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.