Relationship of respiratory tract diseases to CD4+ Lymphocyte count, Demographic Characteristics, and Transmission Category

PCP is the most common lung disease in persons with CD4+ counts < 200 cells per microliter. However, in the PCHIS, 11 (6%) cases of PCP occurred in persons with CD4+ lymphocyte counts > 200 cells per microliter. The patients with higher counts were marked by having other HIV-associated symptoms or findings such as fever, unintentional weight loss, oral thrush, and lymphadenopathy. Other lung diseases that usually occur only in persons with advanced HIV infection include fungal infections, pulmonary Kaposi’s sarcoma (KS), lymphoma, and nontuberculous mycobacterial infections. In the case of Mycobacterium avium complex, it is difficult to determine if the organism is actually causing lung disease or is simply colonizing the airways. Thus, the frequency of M. avium complex lung disease is difficult to establish. The same difficulty applies to determining the frequency of cytomegalovirus (CMV) pulmonary disease.

It is not yet known if the increase in CD4+ count that occurs with combination antiretroviral therapy is associated with a reduction in risk of opportunistic infections or a change in their relative frequency.

Both demographic characteristics and HIV transmission category bear some relationship to the frequency of various lung diseases. Bacterial pneumonia tends to be more common among IDUs (with or without HIV infection) than in the other HIV transmission categories. Presumably, this relates, at least in part, to the effects of opiates on ventilation, cough, and ability to protect the airway. Tuberculosis is also more common in IDUs. Injection drug use had been shown to be a risk factor for tuberculosis prior to the HIV epidemic, so the finding of an increased amount of tuberculosis among drug users with HIV infection is not surprising.

Data from the PCHIS have shown that whites have a higher rate of PCP than blacks. Although the basis for this is unknown, the finding is consistent with the observation that PCP is rare in Africa. It has generally been assumed that the rarity of P. carinii in Africa is related to the organism being less common in the environment. However, the finding of a racial difference in risk suggests that genetic factors may play a role in predisposing whites to or protecting blacks from the disease.