Pulmonary Infection and Colonization with Nontuberculous Mycobacteria, Taiwan, 2000–2012

We analyzed samples from 13,652 patients who had respiratory cultures positive for mycobacteria in Taiwan during 2000–2012 and found that 56.9% were positive for nontuberculous mycobacteria (NTM). Whereas annual prevalence of tuberculosis decreased during the study period, prevalence of NTM disease and colonization increased, particularly among older patients and male patients.

patients >45 years of age who had NTM infection or colonization than among patients in the same age group who had M. tuberculosis infection (p<0.01; online Technical Appendix Table).
Infections caused by MAC, M. abscessus, and M. chelonae were more common in female than in male patients. In contrast, diseases caused by M. fortuitum and M. kansasii were more common in male patients than in female patients. We also found that the prevalence of infection  (Table 2).

Conclusions
Our cross-sectional analysis of data from mycobacterial isolates collected over 13 years in northern Taiwan resulted in several notable findings. First, the prevalence of NTM pulmonary infection and colonization significantly increased during the period, whereas prevalence of M. tuberculosis infection significantly decreased. This phenomenon has been reported previously in Taiwan (8) and in other countries (9,10). We also found that the annual prevalence of NTM pulmonary infections and colonization significantly increased (p<0.01). The increasing trend in NTM infections has also been noted in South Korea, Canada, Denmark, Australia, the United States, and the Netherlands (9-15). These findings suggest that, although the rates of NTM pulmonary infection have gradually increased in Taiwan, more than half of NTM isolates caused colonization only.
Second, we found the frequency of isolation of M. tuberculosis and NTM from patients >85 years of age was 40.7% and 59.3%, respectively. Furthermore, half of NTM infections (54.1%) and colonizations (55.5%) occurred in patients >65 years of age. Our findings are consistent with those in a recent study conducted in South Korea (7) and  suggest that most cases of NTM infection occur in patients of advanced age and that its associated clinical significance may be as important as TB among elderly patients.
Third, we found that gender may be associated with the acquisition of diseases caused by mycobacterial species. We found that M. tuberculosis infection, NTM pulmonary infection, and NTM colonization were more common among men than among women (70.1% vs. 29.3% for TB, 57.6% vs. 42.4% for NTM infections, and 59.6% vs. 40.4% for NTM colonization). In addition, the male:female ratio among patients >45 years of age was significantly higher among patients with TB than among patients with NTM infections or colonization. This finding might indicate that older women are more resistant to TB than to NTM infection/colonization. This study has several limitations. First, because the study was conducted in a single medical center in Taiwan, we cannot safely generalize our findings to other parts of Taiwan. However, this hospital is the only medical center that can fully identify the species of NTM in Taiwan, which suggests that our results still provide useful information about the current status in this country. Second, we did not evaluate the effects of co-existing conditions such as HIV infection. Third, the American Thoracic Society/ Infections Disease Society of America diagnostic criteria for NTM infections were determined on the basis of experience with MAC, M. kansasii, and M. abscessus but not for other NTM species (1). Therefore, we might have overestimated the incidence of lung infections caused by other NTM species (e.g., M. gordonae and M. fortuitum). These   species need further investigation. Fourth, in this retrospective analysis, we did not try to identify factors associated with the changing epidemiology of these diseases. In summary, in Taiwan, the rate of NTM isolation among cultures positive for mycobacteria increased significantly during the period 2000-2012, whereas the rate of M. tuberculosis isolation decreased. Moreover, the prevalence of NTM pulmonary infection and colonization rapidly increased with time. This phenomenon was more evident among patients of advanced age and among male patients.
Dr Chien is an attending physician at Chest Hospital, Ministry of Health and Welfare, Taiwan. His primary research interest is clinical infectious disease, especially tuberculosis, and diseases caused by NTM.