The conceptual relationship between the frequency and spectrum of lung diseases and CD4+ lymphocyte count is shown in Figure 412-1. The data that support this concept have been derived from a large, national, multicenter investigation, The Pulmonary Complications of HIV Infection Study (PCHIS). The cohort that formed the basis for this study generally mirrored the characteristics of the known HIV-infected persons in the United States (that is, reported AIDS cases), had a broad range of severity of immune compromise (47% of the cohort had CD4+ lymphocyte counts > 400 cells per microliter at the time of enrollment), and were followed for a median of 53 months.

Table 412-1 shows the diseases and their rates per 100 person-years of observation in the PCHIS. Because an HIV-negative control group made up of subjects from the two largest HIV transmission categories (homosexual/bisexual men and injecting drug users [IDUs]) was included, it was demonstrated that acute bronchitis, a disorder not usually regarded as opportunistic, is significantly more common among HIV-infected persons.

It should be noted that because there were no study centers in areas in which histoplasmosis and coccidioidomycosis are endemic, there were few instances of these relatively common fungal infections of the lung noted in the cohort. This observation raises an important point: the spectrum of HIV-associated lung diseases varies with geographic location as well as with severity of immune compromise and the demographic (including transmission category) make-up of the HIV-infected population in any given medical center or geographic area.