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1.  Biomarker validation of recent unprotected sexual intercourse in a prospective study of young women engaged in sex work in Phnom Penh, Cambodia 
Sexually transmitted diseases  2013;40(6):462-468.
A study of female sex workers in Phnom Penh, Cambodia found self-reported condom use to be of questionable validity, particularly among amphetamine-type stimulant (ATS) users and those with multiple partners.
Accurate measurement of unprotected sex is essential in HIV prevention research. Since 2001, the 100% Condom Use Program targeting female sex workers (FSW) has been a central element of the Cambodian National HIV/AIDS Strategy. We sought to assess the validity of self-reported condom use using the rapid prostate-specific antigen (PSA) test among Cambodian FSW.
From 2009 to 2010 we enrolled 183 FSW in Phnom Penh in a prospective study of HIV risk behavior. PSA test results from the OneStep ABAcard® were compared to self-reported condom use in the past 48 hours at quarterly follow-up visits.
Among women positive for seminal fluid at the first follow-up visit, 42% reported only protected sex or no sex in the detection period. Discordant results were more likely among brothel and street-based FSW vs. entertainment (56% vs. 17%), recent (last 3 months) ATS users (53% vs. 20%), and those with >5 partners in the past month (58% vs. 13%). In multivariable regression models, positive PSA results were associated with recent ATS use (Adjusted Risk Ratio (ARR) = 1.5; 95% confidence interval (CI):1.1 – 2.2), having a non-paying last sex partner (ARR=1.7; CI:1.2 – 2.5), and sex work venue (ARR=3.0; CI:1.4 – 6.5). Correspondingly, women with a non-paying last sex partner were more likely to report unprotected sex (ARR=1.5; CI:1.1 – 2.2), but no associations were found with sex work venue or ATS use.
Results confirm the questionable validity of self-reported condom use among FSW. The PSA biomarker assay is an important monitoring tool in HIV/STI research including prevention trials.
PMCID: PMC3891890  PMID: 23680902
2.  Mortality Among Young Injection Drug Users in San Francisco: A 10-Year Follow-up of the UFO Study 
American Journal of Epidemiology  2012;175(4):302-308.
This study examined associations between mortality and demographic and risk characteristics among young injection drug users in San Francisco, California, and compared the mortality rate with that of the population. A total of 644 young (<30 years) injection drug users completed a baseline interview and were enrolled in a prospective cohort study, known as the UFO (“U Find Out”) Study, from November 1997 to December 2007. Using the National Death Index, the authors identified 38 deaths over 4,167 person-years of follow-up, yielding a mortality rate of 9.1 (95% confidence interval: 6.6, 12.5) per 1,000 person-years. This mortality rate was 10 times that of the general population. The leading causes of death were overdose (57.9%), self-inflicted injury (13.2%), trauma/accidents (10.5%), and injection drug user-related medical conditions (13.1%). Mortality incidence was significantly higher among those who reported injecting heroin most days in the past month (adjusted hazard ratio = 5.8, 95% confidence interval: 1.4, 24.3). The leading cause of death in this group was overdose, and primary use of heroin was the only significant risk factor for death observed in the study. These findings highlight the continued need for public health interventions that address the risk of overdose in this population in order to reduce premature deaths.
PMCID: PMC3271816  PMID: 22227793
drug users; epidemiology; hepatitis C; mortality; overdose; young adult
3.  Opioid agonist therapy is associated with lower incidence of hepatitis C virus infection in young adult persons who inject drugs 
JAMA internal medicine  2014;174(12):1974-1981.
Injection drug use is the primary mode of transmission for hepatitis C virus (HCV) infection. Prior studies suggest opioid agonist therapy may reduce incidence of HCV among people who inject drugs, however, little is known about its effects in younger injectors.
To evaluate whether opioid agonist therapy was associated with a lower incidence of HCV in a cohort of young adult injectors.
Observational cohort study conducted January 2000 through August 2013 with quarterly interviews and blood samples.
San Francisco community outreach.
Young adult injectors (<30 years old) who were anti-HCV negative.
Recent (within past 3 months) substance use treatment: no treatment, non-opioid agonist forms of treatment, or opioid agonist therapy (methadone or buprenorphine) detoxification or maintenance.
Main Outcome(s) and Measure(s)
Incident HCV infection documented with a new positive HCV RNA result and/or a positive anti-HCV result. Cumulative HCV incidence rates and 95% confidence intervals were calculated assuming a Poisson distribution. Cox Proportional Hazards models were fit adjusting for age, gender, race, years of injection drug use, homelessness and incarceration.
Baseline characteristics of the sample (n=552) were: median age 23 (IQR: 20–26), 32% female, 73% Caucasian, 40% did not graduate high school, and 69% were homeless. Over the observation period of 680 person-years (py), there were 171 incident cases of HCV (incidence rate=25.1/100 py; 95% CI: 21.6–29.2). The rate ratio was significantly lower for participants who reported recent maintenance opioid agonist therapy (0.31; 95% CI: 0.14–0.65), but not for those who reported recent non-opioid agonist forms of treatment (0.63; 95% CI: 0.37–1.08), or opioid agonist detoxification (1.45; 95% CI: 0.80–2.69). After adjustment for other covariates, maintenance opioid agonist therapy was associated with lower relative hazards for becoming infected with HCV over time (AHR=0.39; 95% CI: 0.18–0.87).
Conclusions and Relevance
In this cohort of young adults who inject drugs, recent maintenance opioid agonist therapy was associated with lower incidence of HCV. Maintenance treatment with methadone or buprenorphine for opioid use disorders may be an important strategy to prevent spread of HCV among young injectors.
PMCID: PMC4506774  PMID: 25347412
HCV; PWID; injection drug use; methadone; buprenorphine
4.  Concordance of risk behavior reporting within HCV serodiscordant injecting partnerships of young injection drug users in San Francisco, CA 
Drug and alcohol dependence  2014;142:239-244.
Young injection drug users (IDU, under age 30) often inject with other IDU, creating an environment for risk of blood-borne disease transmission through sharing of needles and drug preparation equipment. Epidemiologic studies rely on self reported injection behavior data for measures of transmission risk, therefore we sought to quantify the degree of concordance of reported injecting risk behaviors between injecting dyads.
From May, 2006 through 2013 we enrolled 72 injecting dyads in San Francisco, California, who were hepatitis C virus (HCV) RNA discordant. Each partnership was followed prospectively for up to six months. Monthly interviews from each partner were date-matched and responses to relationship characteristics and risk behavior questions were compared. Concordance of reporting was estimated with the concordance correlation coefficient for longitudinal data (CCC) and the prevalence adjusted bias adjusted kappa (PABAK).
Participants had a median age of 26 (IQR: 23, 28) years and median years injecting of 7.0 (IQR: 3.0,10.6). Thirty-eight percent of the injecting dyads were also sexual partners. Concordance levels were highest for partnership characteristics, such as length of acquaintance, number of days cohabitating, and sexual intercourse in the past month (CCC = 0.95; 0.82, and 0.90, respectively). Shared injection risk behaviors such as injecting with the HCV+ partner’s previously used syringe and using contaminated injection preparation equipment had slight to fair agreement (CCC = 0.22; 0.23; PABAK = 0.43,0.36, respectively).
Concordance levels ranged from low to high. Potential sources of measurement error for low agreement items include recall and social-desirability biases and question interpretation.
PMCID: PMC4471952  PMID: 25034898
Epidemiology; Drug users; Agreement; Young adult; Hepatitis C; Dyad
5.  Preference, acceptability and implications of the rapid hepatitis C screening test among high-risk young people who inject drugs 
BMC Public Health  2014;14:645.
People who inject drugs (PWID) are at highest risk for hepatitis C virus (HCV) infection, yet many remain unaware of their infection status. New anti-HCV rapid testing has high potential to impact this.
Young adult (<30 years) active PWID were offered either the rapid OraQuick® or standard anti-HCV test involving phlebotomy, then asked to complete a short questionnaire about testing perceptions and preferences. Sample characteristics, service utilization, and injection risk exposures are assessed with the HCV testing choice as the outcome, testing preferences, and reasons for preference.
Of 129 participants: 82.9% (n = 107) chose the rapid test. There were no significant differences between those who chose rapid vs. standard testing. A majority (60.2%) chose the rapid test for quick results; most (60.9%) felt the rapid test was accurate, and less painful (53.3%) than the tests involving venipuncture.
OraQuick® anti-HCV rapid test was widely accepted among young PWID. Our results substantiate the valuable potential of anti-HCV rapid testing for HCV screening in this high risk population.
PMCID: PMC4091768  PMID: 24965699
Hepatitis C virus; Rapid testing; Injection drug users
6.  Injecting Risk Behavior among Traveling Young Injection Drug Users: Travel Partner and City Characteristics 
Young injection drug users (IDUs), a highly mobile population, engage in high levels of injecting risk behavior, yet little is understood about how such risk behavior may vary by the characteristics of the cities to which they travel, including the existence of a syringe exchange program (SEP), as well as travel partner characteristics. In 2004–2005, we conducted a 6-month prospective study to investigate the risk behavior of 89 young IDUs as they traveled, with detailed information gathered about 350 city visits. In multivariable analyses, travel to larger urban cities with a population of 500,000–1,000,000 was significantly associated with injecting drugs (adjusted odds ratio (AOR) = 3.71; 95 % confidence interval (CI), 1.56–8.82), ancillary equipment sharing (AES; AOR = 7.05; 95 % CI, 2.25–22.06) and receptive needle sharing (RNS; AOR = 5.73; 95 % CI, 1.11–27.95), as compared with visits to smaller cities with populations below 50,000. Region of the country, and the existence of a SEP within the city visited, were not independently associated with injecting drugs, AES, or RNS during city visits. Traveling with more than one injecting partner was associated with injecting drugs during city visits (AOR = 2.77; 95 % CI, 1.46–5.27), when compared with traveling alone. Additionally, both non-daily and daily/almost daily alcohol use during city visits were associated with AES (AOR = 3.37; 95 % CI, 1.42–7.68; AOR = 3.03; 95 % CI, 1.32–6.97, respectively) as compared with no alcohol consumption. Traveling young IDUs are more likely to inject when traveling with other IDUs and to engage in higher risk injection behavior when they are in large cities. Risk behavior occurring in city visits, including equipment sharing and alcohol consumption, suggests further need for focused interventions to reduce risk for viral infection among this population.
PMCID: PMC3665972  PMID: 22744293
Young IDUs; Travelers; Injecting risk; Ancillary equipment sharing; Receptive needle sharing; City characteristics; Travel partners
7.  HIV vaccine trial willingness among injection and non-injection drug users in two urban centres, Barcelona and San Francisco 
Vaccine  2011;29(10):1991-1996.
Being able to recruit high-risk volunteers who are also willing to consider future participation in vaccine trials are critical features of vaccine preparedness studies. We described data from two cohorts of injection- and non-injection drug users in Barcelona, Spain [Red Cross centre] and in San Francisco, USA, [UFO-VAX study] at high risk of HIV/HCV infection to assess behaviour risk exposure and willingness to participate in future preventive HIV vaccine trials. We successfully identified drug-using populations that would be eligible for future HIV vaccine efficacy trials, based on reported levels of risk during screening and high levels of willingness to participate. In both groups, Red Cross and UFO-VAX respectively, HCV infection was highly prevalent at baseline (41% and 34%), HIV baseline seroprevalence was 4.2% and 1.5%, and high levels of willingness were seen (83% and 78%).
PMCID: PMC3747033  PMID: 21241735
HIV; HIV vaccines; IDUs; Injection and non-injection drug users; Willingness to participate in future trials
8.  Enhanced retention strategies and willingness to participate among hard-to-reach female sex workers in Barcelona for HIV prevention and vaccine trials 
The potential for implementation of HIV vaccine trials in hard-to-reach female sex workers in an inner city area of Barcelona, Spain was assessed via a study of HIV risk, willingness to participate and the success of retention strategies. In 130 women, serological HIV status, behavioral risk exposures and willingness to participate in future HIV vaccine trials were recorded every six months using a confidential questionnaire. An enhanced retention (ER) strategy was compared with a control retention (CR) strategy comprising the recording of data on appointment cards. HIV seroincidence and retention rates were estimated. Retention rates after 6 and 12 mo of follow-up in the ER group were 76% and 69% respectively compared with 16% and 13% in the CR group. Among the ER group 97% were willing to participate in HIV vaccine trials at baseline and, after 12 mo of follow-up. Willingness was significantly associated with higher HIV risk exposure, and higher education level. Successfully retaining these cohorts over time in settings with a high HIV seroincidence rate is an ongoing challenge that will need to be addressed to ensure participation in future trials. Furthermore, as we have demonstrated, the fact that retaining hard-to-reach populations is difficult should not exclude this target population for HIV vaccine and prevention trials.
PMCID: PMC3859767  PMID: 23291931
HIV; HIV vaccine; female sex workers; hard-to-reach women; vaccine preparedness studies
9.  Correlates of amphetamine-type stimulants use and associations with HIV-related risks among young women engaged in sex work in Phnom Penh, Cambodia 
Drug and alcohol dependence  2011;120(1-3):119-126.
Amphetamine-type stimulant (ATS) use has increased in Cambodia and emerged as a significant problem among female sex workers (FSWs), potentially contributing to increased risk of HIV. We examined the prevalence of ATS use and its effect on sexual risk behaviors, and sexually transmitted infections (STI) among FSWs in Phnom Penh, Cambodia.
A one-year prospective study among young women engaged in sex work in brothels, entertainment establishments and on a freelance basis. Socio-demographics, sexual risks, and recent ATS use were assessed by self-report. Blood and urine samples were collected to detect HIV, Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (GC). Bivariate and multivariate longitudinal analyses were conducted to assess the effects of ATS use on number of sex partners, inconsistent condom use with paying partners and incident STI.
ATS use was higher among women working freelance (35.6%) and in brothels (34.8%) compared to women working in entertainment establishments (17.7%) or in multiple venues (14.8%). ATS users reported more sex partners and days drunk in the previous month. In multivariate longitudinal analysis, ATS use was associated with having a higher number of sex partners (Adjusted Risk Ratio 1.49; 95% CI: 1.00–2.21) and incident STI (Adjusted Odds Ratio 5.41; 95% CI: 1.15–25.48), but not inconsistent condom use with paying partner.
ATS users had more sex partners, high level of alcohol use, and were at increased risk of STI. Our findings underscore ATS use as an important emerging risk exposure that should be integrated into HIV prevention interventions targeting this population.
PMCID: PMC3226861  PMID: 21820251
mphetamine-type stimulant; HIV/STI; Female sex workers; Cambodia; Risk behaviors
10.  Cervical human papillomavirus infection among young women engaged in sex work in Phnom Penh, Cambodia: prevalence, genotypes, risk factors and association with HIV infection 
BMC Infectious Diseases  2012;12:166.
Although cervical cancer is the leading cancer in Cambodia, most women receive no routine screening for cervical cancer and few treatment options exist. Moreover, nothing is known regarding the prevalence of cervical HPV or the genotypes present among women in the country. Young sexually active women, especially those with multiple sex partners are at highest risk of HPV infection. We examine the prevalence and genotypes of cervical HPV, as well as the associated risk factors among young women engaged in sex work in Phnom Penh, Cambodia.
We conducted a cross-sectional study among 220 young women (15–29 years) engaged in sex work in different venues including brothels or entertainment establishments, and on a freelance basis in streets, parks and private apartments. Cervical specimens were collected using standard cytobrush technique. HPV DNA was tested for by polymerase chain reaction (PCR) and genotyping using type-specific probes for 29 individual HPV types, as well as for a mixture of 10 less common HPV types. All participants were also screened for HIV status using blood samples. Multivariate logistic regression analyses were conducted to assess risk factors for any or multiple HPV infection.
The prevalence of cervical HPV 41.1%. HPV 51 and 70 were the most common (5.0%), followed by 16 (4.6%), 71 (4.1%) and 81 (3.7%). Thirty-six women (16.4%) were infected with multiple genotypes and 23.3% were infected with at least one oncogenic HPV type. In multivariate analyses, having HIV infection and a higher number of sexual partners were associated with cervical HPV infection. Risk factors for infection with multiple genotypes included working as freelance female sex workers (FSW) or in brothels, recent binge use of drugs, high number of sexual partners, and HIV infection.
This is the first Cambodian study on cervical HPV prevalence and genotypes. We found that HPV infection was common among young FSW, especially among women infected with HIV. These results underscore the urgent need for accessible cervical cancer screening and treatment, as well as for a prophylactic vaccine that covers the HPV subtypes present in Cambodia.
PMCID: PMC3436768  PMID: 22839728
11.  Are young injection drug users ready and willing to participate in preventive HCV vaccine trials? 
Vaccine  2010;28(37):5947-5951.
Trials to evaluate the efficacy of preventive HCV vaccines will need participation from high risk HCV seronegative injection drug users (IDUs). To guide trial planning, we assessed willingness of young IDU in San Francisco to participate in HCV vaccine efficacy trials and evaluate knowledge of vaccine trial concepts: placebo, randomization and blinding. During 2006 and 2007, a total of 67 participants completed the survey. A substantial proportion (88%) would definitely (44%) or probably (44%) be willing to participate in a randomized trial, but knowledge of vaccine trial concepts was low. Reported willingness to participate in an HCV vaccine trial decreased with increasing trial duration, with 67% of participants surveyed willing to participate in a trial of one year duration compared to 43% of participants willing to participate in a trial of 4 years duration. Willingness to enroll in HCV vaccine trials was higher in young IDU than reported by most at-risk populations in HIV vaccine trials. Educational strategies will be needed to ensure understanding of key concepts prior to implementing HCV vaccine trials.
PMCID: PMC2936506  PMID: 20638453
Hepatitis C; injection drug use; vaccine trial
12.  Hepatitis C virus risk behaviors within the partnerships of young injecting drug users 
Addiction (Abingdon, England)  2010;105(7):1254-1264.
Young injection drug users (IDU) are at high risk for hepatitis C virus (HCV). We sought to determine whether perceiving one's injecting partner to be HCV positive was associated with decreased odds of engaging in receptive needle/syringe sharing (RNS) or ancillary equipment sharing (AES) with that partner.
We conducted a cross-sectional study from 2003 to 2007 in San Francisco (n=212 participants) to examine whether perceived partner HCV status was associated with RNS and AES within injecting partnerships (n=492 partnerships) of young (under age 30) IDU who are HCV antibody negative.
RNS and AES (in the absence of RNS) occurred in 23% and 66% of injecting partnerships in the prior month. The odds of engaging in RNS were significantly lower for relationships in which the participant reported that his/her partner was HCV positive (odds ratio [OR] 0.49; 95% confidence interval [CI] 0.25-0.95). This association was attenuated when adjusted for reusing one's own needle/syringe (adjusted OR 0.57; 95% CI 0.28-1.15). The odds of engaging in AES were lower for participants who did not know the HCV status of their partner, only among non-sexual partnerships (OR 0.47; 95% CI 0.29-0.76).
Because perceiving one's partner to be HCV positive was associated with decreased RNS, increased HCV testing and partner disclosure may be warranted. AES was common and was decreased only among non-sexual partnerships in which the HCV status of the partner was not known. This suggests that interventions to reduce AES in young IDU must be widespread.
PMCID: PMC2907461  PMID: 20491725
13.  Risk Behaviors after Hepatitis C Virus Seroconversion in Young Injection Drug Users in San Francisco 
Drug and alcohol dependence  2009;105(1-2):160-163.
The rationale for screening populations at risk for hepatitis C virus infection (HCV) includes the possibility of altering risk behaviors that impact disease progression and transmission. This study prospectively examined young injection drug users (IDU) to determine if behaviors changed after they were made aware of HCV seroconversion.
We estimated the effects of HCV seroconversion coupled with post-test counseling on risk behaviors (alcohol use, non-injection and injection drug use, lending and sharing injecting equipment, and having sex without a condom) and depression symptoms using conditional logistic regression, fitting odds-ratios for immediately after disclosure and 6 and 12 months later, and adjusting for secular effects.
112 participants met inclusion criteria, i.e. they were documented HCV seronegative at study onset and subsequently seroconverted during the follow-up period, with infection confirmed by HCV RNA testing. HCV seroconversion was independently associated with a decreased likelihood of consuming alcohol (OR=0.51; 95% CI: 0.27 to 0.97, p=0.04) and using non-injection drugs (OR=0.40; 95% CI: 0.20 to 0.81, p=0.01) immediately after disclosure, however, results were not sustained over time. There were significant (p<0.05) declines in the use of alcohol, injection and non-injection drugs, and sharing equipment associated with time that were independent from the effect of seroconversion.
Making young IDU aware of their HCV seroconversion may have a modest effect on alcohol and non-injection drug use that is not sustained over time.
PMCID: PMC2849721  PMID: 19647375
Hepatitis C virus; injection drug use; screening
14.  Predictors of injection drug use cessation and relapse in a prospective cohort of young injection drug users in San Francisco, CA (UFO Study) 
Drug and alcohol dependence  2009;101(3):152-157.
Studies of injection drug use cessation have largely sampled adults in drug treatment settings. Little is known about injection cessation and relapse among young injection drug users (IDU) in the community.
A total of 365 HCV-negative IDU under age 30 years were recruited by street outreach and interviewed quarterly for a prospective cohort between January 2000 and February 2008. Participants were followed for a total of 638 person-years and 1996 visits. We used survival analysis techniques to identify correlates of injection cessation (≥3 months) and relapse to injection.
67% of subjects were male, median age was 22 years (interquartile range (IQR) 20 - 26) and median years injecting was 3.6 (IQR 1.3 – 6.5). 28.8% ceased injecting during the follow-up period. Among those that ceased injecting, nearly one-half resumed drug injection on subsequent visits, one-quarter maintained injecting cessation, and one-quarter were lost to follow-up. Participating in a drug treatment program in the last 3 months and injecting less than 30 times per month were associated with injection cessation. Injecting heroin or heroin mixed with other drugs, injecting the residue from previously used drug preparation equipment, drinking alcohol, and using benzodiazepines were negatively associated with cessation. Younger age was associated with relapse to injection.
These results suggest that factors associated with stopping injecting involve multiple areas of intervention, including access to drug treatment and behavioral approaches to reduce injection and sustain cessation. The higher incidence of relapse in the younger subjects in this cohort underscores the need for earlier detection and treatment programs targeted to adolescents and transition-age youth.
PMCID: PMC2692897  PMID: 19181458
Injection drug use; Cessation; Relapse; Youth
15.  Gender differences in sexual and injection risk behavior among active young injection drug users in San Francisco (the UFO study) 
Female injection drug users (IDUs) represent a large proportion of persons infected with HIV in the United States, and women who inject drugs have a high incidence of hepatitis B virus (HBV) and hepatitis C virus (HCV) injection. Therefore, it is important to understand the role of gender in injection risk behavior and the transmission of blood-borne virus. In 2000–2002, 844 young (<30 years old) IDUs were surveyed in San Francisco. We compared self-reported risk behavior between 584 males and 260 female participants from cross-sectional baseline data. We used logistic regression to determine whether demographic, structural, and relationship variables explained increased needle borrowing, drug preparation equipment sharing, and being injected by another IDU among females compared to males. Females were significantly younger than males and were more likely to engage in needle borrowing, ancillary equipment sharing, and being injected by someone else. Females were more likely than males to report recent sexual intercourse and to have IDU sex partners. Females and males were not different with respect to education, race/ethnicity, or housing status. In logistic regression models for borrowing a used needle and sharing drug preparation equipment, increased risk in females was explained by having an injection partner who was also a sexual partner. Injecting risk was greater in the young female compared to male IDUs despite equivalent frequency of injecting. Overlapping sexual and injection partnerships were a key factor in explaining increased injection risk in females. Females were more likely to be injected by another IDU even after adjusting for years injecting, being in a relationship with another IDU, and other potential confounders. Interventions to reduce sexual and injection practices that put women at risk of contracting hepatitis and HIV are needed.
PMCID: PMC3456106  PMID: 12612103
Epidemiology; Gender differences; Homeless; Injection drug use; Youth

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