Convergence of HIV seroprevalence among injecting and non-injecting drug users in New York City

Des Jarlais, Don Ca; Arasteh, Kamyara; Perlis, Theresaa; Hagan, Hollyb; Abdul-Quader, Abuc; Heckathorn, Douglas Dd; McKnight, Courtneya; Bramson, Heidia; Nemeth, Chrise; Torian, Lucia Vf; Friedman, Samuel Rb

doi: 10.1097/QAD.0b013e3280114a15
Epidemiology and Social: Concise Communication

Objective: To compare HIV prevalence among injecting and non-injecting heroin and cocaine users in New York City. As HIV is efficiently transmitted through the sharing of drug-injecting equipment, HIV infection has historically been higher among injecting drug users.

Design: Two separate cross-sectional surveys, both with HIV counseling and testing and drug use and HIV risk behavior questionnaires.

Methods: Injecting and non-injecting heroin and cocaine users recruited at detoxification and methadone maintenance treatment from 2001–2004 (n = 2121) and recruited through respondent-driven sampling from a research storefront in 2004 (n = 448).

Results: In both studies, HIV prevalence was nearly identical among current injectors (injected in the last 6 months) and heroin and cocaine users who had never injected: 13% [95% confidence interval (CI), 12–15%] among current injectors and 12% (95% CI, 9–16%) among never-injectors in the drug treatment program study, and 15% (95% CI, 11–19%) among current injectors and 17% (95% CI, 12–21%) among never injectors in the respondent driven sampling storefront study. The 95% CIs overlapped in all gender and race/ethnicity subgroup comparisons of HIV prevalence in both studies.

Conclusions: The very large HIV epidemic among drug users in New York City appears to be entering a new phase, in which sexual transmission is of increasing importance. Additional prevention programs are needed to address this transition.

From the aBeth Israel Medical Center, New York

bNational Development and Research Institutes, Inc., New York, New York

cCenters for Disease Control and Prevention, Atlanta, Georgia

dCornell University, Ithaca

eNew York State Department of Health, Albany

fNew York City Department of Health and Mental Hygiene, New York, New York, USA.

Received 13 June, 2006

Revised 31 August, 2006

Accepted 26 September, 2006

Correspondence to Don C. Des Jarlais, Beth Israel Medical Center, 160 Water Street – 24th Floor, New York, NY 10038, USA. e-mail:

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention and the National Institutes on Drug Abuse.

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The multi-person use (‘sharing’) of needles and syringes is an efficient method for transmitting HIV among injecting drug users (IDUs). Extremely rapid spread of HIV has been observed in many populations of IDUs, with incidence rates of 10/100 person-years up to 50/100 person-years [1–3]. Heterosexual transmission of HIV is normally much less efficient than needle-sharing transmission [4], and the hierarchical classification of HIV transmission risk used by the Centers for Disease Control and Prevention has always ranked injecting drug use-related transmission above heterosexual transmission [5].

The large-scale implementation of programs to reduce syringe sharing, such as syringe exchange, may change the relative importance of injection-related and sexual transmission of HIV among IDUs. Recent HIV incidence studies among IDUs in San Francisco [6] and Baltimore [7] have suggested that sexual transmission may be of increasing importance among IDUs.

Comparisons of HIV among IDUs and non-injecting drug users (NIDUs) may provide insight into the relative importance of sexual transmission in a geographic area. In this report, we note a convergence of HIV prevalence among injecting and non-injecting heroin and cocaine users in New York City (NYC). High rates of non-injecting drug use among the IDUs and frequent social linkages between the IDUs and NIDUs were also observed.

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The data reported here are from two different NYC studies: the Risk Factors (RF) study, which recruited participants from persons entering drug abuse treatment programs, and the Respondent Driven Sampling (RDS) study, which used community recruiting of drug users. The two studies were coordinated, using identical questions for most topics, including drug use histories and HIV risk behaviors. This report compares current heroin and/or cocaine IDUs with NIDUs. Current IDUs are defined as persons who had injected heroin and/or cocaine in the 6 months prior to interview, and current NIDUs as persons who used heroin and/or cocaine in the prior 6 months but who had never injected an illicit drug. HIV testing was conducted at the NYC Department of Health Laboratory using repeated enzyme-linked immunosorbent assays (ELISA) testing with western blot confirmation.

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The Risk Factors study

The RF study comprises an ongoing series of surveys of drug users entering the Beth Israel Medical Center drug detoxification and methadone maintenance programs in NYC (methods previously described in [1,8–12]). Data for this report comes from current IDUs recruited between 2001 and 2004, and from current NIDUs recruited from 2002 to 2004.

Briefly, research staff rotated through the general admission wards of the detoxification program in a pre-set order and examined the intake records to identify patients admitted within the past 3 days. All of the eligible newly admitted patients in the specific ward were then asked to participate in the study. Participants entering methadone maintenance treatment were recruited at the central intake facility for the program. Project staff visited the facility starting early in the morning and remained until intake closed. All persons applying for methadone treatment were asked to participate in the study. An honorarium of US$ 20 was provided to each study participant.

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The Respondent Driven Sampling study

During the summer of 2004, we conducted a study of street-recruited drug users in NYC utilizing RDS. Since a detailed description of the methods has been presented elsewhere, a short overview will be given here. RDS [13–15] is a structured form of peer referral sampling, in which persons who have participated in a study are then asked to recruit new participants. RDS starts with a limited number of peers – known as seeds–who are selected by study staff. After participating in the study, these seeds are asked to recruit new participants, who in turn are asked to recruit additional new participants. Recruiting continues in successive ‘waves’ until the desired sample size is reached. Subjects receive honoraria for study participation (US$ 20 in the current study) and for recruiting new subjects (US$ 10 per recruit). A coupon system is utilized to track who recruits whom, and information is obtained about the size and characteristics of the social networks of the subjects.

The RDS procedures led to substantial cross-recruiting among IDUs and NIDUs: 46% of the current IDUs were recruited by NIDUs and 44% of the current NIDUs were recruited by IDUs. (A separate report has been prepared on ‘former injectors’ – participants who had previously injected but had not injected for at least 6 months [16]).

Data from the RF study were analyzed using the SAS statistical programs [17]. The RDS study data were analyzed using custom software designed to analyze RDS data sets, RDS Analysis Tool (RDSAT), version 5.0, which uses recruitment linkages and network sizes to estimate adjusted population prevalence values. The 95% confidence intervals (CI) for the adjusted population values were then calculated by applying the RDS weights to each case and using a procedure for complex survey design in SAS (Proc Surveyselect) [17].

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Table 1 presents sociodemographics of the current IDUs (subjects who reported injecting in the 6 months prior to interview) and NIDUs (subjects who used heroin and/or cocaine within the 6 months prior to interview, but who reported never having injected an illicit drug) in the two studies. Subjects in the RDS study were older and more likely to be African American. The percentages of males and females were very similar across both injecting status groups and across both studies. In both studies, there were higher percentages of Hispanics and whites among the current IDUs, and higher percentages of African Americans among the NIDUs.

Many of the current IDUs also reported non-injecting drug use. In the RF study, 35% reported intranasal heroin use, 15% reported intranasal cocaine use, 9% reported intranasal speedball (combined heroin and cocaine), and 29% reported smoking crack cocaine in the 6 months prior to the interview. In the RDS study, 53% of the IDUs reported intranasal heroin use, 36% reported intranasal cocaine use, 22% reported intranasal speedball use, and 46% reported smoking crack cocaine in the 6 months prior to the interview.

Table 2 shows HIV prevalence with 95% confidence intervals by injecting status in both studies, and by gender and race/ethnicity within injecting status in both studies. The RDS prevalence estimates are based on the weighting procedures calculated by RDS Analysis Tool, with confidence intervals calculated with SAS [17]. These weighted prevalences are generally two to five percentage points lower than the observed values in the unweighted sample. The weighting procedures reduced the prevalence estimates because HIV positive subjects in this RDS study tended to recruit more subjects and tended to have larger drug using networks.

There were few differences in HIV prevalence between the current IDUs and the NIDUs in both studies. There was overlap in the 95% CIs for all comparisons of current IDUs to NIDUs for all of the demographic subgroups in each of the studies. Elevated HIV prevalence among African American IDUs versus NIDUs in the RF study was the only IDU versus NIDU comparison to reach statistical significance (P < 001). There were, however, clear racial/ethnic differences, with whites generally having lower HIV prevalence and African Americans having higher HIV prevalence. This pattern was consistent for both current IDUs and NIDUs.

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The two studies reported here used very different sampling methods but obtained very similar results. This suggests that the findings are likely to apply to large numbers of IDUs and NIDUs in NYC.

Since injecting drug use is generally more stigmatized than non-injecting drug use, it is possible that some participants who reported that they had never injected might actually have injected. Hepatitis C virus (HCV) is strongly associated with injecting drug use and only modestly associated with non-injecting drug use. Anti-HCV testing has been conducted for the RDS study participants. Removing the anti-HCV positive participants from the RDS NIDU group lowered the HIV prevalence among the RDS NIDUs by only 2%, and did not change the observed equivalence of HIV prevalence among IDUs and NIDUs in the RDS study (data not presented, a full report on HCV prevalence is in preparation).

The legalization and large-scale expansion of syringe exchange and other HIV prevention services for IDUs in NYC, which began in 1992, was associated with dramatic reductions in both HIV prevalence and HIV incidence among IDUs in the city. HIV prevalence declined from approximately 50% in 1990 down to the current level and HIV incidence declined from an estimated 4/100 person-years to an estimated 1/100 person-years [12]. The decline in HIV prevalence among IDUs was observed in multiple studies [18]. Longitudinal data on HIV prevalence among NIDUs in New York are not available. Two previous studies that recruited non-injecting heroin and cocaine users found 11% prevalence [19], and 10% prevalence [20]. These results are similar to the 12 and 17% found in the two studies reported here, suggesting that HIV prevalence is either stable or possibly increasing among NIDUs in the city.

There are several reasons to consider HIV infection among IDUs and NIDUs in New York as linked rather than separate phenomena. First, the RDS recruitment data indicate social linkages between IDUs and NIDUs, many IDUs recruited NIDUs and many NIDUs recruited IDUs. Information about HIV/AIDS and social norms about HIV risk behaviors are undoubtedly shared among IDUs and NIDUs. Second, many drug users transition between non-injecting use and injecting use of heroin and cocaine [21,22]. The transitions occur in both directions – from non-injecting use to injecting use and from injecting use to non-injecting use. The social linkages and transitions between IDUs and NIDUs also suggest that there are overlaps in sexual networks between the groups.

We are currently examining possible reasons for the relatively high HIV seroprevalance among the NIDUs in these two studies, including sexual risk behaviors, sexual networks, and the presence of other sexually transmitted diseases that would facilitate sexual transmission of HIV.

In conjunction with the expansion of syringe exchange programs in the US [23], HIV prevalence has been declining among IDUs in many areas in the US [24]. There is not, however, sufficient data for assessing any national trends in HIV among NIDUs.

HIV prevalence among NIDUs in the two studies reported here was equal to the prevalence among IDUs and as high or higher than the HIV prevalence among IDUs in 85 of the 96 largest SMAs in the USA. [25]. New programs to reduce HIV transmission among NIDUs are clearly needed in the city. As many non-injectors are socially networked with injectors, the new programs should probably address sexual transmission among both IDUs and NIDUs. We would also suggest that HIV/AIDS surveillance programs – both in New York and nationally – create a subcategory of ‘non-injecting heroin, cocaine or methamphetamine user’ within the category of ‘heterosexual transmission’ for better monitoring of HIV infection in this high-risk group.

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Sponsorship: These studies were supported by grant 5R01 DA003574 from the National Institute on Drug Abuse and by the Centers for Disease Control and Prevention through program announcement number 00005.

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HIV; seroprevalence; injecting drug users; non-injecting drug uses; New York City

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