Genetic variation in CLDN1 and susceptibility to hepatitis C virus infection.

Claudin-1 is a recently discovered co-receptor for hepatitis C virus (HCV) that is required for late-stage binding of the virus. Because variants in the gene that encodes claudin-1 (CLDN1) could play a role in HCV infection, we conducted a 'whole gene association study' among injection drug users (IDUs) to examine whether CLDN1 genetic variants were associated with the risk of HCV infection or with viral clearance. In a cross sectional study, we examined genotype results for 50 single nucleotide polymorphisms (SNPs) across the CLDN1 gene region, comparing genotypes among participants with chronic HCV (n = 658) to those in IDUs who had cleared HCV (n = 199) or remained HCV-uninfected (n = 68). Analyses were controlled for racial ancestry (African-American or European-American) by stratification and logistic regression modeling. We found that participants who remained uninfected more often carried CLDN1 promoter region SNPs -15312C [odds ratio (OR), 1.72; 95% confidence interval (CI) 1.00-2.94; P = 0.048], -7153A (OR, 2.13; 95% CI, 1.25-3.62; P = 0.006) and -5414C (OR, 1.78; 95% CI, 1.06-3.00; P = 0.03). HCV-uninfected participants less often carried CLDN1 IVS1-2983C (OR, 0.55; 95% CI, 0.31-0.97; P = 0.04), which lies in intron 1. CLDN1 -15312C, -7153A and -5414C formed a haplotype in both the African-American and European-American participants and a haplotype analysis supported the association of CLDN1 -7153A in the HCV-uninfected participants. The analyses of HCV clearance revealed no associations with any SNP. These results indicate that genetic variants in regulatory regions of CLDN1 may alter susceptibility to HCV infection.

Hepatitis C virus-specific T-cell immune responses in seronegative injection drug users.

T-cell responses to hepatitis C virus (HCV) antigens have been reported in high-risk HCV seronegative persons, suggesting that an effective cellular immune response might be able to clear infection without the development of antibodies. Such findings, however, could be explained by waning antibody or cross-reactivity to other antigens. To address these issues, we evaluated HCV-specific T-cell responses in 26 young (age 18-33 years) aviremic, seronegative injection drug users (IDUs) (median duration of injection, 6 years) by interferon-gamma enzyme-linked immunospot (ELISpot) assay using 429 overlapping HCV peptides pooled in 21 mixes. Seventeen aviremic, seropositive IDUs (spontaneous resolvers) and 15 healthy people were used as positive and negative controls, respectively. The percentage of patients with HCV-specific cellular immune responses was similar in seronegative and seropositive aviremic IDUs (46%vs 59%, P = 0.4), while these responses were not detected in any of the negative controls. Among the seronegative IDUs, six (23%) had intermediate to very strong responses to 10-20 peptide mixes and another six (23%) had moderately strong responses for two to six mixes. The 12 seronegative IDUs with HCV-specific T-cell responses had higher demographical and behavioural risk profiles than the 14 IDUs without T-cell responses (estimated risk of HCV infection, 0.47 vs 0.26, P < 0.01). In conclusion, HCV-specific T-cell responses are common among high-risk, seronegative IDUs. The responses are broad and are associated with risk factors for HCV exposure, suggesting that they reflect true exposure to HCV in seronegative persons.

The inverse relationship between chronic HBV and HCV infections among injection drug users is associated with decades of age and drug use.

Infection with hepatitis C virus (HCV) may suppress co-infection with hepatitis B virus (HBV) during acute or chronic HBV infection. We examined relationships between HBV infection, HCV infection and other factors among injection drug users (IDUs) with antibodies to both viruses. Participants enrolled in a cross-sectional study during 1998-2000 were considered to have been infected with HBV if they had core antibody, to be chronically infected if they had hepatitis B surface antigen (HBsAg), to have been infected with HCV if they had HCV antibody and to be chronically infected if they had HCV RNA. Among 1694 participants with antibody to both viruses, HBsAg prevalence decreased with increasing age among those positive for HCV RNA [from 4.55% in those 18-29 years to 1.03% in those >or=50 years old (P(trend) = 0.02)], but not among those who were negative for HCV RNA. Chronic HBV infection was less common overall among those with chronic HCV infection (odds ratio [OR], 0.25; P < 0.0001), but this inverse relationship was much stronger in the oldest (>50 years; OR = 0.15) than the youngest (18-29 years; OR = 0.81) participants (P(trend) = 0.03). Similar results were obtained when duration of injection drug use was substituted for age (P(trend) = 0.05). Among IDUs who have acquired both HBV and HCV, chronic HBV infection is much less common among those with chronic HCV infection, but this inverse relationship increases markedly with increasing years of age and injection drug use. Co-infection with HCV may enhance the resolution of HBsAg during the chronic phases of these infections.

Hepatitis C patients' self-reported adherence to treatment with pegylated interferon and ribavirin.

BACKGROUND: Prior research on adherence to hepatitis C treatment has documented rates of dose reductions and early treatment discontinuation, but little is known about patients' dose-taking adherence. AIMS: To assess the prevalence of missed doses of pegylated interferon and ribavirin and examine the correlates of dose-taking adherence in clinic settings. METHODS: One hundred and eighty patients on treatment for hepatitis C (23% coinfected with HIV) completed a cross-sectional survey at the site of their hepatitis C care. RESULTS: Seven per cent of patients reported missing at least one injection of pegylated interferon in the last 4 weeks and 21% reported missing at least one dose of ribavirin in the last 7 days. Dose-taking adherence was not associated with HCV viral load. CONCLUSIONS: Self-reported dose non-adherence to hepatitis C treatment occurs frequently. Further studies of dose non-adherence (assessed by method other than self-report) and its relationship to HCV virological outcome are warranted.

Prevention of peripheral venous catheter complications with an intravenous therapy team: a randomized controlled trial.

BACKGROUND: More than 25 million patients have peripheral intravenous (IV) catheters placed each year in US hospitals. Infusion therapy is believed to account for one third of all nosocomial bacteremias. METHODS: We performed a randomized, prospective, controlled study in a university-affiliated hospital to determine whether the use of an IV therapy team decreases peripheral venous catheter-related complications in adult medical patients. Patients were randomized to undergo peripheral catheter insertion and/or maintenance either by the IV team or by medical house staff. A dedicated observer reviewed catheter sites daily; findings were applied to a scoring system to define the severity of complications. Bacteremic complications were reviewed by a physician. RESULTS: Patients with catheters started by the house staff and maintained by ward nursing staff more often had signs or symptoms of inflammation (21.7%) than did patients with catheters maintained by the IV team (7.9%) (P<.001). Patients monitored by the IV team had a greater mean number of catheters placed per patient than did patients monitored by house staff (2.1 and 1.6, respectively) (P<.01). Three episodes of catheter-related sepsis occurred in house staff patients and none in IV team patients (P=.004). CONCLUSIONS: An IV therapy team significantly reduced both local and bacteremic complications of peripheral IV catheters. Timely replacement of the catheter appeared to be the most important factor in reducing the occurrence of complications.

The effect of syringe exchange use on high-risk injection drug users: a cohort study.

OBJECTIVE: To determine whether syringe exchange program use is associated with cessation of syringe sharing among high-risk injection drug users. DESIGN AND METHODS: Between 1992 and 1996, street-recruited injection drug users were interviewed and received HIV testing and counseling semi-annually, as part of a dynamic cohort study. We examined a cohort of 340 high-risk injection drug users for whom two observations, 6-months apart, were available and who reported syringe sharing at the first interview. Multivariate logistic regression analysis was performed to determine the relationship between syringe exchange program use and cessation of syringe sharing, while controlling for confounding factors. RESULTS: At follow-up interview, 60% (204 of 340) reported quitting syringe sharing. High-risk injection drug users who began using the syringe exchange program were more likely to quit sharing syringes [adjusted odds ratio (AOR), 2.68; 95% confidence interval (CI), 1.35-5.33], as were those who continued using the syringe exchange program (AOR,1.98; 95% CI, 1.05-3.75) in comparison with non-syringe exchange program users, while controlling for confounding factors. CONCLUSIONS: The initiation and continuation of syringe exchange program use among high-risk injection drug users is independently associated with cessation of syringe sharing. Syringe exchange program use can be an important component in reducing the spread of blood-borne infectious diseases among high-risk injection drug users.

Differences between men and women with HIV-related Pneumocystis carinii pneumonia: experience from 3,070 cases in New York City in 1987.

Although women make up the fastest growing group of persons with AIDS, studies of human immunodeficiency virus (HIV)-infected persons reported to date have included predominantly or exclusively men. We evaluated sex differences in sociodemographic characteristics, hospital characteristics, in-hospital resource use, and short-term mortality rates for 2,526 men and 544 women admitted for their first-episode of HIV-related Pneumocystis carinii pneumonia (PCP) in New York City in 1987. Compared with men, women were significantly less likely to be white (81% vs. 54%, p < or = 0.001) or have private health insurance (80% vs. 58%, p < or = 0.001), and more likely to be admitted through an emergency room (79% vs. 71%, p < or = 0.001) and receive care at hospitals that had less experience treating PCP (p < or = 0.001). Women were more likely than men to die in the hospital [33% vs. 24%; crude odds ratio = 1.56, confidence interval (CI) = 1.28-1.91, p < or = 0.001]. In a logistic regression model, the risk of death in the hospital was associated with age 60-65 years [adjusted odds ratio (AOR) = 4.19, CI = 2.13-8.21], not having private health insurance (AOR = 1.37, CI = 1.08-1.75), admission through the emergency room (AOR = 1.54, CI = 1.21-1.96), and receiving care at hospitals with less experience treating PCP (AOR = 1.63, CI = 1.15-2.30), but women were not significantly more likely to die in the hospital than men (AOR = 1.18, CI = 0.93-1.50). Poorer access to medical care as well as higher use of hospitals with less experience treating AIDS may account for the difference in mortality rates observed in women with HIV-related PCP.

Variations in medical care for HIV-related Pneumocystis carinii pneumonia: a comparison of process and outcome at two hospitals.

BACKGROUND: Institutional variation in the quality of medical care may be evaluated by examining process measures, such as use of diagnostic procedures or treatment modalities, or outcome measures, such as mortality. We undertook this study to examine variations in both process and outcome of care for patients with HIV-related Pneumocystis carinii pneumonia (PCP) at two geographically diverse, HIV-experienced, public municipal hospitals. DESIGN: Retrospective review of hospitalized patients diagnosed as having PCP cared for at two municipal hospitals from 1988 to 1990. At hospital A, charts of all patients diagnosed as having PCP were abstracted (n=209); at hospital B, a random sample of 15% were abstracted (=136). RESULTS: Among all hospitalized patients diagnosed as having PCP, the frequency of making a definitive diagnosis of PCP (as opposed to treating empirically) differed markedly at the two hospitals (85% in hospital A vs 26% in hospital B; p<0.001), as did the use of intensive care (18% vs 3%; p<0.001) and "do-not-resuscitate" orders (39% vs 14%; p<0.001), although the timing of starting anti-Pneumocystis medications (89% vs 88% within the first 2 hospital days) and the use of corticosteroids (21% vs 23%) were similar. Despite differences in the process of care, survival rates were similar at the two institutions (75% vs 76%; p=0.8) and remained similar when logistic regression was used to control for demographic variables and severity of illness (odds ratio for survival, hospital B vs A, 1.2 [95% confidence interval, 0.7, 2.0]). The 95% confidence intervals (0.7, 2.0), however, were consistent with a considerable (and clinically significant) disparity in survival (from 30% lower to a twofold higher odds of survival). Sample size calculations showed that a sample of 10 cases in each hospital would be required to detect the observed difference in definitive diagnosis rates (85% vs 26%), but 722 cases in each hospital would be required to detect a relevant difference in mortality. CONCLUSIONS: The process of care for hospitalized patients with PCP in these two institutions differed considerably, but the survival rates were not significantly different, even after adjusting for confounding factors. While sample sizes available at the individual institutions were sufficient for evaluation of the process of care, they did not provide the power necessary to evaluate outcomes. Comparisons of outcomes such as mortality between individual hospitals may not have the statistical power to exclude important differences.

Evaluation of infection control measures in preventing the nosocomial transmission of multidrug-resistant Mycobacterium tuberculosis in a New York City hospital.

OBJECTIVE: To evaluate the efficacy of Centers for Disease Control and Prevention (CDC)-recommended infection control measures implemented in response to an outbreak of multidrug-resistant (MDR) tuberculosis (TB). DESIGN: Retrospective cohort studies of acquired immunodeficiency syndrome (AIDS) patients and healthcare workers. The study period (January 1989 through September 1992) was divided into period I, before changes in infection control; period II, after aggressive use of administrative controls (eg, rapid placement of TB patients or suspected TB patients in single-patient rooms); and period III, while engineering changes were made (eg, improving ventilation in TB isolation rooms). SETTING: A New York City hospital that was the site of one of the first reported outbreaks of MDR-TB among AIDS patients in the United States. PARTICIPANTS: All AIDS patients admitted during periods I and II. Healthcare workers on nine inpatient units with TB patients and six without TB patients. RESULTS: The epidemic (38 patients) waned during period II and only one MDR-TB patient presented during period III. The MDR-TB attack rate among AIDS patients hospitalized on the same ward on the same days as an infectious MDR-TB patient was 8.8% (19 of 216) during period I, decreasing to 2.6% (5 of 193; P = 0.01) during period II. In a small group of healthcare workers with tuberculin skin test data, conversions during periods II through III were higher on wards with than without TB patients (5 of 29 versus 0 of 15; P = 0.15), although the difference was not statistically significant. CONCLUSIONS: Transmission of MDR-TB among AIDS patients decreased markedly after enforcement of readily implementable administrative measures, ending the outbreak. However, tuberculin skin-test conversions among healthcare workers may not have been prevented by these measures. CDC guidelines for prevention of nosocomial transmission of TB should be implemented fully at all US hospitals.

Urban rape survivors: characteristics and prevalence of human immunodeficiency virus and other sexually transmitted infections. Multicenter Crack Cocaine and HIV Infection Study Team.

OBJECTIVE: To determine the prevalence of recent rape, the characteristics or recent rape survivors, and the seroprevalence of human immunodeficiency virus (HIV), syphilis, and genital herpes (HSV-2) among recent rape survivors. METHODS: We surveyed women 18-29 years old who were recruited from places unassociated with medical or drug treatment or the criminal justice system in three urban communities where illicit drug use is common. We compared characteristics and HIV, syphilis, and HSV-2 seroprevalence of women who reported recent rape with those of women who denied recent rape. RESULTS: One hundred fifty-one of 1104 (13.7%) women reported having been raped in the year before our interview. Rape survivors were more likely than women who denied recent rape to smoke crack cocaine (86.8 versus 56.7%; odds ratio [OR] 5.0, 95% confidence interval [CI] 3.2-7.8), to be homeless (17.2 versus 6.1%; OR 3.2, CI 2.0-5.2), to report a recent sexually transmitted disease (38.7 versus 18.7%; OR 2.7, CI 1.9-3.9), and to be infected with syphilis (42.4 versus 28.4%; OR 1.9, CI 1.3-2.6) and HSV-2 (71.9 versus 57.5%; OR 1.9, CI 1.3-2.8). Survivors were more likely to acknowledge any HIV risk behavior (including sex work) (85.4 versus 49.5%; OR 5.9, CI 3.9-9.0) and to be HIV-infected (23.3 versus 13.4%; OR 1.9, CI 1.3-2.9). Rape was not independently associated with HIV (OR 0.8, 95% CI 0.4-1.3), syphilis (OR 0.9, 95% CI 0.6-1.3), or HSV-2 (OR 1.3, 95% CI 0.9-2.0) infections after adjustment for confounding factors. CONCLUSION: One in seven women reported being raped recently. Rape was most common among sex workers, crack smokers, and the homeless. Most survivors reported HIV risk behaviors, and many were HIV-infected. Programs to prevent repeated rape, voluntary HIV counseling and testing, and other medical and social services may benefit survivors in these and similar communities.

Risk factors among IDUs who give injections to or receive injections from other drug users.

AIMS: To assess risk factors associated with injection drug users (IDUs) who give injections to or receive injections from other IDUs. DESIGN AND SETTING: IDUs were recruited into a cross-sectional study using targeted sampling methods in Oakland, Richmond, and San Francisco, California from August 1996 to January 1997. "Street docs" are IDUs who reported having given injections to other IDUs in the past month. "Injection recipients" are IDUs who reported having received injections from other people in the past month. PARTICIPANTS: Of 1166 IDUs interviewed, 283 (24%) reported being injection recipients and 427 (37%) reported being street docs. MEASUREMENTS: Socio-demographic characteristics and injection-related risk behaviors. FINDINGS: Injection recipients and street docs were significantly more likely (p < 0.001) than other IDUs to report sharing syringes (33% of injection recipients, 21% of street docs and 7% of others), cookers (71% of injection recipients, 55% of street docs and 24% of others), rinse water (44% of injection recipients, 35% of street docs and 13% of others), and filters (60% of injection recipients, 47% of street docs and 20% of others). In a logistic regression model, injection recipients (adjusted odds ratio (AOR) = 4.29) and street docs (AOR = 1.91) were more likely than other IDUs to report having shared syringes. CONCLUSIONS: Giving and receiving injections is common among IDUs in the San Francisco Bay area. Qualitative and epidemiological studies are needed to understand better the infectious disease risks associated with giving and receiving injections. Interventions need to address these issues and provide practical solutions.

Crack cocaine smokers who turn to drug injection: characteristics, factors associated with injection, and implications for HIV transmission. The Multicenter Crack Cocaine and HIV Infection Study Team.

A survey of 1220 street-recruited crack cocaine smokers revealed that crack smokers may turn to drug injection to ease crack withdrawal. Crack smokers who later injected tended to smoke crack more heavily and for longer periods than those who did not inject. The initiation of injection was significantly associated with ever snorting heroin (prevalence ratio [PR] = 3.4, 95% confidence interval [CI] = 2.0-5.9) or snorting heroin specifically while smoking crack (PR = 2.3, 95% CI = 1.3-4.0), suggesting that snorted heroin use may mediate the transition to injection among crack smokers. Programs to prevent and treat crack dependence may prevent later injection and injection-related infections including HIV.

Sex trading and psychological distress in a street-based sample of low-income urban men.

This article examines the relationship between sex trading and psychological distress and assesses sexual human immunodeficiency virus (HIV) risk behaviors and HIV seroprevalence in a sample of young men recruited from the streets of Harlem. The authors interviewed 477 men, aged 18 to 29 years, of whom 43 (9.0%) had received money or drugs in exchange for sex in the preceding 30 days and were categorized as sex traders. Psychological distress was measured by using the Brief Symptom Inventory (BSI). Sex traders scored significantly higher than non-sex traders on the General Severity Index and on all nine subscales of the BSI. According to multivariate analysis after adjusting for perceived HIV risk, current regular crack cocaine use and homelessness, sex traders scored 0.173 units higher on the General Severity Index than non-sex traders (p < .001). More of the sex traders tested positive for HIV (41% versus 19%, p < .001). The alarmingly high HIV seroprevalence rate in sex traders in this sample underscores the need to redouble HIV prevention efforts for this population. The high levels of psychological distress and crack cocaine dependence among sex traders may undermine their ability to adopt safer sex behaviors and should be considered in intervention designs.

Crack cocaine use and sexual activity in Miami, Florida.

Data are analyzed from the Multicenter Study of Crack Cocaine and HIV Infection in Miami, Florida, examining interrelationships among use of crack cocaine, use of other drugs, sexual activity, and exchange of sex for money and drugs. This study was designed to recruit two groups of approximately equal size: persons who reported current use of crack cocaine three or more times per week, and those who had never used crack. Participants (N = 641) were recruited in Miami. Participants' median age for first use of crack cocaine was higher than for use of alcohol, marijuana or powdered cocaine. It was also higher than participants' ages at first sexual activity, and somewhat higher than the median age for reporting initiation of trading sex for money or drugs. The median age of first crack use was lower among younger participants, suggesting that crack use in older participants followed quickly upon availability of the drug. Crack users reported reduced desire for sex and diminished ability to have sex after smoking crack. However, crack use was associated with increased sexual activity, trading sex for money or drugs, and sex with multiple partners. Participants who traded sex for money or drugs (traders) reported higher rates of condom use than nontraders; however, neither traders nor nontraders reported rates of condom use sufficient to substantially reduce the transmission of sexually transmitted diseases and HIV infection.

High-risk sex behavior among young street-recruited crack cocaine smokers in three American cities: an interim report. The Multicenter Crack Cocaine and HIV Infection Study Team.

Since crack cocaine appeared in urban areas in the United States in the mid-1980s, reports have suggested that crack smokers may be at increased risk of sexually transmitted diseases (STDs), including infection with HIV, because they have multiple sex partners, trade sex for money or drugs, and rarely use condoms. A cross-sectional survey is being conducted in urban neighborhoods in Miami, New York and San Francisco--where crack use is common--to explore these issues. Indigenous street outreach workers are recruiting men and women who are either current regular crack smokers or who have never smoked crack; each group is further stratified according to whether participants had ever injected drugs. Participants were interviewed about their sexual and drug-use practices. Overall, crack smokers, whether injectors or not, engaged in higher-risk sexual behaviors than nonsmokers, reported greater numbers of sex partners than nonsmokers, and were more likely than nonsmokers to have exchanged sex for money or drugs or to have had an STD. Differences between crack smokers and nonsmokers were generally greater among non-injectors than among injectors, and generally greater among women than among men. Condom use, although somewhat more common with paying than nonpaying partners, was infrequent overall. Most of the subjects had not been in substance abuse treatment in the preceding 12 months, and a majority had never been in substance abuse treatment. Education and prevention programs specifically targeted at crack smokers not currently in substance abuse treatment are needed to reach these high-risk persons.

Tuberculosis in patients infected with human immunodeficiency virus: perspective on the past decade.

Tuberculosis (TB) is the most common opportunistic infection and the leading cause of death in persons infected with human immunodeficiency virus (HIV) worldwide. Because HIV is spreading in regions with the highest rates of Mycobacterium tuberculosis infection, HIV is responsible for an increasing proportion of the world's cases of TB. However, advances in molecular biology, clinical practice, and public health policy during the past 5 years offer reasons for hope. Molecular methods have provided insights into the epidemiology of M. tuberculosis transmission and the mechanisms of drug resistance. Rapid diagnostic tests have been developed to facilitate the diagnosis of TB. Retrospective and prospective studies have shown that TB in the HIV-infected person is highly treatable and often preventable. Moreover, directly observed therapy can decrease rates of treatment failure, relapse, drug resistance, and secondary spread. For two consecutive years, the incidence of TB in the United States has declined. Additional resources are needed, however, to achieve similar gains in the developing world.

Sex- and drug-related risk among populations of younger and older injection drug users in adjacent neighborhoods in San Francisco.

The objective of this study was to compare drug injection- and sex-related risk behaviors of younger and older injection drug users (IDUs) in two adjacent neighborhoods. IDUs were recruited from street settings in two adjacent neighborhoods in San Francisco in April, 1997. All participants were interviewed using a standardized questionnaire and were tested for HIV antibodies. Drug injection- and sex-related risk behaviors were compared between younger IDUs (< 30 years; n = 56) and older IDUs (> or = 30 years; n = 116). Younger IDUs were more likely to be white, be homeless, have injected amphetamines, and have been arrested in the past year. Older IDUs were more likely to be African American and smoke crack cocaine; they had injected a mean of 18 years longer. Younger IDUs were more likely to have shared syringes in the past month (52% versus 10%; p < .05), report drug overdose in the past 15 months (39% versus 7%; p < .05), and to have had unprotected vaginal intercourse in the past 6 months (77% versus 53%; p < .05). After controlling for confounding factors using logistic regression analysis, all these associations remained significant. There is an urgent need for innovative prevention programs that target younger, homeless IDUs.

Health care use by human immunodeficiency virus-infected students at a California student health service.

We report characteristics of 16 college students with human immunodeficiency virus (HIV) infection but without the acquired immunodeficiency syndrome who received care at a student health center at a major university in California. Sociodemographic and clinical data and medical expenditures were obtained retrospectively from medical charts and computerized billing records. All 16 students were men who had sex with men, and 3 had also used intravenous drugs. Dermatologic conditions, upper respiratory tract infections, gastrointestinal conditions, anemia, lymphadenopathy, sexually transmitted diseases, and ophthalmologic conditions were more frequent among HIV-infected students than among the general student population using the health center. On average, HIV-infected students visited the student health service about 3 times more often and incurred charges about 10 times higher than the general population of students visiting the health center. Student health centers, which have been at the forefront of developing strategies for HIV prevention, education, and counseling, must also develop treatment programs for HIV-infected students.

Use of an illegal syringe exchange and injection-related risk behaviors among street-recruited injection drug users in Oakland, California, 1992 to 1995.

OBJECTIVE: To determine factors associated with syringe and injection supply sharing among injection drug users (IDUs) in a community with an illegal underground syringe exchange program (SEP). METHODS: From 1992 to 1995, semiannual cross-sectional samples of IDUs were recruited in Oakland, California. To account for multiple observations from the same individual, we used general estimating equations with logit transformations to determine factors associated with sharing syringes and other injection supplies. RESULTS: 1304 IDUs were interviewed; 684 (53%) returned for more than one interview. 2830 interviews were available for analysis. SEP use increased and syringe and supply sharing declined from 1992 to 1995 among study participants. In multivariate analysis, SEP users were less likely to share syringes than non-SEP users (adjusted odds ratio [AOR] = 0.57; 95% confidence interval [CI] = 0.46-0.72). SEP use was not significantly associated with the sharing of injection supplies (AOR = 0.85; 95% CI = 0.68-1.07). Syringe sharing and injection supply sharing were significantly less likely to occur among African American and HIV-positive IDUs. CONCLUSIONS: These data suggest that illegal SEPs can be effective HIV prevention programs. Lower rates of syringe-based risk behaviors among African American and HIV-positive IDUs are encouraging.