Increasing frequency of pulmonary nontuberculous mycobacteria (pNTM), and accumulation of the patients, observed in a city hospital in Tokyo

Introduction: There are many papers reporting that the prevalence of pNTM is increasing especially in developed countries including Japan. However, there were few articles that discuss yearly accumulation of the patients. We planed to elucidate the frequency of NTM isolation and also the accumulation of pNTM patients in a center hospital of mycobacteriosis in Tokyo area. Methods: Initially, we reviewed all kinds of pulmonary mycobacteria isolation from January 2004 to December 2009, based upon the laboratory database with clinical chart. When multiple isolates were detected, species identification was performed for one species per patient per year. Next, we investigated, on the 2009 patients, the initial year of MAC diagnosis during the past 20 years.Thirdly, we followed the course of 2004 MAC patients up to 2009, speculating the yearly accumulation of the disease. Results: From laboratory data, the yearly number of all NTM isolation increased from 353 in 2004 to 488 in 2009 (mean annual increase,5.9%), and of MAC from 291 to 418 (increase,6.8%). Proportion of MAC to all NTM showed a constant value of 81.4%, indicating that increase was due to an increase of MAC. From clinical data, many of MAC patients in 2009 had an initial diagnosis of MAC during the period from 1978 to 2008. Follow up analysis on the cases found in 2004 and having yearly bacteriological examination, showed over half of the positive MAC patients in 2004, were still culture positive in 2009. MAC- related death was observed on 8 cases among the total 99 cases in 2004. Conclusion: An accumulation of MAC patients in recent years was likely to occur in Tokyo, Japan.