Prevalence and Species Spectrum of Pulmonary Nontuberculous Mycobacteria Isolates at a Tertiary Care Center

A Two-Step Real-Time PCR Method To Identify Mycobacterium tuberculosis Infections and Six Dominant Nontuberculous Mycobacterial Infections from Clinical Specimens

Tuberculosis (TB) is an ongoing threat to public health, and furthermore, the incidence of infections by nontuberculous mycobacteria (NTM), whose symptoms are not distinguishable from TB, is increasing globally, thus indicating a need for accurate diagnostics for patients with suspected mycobacterial infections. Such diagnostic strategies need to include two steps, (i) detecting the mycobacterial infections and, if the case is an NTM infection, (ii) identifying the causative NTM pathogen. To eliminate a false-positive TB diagnosis for a host vaccinated by the bacillus Calmette-Guérin (BCG) strain of Mycobacterium bovis, a new target specific for M. tuberculosis species was selected, together with the species-specific targets for the six dominant NTM species of clinical importance, i.e., M. intracellulare, M. avium, M. kansasii, M. massiliense, M. abscessus, and M. fortuitum. Using sets of primers and probes, a two-step real-time multiplex PCR method was designed. The diagnostic performance was assessed by using a total of 1,772 clinical specimens from patients with suspected TB or NTM infection. A total of 69.4% of M. tuberculosis and 28.8% of NTM infections were positive for the primary step of the real-time PCR corresponding to the culture within 10 weeks, and mycobacterial species of 75.5% of the NTM-positive cases were identified by the secondary step. The two-step method described herein presented promising results and similar diagnostic sensitivity and specificity to commercially available real-time PCR kits for detecting TB and NTM infections. The method also enabled the identification of mycobacterial species in three-quarters of NTM infection cases, thus providing a better treatment strategy. IMPORTANCE Tuberculosis (TB) is an ongoing threat to public health. In addition, infection by nontuberculous mycobacteria (NTM) is a nonnegligible issue for global public health, with increasing incidences. Since the antimicrobial treatment strategy needs to be differed by the causative pathogen, a rapid and accurate diagnostic method is necessary. In this study, we developed a two-step molecular diagnostic method using clinical specimens of TB and NTM infection-suspected patients. The diagnostic power of the new method using the novel target was similar to the widely used TB detection kit, and, among the NTM-positive specimens, three-quarters of the NTM species were able to be identified. This simple and powerful method will be useful as it is, and it could be applied easily to a point-of-care diagnostic apparatus for better application to patients, especially those living in developing countries.

Continued Upward Trend in Non-Tuberculous Mycobacteria Isolation over 13 Years in a Tertiary Care Hospital in Korea

PURPOSE

Despite decreased prevalence of tuberculosis, the incidence of the diseases associated with nontuberculous mycobacteria (NTM) has been increasing in South Korea and around the world. The present retrospective study was conducted to determine longitudinal changes in the epidemiology and distribution of NTM over 13 years at a tertiary care hospital in Korea.

MATERIALS AND METHODS

We retrospectively analyzed data on Mycobacterium species over 13 years (January 2007 to December 2019) by utilizing the laboratory information system. Mycobacterium species were identified using biochemical tests and PCR-restriction fragment length polymorphism and Mycobacteria GenoBlot assays.

RESULTS

After excluding duplicates from the initial pool of 17996 mycobacterial isolates, 7674 strains were analyzed and 2984 (38.9%) NTM were isolated. The proportion of NTM continuously increased over the 13-year period, from 17.0% in 2007 to 57.5% in 2019. Among the NTM isolates, the most common species were Mycobacterium intracellulare (50.6%), M. avium (18.3%), M. fortuitumcomplex (4.9%), M. abscessus (4.5%), M. gordonae (3.3%), M. kansasii (1.1%), M. chelonae (1.0%), and M. massiliense (0.9%). In patients over the age of 70 years, the proportion of NTM among the isolates increased from 26.6% in 2007 to 62.0% in 2019, and that of M. intracellulare isolates among the NTM increased from 13.9% (11/79) in 2007 to 37.4% (175/468) in 2019.

CONCLUSION

The number of NTM isolates continuously increased over the study period, and the increase in the proportion of M.intracellulare in patients aged over 70 years was notable.

Redevelopment after spontaneous sputum conversion in noncavitary nodular bronchiectatic Mycobacterium avium complex lung disease

BACKGROUND

Although spontaneous sputum conversion can occur in noncavitary nodular bronchiectatic (NC-NB) Mycobacterium avium complex lung disease (MAC-LD), little is known about redevelopment after spontaneous conversion. We investigated the redevelopment phenomenon after spontaneous sputum conversion in patients with NC-NB MAC-LD.

MATERIAL AND METHODS

Among patients diagnosed with NC-NB MAC-LD between 2000 and 2013, 140 patients who experienced spontaneous sputum conversion, and whose follow-up duration after conversion was ≥6 months, were enrolled at a tertiary referral center in South Korea. Their medical records were retrospectively reviewed.

RESULTS

Of the 140 patients, 34 (24.3%) underwent redevelopment during the median follow-up period of 71.0 months (interquartile range [IQR], 58.8-87.5). Redevelopment occurred at a median interval of 25.0 months (IQR, 11.5-41.8) after spontaneous sputum conversion. The mean age of the 34 patients with redevelopment was 63.6 years, and 73.5% were women. No statistically significant differences in clinical characteristics were noted between the 34 patients with redevelopment and those with persistent conversion. Among the 34 patients with redevelopment, 6 received treatment at a median interval of 8 months (IQR, 1.5-16.8) after redevelopment. No significant differences in clinical characteristics were noted between the six treated and 28 untreated patients.

CONCLUSION

At least approximately 24% of patients with spontaneous sputum conversion in NC-NB MAC-LD had redevelopment, and a portion of them required treatment. These findings suggest that long-term follow-up is necessary for patients with NC-NB MAC-LD, even those who experience spontaneous sputum conversion.