born from 1930 to 1954, respectively, were more likely to report their injecting partner as HCV positive relative to persons who had never been homeless and those born between 1975 and 1991.

DISCUSSION

The strong association between the HCV status of survey respondents and the HCV status of their last injection partner is evidence indicating that PWID are injection equipment serosorting. Our analysis found that PWID are injection equipment serosorting given that study participants were more likely to share injection equipment (IE) with people of concordant HCV status. This outcome corroborates earlier findings demonstrating a correlation between a person's awareness of his/her HCV status and choice of injecting partners [10].

Serosorting is well documented in the literature but largely in the context of HIV risk reduction. Researchers focusing on the sexual choices of MSM [15, 16] have found serosorting is associated with decreased risk of HIV infection [17] and changes in the sexual behavior of MSM when it is employed as an HIV risk-reduction strategy [18]. Serosorting has also been documented among HIV-positive PWID [19]. They have been shown to be more likely to disclose their infection status to other infected persons and more likely to seek out concordant drug-using relationships [12] than HIV-negative persons. HIV-positive PWID in serodiscordant sexual relationships were also found to be more likely to modify their injecting and sexual behavior than participants who were HIV-negative [20] and less likely to engage in less safe drug use and risky sexual behaviors [21]. These findings demonstrate that PWID have the capacity to employ risk reduction behaviors meant to protect their health and that of their injection partners [22, 23].

In this way, serosorting can be applied to drug injection behavior when the act of choosing an injecting partner is based in part on one's own infection status and that of the prospective injecting partner's for the specific purpose of reducing the risk of acquiring or transmitting bloodborne pathogens during an injection episode. Here, serosorting can be categorized as a risk-reduction strategy when the decision to share or not to share injection equipment is influenced by serostatus and enacted by people unable or unwilling to cease injecting drugs, but who nevertheless want to protect their and their injecting partner's health when injecting drugs together. Following this logic, both the act of selecting an injecting partner of concordant infection status and the act of avoiding sharing injection equipment with a person of discordant infection status would be categorized as injecting equipment serosorting [24].

The hepatitis C literature provides a modicum of evidence that knowledge of one's own or another's HCV status can influence how or with whom people inject. One study in Seattle reported PWID were more likely to share injection equipment with the last injecting partner of concordant status [10], while in San Francisco those who perceived their injecting partner to be HCV-positive were found to be less likely to engage in receptive needle sharing [11]; and in Baltimore, HIV-positive participants reported being less likely to injection equipment serosort than HIV-negative participants [12]. The evidence, however, is not entirely positive. Numerous studies show that knowledge of one's HCV status has nominal influence on reducing behaviors that put PWID at risk for acquiring or transmitting blood-borne disease [25-27]. A study of young PWID found no association between HCV-positive status and reductions in less safe injecting practices or choice of injecting partners [28], and another found injecting partners not discriminating based on serostatus and sharing injection equipment just as frequently with sexual partners of concordant and discordant status [29].

This variation notwithstanding, our analysis of the NHBS-IDU2 data establishes a strong association between a survey respondent's knowledge of their HCV status and the selection of an injecting partner. This correlation is deduced from 4 significant findings: (1) a person knowing their HCV status was more likely to know their last injection partner's HCV status; (2) a person knowing their HCV status was less likely to share injection equipment with a partner of unknown HCV status; (3) a person knowing their HCV-negative status was more likely to share injection equipment with a partner that was also HCV-negative; (4) a person knowing their HCV-positive status was more likely to share equipment with a partner reporting an HCV-positive status. These findings suggest that PWID may be serosorting by selectively sharing injecting equipment with persons of corresponding HCV status.

This article is not intended to promote injection equipment serosorting as a HCV risk-reduction strategy for PWID but to report that participants were more likely to share syringes with persons of concordant serostatus. One problem that can be expected if injection equipment serosorting is adopted by PWID is the potential effect of incomplete knowledge of infection status. If PWID know they are anti-HCV positive but mistakenly believe they are infected (when they have actually cleared the virus and are negative for HCV RNA), they could opt to serosort injection equipment with infected persons based on this misunderstanding, placing themselves at risk. This issue highlights the importance of conducting HCV RNA tests for all HCV antibody-positive persons and ensuring that they receive and understand their results.

A similar challenge that arises when PWID serosort by injection equipment is the injecting partner's knowledge of their own HCV status. This requires both accurate knowledge and understanding by the injection partner and full disclosure of their HCV status. Although there are proven effective HIV testing and counseling interventions [30], as well as effective interventions to improve disclosure skills for HIV-positive persons [31], there are no HCV-specific interventions to improve either of these factors. Much can be learned from these established interventions, but HCV test results and counseling messages and disclosure issues require more nuanced communication given the 2-step testing process to determine HCV-infection status and the knowledge needed to understand and disclose that information to injection partners.

This study has some limitations. Unlike several previous studies of serosorting [10], the national data collected through the NHBS-IDU2 study did not include information regarding participants' intention to serosort. It thus remains unknown if the high level of serosorting observed in this study was driven by an intention to do so. Further research needs to be conducted to explore whether intention to serosort is based on the HCV infection status of self and other, and what other factors may be contributing to this behavior. Additional limitations were related to the participant recruitment. The lack of adjustment for the design effect of RDS may have resulted in biased prevalence estimates and artificially smaller standard errors in bivariate analysis; however, there is no consensus on the statistical methods for conducting multivariate analysis [32-37]. Moreover, participants' and their partners' HCV status were self-reported and do not represent actual prevalence, and injecting equipment serosorting behavior is based on participants' perceived HCV status. Future research should thus include analyses of serosorting behavior based on actual vs perceived HCV status. Finally, given the unexplained differences in knowledge of serostatus by gender, race, educational attainment, and homelessness, additional research should be conducted to examine these issues fully.

CONCLUSION

Our analysis of the NHBS-IDU2 data points to the possibility that PWID are serosorting based on knowledge of their and their injecting partners' HCV status. If accurate, the ability to increase PWID's awareness of their HCV status will have important consequences for public health and disease prevention, as it could be an influential element in a person's decision to make health-promoting behavioral changes and their choice of medical treatment. In sum, increasing the proportion of PWID who are aware of their HCV status may contribute to a general increase in the adoption of risk reduction strategies by persons who inject drugs.

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