In Brazil, molecular studies have shown that the predominant HIV subtype is B-Br, a subtype B variant.1,2 The HIV-1 epidemic has been well described, with a rapidly expanding epidemic among men who have sex with men. In Rio de Janeiro, 86% of reported AIDS cases in 1997 were among men, and more than two thirds of these men reported sex with other men as their main risk factor.3 To better understand the natural history of HIV-1 disease and plan for health care, reliable estimates of HIV disease progression and survival are essential. Plasma viral load and CD4 counts have been shown to be robust predictors of disease progression and clinical outcome. Magnitude of HIV viral load within 6 months after infection is highly predictive of disease progression.4 In addition, higher viral load has been strongly associated with increased sexual and perinatal transmission.5 Moreover, viral load is increasingly considered to be a surrogate endpoint in trials evaluating vaccines that might only modulate HIV infection, as most candidate vaccines presently being evaluated are unlikely to prevent acquisition of HIV infection in all recipients.6
Most of the available information on early HIV-1 infection comes from studies of persons infected with subtype B in North America and Europe.7,8 Less is known about the natural history of HIV infection in developing countries, where most infections occur.9 It is important to understand within the context of treatment and secondary prevention whether disease progression is likely to differ in populations around the globe. The objectives of this study were to describe the virologic and immunologic events following seroconversion among homosexual and bisexual men in Rio de Janeiro and to compare the viral load and CD4 counts with those of persons recently infected in other parts of the world.
The subjects in this study were seroconverters from 2 cohorts. The first cohort study-enrolled from July 1995 to June 1998-assessed willingness to participate in vaccine trials and enrolled 815 high-risk, HIV-seronegative homosexual and bisexual men, aged 18 to 50 years, who did not report injection drug use.3 The second cohort, enrolled from December 1998 to May 2001, involved 200 high-risk HIV-seronegative homosexual and bisexual men, former participants from the first cohort, aged 18-35 years, who were willing to participate in a postexposure prophylaxis study using antiretroviral therapy.10 These studies were approved by the institutional review board of the Universidade Federal do Rio de Janeiro and all subjects gave written informed consent.
Participants in both cohorts from which seroconverters for the present study were identified had a minimum of one laboratory evaluation every 6 months. At baseline, all participants were seronegative by HIV enzyme-linked immunosorbent assay (ELISA); seroincident HIV infection was defined as positive ELISA and Western blot at a follow-up visit. The estimated date of seroconversion was the midpoint between the last negative and the first positive serology. Unless noted, all time points in the present article refer to time after estimated date of seroconversion. HIV-1 viral load was quantified using Nuclisens (Organon, Roseland, NJ). The lower limit of viral detection is 80 copies/mL. Laboratory tests were performed using commercial kits according to the manufacturer's instructions.
Summary curves for the evolution of viral load and CD4 cell counts over time were computed using the estimated date of seroconversion and were obtained by least squares estimates of the coefficients of a restricted cubic spline function after adjusting for subject effects through the use of subject dummy variables. The fit is bootstrapped 500 times, by treating time and subject ID as random variables. Using this approach, samples are taken jointly from the time, subject ID, and response vectors to obtain unconditional distributions and simultaneous confidence sets for the set of coefficients of the spline function and the average intercept parameter (over subjects). This method is implemented as function rm.boot11 available in the R package Hmisc.12
HIV incidence documented in the 2 cohorts was 3.1 (95% CI: 2.1 to 3.1) and 2.9 (95% CI: 1.4 to 5.1), respectively. A total of 44 seroconverters were identified. Of these, 5 had no follow-up data and were excluded from further analysis. The analysis presented is based on the remaining 39 participants who were all male, with a median age at enrollment of 28.5 years (range 19-47 years). Thirty-six (92%) had at least 6 years of formal education; 19 (48%) reported to have engaged in unprotected receptive anal sex and 29 (74%) reported a history of sexually transmitted diseases before seroconversion.
The mean number of observations per individual after infection was documented was 4.9 (median 4, range 1-16); the mean follow-up time after estimated date of seroconversion was 423 days (median 301, range 99-1098). All patients included in this study remained antiretroviral drug naive during the follow-up. Two patients initiated antiretroviral therapy during follow-up and were subsequently censored at therapy initiation. No HIV-1 RNA viral load or CD4 count measurement after initiation of therapy was included in the analysis.
HIV-RNA viral load I at first positive serology is defined as the viral load result obtained within 6 months of the documented infection. This data was available for only 31 participants. CD4 cell counts, defined in a similar way, were available for 32 patients. All measurements in this analysis were done counting time since the estimated date of seroconversion, defined as the midpoint between the date of the last seronegative serology and first date of positive serology. As shown in Table 1, only 21 patients had viral load measurements <6 months after seroconversion and 20 patients had CD4 cell counts <6 months after seroconversion. For the modeled viral load, mean and median values were 24,480 (4.36 log10) and 19,720 (4.29 log10) copies/mL (range 14,880-58,090), respectively. Median CD4 count was 373 cells/μL (range 260-508). CD4 count was >500 cells/μL for 8% of study participants and <200 cells/μL for 11% at first measurement within 6 months of estimated date of seroconversion.
Figure 1 shows these fitted results over time. The viral loads were 4.41 log10 copies/mL at 200 days (95% CI: 3.97 to 4.77) and 4.63 log10 copies/mL at 1000 days (95% CI: 4.16 to 5.59). Overall variation on viral load ranged from 4.3 to 5.2 log10 copies/mL with a visible increase in the viral load starting at approximately 600 days after estimated date of seroconversion. The initial period of HIV infection was characterized by an increase in CD4 count followed by a steep decline starting at approximately 200 days (508 cells, 95% CI: 425 to 569) after estimated date of seroconversion. A gradual decrease was observed in the median CD4 count starting thereafter, reaching 281 (95% CI: 100 to 466) at 1000 days after the estimated date of seroconversion.
During the first 36 months of follow-up, viral load measurements estimated in our study seemed to be lower than that of the Multicenter AIDS Cohort Study (MACS) at comparable time points (Table 1).7 However, the interquartile ranges from our study and those of the MACS are overlapping. Also the interquartile ranges in our cohort are narrower around the median compared with those of the MACS at comparable time points. There was an apparent trend towards lower CD4 counts in our study compared with the MACS at comparable time points (Table 1). However, because raw data from the MACS cohort were unavailable, statistical comparisons were not performed.
This study examined virologic and immunologic dynamics among high-risk homosexual and bisexual men in Brazil after HIV-1 infection. We analyzed variation in HIV RNA viral load and CD4 count cell counts after seroconversion for a period of approximately 36 months. Viral load remained stable for 600 days after estimated date of seroconversion, and CD4 counts were characterized by an initial rebound followed by a gradual decline, consistent with findings of previous studies of seroconverters.7
An unusual finding was the HIV RNA viral load in the serum samples shortly after seroconversion, which was relatively low in comparison with reports from cohort studies of untreated participants in developed countries. This difference may be due to the fairly small sample size in our study. This finding is not unprecedented; for example, Rinke de Wit et al13 found that shortly after seroconversion viral load was lower in Ethiopian subjects than in Dutch subjects at comparable time points, 4.07 and 4.72 log10 copies/mL, respectively.
In general, however, most reports from developing countries describe high initial viral load levels among seroconverters. Rangsin et al14 found a higher median HIV-1 RNA levels after seroconversion in young Thais compared with seroconverters from the MACS cohort. Similarly, Mehendale et al15 found a trajectory of increasing viral load in seroconverters in India greater than that of seroconverters in the United States. These reports raise the possibility that initial viral load measurements after HIV infection may differ by subtype. Supporting this hypothesis is the report of slower progression of HIV disease in Brazilian patients infected with HIV-1 serotype B-Br as compared with patients infected with serotype B. (B and B-Br are the predominant serotypes in Brazil.)2 Another report indicated slower disease progression among sex workers in Senegal who were infected with HIV-1 subtype A, compared with those infected with other subtypes.16 Hu et al17 found that viral load in the first 6 months in seroconverters in Thailand who were infected with subtype E was higher than in those infected with subtype B, but this difference decreased over time. In summary, these studies suggest the magnitude of viral load may differ in persons infected with different HIV subtypes and the rate of disease progression. This may be of relevance for vaccine studies that evaluate the effects of HIV vaccines on disease progression and/or laboratory endpoints; such studies will be further complicated if there are differences in HIV disease course in different locales.
We found that the absolute CD4+ cell counts for Brazilian seroconverters were lower than those reported from the MACS cohort at comparable time points. The majority of seroconverters in our study had CD4 counts between 200 and 500 cells/μL. Rinke de Wit et al found lower CD4 counts in Ethiopian patients compared with Dutch seroconverters.13 The same observations were reported in patients in Thailand and Côte d'Ivoire when compared with patients from developed countries.17,18 Lower CD4 counts may be a factor contributing to enhancement of disease progression, although recent reports from Zambia and Tanzania highlighted slow disease progression in individuals with low CD4 counts.19,20
Major limitations of this study include relatively infrequent laboratory assessments and, therefore, limited documentation of the early events that occurred immediately after infection. The relatively short follow-up time (36 months) is another limitation. After longer follow-up, further analyses of disease progression and survival data are planned.
In summary, these data on the natural history of HIV infection in Brazilian subjects can serve as a useful indicator in the evaluation of interventions such as HIV vaccines and antiretroviral therapy. Consideration of expected viral load trajectories in various settings should be included in the design of trials that involve sites in multiple countries because country- or population-specific differences in disease course will affect time to initiation of therapy or apparent vaccine efficacy. More complete data are needed to characterize clinical and biological evolution of HIV infection. This information will be useful in assessing the impact of additional interventions (such as new drugs) and the way in which prior HIV preventive vaccinations may affect clinical course in those who subsequently seroconvert.
The authors thank study participants and the Praça Onze study team. We also thank Erik Schwab for editorial assistance.
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