Incidence of the acquired immunodeficiency syndrome in San Francisco, 1980-1983.

Incidence data for the acquired immunodeficiency syndrome (AIDS) are presented on the basis of a surveillance file maintained by the San Francisco Bureau of Communicable Disease Control. The incidence of AIDS among residents of San Francisco rose steadily from the first case diagnosed in the last quarter of 1980 through the last quarter of 1983. New cases were diagnosed at a rate of 25 per month in the last quarter of 1983. Reported incidence declined in mid-1983, but the decline was probably a case-finding artifact. Smoothed incidence rates show a steady progressive rise, which is approximated equally well by quadratic or exponential curves. Among the patients diagnosed in San Francisco, 99% were homosexual or bisexual men. The cumulative incidence rate among homosexual or bisexual men was estimated to be 770 per 100,000 in the last quarter of 1983. The incidence rate of AIDS increased with age, and the increase was greater than that found with other sexually transmitted diseases. The difference in the age distributions between cases of AIDS and syphilis suggests either that susceptibility to AIDS increases with age or that the average latency associated with AIDS is longer than previously thought.