An outbreak of pulmonary tuberculosis probably due to exogenous reinfection at a nursing home for the elderly

: In Japan and other countries where tuberculosis is not so common, people who were once infected with tuberculosis are thought to rarely suffer from the disease again due to exogenous reinfection. We experienced a mass outbreak of tuberculosis with 27 patients (including the source of infection) at a nursing home for the elderly. Epidemiological investigation suggested that the source of infection was an 82-year-old woman resident. For about 2 years before this outbreak, she had complained of a productive cough. At the time of the diagnosis of tuberculosis, chest radiography revealed a cavitary lesion and a smear of her sputum revealed organisms rated as Gaffky No. 8. Sputum culture was also positive (++++). Of the 27 patients, 19 (including the source) underwent restriction fragment length polymorphism (RFLP) analysis of isolates from the sputum. Eighteen patients showed an identical RFLP pattern, indicating that the infection had arisen from one source. Out of all patients, the source case of infection, 9 others with the same RFLP pattern, and other 3 who did not undergo RFLP analysis were admitted to our hospital. In 12 patients (3 men and 9 women excluding the source case) aged 80.6 years (range: 67-89 years), chest radiography disclosed tuberculous lesions, and smears, the polymerase chain reaction, and culture of sputum demonstrated Mycobacterium tuberculosis. As the prevalence of tuberculosis infection in Japanese aged 80 years at the time of the mass outbreak (1995) was presumed to be about 80%, the disease seemed to be caused by exogenous reinfection in most of these patients. All of the patients had senile dementia and other complications, and they were bedridden and undernourished. Anemia, hypoalbuminemia and lymphocytopenia were also observed in most of the cases. Malnutrition due to these complications appeared to be a possible risk factor of tuberculosis caused by exogenous reinfection.