Infections caused by Mycobacterium avium complex in immunocompromised patients: diagnosis by blood culture and fecal examination, antimicrobial susceptibility tests, and morphological and seroagglutination characteristics.

The Mycobacterium avium complex, only rarely described as an invasive pathogen in humans, has recently been reported to frequently cause disseminated disease in patients with the acquired immune deficiency syndrome. Between February 1981 and February 1984 at Memorial Sloan-Kettering Cancer Center, 30 patients with acquired immune deficiency syndrome, 3 patients with leukemia, and 2 patients with congenital severe combined immunodeficiency syndrome developed disseminated M. avium complex infection. Mycobacteria were often found in multiple sites both antemortem and postmortem. Blood cultures were a reliable method for detecting disseminated infection, and the new lysis blood culture systems provided an efficient technique for determining the number of organisms per milliliter of blood. Acid-fast stains and cultures of fecal specimens were also helpful in diagnosing infection. Most of the mycobacteria were serovar 4 (77%), and most (86%) produced a deep yellow pigment. All isolates were susceptible to standard concentrations of clofazimine, cycloserine, and ansamycin, but tended to be resistant to isoniazid, streptomycin, ethambutol, ethionamide, and rifampin.