Objective: To determine whether the incidence of Pneumocystis carinii pneumonia (PCP) as the initial AIDS-defining disease in adult AIDS cases in the United Kingdom is changing over time and to examine factors likely to affect it.
Subjects and methods: A total of 4419 adult AIDS cases diagnosed in the United Kingdom between January 1989 and December 1992 were analysed using logistic regression models. An initial diagnosis of PCP was used as the outcome variable and the possible effects of age, sex, exposure category, ethnic group, half year of diagnosis, geographical area of report, and whether or not the individuals had been aware of their HIV infection when AIDS was diagnosed was examined.
Results: A significant decline in PCP incidence was observed over time. Incidence of PCP declined among subjects who had been aware of their infection for 9 months or more before AIDS diagnosis. There was no evidence of a change in PCP incidence over time for subjects who had had HIV infection diagnosed 3 or less months before an AIDS diagnosis. Individuals who had been aware of their HIV infection, individuals reported from the Thames health regions, and non-white patients were much less likely to have had a diagnosis of PCP.
Conclusions: The decline of PCP incidence in subjects aware of their serostatus, and therefore more likely to have received primary prophylaxis, suggests that they may have benefited from this treatment. Our findings provide evidence of the value of an early HIV diagnosis and confirmation of the beneficial effects of primary prophylaxis for PCP.