Sexually Transmitted Diseases:
Needle Exchange and Sexual Risk Behaviors Among a Cohort of Injection Drug Users in Chicago, Illinois
Huo, Dezheng PhD*; Ouellet, Lawrence J. PhD†
From the *Department of Health Studies, University of Chicago, Chicago, Illinois; and the †Division of Epidemiology and Biostatistics, Community Outreach Intervention Projects, School of Public Health, University of Illinois at Chicago, Chicago, Illinois
For their assistance in assessing the NEP they provided, the authors thank Heidi Nelson, Executive Director of Heartland Health Outreach, and her dedicated staff. They also thank the Reverend Dr. Sid L. Mohn, President of Heartland Alliance for Human Needs and Human Rights, the parent organization of Heartland Health Outreach, for his strong interest in and support for evaluating community health services. They thank the staff of the Community Outreach Intervention Projects and particularly two outreach workers, Hermenegildo Lira and Michael Phillips. Finally, they thank Dr. Donald Hedeker for his advice regarding data analysis.
Correspondence: Dezheng Huo, Department of Health Studies, University of Chicago, 5841 South Maryland Avenue, MC2007, Chicago, IL 60637. E-mail: firstname.lastname@example.org.
Received for publication February 25, 2008, and accepted July 15, 2008.
Objective: To examine the impact of a needle exchange program (NEP) on sexual risk behaviors of injecting drug users (IDUs).
Methods: Between 1997 and 2000, 889 IDUs in Chicago were recruited from NEPs and an area with no NEP into a cohort study. They were interviewed and tested for HIV at baseline and 3 annual follow-up visits. Random-effect logistic models were used to compare NEP users and nonusers regarding the number of sex partners, number of unprotected sex acts, and frequency of condom use.
Results: Compared to NEP nonusers, NEP users had a similar number of sex partners over time, but had 49% higher odds of using condoms with their main partners (P = 0.047). At baseline, there was no difference between NEP users and nonusers in episodes of vaginal intercourse, but over time the odds of having a higher number of unprotected instances of vaginal intercourse were reduced by 26% per year for NEP users but only 10% per year for nonusers (P = 0.02).
Conclusion: This study suggests that NEP participation may help reduce the absolute risk of HIV sexual transmission.
SHARING SYRINGES AND OTHER injection equipment has been the major route of HIV transmission among injection drug users (IDUs),1–3 but sexual transmission increasingly accounts for new HIV infections in this population.4–6 In contrast to the rapid and marked declines in injection risk practices observed over the past two decades in the United States, Western Europe, and Australia, the sexual risk practices of IDUs change slowly if at all.7–13 Among heterosexual adults who do not inject drugs in the United States, an estimated 80% of HIV infections were contracted through heterosexual contact with HIV-infected injection drug users based on studies conducted in early 1990s.14 The relative increase of AIDS cases among blacks in recent years have been attributed to a higher level of concurrent sexual partnerships in blacks.15,16 In 2005, heterosexual contact accounted for 79% of newly diagnosed HIV and AIDS cases in females and 15% in males in the United States.15
One of the major interventions associated with declines in injection risk practices is needle exchange.17–21 Surveys indicate that condoms are provided in most needle exchange programs (NEPs) in North America,22,23 but few studies have examined the effects of NEP use on sexual risk behaviors and the findings are not consistent. Early studies found NEP had no or little effect on sexual risk behaviors.17,18 A more recent longitudinal study in Dublin also found no significant change in condom use among NEP attendees.24 However, a recent cross-sectional study conducted among young injection drug users in Chicago found frequent NEP users were almost 3-fold more likely than NEP nonusers to use condoms with regular sex partners.25
In this paper, we examined the impacts of needle exchange use on 3 aspects of sexual risk behaviors (number of sex partners, frequency of condom use, and number of episode of unprotected vaginal intercourse) using data from a longitudinal study designed to evaluate the effectiveness of a needle exchange program in Chicago, IL. Although NEP nonusers in this study were provided with street outreach, HIV education, risk reduction counseling, and condoms, we hypothesized that NEP users would have a lower level of sexual risk behaviors than nonusers because: (1) access to HIV prevention services and condoms was easier and more reliable at the NEP compared to street outreach and (2) the NEP constituted a more holistic HIV prevention setting than street outreach.
Materials and Methods
The study setting and design have been described in detail elsewhere.26 The NEP evaluated in this study was founded in 1996 through a collaboration between a community-based group, Chicago Health Outreach, and the University of Illinois at Chicago. The NEP was a legal entity funded by the Chicago Department of Public Health and the AIDS Foundation of Chicago. The NEP operated at 3 storefront offices (South Side, Northwest Side, and North Side) and a motorhome (West Side) that together served a racially and ethnically diverse population. All NEP sites conducted individual risk assessments and provided other risk reduction materials including condoms. A mostly indigenous staff at the storefront offices also offered other services, including street outreach, HIV counseling and testing, case management and referrals to offsite services such as drug treatment programs, and medical care for persons living with HIV.
The Southeast Side of Chicago had no NEP during the study period. Neighborhoods vary across the Southeast Side, as they do at the NEP sites, but for any particular community demographic characteristic, the Southeast Side resides within the range found at the NEP sites.
Between 1997 and 2000, adult IDUs were enrolled at the aforementioned NEP sites into a prospective cohort study. Participants recruited as NEP users were required to have used the NEP at least twice ever and to have enrolled in the NEP at least 30 days before enrolling into the study. These criteria discouraged enrollment in the NEP only to qualify for the study and its compensation payment, and helped avoid recruiting the sizeable minority of one-time NEP users. Participation in the NEP was verified by checking its records. Less than 10% declined enrollment, most of whom said they did not have enough time to do the interview.
A comparison group of IDUs without local access to NEP were recruited in Southeast Side street settings and through chain referral sampling.27–29 Outreach workers, indigenous former IDUs, initiated recruiting by contacting IDUs in a variety of Southeast Side congregation areas. To reduce sampling bias from outreach workers recruiting only IDUs they knew and liked, we encouraged persons contacted on the street and all control group participants to refer eligible persons to the study. Our staff provided all comparison group members with HIV education, client-centered risk reduction counseling, prevention materials including condoms, and referral to offsite services. Consistent with the study's longitudinal design, outreach staff spent much of their time in Southeast Side neighborhoods maintaining contact with study participants and, while doing so, promoting HIV risk reduction.
Eligible participants had to have injected drugs in the 6 months preceding the baseline interview, speak English or Spanish, and be at least 18 years old. Participants in our earlier National AIDS Demonstration Project (NADR) study were excluded because of the low levels of HIV risk practices they exhibited subsequent to that intervention.3 NEP users recruited at office-based NEPs were screened and interviewed at those sites. NEP users at the motorhome and IDUs recruited in the area with no NEP were screened and interviewed by study staff in offices rented from nearby community-based organizations and occasionally in cars.
After obtaining informed, signed consent, trained interviewers administered a standardized face-to-face interview in a private area, followed by pretest counseling and a blood draw for HIV testing. Specimens repeatedly reactive in whole-virus lysate enzyme-linked immunosorbent assays were confirmed by Western blot. Participants were compensated $25 for their time and effort in answering the survey and given appointments to return to receive their HIV test results and posttest counseling.
All participants, except those from the South Side NEP, were monitored at enrollment and 3 follow-up visits, separated by 12 months. South Side participants were only administrated 1 follow-up visit because this site was later in the study. Data collection procedures at follow-up visits were the same as those at the baseline. The study was approved by the Institutional Review Board at the University of Illinois at Chicago.
To evaluate effectiveness of NEP on sexual risk behaviors, we compared IDUs who used a needle exchange program with those who did not use NEP in the 6 months before the baseline interview.
We examined 3 aspects of sexual risk behaviors: number of sex partners, number of unprotected sex acts, and frequency of condom use. A simulation study showed that changes in the number of sex partners is the preferred marker for estimating changes in the risk of contracting highly infectious sexually transmitted diseases (STDs) such as gonorrhea, whereas the number of unprotected acts of sexual intercourse is the better marker for less infectious diseases such as HIV.30 Although studies indicate that the relative frequency of condom use is not a strong marker for STD incidence regardless of prevalence and infectivity, we examined this outcome because behavioral interventions that promote sexual risk reduction typically aim to increase condom use.
In this paper, “number of sex partners” was defined at baseline as the total number of sex partners in the last six months and – at follow-up – as the total number of sex partners since the last interview (12 months on average), regardless of partner type. Because of its skewed distribution, we recoded the number of sex partners as an ordinal variable: 0, 1, 2 to 4, 5 or more. “Multiple sex partners” was defined as having two or more sex partners. Frequency of condom use was assessed separately for vaginal intercourse with 3 types of partners (main, casual, and commercial) using a 7-category question: always, almost always, more than half the time, half the time, less than half the time, almost never, or never. Frequency of condom use referred to “the last 6 months” at the baseline interview and “since the last interview” at follow-up visits. Because of bimodal distributions, these measures were recoded as 3 categories: always, sometime, or no condom use. “Commercial sex partners” were defined as sex partners who gave money/drugs for sex or received money/drugs for sex. We defined the number of unprotected sex acts as the total instances of vaginal intercourse without using a condom with one's main sex partner in last 30 days and then recoded this as an ordinal variable (0, 1–4, 5–9, 10–19, 20 or more). Number of unprotected vaginal sex acts with casual partners and condom use in anal sex were not presented because these sexual behaviors were infrequent in this population.
Baseline measures examined as potential confounders and predictors included age, gender, race/ethnicity, education, married/common law relationship, self-reported homelessness in the past 6 months, main source of income in the past 6 months, monthly income, HIV status, sexually transmitted diseases (ever having gonorrhea, syphilis, chlamydia, herpes, pelvic infection, and other sexually transmitted diseases), age at first intercourse, sexual orientation, and drug treatment in the past 6 months. We also examined cocaine injecting and smoking in the past 6 months, because these practices have been found to predict greater sex risk.31–37 Most measures were recoded based on conceptual and distributional considerations.
Continuous variables at enrollment were compared between NEP users and nonusers using t tests or Wilcoxon rank sum test, and categorical variables were compared using χ2 tests or Fisher exact tests. The frequency of condom use in vaginal sex act and the number of unprotected sex episodes were analyzed using random-effects ordinal logistic regression models (proportional odds models) to account for correlation among repeated measurements within subjects and the order of outcome categories.38 The proportional odds assumption was tested and, if it did not hold, a partial proportional odds model was fitted. The proportion of multiple sex partners was analyzed using random-effects logistic regression models.39 Specifically, intercept was allowed to vary across subjects in the models. We first examined whether there was an interaction between the study group (NEP nonusers, NEP users) and visit time, after controlling for baseline demographics, sexual, and drug use histories, and HIV status. If the group by time interaction term was not significant, we dropped this term and the reduced model essentially examined the averaged difference between NEP users and nonusers. Other covariates were further dropped using a backward variable selection procedure with the study group always included. The final models include only variables that are significant (P <0.05) or close to significant (P < 0.10). To have a population-averaged interpretation, we transformed the obtained regression coefficients and standard errors to marginalized odds ratios (ORs) and corresponding 95% confidence intervals (CI).39 Data were managed using SAS 9.1 (SAS institute, Cary, NC) and statistical models were fit with the xtlogit and gllamm programs in Stata 9.0 (StataCorp, College Station, TX).
Of 889 IDUs enrolled between 1997 and 2000, 717 (80.7%) reported using NEPs in the 6 months before baseline interview and 172 (19.3%) were NEP nonusers. At baseline, NEP users had exchanged needles for a median of 12 months (median, interquartile range 4–36 months). Baseline characteristics of NEP users and nonusers are summarized in Table 1. NEP users were younger and more likely to have a monthly income of at least $1000, to be HIV-positive, and to recently have been in a drug treatment program, and less likely to consider themselves homeless or to smoke crack cocaine. No significant differences were observed between the two groups about gender, race, marital status, education, main source of income, proportion of having injected cocaine in the 6 months before baseline, history of having a sexually transmitted disease, and sexual orientation. Only 5% of study participants considered themselves to be homosexual or bisexual.
Table 2 shows the prevalence of sexual risk behaviors for NEP users and nonusers across 4 study visits. At baseline, about one half of study participants had 1 sex partner and nearly 30% had multiple sex partners. During follow-up, the proportion of study participants reporting sexual abstinence increased despite a longer recall time frame (“since the last interview”) than at baseline (past 6 months). In the logistic model that adjusted for study visit, NEP users and nonusers had no significant difference in the proportion of multiple sex partners (2 or more partners) across time (P = 0.40).
At baseline, two-thirds of IDUs reported not using condoms during vaginal sex with their main sex partners in the past 6 months. NEP users were more likely than nonusers to use condoms consistently with their main partners during vaginal sex across 4 study visits (P = 0.001).
Overall, half of study participants always used a condom with their casual sex partners and there was only marginally significant difference between NEP users and nonusers across study visits (P = 0.059). About 17% of study participants had commercial sex in the 6 months before the baseline interview and less than 40% of these participants always used condoms. There was no significant difference between the two groups across study visits (P = 0.33).
Finally, 43% of both NEP users and nonusers reported unprotected vaginal intercourse with their main sex partners in the 30 days before the baseline interview. NEP users experienced a reduction in the number of episodes of unprotected vaginal sex, whereas nonusers had little change during follow-up; the group by time interaction was significant in the univariate analysis (P = 0.014).
Table 3 presents the adjusted ORs for sexual risk behaviors from the random-effects ordinal or binary logistic regression models. Note that an OR of greater than 1 indicates increased risk for outcome variables “multiple sex partners” and “number of unprotected sex acts,” whereas an OR of less than 1 indicates increased risk for the three outcome variables of “condom use.” NEP users and nonusers had no significant difference in the proportion having multiple sex partners across 4 study visits. NEP users were more likely than nonusers to wear a condom during vaginal sex with their main partners (P = 0.047). There was no difference between the two groups in condom use during vaginal sex acts with casual and commercial sex partners. At baseline, there was no difference in number of unprotected vaginal sex episodes between the 2 groups. However, there was a significant differential change from baseline to follow-ups between the 2 groups (P = 0.02); the odds of having a higher number of instances of unprotected vaginal intercourse were reduced by 26% per year in NEP group, whereas the odds declined only 10% per year in control group, after adjustment for age, gender, race/ethnicity, education, marital status, HIV status, age at first intercourse, sexual orientation, and smoking crack cocaine.
Older IDUs were less likely to have multiple sex partners, had less unprotected sex with main partners but were less likely to use a condom with commercial partners. Women tended to have multiple sex partners and more unprotected sex with their main partners but were more likely to use a condom with casual and commercial partners. Black, compared with other ethnic groups, tended to have multiple sex partners and more unprotected vaginal intercourse with main partners. As expected, participants who were married or lived with a person as if married were less likely to have multiple partners but less likely to use condom with their main or casual partners. Homeless persons were more likely than the housed to have multiple partners. HIV-infected IDUs were less likely to have multiple partners and more likely to use condoms with all types of partners, and they significantly reduced the number of episodes of unprotected vaginal sex with their main partners. Last, IDUs who also smoked crack were more likely to have multiple sex partners and more unprotected intercourse with main partners.
The primary finding of this study is that whereas NEP users and nonusers at baseline reported a similar number of instances of recent unprotected intercourse with their main partners, only NEP users experienced a substantial reduction in this behavior during the 3-year study follow-up. This finding suggests that use of an NEP may have contributed to reducing a behavior that best represents the absolute risk of HIV sexual transmission.
Of the relative sexual risk indicators, consistent condom use with regular partners was marginally significantly higher in NEP users than in nonusers. In contrast, frequency of condom use with other partners and the number of sex partners were not different between the two groups. The significant difference we observed in the proportion of consistent condom use with main partners in the univariate analysis may have been because of differences between the 2 groups in HIV prevalence and crack smoking. Awareness of HIV infection has been shown in the current study and several previous studies of IDUs to be associated with fewer sexual risk practices,40–43 whereas smoking crack cocaine has been associated with greater sexual risk practices.33,35–37
Consistent with previous studies,10,42,44–46 we found IDUs were more likely to use condoms consistently with casual and commercial partners than with their main partners. Not using a condom with a main partner may be a way of showing trust,47–49 but this behavior puts both partners at risk of HIV infection. For example, findings from a study of drug users in Amsterdam suggest unprotected sexual contact that mainly occurs with a regular partner accounted for 23% of observed HIV seroconversions.50 Even with casual partners, only about half of study participants at each round of data collection in the current study reported consistently using condoms. Clearly more work is needed to prevent the sexual transmission of HIV, particularly given that HIV infected people often delay or refrain from disclosing their HIV status to sex partners.51–53 In this study, we also found that an HIV-positive serostatus increased the odds of condom use 6-fold with regular partners but only 2-fold with casual or commercial partners.
Several limitations are relevant. First, behaviors were self-reported and thus may subject to recall bias. To minimize inaccuracy in reporting, the primary outcome, number of unprotected sex acts, asked about the past 30 days. Socially desirable reporting may have been present but we think it is unlikely because no systematic change across interviews was observed in the proportion of participants reporting condom use. Second, a sizeable number of subjects did not come back for follow-up interviews. However, attrition analysis showed that there were no significant differences at baseline between those followed and those not followed in the sexual risk behaviors we examined, suggesting that the results were unlikely to be biased because of selective loss to follow-up, although study efficiency (statistical power) was compromised. Third, NEP users and nonusers were not comparable in several baseline characteristics, especially HIV status and crack smoking. Smoking crack has been associated with high-risk sexual behaviors33,35,37 and HIV-infected people are more likely to use condom with their regular sexual partner than uninfected persons.42,43 We used proportional odds models to adjust for these imbalances and found consistent condom use was not associated with NEP use but the absolute number of instances of unprotected intercourse with a main partner decreased in NEP users more than nonusers. Finally, study findings may not be generalizable to other populations of IDUs because participants were not randomly selected.
Despite these limitations, this study suggests that participation in needle exchange programs may help to reduce the absolute risk of HIV sexual transmission. At the least, NEPs should be considered as a promising venue for accessing persons at high risk for sexually transmitted diseases including HIV and for providing sexual risk reduction interventions to this high-risk population.
1. Des Jarlais DC, Friedman SR. HIV infection among intravenous drug users: epidemiology and risk reduction. AIDS 1987; 1:67–76.
2. Schoenbaum EE, Hartel D, Selwyn PA, et al. Risk factors for human immunodeficiency virus infection in intravenous drug users. N Engl J Med 1989; 321:874–879.
3. Wiebel WW, Jimenez A, Johnson W, et al. Risk behavior and HIV seroincidence among out-of-treatment injection drug users: a four-year prospective study. J Acquir Immun Defic Syndr Hum Retrovirol 1996; 12:282–289.
4. Kral AH, Bluthenthal RN, Lorvick J, et al. Sexual transmission of HIV-1 among injection drug users in San Francisco, USA: risk-factor analysis. Lancet 2001; 357:1397–1401.
5. Strathdee SA, Galai N, Safaiean M, et al. Sex differences in risk factors for HIV seroconversion among injection drug users: a 10-year perspective. Arch Intern Med 2001; 161:1281–1288.
6. Lindenburg CE, Krol A, Smit C, et al. Decline in HIV incidence and injecting, but not in sexual risk behaviour, seen in drug users in Amsterdam: a 19-year prospective cohort study. AIDS 2006; 20:1771–1775.
7. Rhodes T, Stimson GV, Quirk A. Sex, drugs, intervention, and research: from the individual to the social. Subst Use Misuse 1996; 31:375–407.
8. Watters JK. Trends in risk behavior and HIV seroprevalence in heterosexual injection drug users in San Francisco, 1986–1992. J Acquir Immun Defic Syndr 1994; 7:1276–1281.
9. Semaan S, Kotranski L, Collier K, et al. Temporal trends in HIV risk behaviors of out-of-treatment injection drug users and injection drug users who smoke crack. J Acquir Immun Defic Syndr Hum Retrovirol 1998; 19:274–281.
10. Paone D, Caloir S, Shi Q, et al. Sex, drugs, and syringe exchange in New York city: women's experiences. J Am Med Womens Assoc 1995; 50:109–114.
11. Garfein RS, Golub ET, Greenberg AE, et al. A peer-education intervention to reduce injection risk behaviors for HIV and hepatitis C virus infection in young injection drug users. AIDS 2007; 21:1923–1932.
12. McCoy CB, Metsch LR, Comerford M, et al. Trends of HIV risk behaviors in a cohort of injecting drug users and their sex partners in Miami, Florida, 1988–1998. AIDS Behav 2005; 9:187–199.
13. Crofts N, Webb-Pullman J, Dolan K. An analysis of trends over time in social and behavioural factors related to the transmission of HIV among injecting drug users and prison inmates. Evaluation of the National HIV/AIDS Strategy 1993–94 to 1995–96, Technical Appendix 4. Canberra: AGPS Australian Government Publishing Service, 1996.
14. Holmberg SD. The estimated prevalence and incidence of HIV in 96 large US metropolitan areas. Am J Public Health 1996; 86:642–654.
15. Centers for Disease Control and Prevention. HIV/AIDS Surveillance Report, 2005. Atlanta: US Department of Health and Human Services, Centers for Disease Control and Prevention, 2007.
16. Adimora AA, Schoenbach VJ, Martinson F, et al. Concurrent sexual partnerships among African Americans in the rural south. Ann Epidemiol 2004; 14:155–160.
17. Lurie P, Reingold AL, Bowser B, et al. The Public Health Impact of Needle Exchange Programs in the United States and Abroad. San Francisco: University of California, 1993.
18. Normand J, Vlahov D, Moses LE. Preventing HIV transmission: The Role of Sterile Needles and Bleach. Washington, DC: National Academy Press, 1995.
19. US General Accounting Office. Needle Exchange Programs: Research Suggests a Promising AIDS Strategy. Washington, DC: US Government Printing Office, 1993.
20. Gibson DR, Flynn NM, Perales D. Effectiveness of syringe exchange programs in reducing HIV risk behavior and HIV seroconversion among injecting drug users. AIDS 2001; 15:1329–1341.
21. Wodak A, Cooney A. Effectiveness of Sterile Needle and Syringe Programming in Reducing HIV/AIDS Among Injecting Drug Users. Geneva: World Health Organization, 2005.
22. Paone D, Clark J, Shi Q, et al. Syringe exchange in the United States, 1996: a national profile. Am J Public Health 1999; 89:43–46.
23. Centers for Disease Control and Prevention. Update: syringe exchange programs-United States, 1998. MMWR Morb Mortal Wkly Rep 2001; 50:384–387.
24. Cox GM, Lawless MC, Cassin SP, et al. Syringe exchanges: a public health response to problem drug use. Ir Med J 2000; 93:143–146.
25. Bailey SL, Huo D, Garfein RS, et al. The use of needle exchange by young injection drug users. J Acquir Immun Defic Syndr 2003; 34:67–70.
26. Ouellet L, Huo D, Bailey SL. HIV risk practices among needle exchange users and nonusers in Chicago. J Acquir Immun Defic Syndr 2004; 37:1187–1196.
27. Biernacki P, Waldorf D. Snowball sampling: problems and techniques of chain referral sampling. Sociol Methods Res 1981; 10:141–161.
28. Watters JK, Biernacki P. Targeted sampling: options for the study of hidden populations. Soc Probl 1989; 36:416–430.
29. Wiebel WW. Combining ethnographic and epidemiologic methods in targeted AIDS interventions: the Chicago model. In: Pickens RW, ed. Needle Sharing among Intravenous Drug Abusers: National and International Perspectives. NIDA Research Monograph 80. Washington, DC: US Government Printing Office, 1988:137–150.
30. Pinkerton SD, Chesson HW, Layde PM. Utility of behavioral changes as markers of sexually transmitted disease risk reduction in sexually transmitted disease/HIV prevention trials. J Acquir Immun Defic Syndr 2002; 31:71–79.
31. Somlai AM, Kelly JA, McAuliffe TL, et al. Predictors of HIV sexual risk behaviors in a community sample of injection drug-using men and women. AIDS Behav 2003; 7:383–393.
32. Lejuez CW, Bornovalova MA, Daughters SB, et al. Differences in impulsivity and sexual risk behavior among inner-city crack/cocaine users and heroin users. Drug Alcohol Depend 2005; 77:169–175.
33. Edlin BR, Irwin KL, Faruque S, et al. Intersecting epidemics–crack cocaine use and HIV infection among inner-city young adults. Multicenter Crack Cocaine and HIV Infection Study Team. N Engl J Med 1994; 331:1422–1427.
34. Edwards JM, Halpern CT, Wechsberg WM. Correlates of exchanging sex for drugs or money among women who use crack cocaine. AIDS Educ Prev 2006; 18:420–429.
35. Booth RE, Watters JK, Chitwood DD. HIV risk-related sex behaviors among injection drug users, crack smokers, and injection drug users who smoke crack. Am J Public Health 1993; 83:1144–1148.
36. Flom PL, Friedman SR, Kottiri BJ, et al. Stigmatized drug use, sexual partner concurrency, and other sex risk network and behavior characteristics of 18–24-year-old youth in a high-risk neighborhood. Sex Transm Dis 2001; 28:598–607.
37. Chiasson MA, Stoneburner RL, Hildebrandt DS, et al. Heterosexual transmission of HIV-1 associated with the use of smokable freebase cocaine (crack). AIDS 1991; 5:1121–1126.
38. Hedeker D, Gibbons RD. A random-effects ordinal regression model for multilevel analysis. Biometrics 1994; 50:933–944.
39. Diggle PJ, Heagerty P, Liang KY, et al. Analysis of Longitudinal Data. 2nd ed. New York, NY: Oxford University Press, 2002.
40. Colon HM, Robles RR, Marrero CA, et al. Behavioral effects of receiving HIV test results among injecting drug users in Puerto Rico. AIDS 1996; 10:1163–1168.
41. Deren S, Beardsley M, Coyle S, et al. HIV serostatus and risk behaviors in a multisite sample of drug users. J Psychoactive Drugs 1998; 30:239–245.
42. Vanichseni S, Des Jarlais DC, Choopanya K, et al. Sexual risk reduction in a cohort of injecting drug users in Bangkok, Thailand. J Acquir Immun Defic Syndr 2004; 37:1170–1179.
43. Booth RE, Mikulich-Gilbertson SK, Brewster JT, et al. Predictors of self-reported HIV infection among drug injectors in Ukraine. J Acquir Immun Defic Syndr 2004; 35:82–88.
44. Franken IH, Kaplan CD. Risk contexts and risk behaviors in the Euregion Maas-Rhein: the Boule de Neige intervention for AIDS prevention among drug users. AIDS Educ Prev 1997; 9:161–180.
45. Bogart LM, Kral AH, Scott A, et al. Sexual risk among injection drug users recruited from syringe exchange programs in California. Sex Transm Dis 2005; 32:27–34.
46. Rosengard C, Anderson B, Stein MD. Intravenous drug users' HIV-risk behaviors with primary/other partners. Am J Drug Alcohol Abuse 2004; 30:225–236.
47. Misovich SJ, Fisher JD, Fisher WA. Close relationships and elevated HIV risk behavior evidence and possible underlying psychological processes. Review of Gen Psy 1997; 1:72–107.
48. Rhodes T, Quirk A. Drug users' sexual relationships and the social organisation of risk: the sexual relationship as a site of risk management. Soc Sci Med 1998; 46:157–169.
49. de Visser R, Smith A. Relationship between sexual partners influences rates and correlates of condom use. AIDS Educ Prev 2001; 13:413–427.
50. Van Ameijden EJ, Langendam MW, Notenboom J, et al. Continuing injecting risk behaviour: results from the Amsterdam Cohort Study of drug users. Addiction 1999; 94:1051–1061.
51. O'Brien ME, Richardson-Alston G, Ayoub M, et al. Prevalence and correlates of HIV serostatus disclosure. Sex Transm Dis 2003; 30:731–735.
52. Parsons JT, Missildine W, Van Ora J, et al. HIV serostatus disclosure to sexual partners among HIV-positive injection drug users. Aids Patient Care STDS 2004; 18:457–469.
53. Ciccarone DH, Kanouse DE, Collins RL, et al. Sex without disclosure of positive HIV serostatus in a US probability sample of persons receiving medical care for HIV infection. Am J Public Health 2003; 93:949–954.
© Copyright 2009 American Sexually Transmitted Diseases Association
What does "Remember me" mean?
By checking this box, you'll stay logged in until you logout. You'll get easier access to your articles, collections,
media, and all your other content, even if you close your browser or shut down your
To protect your most sensitive data and activities (like changing your password),
we'll ask you to re-enter your password when you access these services.
What if I'm on a computer that I share with others?
If you're using a public computer or you share this computer with others, we recommend
that you uncheck the "Remember me" box.
Data is temporarily unavailable. Please try again soon.