Hey, MAC! Get Out of the Tub!
ABSTRACT & COMMENTARY
Synopsis: Hot tub water was identified as the apparent source of MAC infection of the lungs of an otherwise normal young woman.
Source: Kahana LM, et al. Mycobacterium avium complex infection in an immunocompetent young adult related to hot tub exposure. Chest 1997;111:242-235.
Kahana and colleagues report the case of a previously healthy, non-smoking 20-year-old woman who developed a spasmodic cough and breathlessness on exertion, but no fever. Chest X-ray revealed a finely nodular pattern involving the mid and lower zones, and high resolution computerized tomography demonstrated a ground-glass appearance without lymphadenopathy. Lingular biopsy revealed granulomas and acid-fast bacilli; culture grew an organism of the Mycobacterium avium complex (MAC). The infection resolved completely after administration of a clarithromycin-based multidrug regimen. There was no evidence of relapse 11 months after completion of therapy.
Immunological analysis two months after the start of antimycobacterial therapy revealed that she had normal numbers of B cells as well as of CD4+ and CD8+ T lymphocytes, and a normal in vitro response to phytohemagglutinin. She demonstrated dermal delayed hypersensitivity to tetanus, diphtheria, and mumps antigens but not to PPD.
The patient had frequently used a hot tub in her apartment, and MAC was isolated from water in the tub. The MAC isolates from the patient and the hot tub had identical enzyme profiles by multilocus enzyme electrophoresis, as well as a high degree of relatedness of their insertion sequences IS1245 by restriction fragment length polymorphisms (RFLP) analysis.
COMMENTBYSTANDERESINSKI, MD, FACP
This young patient developed widespread pulmonary infection with MAC in the absence of a demonstrated gross immune abnormality or underlying lung disease. It is possible, however, that she suffered from a more subtle and/or a specific immune deficit, as has been described (e.g., in a family, a number of members of which have suffered from disseminated MAC). The absence of relapse 11 months after completion of therapy argues against severe immuno-incompetence, however.
MAC confined to the lungs occurs with some frequency in two groups of patients without apparent underlying systemic immunodeficiency: elderly subjects, mostly male, with underlying chronic pulmonary disease, and elderly females without underlying lung disease (Iseman MD. N Engl J Med 1989;321:896-899; Prince DS, et al. N Engl J Med 1989;321:863-868). This patient failed to fit either category.
MAC is ubiquitous within the environment and has been recovered from animals, sediments, dust, soil, water, and natural water aerosols. MAC has been isolated from 28% of environmental water samples and from 20% of water supply samples in the United States, Finland, Congo, and Kenya. MAC has been isolated from potable water supplies in Los Angeles reservoirs, homes, and hospitals MAC in hospital water has been identified as the apparent source of infection in a group of AIDS patients (von Reyn CF, et al. Lancet 1994;343:1137-1141). The evidence that hot tub water was the source of infection in this patient is strong but not indisputable. The absence of examination of control strains weakens the argument. Nonetheless, it is reasonable to believe that hot tub water may have been the source of pulmonary infection in this young woman. Thus, another hazard has been added to hot tubbing. It’s getting harder and harder to be a Californian!
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