Fewer data are available concerning time from a CD4

Fewer data are available concerning time from a CD4 lymphocyte count of 200/µl to death. An analysis of time from a CD4 lymphocyte count of 200/µl to death among two cohorts of homosexual men in San Francisco found the median survival time was 38 months and had increased about 12 months over the median time in the period from 1983 to 1986.(24) Comparable estimates were reported from the Multicenter AIDS Cohort Study; 53% of subjects with a CD4 count in the range 101 to 200 cells/µl survived 30 months in the period from 1985 to 1988 and 71% in the period from 1989 to 1993.(29)

Median survival times reported from clinical trials have been 6 to 18 months longer than the times cited here from cohort studies of HIV-infected persons and from AIDS case registries. Clinical trial participants usually have to meet inclusion criteria that may tend to result in a healthier population than other HIV-infected persons with comparable CD4 lymphocyte counts, and trials necessarily do not include persons who may avoid treatment or may not even be aware of their HIV infection.

In 1996, combination antiretroviral therapy that includes use of a protease inhibitor was widely adopted. From 1996 to 1997, the percentage of HIV-infected persons receiving this therapy increased rapidly. The use of the new combination therapy is having a significant effect in lengthening survival time. The size of this latest treatment effect on survival is still uncertain, but surveillance data showing rapidly declining death rates suggest the short-term effect is dramatic (see Epidemiology of HIV/AIDS in the United States). More direct evidence of longer AIDS survival associated with use of combination antiretroviral therapy is emerging from longitudinal studies. In the Multicenter AIDS Cohort Study, the estimated median time from seroconversion to death for a person infected at age 30 was associated with use of combined therapy and increased nearly 2 years from the 1993 to 1995 period to the 1995 to 1997 period (11.4 years versus 13.3 years).(33) In Ontario province, Canada, where health care access is universal and all treatment is government subsidized, median survival time increased from 19 to 30 months among all AIDS patients over age 35 years with a CD4 lymphocyte count of less than 100 cells/µl and receiving antiretroviral therapy.(34) These early estimates of the impact of the new treatments include individuals diagnosed before they were available and individuals who had previously been treated with monotherapy and were therefore less likely to obtain the full benefit of combination therapy. Although it is still too early for more definitive quantitative estimates of the changes in AIDS survival time, they appear to be significantly greater than the previous increase from the early pre-antiviral treatment era of the epidemic.