Objectives: To estimate the HIV incidence and assess the behavioral, clinical, and quality-of-life risk factors for HIV transmission among serodiscordant couples from Henan Province, China.
Methods: Between January 2006 and December 2008, initially seronegative spouses were tested for HIV at 6-month intervals. Retrospectively identified subjects were interviewed through face-to-face questionnaire. Cox proportional-hazards model was used to assess the relationship between risk factors and HIV seroconversion.
Results: Of 1927 couples, 84 (4.3%) seroconversions occurred, representing a seroconversion rate of 1.71 per 100 person-years. Seroconversion rates increased over time. Not always using condoms [relative ratio (RR) = 8.42; 95% confidence interval (CI): 4.83 to 14.67], sexual activity ≥4 times per month (RR = 5.24; 95% CI: 2.55 to 10.77), not switching antiretroviral treatment regimen (RR = 1.99; 95% CI: 0.85 to 4.65), and a quality-of-life score <12 on the psychological domain (RR = 2.33; 95% CI: 1.21 to 4.48) were associated with increased risk of seroconversion. Seventy-one percent of index spouses were on antiretroviral therapy. There was no association between rate of HIV seroconversion and last recorded CD4 cell count level of the index spouse.
Conclusions: Effective HIV prevention interventions targeting discordant couples should focus on sustaining health education, increasing psychosocial support services, and increasing medication adherence monitoring.
From the *Department of Epidemiology, National Center for AIDS/STD Control & Prevention, Chinese Center for Disease Control & Prevention, Beijing, China; †School of Public Health, Peking Union Medical College, Beijing, China; ‡University of Illinois at Chicago College of Medicine, Chicago, IL; and §Zhumadian Center for Disease Control and Prevention, Zhumadian City, Henan Province, China.
Received for publication February 25, 2010; accepted May 25, 2010.
Supported by the megaprojects of national science research for the 11th 5-Year Plan (2008ZX10001-001) of China and the Fogarty International Center, National Institutes of Health Office of the Director, Office of AIDS Research, National Cancer Center, National Eye Institute, National Heart, Blood, and Lung Institute, National Institute of Dental and Craniofacial Research, National Institute On Drug Abuse, National Institute of Mental Health, and National Institute of Allergy and Infectious Diseases Health, through the International Clinical Research Fellows Program at Vanderbilt (R24 TW007988).
Part of this work has been submitted as an abstract to the International AIDS Conference, July 18-23, 2010, Vienna, Austria.
The authors L.W. and Z.G. contributed equally to this article.
Correspondence to: Wang Ning, MD, PhD, National Center for AIDS/STD Control and Prevention, Chinese Center for Disease Control and Prevention, No 27 Nanwei Road, Xuanwu District, Beijing 100050, P. R. China (e-mail: firstname.lastname@example.org).
The transmission of HIV through heterosexual sex has been one of the primary drivers of the AIDS epidemic world wide. In China, HIV transmission through heterosexual sex has surpassed that due to either injection drug use (IDU) or homosexual sex and has become the dominant mode of HIV transmission.1-3 Serodiscordant couples, defined as couples in which 1 partner is HIV positive and the other HIV negative, have been used to study heterosexual transmission risk because of the high frequency of sexual acts that occur in stable relationships. Studies from mature epidemics in sub-Saharan Africa have found that women living with HIV-positive partners were 57.9-105.8 times more likely to seroconvert than those living in concordant-negative partnerships.4,5
Although many studies attempting to quantify HIV incidence among discordant couples have been conducted globally, few have been conducted outside of Africa,6-9 and to our knowledge, none from China have been published in English. The only other Chinese study had a small sample size (22) and was conducted in Xinjiang province, where IDU is the main mode of transmission.10 According to census statistics, people living with HIV in Zhumadian city account for almost 1/3 of all HIV cases in Henan province. Most became infected through the sale of plasma between 1992 and 1995.11-13 This cohort is different from those in other serodiscordant couple studies because they are older, live in rural communities, and have low rates of homosexual or extramarital sex.13 In this study, we describe the incidence rate, risk factors for HIV transmission, and quality-of-life indicators in a cohort of serodiscordant couples from Zhumadian City, Henan province.
This cohort study followed HIV serodiscordant couples between January 1, 2006, and December 31, 2008, in Zhumadian city, Henan province, China. HIV discordant couples were retrospectively identified from the HIV-positive database administered by Zhumadian city's Center for Disease Control and Prevention (CDC). Local staff enrolled study participants at county hospitals, at community health centers, or at home residences using the following inclusion criteria: (1) HIV negative living with a HIV-positive partner; (2) in a stable marriage (no separation or divorce); (3) participated voluntarily and provided informed consent.
Study participants had been receiving follow-up every 6 months for HIV testing at the local community health center or county hospital as part of Zhumadian CDC's routine screening programs. Blood specimens were transmitted to county level CDC laboratories and screened for HIV antibodies by enzyme-linked immunosorbent assay (Wantai, Beijing, China). Positive tests were confirmed by HIV-1 Western blot assay (Wantai, Beijing, China) at Zhumadian city's CDC laboratories.
The primary outcome was HIV seroconversion. We defined seroconverter as an individual who had a negative HIV test before entering the cohort and subsequently had a positive HIV test during follow-up. Time of seroconversion was estimated as the mid-point between the last HIV-negative test and the first HIV-positive test. The last recorded CD4+ cell counts of index spouses were obtained from the China CDC national case-reporting database.
A standardized questionnaire was administered in Chinese by trained local health care workers to initially HIV-negative spouses between October 2008 and May 2009. Survey questions included information on demographic characteristics, sexual activity, condom use, quality-of-life, sexually transmitted infection (STI) history, and medical history of their HIV-positive spouses. If subjects had seroconverted during follow-up, they were asked to report sexual behaviors in the month(s) before their first HIV-positive test. Quality-of-life was measured by a Chinese version of the brief World Health Organization Quality-of-Life instrument (WHOQOL-BREF). This instrument has been previously described and validated in patients with HIV.14 Our adapted survey consisted of 29 items, including 1 item each for general quality-of-life, health-related quality-of-life, marital conflict, appetite, self-evaluation, and 24 items belonging to 4 comprehensive domains (physical, psychological, social, and environment). Scores for each domain ranged from 4 to 20, with higher scores indicating better functional status.
The study received approval from the institutional review board of the National Center for AIDS/STD Control and Prevention, China CDC. All participants were given pretest and posttest counseling, and HIV-positive subjects were referred to the Zhumadian CDC for free counseling and evaluation for treatment.
Statistical analysis was performed using SPSS 15.0 (SPSS Inc, IL). Continuous variables were described using mean and standard deviation. Cox proportional-hazard modeling was used to assess the relationship between seroconversion and potential risk factors. Subjects that never seroconverted or were lost-to-follow-up in December 2008 were censored. Univariate Cox models were run to assess the unadjusted relationship between seroconversion and specified covariates of interest for all subjects. Survival time was defined as the time from baseline to when the initially HIV-negative spouse was confirmed positive or censored. Covariates with a P value <0.10 from the univariate analysis were entered into a full multivariate Cox model with step-wise selection used to include significant covariates. All hypothesis testing was based on 2-sided tests with alpha level of 0.05.
According to data from the Zhumadian CDC's database of HIV-positive persons, there were 4348 HIV-negative spouses married to and living with HIV-positive partners in the city in 2006. By December 31, 2008, 238 more serodiscordant couples were identified. Of the 4301 people who met the study's inclusion criteria, 1927 (44.8%) completed the questionnaire. Baseline characteristics of study participants and nonparticipants were comparable in terms of age and sex. Of those who participated, 835 (43.3%) were women and 1092 (56.7%) were men. Their average age was 44.16 ± 7.69 years (range 30-69). One thousand and nineteen were of Han ethnicity (99.6%), 8 were Hui (0.4%). One thousand seven hundred and forty-one (90.4%) were farmers, and 186 (9.7%) had other occupations.
Over 3 years, there were 84 seroconversions among 1927 serodiscordant couples. The total follow-up time was 4918 person-years (median 2.84 years), and the incidence rate was 1.71 per 100 person-years. There was no statistical difference between the male and female seroconversion rates at 1.75 and 1.66 per 100 person-years, respectively (P = 0.65). On average, female index cases (1078) were older than males (849) (t = −6.7 P < 0.001). Female index cases were also more likely to be on antiretroviral therapy (ART) (χ2 = 0.502 P = 0.025). There was no difference in the mean last recorded CD4 between males and females (t = 0.10 P = 0.93) or in other variables such as AIDS diagnosis, frequency of sexual intercourse, or whether or not the index case had switched ART regimens. Figure 1 shows the cumulative and interval seroconversion rates expressed as a function of follow-up time. As length of follow-up increases, so does the interval seroconversion rate (Fig. 1).
High Risk Behaviors
In the past 3 months, 1611 (83.6%) reported having sexual intercourse. The reported mean frequency of intercourse was 3.5 times per month (range 1-9). Compared with those who did not seroconvert, those who seroconverted were more likely to have reported having sexual intercourse in the past 3 months (90.5% vs. 83.3%, P < 0.05). Seven hundred and thirty-five spouses who were HIV negative at baseline reported having sex less than 4 times per month, and 866 spouses reported having sex 4 times or more per month. Fifteen seroconversions occurred among couples who had less frequent sex (<4 times per month), and 61 seroconversions occurred in couples who had more frequent sex (≥4 per month). Spouses reporting more frequent sex were 5.13 times more likely to seroconvert than spouses reporting less frequent sex [relative ratio (RR) = 5.13; 95% confidence interval (CI): 2.76 to 9.53], and this difference retained significance in multivariate analysis (RR = 5.24; 95% CI: 2.55 to 10.77) (Fig. 2A). Compared with couples who reported always used condoms (93.0%) during the past month, those who did not always use condoms (7.0%) had a 12.64 times higher risk of transmitting HIV in univariate analysis (RR = 12.64; 95% CI: 8.18 to 19.57). This risk remained significant in multivariate analysis (RR = 8.42; 95% CI: 4.83 to 14.67) (Fig. 2B). Spouses reported the following reasons for not always using condoms: (1) too expensive (43.8%), (2) not necessary (25.8%), (3) did not want to use (16.8%), (4) forgot (3.4%), or other (10.2%). Among the 54 (3%) HIV-negative spouses who reported having a STI symptom, 33 (61.1%) went to a hospital, 3 (6%) went to a private clinic, and 16 (29.6%) did not seek treatment. Only 7 people reported having extramarital sexual relationships in the past year, and only one of these seroconverted. One person reported a history of drug abuse, and this individual did not seroconvert. None of the surveyed men reported ever having sex with another man.
Effect of ART and Last Recorded CD4 Count on Seroconversion Rate
There were 73 seroconversions among the 1656 serodiscordant couples who had a spouse with a clinical diagnosis of AIDS. Among the 271 couples who had a HIV-positive spouse without AIDS, there were 11 seroconversions. There was no statistical difference between these seroconversion rates (P = 0.79). Most respondents (80.4%) had spouses who were on antiretroviral treatment.15 There was also no statistical difference in the seroconversion rates between those couples who had a spouse on ART (4.8%) and those couples whose HIV-positive spouse was not on ART (3.2%) (P = 0.12). Of 1369 individuals receiving ART, 266 had switched regimens and 1103 had never switched. Those on ART who had never switched regimens were significantly more likely to transmit HIV to their spouses than those who did (RR = 2.66; 95% CI: 1.15 to 6.15), but this difference was only marginally significant under multivariate analysis (P = 0.11) (Fig. 2C). Clinicians reported that most people switched regimens due to adverse side effects (97.4%) such as severe gastrointestinal symptoms (74 of 233, 31.8%), skin rash (20 of 233, 8.6%), anemia (13 of 233, 5.6%), abnormal liver function tests (11 of 233, 4.7%), and bone marrow suppression (9 of 233, 3.9%). Among other reasons for stopping or switching regimens, 1 patient voluntarily asked to stop treatment, 2 patients became pregnant, and 3 patients developed resistance.
There was no statistical difference in the median CD4 counts between those index cases who transmitted HIV to their spouses and those index partners who did not transmit HIV (P = 0.78). After stratification into 3 groups based upon last recorded CD4 count level (>350, 200-349, 0-199 cells/μL), the association remained nonsignificant (Table 1). Of the 883 patients who did not switch ART and had a recorded CD4 count, the overall transmission rate was 2.64 per 100 person-years. Of 218 patients who had switched ART and had a CD4 count, the overall rate of transmission was 1.00 per 100-person years.
HIV-negative spouses had a mean physical domain score of 12.99 ± 1.94, psychological score of 12.42 ± 1.81, social score of 13.88 ± 2.41, and environmental score of 12.47 ± 1.89. There were no statistical differences in the quality-of-life scores of those who seroconverted when compared with those who did not seroconvert. However, when divided into 2 subgroups, those who scored less than 12 points on physical and psychological domains had a significantly higher risk of seroconversion than those who scored 12 or more points (RR = 1.67; 95% CI: 1.03 to 2.72 and RR = 2.27; 95% CI: 1.46 to 3.54, respectively) (Fig. 2D). In multivariate analysis, this association remained significant for the psychological domain but not for the physical domain (Table 1).
Our study of 1927 HIV discordant couples in Zhumadian city, Henan province is the largest of its kind in China and found an incidence rate of 1.71 per 100 person-years. The only other study of discordant couples in China was conducted in Xinjiang province but had a sample size of only 22.10 The incidence rate from our study is similar to the incidence rate of 2.3 per 100 person-years reported among a cohort of injecting drug users from a high prevalence region in southwestern China.16 This suggests that HIV-negative spouses living in discordant relationships in Zhumadian could be considered one of China's high-risk groups.
The overall seroconversion rate also showed an increasing upward trend as the duration of follow-up lengthened. There are several possibilities for why this occurred. First, chronically HIV-infected patients may undergo immunologic failure, virologic failure, advance to later stages of disease, or acquire resistance leading to higher rates of transmission over time.15,17-19 Second, couples may engage in riskier behaviors such as increasing the frequency of sex or reducing the percentage of condom use, as knowledge and awareness of self protection gradually declines.20,21 Third, a desire to have children may be influencing the risk taking behaviors among these couples.7 Our findings highlight the importance of strengthening comprehensive HIV prevention interventions such as health education, condom promotion, STI treatment, and psychosocial care and support services.
Our study found no statistical difference between the male-to-female transmission and female-to-male transmission rates. These results are consistent with several other studies of discordant couples from Brazil, Haiti, Tanzania, Rwanda, Uganda, and India.4,7-9,22 It is unclear whether the higher rate of female-to-male transmission (1.75 per 100 person-years) is a result of a chance or some other unmeasured biological or behavioral characteristic. Although the literature has been inconclusive, one large prospective study from Masaka region Uganda attributed the age-adjusted RR for infection for women of 2.2 (95% CI: 0.9 to 5.4) to extramarital sexual behavior among men and increased biological susceptibility in the female genital tract.5 However, in Henan province, the majority of those infected are nonmigrant farmers with low rates of STIs, IDU, or extramarital sex. In our cohort, only 7 of 1927 interviewed reported ever engaging in sex outside of marriage. Thus, in this cultural context, it is reasonable to assume that behavioral factors which influence higher HIV transmission in some parts of Africa are different than those of China.23 Male circumcision was not analyzed as a factor in this study because the prevalence of circumcision is extremely low among ethnic Han Chinese.
As with other studies, we found not always using condoms and a higher frequency of sexual activity to be associated with increased risk of HIV transmission.7,24,25 Having sex within the past 3 months and extramarital sex were not statistically significant associations.
Our study also found that ART use in the HIV-positive spouse was associated with a decreased risk of seroconversion, but this result was not statistically significant (RR = 0.76; 95% CI: 0.45 to 1.28). A meta-analysis of serodiscordant couples studies found that ART reduced heterosexual transmission rates from 5.64 to 0.46 per 100 person-years.26 This suggests that our study may have been subject to misclassification as those who were labeled as on ART may have been nonadherent to treatment. One study of drug-resistant HIV-1 variants in Henan found that 66% of patients had low adherence after 6 months of therapy.27 Another possibility is that patients were adherent to ART but were on regimens that had become suboptimal or acquired drug resistance. This is supported from data from a recently published study which reported immunologic failure rates of 50% by year 5 among patients enrolled in China's free national antiretroviral treatment program, most likely due to the lack of readily available second-line drugs.18
Furthermore, our data indicates that those who did not switch treatment regimens were more likely to transmit HIV (RR: 2.66, 95% CI: 1.15 to 6.15). Although this value became nonsignificant in multivariate analysis (most likely due to small sample size in those who had switched ART regimens), the data suggests that remaining on an originally prescribed ART regimen may have a detrimental effect on population-level heterosexual transmission dynamics in China because a large proportion of patients may be on ineffective treatment regimens.
As in other studies, we did not find CD4 cell levels to be associated with an increased rate of seroconversion.28,29 Although viral load has been more directly correlated with rate of transmission, we were unable to obtain viral load data from these rural areas because of problems with physical infrastructure and human resource capacity.2,30 The stage of disease has been associated with increased risk of transmission, but we did not find that an association between lower CD4 levels and with higher rates of seroconversion.31,32 One explanation may be that the spouses with late-stage disease in this cohort may have had less frequent sex or used condoms more than those spouses in latency. Our data provide some support to the hypothesis that partners with late-stage disease may have less contribution to the HIV epidemic than early-stage partners or those who are acutely infected and do not know their status.32
One of the primary limitations of our study is that we were unable to obtain adherence data from those on ART because almost all patients received treatment from local community health care centers. Unfortunately, these centers did not reliably track adherence data. To address this limitation, future studies in this cohort will incorporate more detailed questions on drug adherence and attempt to better quantify drug resistance. Although the lack of adherence or viral load data are problematic, it reflects real-world challenges associated with ART roll-out in resource-limited settings.33 Our findings suggest that ART treatment with first-line drugs alone may not be sufficient to reduce HIV transmission among discordant couples in China. Another limitation of this study is that our data may be subject to recall bias because some subjects were surveyed at the end of the enrollment period and asked to recall behavior from the month(s) preceding their date of seroconversion. Self-reporting bias may also have resulted in the under reporting of unprotected sex.34
On quality-of-life, we found that those who scored lower in the psychological, but not physical, social, or environmental domains were significantly associated with HIV seroconversion (RR = 2.33; 95% CI:1.21 to 4.48). Although the link between HIV transmission and indicators of psychological well being is not well understood, the World Health Organization quality-of-life assessment has been previously validated in patients with HIV.14 A study conducted in Moscow among Tajik migrant workers found that lack of social support and feeling unprotected by law may reduce self efficacy and self-protective behaviors.35 Thus, it is possible that initially HIV-negative spouses who had lower scores on the psychological domain may be engaging in more risky behaviors, such as having unprotected sex. Our results suggest that psychological assessments may serve as novel indicators of HIV transmission among serodiscordant couples and that interventions aimed at improving quality-of-life and reducing psychological distress may reduce this risk in China.36 However, more research on the type and effectiveness of these interventions and on the appropriateness of the survey instrument is needed for HIV discordant families in China.
Our study found a relatively low rate of HIV transmission among serodiscordant couples in Henan, but the rate increased over time. We also found that not always using condoms, more frequent sex, not switching ART regimens, and a lower quality-of-life score on psychological domains were associated with increased risk of transmission. Although adherence to treatment probably played an important factor, ART use and last recorded CD4 count were not found to be associated with HIV transmission. Our study suggests that the use of blanket ART programs alone may not necessarily reduce transmission among rural serodiscordant couples in China. To be most effective, treatment programs in these areas should be combined with HIV prevention interventions that emphasize always using condoms, less frequent sex, switching to more effective ART regimens, and care and support services for those affected by AIDS.
We would like to thank all study participants from Zhumadian City, Henan Province, for their contribution.
1. Ministry of Health of China UNTGoA. A Joint Assessment of Prevention, Treatment, and Care in China (2007)
. Beijing, China: Ministry of Health; 2007.
2. Wu Z, Sullivan S, Wang Y, et al. Evolution of China's response to HIV/AIDS. Lancet
3. Lu L, Jia M, Ma Y, et al. The changing face of HIV in China. Nature
4. Hugonnet S, Mosha F, Todd J, et al. Incidence of HIV infection in stable sexual partnerships: a retrospective cohort study of 1802 couples in Mwanza Region Tanzania. J Acquir Immune Defic Syndr
5. Carpenter LM, Kamali A, Ruberantwari A, et al. Rates of HIV-1 transmission within marriage in rural Uganda in relation to the HIV sero-status of the partners. AIDS
6. Vitinghoff E, Douglas J, Judon F, et al. Per-contact risk of Human Immunodificiency Virus tramnsmision between male sexual partners. Am J Epidemiol
7. Melo M, Santos B, De Cassia Lira R, et al. Sexual transmission of HIV-1 among serodiscordant couples in Porto Alegre, Southern Brazil. Sex Transm Dis
8. Deschamps M, Pape J, Hafner A, et al. Heterosexual transmission of HIV in Haiti. Ann Intern Med
9. Mehendale S, Ghate M, Kishore Kumar B, et al. Low HIV-1 incidence among married serodiscordant couples in Pune, India. J Acquir Immune Defic Syndr
10. Mao YR, Zheng XW, Re ZY, et al. An epidemiological study on sexual transmission of human immunodeficiency virus among pre-marital group in Yining city, Xinjiang. Chin J Epidemiol
11. Yang H, Li X, Stanton B, et al. Heterosexual transmission of HIV in China: a systematic review of behavioral studies in the past two decades. Sex Transm Dis
12. Yan J, Zheng X, Zhang X, et al. The survey of prevalence of HIV infection among paid blood donors in one county in China. Chin J Epidemiol
13. Wu Z, Rou K, Detels R. Prevalence of HIV infection among former commercial plasma donors in rural eastern China. Health Policy Plan
14. Fang C, Hsiung P, Yu C, et al. Validation of the World Health Organization quality of life instrument in patients with HIV infection. Qual Life Res
15. Novak R, Chen L, MacArthur R, et al. Prevalence of antiretroviral drug resistance mutations in chronically HIV-infected, treatment-naive patients: implications for routine resistance screening before initiation of antiretroviral therapy. Clin Infect Dis
16. Ruan Y, Qin G, Yin L, et al. Incidence of HIV, hepatitis C and hepatitis B viruses among injection drug users in southwestern China: a 3-year follow-up study. AIDS
17. Blower S, Ma L, Farmer P, et al. Predicting the impact of antiretrovirals in resource-poor settings: preventing HIV infections whilst controlling drug resistance. Curr Drug Targets Infect Disord
18. Zhang F, Dou Z, Ma Y, et al. Five-year outcomes of the China National Free Antiretroviral Treatment Program. Ann Intern Med
19. Hira SK, Nkowane BM, Kamanga J, et al. Epidemiology of Human Immunodeficiency Virus in families in Lusaka, Zambia. J Acquir Immune Defic Syndr
20. Blower S, Gershengorn H, Grant R. A tale of two futures: HIV and antiretroviral therapy in San Francisco. Science
21. Gray R, Li X, Wawer M, et al. Stochastic simulation of the impact of antiretroviral therapy and HIV vaccines on HIV transmission; Rakai, Uganda. AIDS
22. Gray R, Wawer M, Brookmeyer R, et al. Probability of HIV-1 transmission per coital act in monogamous, heterosexual, HIV-1-discordant couples in Rakai, Uganda. Lancet
23. Dunkle K, Stephenson R, Karita E, et al. New heterosexually transmitted HIV infections in married or cohabiting couples in urban Zambia and Rwanda: an analysis of survey and clinical data. Lancet
24. Guthrie B, de Bruyn G, Farquhar C. HIV-1-discordant couples in sub-Saharan Africa: explanations and implications for high rates of discordancy. Curr HIV Res
25. Freeman E, Glynn J. Factors affecting HIV concordancy in married couples in four African cities. AIDS
26. Attia S, Egger M, Müller M, et al. Sexual transmission of HIV according to viral load and antiretroviral therapy: systematic review and meta-analysis. AIDS
27. Jing Yun L, Han Ping L, Lin L, et al. Prevalence and evolution of drug resistance HIV-1 variants in Henan, China. Cell Res
28. Fideli Ü, Allen S, Musonda R, et al. Virologic and immunologic determinants of heterosexual transmission of human immunodeficiency virus type 1 in Africa. AIDS Res Hum Retroviruses
29. Pedraza M, del Romero J, Roldán F, et al. Heterosexual transmission of HIV-1 is associated with high plasma viral load levels and a positive viral isolation in the infected partner. J Acquir Immune Defic Syndr
30. Quinn T, Wawer M, Sewankambo N, et al. Viral load and heterosexual transmission of human immunodeficiency virus type 1. N Engl J Med
31. De Vincenzi I. A longitudinal study of human immunodeficiency virus transmission by heterosexual partners. N Engl J Med
32. Wawer M, Gray R, Sewankambo N, et al. Rates of HIV-1 transmission per coital act, by stage of HIV-1 infection, in Rakai, Uganda. J Infect Dis
33. Bishai D, Colchero A, Durack D. The cost effectiveness of antiretroviral treatment strategies in resource-limited settings. AIDS
34. Allen S, Meinzen-Derr J, Kautzman M, et al. Sexual behavior of HIV discordant couples after HIV counseling and testing. AIDS
35. Weine S, Bahromov M, Mirzoev A. Unprotected Tajik Male Migrant Workers in Moscow at Risk for HIV/AIDS. J Immigr Minor Health
36. Molassiotis A, Callaghan P, Twinn S, et al. A pilot study of the effects of cognitive-behavioral group therapy and peer support/counseling in decreasing psychologic distress and improving quality of life in Chinese patients with symptomatic HIV disease. AIDS Patient Care STDS