Researchers first described Mycobacterium xenopi in 1959 after isolating it from skin lesions of the South African toad Xenopus laevis.M xenopi, a slow-growing, nontuberculous mycobacterium, is often considered to be a saprophyte or an environmental contaminant. It grows optimally at 45°C (113°F) and has been found, occasionally in large numbers, in hospital hot water supplies at the outlet valves of water heaters. [1, 2] M xenopi colonization occurs from ingestion or inhalation of, or cutaneous exposure to, organisms in water, soil, or airborne particles. Colonization of hospital water systems is associated with infection, disease, and nosocomial isolation.
M xenopi has low pathogenicity, and host impairment is required to contract disease from the organism. Most M xenopi infections occur in the lungs, usually in patients with preexisting lung disease or with predisposing conditions (eg, extrapulmonary malignancy, alcoholism, diabetes mellitus, HIV infection). Extrapulmonary and disseminated disease may develop in patients with AIDS or other immunodeficiencies.
For pulmonary disease, inhalation of infected airborne particles is the usual route of infection. For skin and soft tissue infections, direct contact through penetrating injuries and surgical procedures provide the route. Person-to-person transmission of nontuberculous mycobacterial disease has never been documented.
Surveillance data for M xenopi infection are not available because such infection is not a reportable disease. More than 500 cases have been reported, but only approximately 70 cases seem to document true disease.
Prevalence is unknown.
Subjects with documented M xenopi infections are divided into the following broad categories:
The first group comprises young, severely immunocompromised individuals in whom M xenopi infection occurs as an opportunistic infection that may then become disseminated, conferring a high risk of mortality and morbidity. Persons with CD4+ cell counts of less than 50/µL are susceptible hosts for pathogens such as M xenopi. M xenopi can cause 2 patterns of disease in these patients: localized pulmonary disease that can mimic tuberculosis in persons with early-stage HIV infection and disseminated disease in those with advanced AIDS.
The second group comprises immunocompetent adults with chronic lung disease or chronic obstructive pulmonary disease (COPD) in whom M xenopi infection usually follows a long-term, indolent course.
No racial predilection has been identified.
No predilection for either sex has been demonstrated.
No age predilection has been reported.
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