Risk of prevalent HIV infection associated with incarceration among injecting drug users in Bangkok, Thailand: case-control study.

OBJECTIVES: To identify risks for HIV infection related to incarceration among injecting drug users in Bangkok, Thailand. DESIGN: Case-control study of sexual and parenteral exposures occurring before, during, and after the most recent incarceration. SETTING: Metropolitan Bangkok. PARTICIPANTS: Non-prison based injecting drug users formerly incarcerated for at least six months in the previous five years, with documented HIV serostatus since their most recent release; 175 HIV positive cases and 172 HIV negative controls from methadone clinics. MAIN OUTCOME MEASURE: Injection of heroin and methamphetamine, sharing of needles, sexual behaviour, and tattooing before, during, and after incarceration. RESULTS: In the month before incarceration cases were more likely than controls to have injected methamphetamine and to have borrowed needles. More cases than controls reported using drugs (60% v 45%; P=0.005) and sharing needles (50% v 31%; P<0.01) in the holding cell before incarceration. Independent risk factors for prevalent HIV infection included injection of methamphetamine before detention (adjusted odds ratio 3.3, 95% confidence interval 1.01 to 10.7), sharing needles in the holding cell (1.9, 1.2 to 3.0), being tattooed while in prison (2.1, 1.3 to 3.4), and borrowing needles after release (2.5, 1.3 to 4.4). CONCLUSIONS: Injecting drug users in Bangkok are at significantly increased risk of HIV infection through sharing needles with multiple partners while in holding cells before incarceration. The time spent in holding cells is an important opportunity to provide risk reduction counselling and intervention to reduce the incidence of HIV.

HIV-1 prevalence, HIV-1 subtypes and risk factors among fishermen in the Gulf of Thailand and the Andaman Sea.

OBJECTIVE: Mobile populations are thought to be at high risk for HIV-1 infection. This study aims to determine the prevalence of HIV-1 infection, HIV-1 subtypes and socio-demographic and behavioural risk factors among fishermen in the Gulf of Thailand and the Andaman Sea. METHODS: A cross-sectional survey, consisting of face-to-face interviews and the collection of oral fluid samples, was conducted in Samut Sakorn, Ranong, Songkhla and Traat Provinces, Thailand, between January and April 1998. Oral fluid samples were double-tested for HIV-1 antibody by IgG antibody capture enzyme-linked immunosorbent assay and enzyme immunoassay, and confirmed by Western blot. The presence of subtypes B' and E was assessed using a peptide enzyme immunoassay. RESULTS: Of the 818 fishermen (582 Thai, 137 Burmese, 99 Khmer) 15.5% were HIV-1 positive: 14.6% among Thai, 16.1% among Burmese and 20.2% among Khmer. Of the 119 HIV-1 positive samples available for subtyping, 72 (61%) were subtype E, 15 (13%) were subtype B'; the subtype could not be determined for 32 (27%) samples. Sixteen per cent of subjects had ever visited a commercial sex worker outside Thailand. This behaviour was more prevalent among Khmer (40%) than among Thai and Burmese (12%). In univariate logistic regression analysis, being 25 to 32 years of age, compared with being older or younger; working as a fisherman between 4 and 10 years, compared with working for a shorter or longer period; being unmarried; being a steersman or mechanic, compared with being a skipper or ship hand; greater number of visits to commercial sex workers; having visited a commercial sex worker outside Thailand; alcohol or drug use before or during sex; being tattooed; and having a history of sexually transmitted disease were significantly related to prevalent HIV-1 infection. Male-to-male sex and injection drug use were rarely reported in this population. In multivariate analysis, being 25 to 32 years of age, being unmarried, having a tattoo and a greater number of visits to commercial sex workers remained in the model to predict HIV-1 prevalence. A history of drug injection was predictive for infection with HIV-1 subtype B'. CONCLUSIONS: These findings indicate a high HIV-1 prevalence among fishermen in the Gulf of Thailand and the Andaman Sea. Risk factor analysis suggests that heterosexual intercourse is the major mode of transmission in this population. Increased efforts to reduce the spread of HIV-1 among this epidemiologically important group are urgently needed.

Secular trends in the survival of HIV-infected homosexual men in Amsterdam and Vancouver estimated from a death-included CD4-staged Markov model.

BACKGROUND: The purpose of this study was to investigate secular trends in waiting times in CD4-based stages of human immunodeficiency virus (HIV) disease progression in two cohorts of homosexual men, one in Vancouver and one in Amsterdam. All HIV-positive men with two or more CD4 counts in their AIDS-free period between 1 January 1985 and 1 January 1997 were included in this study. Data regarding clinical AIDS diagnoses (using the 1987 Centers for Disease Control and Prevention [CDC] AIDS case definition) and death were collected through active follow-up, review of hospital records, and municipal/national registries. The Vancouver Lymphadenopathy-AIDS Study (VLAS), was started in November 1982 and had enrollment until December 1984. Both HIV-negative and HIV-positive men were followed at intervals of 3-6 months until 1986 and annually thereafter. The Amsterdam cohort study on HIV and AIDS (ACS) started in December 1984, has ongoing enrollment and follow-up of both HIV-negative and HIV-positive homosexual men. The HIV-positive men were followed at intervals of 3 months. METHODS: The CD4-based stage of an individual at each visit was determined using smoothed data. For each cohort and in each calendar time period, a CD4-based Markov model with death as the absorbing stage was fitted to the data. The parameters in this model were estimated using the method of maximum likelihood and confidence intervals were calculated using bootstrap methods. RESULTS: A total of 509 homosexual men participating in the VLAS were included in this study, providing 5356 visits. Some 292 men developed AIDS before 1 January 1997 and 239 died before this date. In all, 232 of the 239 deaths were AIDS related. Thirty-seven per cent of all visits were related to treatment. A total of 543 homosexual men participating in the ACS were included in this study, providing 10 043 visits; 277 men developed AIDS before 1 January 1997 and 250 died before this date. The date of AIDS diagnosis was known for 225 of the 250 deaths. Twenty per cent of all visits were related to treatment. We found that in both cohort studies the stage-specific waiting times were longer in the low CD4-based stages (stages 4, 5 and 6: i.e. CD4 count <500 cells per mm(3)) after March 1990 compared to waiting times before March 1990. The increase in mean waiting time in these stages with low CD4 count was 21%, 33% and 53%, respectively in the ACS and 20%, 2% and 29% in the VLAS. Because waiting times alone are not exclusive for progression in a reversible model we also calculated the stage-specific median incubation periods till death. Men spent considerably longer in these CD4-based stages after March 1990 compared to before March 1990. CONCLUSIONS: Data from these population-based cohort studies showed that HIV disease progression in the calendar period where treatment was administered was slower for individuals in stages with low CD4 counts. We found no evidence for shortening of the incubation period that may have appeared from increasing virulence of the HIV in the population.

Long-term survival after infection with human immunodeficiency virus type 1 (HIV-1) among homosexual men in hepatitis B vaccine trial cohorts in Amsterdam, New York City, and San Francisco, 1978-1995.

Information on long-term survival after infection with human immunodeficiency virus type 1 (HIV-1) is limited. In hepatitis B vaccine trials in Amsterdam, New York City, and San Francisco, 362 gay men were followed up to 18 years (1978-1995). The median survival time from seroconversion was 12.1 years (95% confidence interval: 11.4, 12.9). The annual risk of dying increased at a constant rate until 8 years after seroconversion and then leveled off, suggesting a group that is relatively resistant to progression. These data provide a picture of the natural history of HIV-1 infection, especially in the era prior to widespread use of highly effective treatments.

Avoidance as a predictor of the biological course of HIV infection over a 7-year period in gay men.

The present study prospectively investigated the relation between avoidance coping and active cognitive and behavioral coping and the progression of HIV infection over 7 years in 181 gay men. Findings revealed that for a number of medical and behavioral factors, (a) avoidance coping predicted a lower rate of decline in CD4 cells, (b) the proportional hazard (PH) attributable to avoidance of developing a syncytium-inducing HIV variant was 0.72 (95% confidence interval [CI]: 0.53 - 0.99, p < .05), and (c) the PH attributable to avoidance of dropping below 200 CD4 cells/microl was 0.66 (95% CI: 0.50 - 0.89, p < .01). Avoidance coping was not related to the development of AIDS-defining clinical symptoms. Active cognitive and behavioral coping was not related to the outcome measures.

The incubation period to AIDS in injecting drug users estimated from prevalent cohort data, accounting for death prior to an AIDS diagnosis.

OBJECTIVE: To estimate the incubation-period distribution (time from seroconversion to AIDS) accounting for death before an AIDS diagnosis (DBAD) in a cohort of injecting drug users (IDU) in Amsterdam, The Netherlands and to compare these estimates with those previously obtained from a contemporaneous study of homosexual and bisexual men in Amsterdam carried out using the same facilities. DESIGN: Participants in a cohort study begun in Amsterdam at the end of 1985 have scheduled follow-up visits every 4 months. All participants of Dutch nationality and who had two or more follow-up visits before January 1996 from which CD4 measurements were available were included in this study. Data concerning AIDS diagnosis and death were verified through review of national and municipal registries. METHODS: Because time of seroconversion was unknown for study participants and because IDU are at substantial risk for DBAD, we used a Markov model with CD4-based stages that allows for DBAD. The parameters in this model were estimated using the method of maximum likelihood and confidence intervals were calculated using bootstrap methods. RESULTS: A total of 173 IDU (134 seroprevalent, 39 seroincident) made 1829 visits. Nearly 10% of the visits were non-consecutive. Forty-five IDU developed AIDS and 25 died without an AIDS diagnosis. We estimated that 24% [95% confidence interval (CI), 17-25%] of IDU die before an AIDS diagnosis. As a result, the median time from seroconversion to AIDS (10.5 years; 95% CI, 9.1-10.7 years) is considerably longer than the median time from seroconversion to death (8.3 years; 95% CI, 7.9-8.5 years). Conditional on survival to an AIDS diagnosis, the median time to AIDS is 8.2 years (95% CI, 7.7-8.7 years). The median survival time after a diagnosis of AIDS is estimated to be 1.0 years. CONCLUSION: The high occurrence of DBAD in IDU has a considerable influence on estimates of the incubation-period distribution. Progression from seroconversion to death was faster in the IDU cohort than in a cohort of homosexual men in Amsterdam (median, 8.3 years and 9.6 years, respectively). However, progression to AIDS conditional on survival to an AIDS diagnosis seems to be similar in both the IDU cohort and in the cohort of homosexual men (median, 8.2 years and 8.3 years, respectively).

Is AIDS a floating point between HIV seroconversion and death? Insights from the Tricontinental Seroconverter Study.

OBJECTIVE: To investigate the significance of the time from seroconversion to AIDS (incubation time) and other covariates for survival from AIDS to death. METHODS: In survival analysis, survival from AIDS to death was compared for different categories of length of incubation time adjusted and unadjusted for other covariates, and significant predictors for survival from AIDS to death were investigated. RESULTS: Survival after AIDS was not affected by the incubation time in univariate as well as in multivariate analyses. Predictive factors for progression from AIDS to death were age at seroconversion, type of AIDS diagnosis, and CD4 cell count at AIDS. The relative hazard for age at seroconversion increased 1.38-fold over 10 years. Men with a CD4 cell count at AIDS of <130 x 10(6)/l had a twofold higher risk in progression to death than men with higher CD4 cell counts. Persons diagnosed with lymphoma had a sixfold higher risk of progression to death than persons with Kaposi's sarcoma or opportunistic infections. CONCLUSIONS: The incubation time as well as other factors before AIDS did not affect survival after AIDS. Survival from AIDS to death can be predicted by data obtained at the time of AIDS diagnosis, such as type of diagnosis, age and CD4 cell count. AIDS seems to be a significant point in progression to death, and not just a floating point between infection and death affected by prior factors for persons who did not receive effective therapy and did not have long incubation times.

Demographic impact of the HIV epidemic in Thailand.

OBJECTIVE: To assess the impact of the HIV epidemic on the demographic development of the Thai population. METHODS: A deterministic mathematical model was used to predict simultaneously epidemiological and demographic processes. Partial differential equations express the relationships between biological, behavioural and demographic variables. The model allows the evaluation of different sexual mixing patterns, variable transmission probabilities and incubation times. Validity analysis was performed by generating antecedent HIV prevalence patterns among military recruits and pregnant women. RESULTS: On the national level in Thailand we predict that the cumulative number of people in Thailand with HIV infection will exceed 1 million by 1999; the number of deaths from AIDS will be 555000 by the year 2000 but will not reach 1 million until after the year 2014. Without the HIV epidemic the population growth rate was estimated at 1.3% per annum until 1995, after which a decline to 0.9% by 2005 is predicted. The HIV epidemic started to affect the population growth rate by 0.026% per year in 1991, and the difference is predicted to rise to about 0.12% per year during the period 1995-2000, to decline to 0.06% in 2005 and then to disappear. In the mid-1990s HIV affected mainly the 15-35-year-old age group, but over time younger and older age groups have been affected as a result of perinatal transmission, and a decline in fertility as well as ageing of the 15-35-year-old birth cohort. Because of HIV, in 2000 there will be 612000 (1%) fewer people than expected and by 2010, 1140000 fewer (1.6%). We predict that the demographic impact of the HIV epidemic in the northern region will follow the same pattern, but with greater severity. Here, the effect on the population growth rate and the population age distribution is likely to be twice as high as at the national level. CONCLUSIONS: It is estimated that 1 million Thais will be infected with HIV by the year 2000 and an almost equal number will have died of AIDS by the year 2014. Although these numbers seem high, their direct and indirect effects on the demographic structure of the Thai population are small. However, at a regional level, for example in the northern region, the effect of the HIV epidemic may be more severe.

Evaluation of a targeted HIV prevention programme among female commercial sex workers in the south of Thailand.

OBJECTIVE: To evaluate a targeted HIV prevention programme among female commercial sex workers (CSWs) in the south of Thailand. SUBJECTS AND METHODS: A pretest-post-test comparison group study was carried out in Sungai Kolok and Betong between June and December 1994. In June 408 CSWs were entered in Sungai Kolok (the intervention area) and 343 CSWs were enrolled in Betong (the comparison area). In December 1994, 416 women were enrolled in Sungai Kolok and 342 in Betong. Of these women 37% (n = 283) also participated in the June survey. All women completed an oral interview and blood samples were collected for HIV serology. The intervention programme consisted of an informational and educational campaign and peer educator training. RESULTS: Increase in knowledge and perceived vulnerability was more pronounced in the intervention area but did not translate into a greater increase in condom use. Refusal of customers unwilling to use a condom and manager support in doing so were the only factors independently related to positive changes in condom use. HIV prevalence (approximately 20%) and incidence (approximately 4.2 per 100 women years) were the same in both study locations. Women in the intervention area reported significantly fewer customers and income from sex work, possibly as a result of a coincidental police campaign to suppress (child) prostitution. CONCLUSIONS: HIV incidence among CSWs in the south of Thailand is still high. Prevention programmes should focus on improvement of negotiation and refusal skills and manager support in using condoms.

Sexual risk behavior and risk factors for HIV-1 seroconversion in homosexual men participating in the Tricontinental Seroconverter Study, 1982-1994.

Trends in sexual behavior associated with incident infection with human immunodeficiency virus (HIV) type 1 are described and a case-control study was conducted to examine risk factors for HIV seroconversion in homosexual men who became infected with HIV between 1982 and 1994 from four geographic sites: Amsterdam, the Netherlands; San Francisco, California; Vancouver, Canada; and Sydney, Australia. Changes in sexual behaviors were evaluated from cohort visits in the preseroconversion, seroconversion, and postseroconversion intervals and were further examined over three time periods: 1982-1984, 1985-1987, and 1988-1994. In a case-control study, sexual behaviors, substance use, and presence of sexually transmitted disease were compared between 345 HIV-positive cases and 345 seronegative controls matched by visit date and site. Receptive anal intercourse was the sexual behavior most highly associated with seroconversion. The odds ratio (OR) per receptive anal intercourse partner increase was 1.05 (95% confidence interval (CI) 1.02-1.09). To more carefully examine risk associated with receptive oral intercourse, analyses were done in a subgroup of men who reported no or one receptive anal intercourse partner. The risk (OR) associated with receptive oral intercourse partner increase was 1.05 (95% CI 1.0-1.11). In multivariate conditional logistic regression analyses, presence of sexually transmitted disease (OR = 3.39, 95% CI 1.95-5.91) and amphetamine use (OR = 2.55, 95% CI 1.26-5.15) were independently associated with seroconversion. Although the prevalence of major risk factors has decreased over time, the associations of these behaviors and HIV infection persist, suggesting that these risk behaviors remain important avenues for public health interventions.

Incidence and prognostic significance of symptomatic primary human immunodeficiency virus type 1 infection in homosexual men.

To investigate the incidence of symptomatic primary human immunodeficiency virus type 1 (HIV-1) infection and its prognostic significance for HIV-1 disease progression, data for 328 homosexual men from four cohort studies were evaluated. Rates of diarrhea, fever, night sweats, cough, and fatigue prior to, during, and after seroconversion were compared by use of Poisson regression, and the prognostic significance of these symptoms was evaluated with survival methods. The incidence of all symptoms was elevated during seroconversion; however, only fever was associated with faster disease progression. Seven or more days of fever was reported by 13.8% of subjects; half of them developed AIDS within 6 years, whereas only one-fourth of the men without fever developed AIDS within 6 years. In addition, fever was the only symptom associated with shortened survival and increased CD4 cell loss. Persons experiencing prolonged periods of fever during seroconversion should therefore be considered for early treatment, including prophylaxis against opportunistic infections and combinations of antiretroviral drugs.

Associations of age, immunosuppression, and AIDS among homosexual men in the Tricontinental Seroconverter Study.

To characterize the associations of age, immunosuppression, and AIDS outcomes, we evaluated serial measures of CD4+ lymphocytes from 376 homosexual men with documented dates of HIV-1 seroconversion registered in the Tricontinental Seroconverter Study. Using regression models and adjusting for variation within individuals, we found no association between age and the number of CD4+ lymphocytes at seroconversion or with CD4+ lymphocyte decline after seroconversion. Men who developed opportunistic infections had fewer CD4+ lymphocytes at the time of diagnosis compared with men who developed AIDS-defining Kaposi's sarcoma. Older age was significantly associated with higher numbers of CD4+ lymphocytes in individuals diagnosed with AIDS-defining Kaposi's sarcoma but was not significant for individuals with opportunistic infections. Because older age shortens the latency period of Kaposi's sarcoma and does not affect the CD4+ lymphocyte loss, it results in higher CD4+ lymphocytes at the time of diagnosis. These findings suggest distinct biologic mechanisms for various AIDS manifestations, which is important for clinical decision making and health care planning.

Homosexual encounters in different venues.

We aim to provide empirical data regarding the role of various sex-on-premises venues for gay men in the spread of HIV infection and homosexual activity with casual partners at different (public) venues was assessed. A questionnaire was filled out by participants in a cohort study in Amsterdam, The Netherlands. Questions were asked regarding sex in private homes, baths, cruising areas, darkrooms, cinemas, and hotel rooms. The majority of the 410 men who had sex with casual partners had done so in private homes (67.8%). However, cruising areas, baths and darkrooms were also highly frequented. Three general 'scenes' of venues frequented could be distinguished, and characteristics of men frequenting different types of venues were found to differ. Men who reported unprotected anal sex did so for only one type of venue. Private homes were the locations where most men engaged in high-risk behaviours. However, the number of partners practising unprotected anogenital sex was highest in (semi) public venues.

[HIV infection and risky sexual behavior in a new cohort of young homosexual men in Amsterdam, 1995-1996]. / HIV-infectie en riskant seksueel gedrag in een nieuwe cohort jonge homoseksuele mannen te Amsterdam, 1995-1996.

OBJECTIVE: The surveillance of HIV prevalence and incidence and of sexual risk behaviour among young homosexual men. DESIGN: Cohort study, cross-sectional data presentation. SETTING: Municipal Health Service of the City of Amsterdam, the Netherlands. METHODS: At entry into the study participants were questioned about their sexual behaviour and blood or saliva samples were collected for laboratory determination of antibodies against HIV, hepatitis B and syphilis. RESULTS: In June 1995-October 1996, 429 men with a mean age of 25 years were enrolled in the cohort study. Of these 22 (5%) were positive for antibodies against HIV. Based on the duration of homosexual activity of the participants the HIV incidence in this group was estimated at 1% per year. Furthermore, 10% of the participants had experienced hepatitis B infection and 1% had serological evidence of syphilis. Of those under investigation 38% had practised unprotected anogenital intercourse with steady or non-steady partners in the last six months. CONCLUSIONS: The data suggest that HIV is spreading among young homosexual men. Given the high levels of risk behaviour continued prevention activities in this group are necessary.

[HIV incidence in a cohort of homosexual men and a cohort of injecting drug users in Amsterdam, 1985-1995]. / HIV-incidentie in een cohort homoseksuele mannen en een cohort injecterende drugsgebruikers in Amsterdam, 1985-1995.

Since 1984/1985 a cohort of homosexual men (HM; n = 770 initially HIV-seronegative) and one of injecting drug abusers (IDU; n = 675 initially seronegative) are being followed in Amsterdam, in order to assess the HIV epidemic in these high-risk groups. The HIV incidence in HM fell from 7.2/100 person years in 1985 to 1.0 in 1989, due to safer sexual behaviour. In 1990 there was a temporary rise in HIV incidence coinciding with an increase in gonorrhoea and syphilis in homosexual/bisexual men (not in the cohorts) attending a sexually transmitted diseases outpatient clinic. The rise was due to a relapse in unsafe sexual behaviour. After 1990 the HIV incidence dropped again and it remained at 1/100 person years in 1995. In IDU, in whom a reduction was found in both injecting and sexual risk behaviour, the incidence fell from 8.9 in 1986 to 2.0-3.6/100 person years in 1991-1995. In order to follow the future course of the HIV epidemic, it is argued to open the cohorts particularly for young HM and IDU.

Lack of consistency between five definitions of nonprogression in cohorts of HIV-infected seroconverters.

OBJECTIVE: To identify appropriate criteria for characterizing HIV-infected nonprogressors. DESIGN: Five definitions were compared as follows: (1) last CD4 count > 500 x 10(6)/l; (2) two most recent CD4 counts > 500 x 10(6)/l; (3) calculated CD4 count based on linear regression > 500 x 10(6)/l; (4) CD4 slope > or = 0 with no antiretroviral use; (5) all CD4 counts > 500 x 10(6)/l, decline in CD4 slope < 5 cells per year, no antiretroviral use. PARTICIPANTS: Five prospective cohorts of homosexual men with documented dates of HIV-1 seroconversion. MAIN OUTCOME MEASURES: Proportions of nonprogressors were calculated 7, 8, 9 and 10 years following seroconversion (n = 285). Definitions were evaluated with respect to consistency over time and across sites. Subjects lacking CD4 counts within 3 years preceding end of follow-up were excluded. RESULTS: Across sites, proportions of nonprogressors ranged from 1% (definition 5) to 17.5% (definition 1) 10 years after seroconversion. Definitions based on absolute CD4 counts (definitions 1-3) had higher proportions and were less consistent than those based on stable slopes (definitions 4 and 5). For each definition, proportions decreased as follow-up increased, but were most stable for definition 4 (3%). Site differences decreased as follow-up increased, but remained nearly threefold for definitions 1-3. None of the definitions classified the same subjects as nonprogressors at any timepoint. CONCLUSIONS: Observations regarding nonprogression are highly dependent on the definition and the duration of follow-up. Our findings highlight methodological challenges which will need to be overcome in natural history studies of nonprogression.

Use of immunological markers and continuous-time Markov models to estimate progression of HIV infection in homosexual men.

OBJECTIVES: We used continuous-time Markov models based on CD4 cell counts and anti-CD3 reactivity (i.e., measure for T-cell quality) to study the progression of HIV infection in a cohort study of homosexual men in Amsterdam. We also compared the effectiveness of anti-CD3 reactivity as a marker for disease progression with that of CD4 cell counts. METHODS: We used data from 467 men (6905 visits) with visits at 3-month intervals between October 1984 and March 1993. To account for measurement error and short time-scale variability, the immunological stage at each visit was determined using a kernel smoother on log-transformed data from each individual. The Markov model had six marker-defined stages and a seventh stage for clinical AIDS. The initial stage-occupation probabilities for seroconverters were used to estimate the incubation time from infection to AIDS. Confidence intervals were calculated using the bootstrap method to account for the effect of smoothing on the variability of our estimates. RESULTS: The CD4 staging scheme estimated the median time from seroconversion to AIDS at 8.3 years [95% confidence interval (CI), 8.1-8.6], and a similar estimate was obtained with the anti-CD3 staging model. The CD4 model predicts that 10.2% (95% CI, 9.9-13.1) will remain AIDS-free 15 years after seroconversion. The mean number of stages visited before AIDS is lower with the CD4 model (7.4; 95% CI, 7.2-7.7) than with the anti-CD3 model (11.3; 95% CI, 10.8-12.0), implying that anti-CD3 predicts progression less well than CD4 cell count. CONCLUSIONS: CD4 lymphocyte counts and anti-CD3 reactivity are each associated with an increased hazard for progression to AIDS. Therefore, men in different CD4-stages (anti-CD3 stages) follow different incubation period distributions to AIDS. However, anti-CD3 predicts progression less well than CD4 cell count. Staged time-continuous Markov models are useful to study immunological markers for HIV disease progression.