A Steady Increase in Nontuberculous Mycobacteriosis Mortality and Estimated Prevalence in Japan

Abstract

Rationale: Pulmonary disease caused by nontuberculous mycobacteria is generally reported to have a good prognosis. However, the actual mortality rate over time has not been reported in a large-scale survey. Objectives: To determine the annual trend in mortality from nontuberculous mycobacteriosis, based on nearly four decades of patient data, and to estimate the prevalence of these cases in 2005. Methods: The annual mortality rate and regional distribution of nontuberculous mycobacteriosis–related deaths in Japan were obtained from Vital Statistics of Japan, which is published annually. The crude and age-adjusted mortality rates and associated regional differences were calculated from the Japanese census data. A 5-year follow-up study including 309 patients with pulmonary nontuberculous mycobacteriosis who visited and registered at our institute from 2004 to 2006 was conducted to determine the 5-year prognosis and the annual mortality rate. Measurements and Main Results: The crude mortality rates for both sexes have increased since 1970, and the mortality rate from pulmonary disease was greater in women after 2005. The age-adjusted rates of disease also showed a gradual increase until 2010 in women. Geographically, higher standardized mortality ratios were observed in middle and western Japan, particularly in the southern coastal regions along the Pacific Ocean. In a clinical follow-up study, the mortality rate was approximately 1–2% annually. The prevalence of pulmonary nontuberculous mycobacteriosis was estimated to be 6- to 10-fold higher than the annual incidence. Conclusions: There was a constant and steady increase of nontuberculous mycobacteriosis–related mortality in Japan, and this mortality rate showed significant geographical variation. The prevalence of environmental mycobacterial disease in Japan is higher than reported in most other countries.