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.

Clinical sexually transmitted diseases among human immunodeficiency virus-infected and noninfected drug-using prostitutes. Associated factors and interpretation of trends, 1986 to 1994

OBJECTIVES

To describe among drug-using prostitutes from the Amsterdam cohort study: 1) trends in clinical sexually transmitted disease (STD) diagnoses from 1986 through 1994; 2) identify factors associated with STD incidences; and 3) determine explanatory factors for time trends in STD.

METHODS

Sexual behavior data and human immunodeficiency virus (HIV) serostatus from the cohort study were linked to diagnoses of gonorrhea (GC), Chlamydia trachomatis infection (CT), and trichomoniasis (TV) made at a special STD clinic for drug-using prostitutes. Diagnosis-specific incidences were calculated per 100 person-years of follow-up. Factors associated with STD incidence were determined bivariately. Crude time trends in incidences were determined and then multivariately adjusted for sets of potential explanatory factors using Poisson regression.

RESULTS

Cohort data from 229 current prostitutes were linked to clinical STD diagnoses. During the study period, a fivefold decline in GC was found, and CT declined twofold; trends in TV initially declined, but tended to increase after 1991. Higher incidences for STD were associated with inconsistent condom use, higher numbers of clients, shorter history of prostitution, younger age, non-Dutch nationality, and HIV infection. About half of the decline in STD could be explained by changes toward safer commercial sexual behaviours or changes in the characteristics of the study population.

CONCLUSIONS

From 1986 through 1994, the incidence in clinical STD declined significantly among drug-using prostitutes in Amsterdam. Trends in STD were only partly due to risk reduction in commercial sexual contacts. Thus, it may be hazardous to use trends in STD as markers for sexual risk behavior. Other factors probably played a substantial role in the observed declines, including declining STD prevalence among male clients, changes in health-seeking behaviors, and improved quality of STD control.

[HIV infection and risk behaviour among prostitutes in the Amsterdam streetwalkers' district; indications of raised prevalence of HIV among transvestites / transsexuals]

OBJECTIVE

To determine the prevalence of HIV infection and risk behaviour among various groups of streetwalkers in Amsterdam and the extent of overlap between different prostitution networks.

SETTING

The family room project in the streetwalkers' district in Amsterdam, the Netherlands.

METHODS

In November 1996, saliva was taken from 32 female and 25 transsexual/transvestite prostitutes and tested for antibodies against HIV. Besides, prostitutes were interviewed on risk behaviour, history of sexually transmitted diseases and mobility.

RESULTS

Only one of the participants (a female prostitute) had ever injected drugs. None of the female prostitutes, but 6 of the 25 transsexuals/transvestite prostitutes (24%; 95% confidence interval: 7-41) proved seropositive. None of the HIV infected participants was aware of his serostatus. The transsexual/transvestite prostitutes frequently had receptive anal intercourse with their clients. Condom use was high, but most did not use condoms made for anal intercourse. Female prostitutes also reported a high rate of condom use with their clients. Both groups of prostitutes reported few private partners and a low rate of condom use with these partners. According to the transsexual/transvestite prostitutes many of their clients had sexual contacts with women in their private lives. Many prostitutes thought that they shared the same clients in the district.

CONCLUSION

HIV infections occur quite often among transsexual/transvestite prostitutes in the streetwalkers' district in Amsterdam. The risk of further spread HIV infection to their clients (and through them to other heterosexual populations) is present. AIDS education targeted at this group is important. The use of (special) condoms when having anal intercourse in private as well as in prostitution contacts should be emphatically advised.

[AIDS; new developments. I. HIV tests: time for a more active policy]

Until recently, an HIV test was of limited importance for persons who had been at risk for HIV as effective drugs were not available. With the advent of a new generation of antiretroviral drugs with beneficial effect after early treatment, knowledge of the HIV serostatus has become of more importance to asymptomatic persons. There is no need for a mass screening campaign however, as there is no cure as yet.

Rapid disease progression in human immunodeficiency virus type 1-infected individuals with adverse reactions to trimethoprim-sulfamethoxazole prophylaxis

We studied the relation between the occurrence of adverse reactions to trimethoprim-sulfamethoxazole (TMP-SMZ) prophylaxis and the subsequent course of human immunodeficiency virus (HIV) infection in a cohort of homosexual men. Adverse reactions to TMP-SMZ were associated with a more rapid progression to AIDS (P < .001) and death (P < .001) and with a more rapid decline in CD4+ cell counts (P = .001). The median time to progression to AIDS was 14.9 months in subjects with adverse reactions to TMP-SMZ and 32.5 months in those without adverse reactions. After exclusion of Pneumocystis carinii pneumonia (PCP) and toxoplasmosis from the case definition of AIDS, the differences in the rate of progression to AIDS between subjects with and without adverse reactions to TMP-SMZ were still highly significant (P = .004). A low CD4+ cell count at baseline and the use of antiretroviral agents before the start of prophylaxis were predictors of adverse reactions to TMP-SMZ but did not account for the difference in progression to AIDS between subjects with and without adverse reactions to TMP-SMZ. In a univariate analysis, the relative hazard of adverse reactions to TMP-SMZ for progression to AIDS was 2.54 (95% confidence interval [CI], 1.50-4.28); in a multivariate analysis, it was 2.21 (95% CI, 1.29-3.81). The relative hazards of adverse reactions to TMP-SMZ for progression to AIDS with the exclusion of PCP and toxoplasmosis, CD4+ cell counts of <50/mm3, and death were 2.16 (95% CI, 1.25-3.72), 2.37 (95% CI, 1.36-4.12), and 3.21 (95% CI, 1.80-5.72), respectively. It is unclear whether adverse reactions to TMP-SMZ induce or merely predict progression of HIV disease.

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.

Estimating the size of the HIV epidemic among injecting drug users in Amsterdam

Aim of this study was to assess the cumulative incidence of HIV-infection, AIDS and pre-AIDS death in the population of injecting drug users (IDU) in Amsterdam. By assuming equivalence, between a cohort of IDU and the IDU population, of the ratios of incidences of AIDS and pre-AIDS death to the number of HIV positive persons giving rise to these incidences, the numbers of HIV positive persons and pre-AIDS deaths in the population could be calculated, given that other parameters were known. Cohort study data on HIV prevalence and incidences of HIV infection, AIDS, and pre-AIDS death, were combined with national AIDS surveillance data. As of 1 October 1994, the estimated cumulative number of HIV positive IDU in Amsterdam was approximately 1280, far higher than a recent back-calculation estimate. Of the 1280, 204 HIV positive IDU had been diagnosed with AIDS, while about 270 had died pre-AIDS. The HIV prevalence of IDU residing in Amsterdam that were still alive and free of AIDS was hence estimated at around 800. Since the incidence of pre-AIDS death and AIDS exceeded the number of seroconversions during the past four years, the HIV epidemic among IDU in Amsterdam appears to be dwindling. A lower bound of the number of HIV positive IDU being alive, AIDS-free and living elsewhere in the Netherlands was roughly estimated at 600. Because of untimely deaths, only a limited number of HIV positive IDU can be expected to be diagnosed with AIDS in the future. Since these estimates are based upon some rather bold assumptions, they should be interpreted with caution and require further validation by independent sources.

Gag-specific immune responses after immunization with p17/p24:Ty virus-like particles in HIV type 1-seropositive individuals

Gag-specific immune responses and changes in HIV-1 RNA levels were evaluated in eight HIV-1-infected persons, in order to assess the immunotherapeutic potential HIV-1 p17/p24: Ty virus-like particles (p24-VLP). All treated subjects showed transient and dose-dependent proliferative responses to the Ty-VLP carrier (stimulation index [SI], 2.0-119.5). Three of four individuals who received either 500 or 1,000 micrograms of p24-VLP also showed proliferative responses to p17 or p24 (SI, 2.0-15.7). In 2 subjects who were treated with either 500 or 1,000 micrograms of p24-VLP, enhanced Gag-specific CTL precursor (CTLp) frequencies were observed after immunization (10- to 14-fold). Both subjects had low baseline Gag-specific CTL activity (< 25 cTLp/10(6) PBMCs). In the other participants studied no significant boosting of preexisting Gag-specific CTL responses was observed. Short-term elevation of HIV-1 RNA levels at weeks 2 and 4 was observed in two subjects treated with the highest dose of p24-VLP. However, HIV-1 RNA levels at week 24 did not significantly differ from those found in the placebo group. In conclusion, p24-VLP induced marginal Gag-specific immune responses in limited numbers of HIV-1-seropositive individuals, with some showing transient elevation of HIV-1 viral load. Further studies are needed to establish potential clinical effects of these observations.

Summary of track C: epidemiology and public health

AIM

To review Track C on epidemiology and public health.

DESCRIPTIVE EPIDEMIOLOGY

Recent trends in the descriptive epidemiology are reported, for example, the rapid spread of HIV in certain Asian countries and the more precise insights in the spread thanks to subtyping of HIV-1 (and HIV-2).

TRANSMISSION

There is now ample evidence that sexually transmitted diseases enhance the rate of transmission. Viral load in the plasma of the mother is highly predictive for perinatal transmission.

PROGRESSION

Natural history studies have shown that true non-progressors are probably rare. Preliminary evidence indicates that the progression rate to AIDS and death does not differ by HIV-1 subtype. Some genetic factors are associated with the rate of disease progression and a few with susceptibility to HIV infection.

INTERVENTIONS AND PREVENTION

Needle-exchange programmes as an intervention measure for injecting drug users were hotly debated and so were HIV (home) testing and counselling. Successes in prevention were reported from Thailand and Uganda, and also from small scale programmes.

T cell telomere length in HIV-1 infection: no evidence for increased CD4+ T cell turnover

Progression to acquired immunodeficiency syndrome (AIDS) has been related to exhaustion of the regenerative capacity of the immune system resulting from high T cell turnover. Analysis of telomeric terminal restriction fragment (TRF) length, a marker for cellular replicative history, showed that CD8(+) T cell TRF length decreased but CD4(+) T cell TRF length was stable during the course of human immunodeficiency virus type-1 (HIV-1) infection, which was not explained by differential telomerase activity. This observation provides evidence that turnover in the course of HIV-1 infection can be increased considerably in CD8(+) T cells, but not in CD4(+) T cells. These results are compatible with CD4(+) T cell decline in HIV-1 infection caused by interference with cell renewal.

[Results of screening for HIV antibodies in pregnant women in Amsterdam reference stations, 1988-1995]

In order to determine the prevalence of HIV in the general heterosexual population of Amsterdam, 16,709 pregnant women attending two hospitals and one maternity clinic in the period 1988-1995 were asked to undergo a HIV test, of whom 15,276 gave informed consent (91.4%). Pregnant women with a risk of HIV infection were possibly overrepresented in those who refused. The overall HIV prevalence in 1988-1995 was 0.28% and showed no significant differences over the years. In women with a known risk factor for infection the prevalence was 240:10,000, in those without 5:10,000. Whereas intravenous drug use was the most probable cause of infection before 1993, since then it was observed in only 2/20 of the HIV positive pregnant women. Heterosexual transmission appears to be increasing.

Differences in progression to AIDS between injection drug users and homosexual men with documented dates of seroconversion

We compared rates of progression to AIDS for 99 injection drug users and 120 homosexual men with documented dates of HIV-1 seroconversion. The crude risk of developing AIDS was higher among homosexual men than injection drug users [relative hazard (RH) = 2.4; 95% confidence interval (CI) = 1.3-4.4]. The relative hazard was slightly smaller among participants with a seroconversion interval of < or = 1 year (RH = 2.2; 95% CI = 1.0-5.2). The effect was partially explained by the inclusion of Kaposi's sarcoma in the AIDS case definition. Excluding those with Kaposi's sarcoma, the relative hazard was 2.0 (95% CI = 1.1-3.8). Using the 1993 AIDS case definition decreased the effect (RH = 1.9; 95% CI = 1.1-3.4). Finally, the high pre-AIDS mortality among injection drug users could partially explain the difference in progression rate between injection drug users and homosexual men. Combining the effect of the above-mentioned factors resulted in a relative hazard of 1.3 (95% CI = 0.7-2.6). Thus, the slower progression to AIDS among injection drug users compared with homosexual men was largely explained by differences in the spectrum of AIDS-defining illnesses, pre-AIDS mortality, and length of seroconversion interval.

Large declines in sexual risk behavior with noncommercial partners among heterosexual injection drug users in Amsterdam, 1989-1995

Previous studies among injection drug users have reported small or nonexistent reductions in sexual risk behavior with noncommercial partners, and a large potential for further heterosexual spread of human immunodeficiency virus (HIV) is thought to be present. In the present study, a long-term follow-up and detailed data on sexual behavior were available. Trends were determined using data collected at 5,214 visits of 653 heterosexual injection drug users who participated in the Amsterdam Cohort Study in Amsterdam, the Netherlands between April 1989 and May 1995. Analysis accounted for repeated measurements of one individual and the effect of participation in the study itself. The authors observed a large reduction in sexual risk behavior with noncommercial partners that became apparent only after stratification of trends by knowledge of HIV serostatus. Sex with noncommercial partners and inconsistent condom use both decreased, especially among known HIV-positive individuals. Apart from nonrandom condom use, there also was nonrandom mixing (selective partner choice). Because this was like-with-like mixing, the risk for further sexual transmission of HIV is diminished. In future studies, more detailed information on sexual behavior, mixing, and knowledge of serostatus should be collected. HIV-epidemic modelers should incorporate nonrandom condom use and nonrandom mixing to improve forecasting.

Immunization with recombinant p17/p24:Ty virus-like particles in human immunodeficiency virus-infected persons

In studies of the natural history of human immunodeficiency virus type 1 (HIV-1) infection, it has been repeatedly shown that higher-titer antibody responses to the HIV gag p24 protein correlate with less rapid disease progression. In HIV-negative persons, immunization with HIV-1 p17/p24:Ty virus-like particles (p24-VLP) induced humoral and cellular immune responses to p24. This construct was therefore studied as a potential immunotherapeutic agent with the objective of augmenting the immune response to p24 in a double-blind placebo-controlled trial involving 74 p24 antibody-positive, asymptomatic HIV-1-infected subjects with CD4 cell counts > 350/mm3. Immunization with p24-VLP was generally well tolerated. Immunization with p24-VLP did not increase p24 antibody levels and had no effect on CD4 cell counts or virus load. The failure to increase p24 antibody titers cannot entirely be explained by the subjects' immunodeficiency because most generated an antibody response to Ty, a yeast component of the immunogen.

Human immunodeficiency virus infection and other risk factors for skin abscesses and endocarditis among injection drug users

OBJECTIVE

To study incidence rates of and risk factors for skin abscesses at the site of injection and episodes of endocarditis among injection drug users (IDU).

DESIGN

A comprehensive, open cohort study of drug users on the natural history of human immunodeficiency virus (HIV) infection.

METHODS

From 1986 to 1994, injection drug users in Amsterdam were included in the study. Incidence rates of self-reported skin abscesses and verified episodes of endocarditis were calculated. In uni- and multivariate Poisson regression analysis, risk factors for skin abscesses and endocarditis were determined.

RESULTS

521 HIV-seronegative and 237 HIV-seropositive IDU were followed for 1640 person-years. A total of 545 skin abscesses were reported by 269 IDU (incidence 33/100 person-years). HIV infection, female gender, prostitution among females, foreign nationality, injection of heroin and cocaine, a high frequency of injecting, and obtaining syringes through the needle exchange program were independently and positively associated with skin abscesses. During follow-up, 17 verified episodes of endocarditis were observed (incidence 1.3/100 person-years). Endocarditis was independently associated with HIV infection and a previous history of endocarditis. Furthermore, women and IDU with a skin abscess appeared to be at an increased risk for endocarditis.

CONCLUSIONS

HIV infection is an independent risk factor for skin abscesses and endocarditis. Also, women are at an increased risk for these injection-related infections. Prevention activities, like promotion of skin cleaning, should be directed at those IDU in whom one or more risk factors have been identified.

Low T cell reactivity to combined CD3 plus CD28 stimulation is predictive for progression to AIDS: correlation with decreased CD28 expression

In 219 HIV-1-infected men of the Amsterdam cohort we measured CD4+ T cell numbers and in vitro T cell responses to CD3 MoAbs with or without CD28 costimulation and phytohaemagglutinin (PHA). The value of these markers was estimated for disease progression within 4 years. CD28 expression on T cells has been related to T cell responses. CD28 costimulation considerably enhanced T cell reactivity (approximately 8-10-fold) with lower coefficients of variation compared with reactivity to CD3 MoAb alone (median 5 versus 20). T cell reactivity to CD3 plus CD28 MoAb was decreased during HIV-1 infection and was besides CD4+ T cell numbers the only independent predictor for progression to AIDS. Compared with the group with high CD4+ T cell numbers the relative risk (RR) for the group with intermediate levels was 2.28, with low levels 5.20. In the groups with intermediate and low CD3 plus CD28 responses the RR was 2.04 and 4.16, respectively. The combined RR for both was 4.65 and 21.63. The independence of this marker was confirmed when the group with low CD4+ T cell numbers was subdivided into groups with high, intermediate and low T cell responses. The expansion of CD8+CD28- T cells was already apparent in HIV- homosexual men, but CD8+CD28+ T cells specifically decreased in patients with AIDS. CD28 expression on T cells correlated moderately with T cell responses to CD3 plus CD28 MoAb. T cell reactivity to CD3 MoAb in the presence of CD28 MoAb is a stronger prognostic marker than T cell reactivity to CD3 MoAb alone.

[HIV incidence in a cohort of homosexual men and a cohort of injecting drug users 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.

Evidence for HIV type 1 strains of U.S. intravenous drug users as founders of AIDS epidemic among intravenous drug users in northern Europe

To establish an epidemiological link between HIV-1 epidemics in U.S. and European homosexual men and intravenous drug users (IVDUs) we analyzed the HIV-1 gp120 V3 sequences in both risk groups. Signature pattern analysis revealed that the V3 sequences of viruses from IVDUs in Northern Europe are distinguishable from those of homosexual men on the basis of one amino acid and two synonymous nucleotide substitutions, which the most conserved was a synonymous nucleotide substitution in the second glycine codon at the tip of the gp120 V3 loop (GGC). This substitution was seen in 17 of 20 (85%) viruses of IVDUs in Northern Europe, in none of 41 homosexual men in either Europe or the United States, and in 5 of 11 (45%) U.S. IVDUs sequences analyzed. Subsequent phylogenetic and multivariate principal coordinate (PCOORD) analyses showed that 16 of 20 (80%) of the Northern European IVDU sequences clustered together with the 5 U.S. IVDU sequences carrying the GGC substitution and away from the sequences of homosexual men from either Europe or the United States. Taken together with the higher level of heterogeneity of U.S. IVDU sequences compared to the Dutch IVDU sequences taken at the same time, these data present suggestive evidence for a U.S. instead of a European origin of the AIDS epidemic among Northern European IVDUs.

Differences in clinical manifestations of genital chlamydial infections related to serovars

OBJECTIVES

To study the association of serovars of Chlamydia trachomatis with clinical manifestations of genital tract infection and socio-demographic characteristics.

METHODS

In 1986-88 the C trachomatis isolates from 159 heterosexual men and 116 women attending a sexually transmitted disease (STD) clinic were collected and typed accordingly. A medical history was recorded, a physical examination took place and samples were taken for laboratory diagnostics.

RESULTS

Serovars E, F and D were the most common for both men (75%) and women (67%). Men infected with serovars of the C-complex had more often a history of STD (p = 0.06). The opposite was demonstrated in women (p = 0.07). In addition, women younger than 18 years at first intercourse were more often infected with C-complex serovars (p = 0.05). For men, the serovars F/G less often produced symptoms of urethral discharge (p = 0.01) than the serovars of the B-complex and C-complex and were less often associated with the presence of 10 or more leukocytes in a Gram-stained smear (p = 0.04).

CONCLUSIONS

In this study, infections with serovars F and G caused less obvious symptoms and signs of inflammation in men; in women no differences were found in the clinical manifestation of infections with different serovars.

The impact of drug users on inpatient hospital care during the human immunodeficiency virus epidemic in Amsterdam

BACKGROUND

As a consequence of the human immunodeficiency virus (HIV) epidemic, which continues among illicit drug users, high rates of HIV-associated morbidity are believed to exist. This study focuses on hospitalizations of drug users and on the relative contribution of drug users to the total burden of inpatient hospital care in Amsterdam.

METHODS

During the years 1990-1992, data were collected on hospital admissions of injecting and non-injecting drug users to all 10 general and university hospitals in the city of Amsterdam (population 700 000; estimated number of drug users 5800). Total number of admissions, total days of hospitalization and primary discharge diagnoses according to HIV serostatus and sex were determined for drug users.

RESULTS

A total of 1293 admissions were recorded among 842 hospitalized drug users. Between 53% and 77% of days of hospitalization attributable to drug users related to HIV-infected patients, and at least 23% to patients with AIDS. In the 20-44 age group of the Amsterdam population, 5.1% of days of hospitalization for men and 1.8% for women could be attributed to drug users, or about twice as much as could be expected from their numbers alone. For all ages, the contribution of drug users to hospitalizations was 1.2% for males, 0.4% for females, and 0.8% for all. Drug users occupied an average of 19 hospital beds, corresponding to an annual cost of US$ 3.1 million. Due to underreporting of admissions, these figures should be considered lower bound estimates.

CONCLUSIONS

On the total scale of inpatient hospital expenditure in Amsterdam, the contribution of illicit drug users appears to be small.

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.