Emerging significance of Mycobacterium avium-complex infection in an inner-city hospital

This study ascertains the incidence, trends, and clinical significance of acid-fast bacilli (AFB) isolates at Bridgeport Hospital from January 1, 1995 through September 30, 1999. One hundred twenty-two isolates of nine different types of mycobacteria and nocardia were cultured from 117 patients. About 30% were HIV-positive, 34% were HIV-negative, and the HIV status of 36% was unknown. The predominant isolates were Mycobacterium avium-complex (MAC) (60%) and Mycobacterium tuberculosis (Mtb) (21.3%). Pulmonary sources accounted for 74% of the isolates. The incidence of Mtb remained stable at 2.6-4.1 cases/100,000 total patient discharges/year. In contrast the incidence of MAC soared from a baseline rate of 1.6/100,000 total patient discharges/year in 1995/96 to 19.5/100,000 total patient discharges/year in 1999. The increase was consistent across pulmonary and nonpulmonary sources, HIV status, and across disease likelihood. Seventy-three percent of MAC isolates were associated with definite or probable disease. Physicians need to consider the increased MAC incidence in the choice of empiric therapy for AFB-positive patients.