This study provides further support that the risk for PCP decreases dramatically with the rebound in CD4 counts that have been evidenced with institution of HAART. These data were analyzed from a multi-site, longitudinal database of over 43,000 HIV infected patients from the period from 1990-1998. Two subgroups were selected for analysis. Group 1 (N=626) included individuals whose baseline CD4 count was < 200 cells/µL, and who experienced a >100 cell increase in CD4 after antiretroviral therapy, with a subsequent CD4 lymphocyte count > 200 cells/µL. Group 2 (N=3497) had also been initiated on antiretroviral therapy, but had never had a CD4 count < cells/µL. No individual in either group had previously had PCP and follow-up time was calculated for individuals not prescribed prophylaxis for PCP.
Characteristics for Groups 1 and 2, respectively are as follows: CD4 count (332 vs. 409); CD4 nadir (151 vs. 350); CD4 increase (184 vs. N/A); on combination antiretroviral therapy (53% vs. 26%); and being on a protease inhibitor (24% vs. 6%). The risk for PCP was low for all groups evaluated; for Group 1 it was 0.8 cases of PCP/100 person-year at risk vs. 0.7 cases of PCP/100 person-year at risk for Group 2. These rates of PCP were calculated for the 3 cases of PCP over the 471 person-years of observation in Group 1 and 32 cases of PCP in the 4200 years of observation among individuals in Group 2. The CD4 nadir among the individuals in Group 1, particularly for those whose CD4 nadir was < 25 cells/µL. For this sub-group, there was one case of PCP in 23 person years of observation (4.4 cases/100 p-yrs), compared to 2 cases of PCP in 448 years of observation (0.5 cases/ 100 p-yrs) among individuals whose nadir CD4 ranged from 25 to 200 cells/µL. Though this did not achieve statistical significance, had the observation period been longer for the patients with the most advanced disease, significance may have been achieved, suggesting for this group of patients, continuing PCP prophylaxis may be warranted until further data are available.