Growing Knowledge about Mycobacterium simiae from Two Recent Studies

LETTER

Mycobacterium simiae is an emerging pathogen described mainly in Asia and to a lesser extent in the United States. We read with great interest the study by Coolen-Allou et al. (1) entitled “Mycobacterium simiae: clinical, radiological and microbiological characteristics in 97 patients,” which is one of the first studies to describe M. simiae infection in Africa. This study included 97 patients with M. simiae infection and described several aspects related to this mycobacterium, including clinical presentation, treatment, and outcomes. The study had a design similar to that of our study entitled “Emergence of Mycobacterium simiae: a retrospective study from a tertiary care center in Lebanon” (2); however, their results were different in several aspects. First, the infectivity of M. simiae was lower in their review than in ours, with 21.6% of their isolates and 47% of our isolates meeting the American Thoracic Society (ATS) criteria for a nontuberculous mycobacterial infection. This lower infectivity is in accordance with that described by Van Ingen et al. from the Netherlands (3) and Hashemi-Shahraki et al. (4) from Iran.

Moreover, non-cystic fibrosis bronchiectasis was the most common underlying lung comorbidity in the work of Coolen-Allou et al. (1), whereas recurrent pneumonias and asthma were most common in our study. Chronic obstructive pulmonary disease was commonly seen in both studies, a finding which is similar to the results of the series by Shitrit et al. (5). Among nonpulmonary comorbidities, a high number of patients (11%) had chronic kidney disease in their study, unlike our study and the study by Baghaei et al. (6), where diabetes was mostly found. More patients received steroids, whether systemic or inhaled, in the Reunion Island study than in ours.

Regarding symptomatology, the patients in the former study developed more weight loss, less cough and sputum production, and much less hemoptysis than our patients.

When comparing radiological findings, the two studies described similar findings, except for more ground glass predominance in our study.

Finally, clarithromycin was the backbone of therapy in both studies and was used in combination with 3 or more drugs to which the organism was found to be susceptible, as is the case in other M. simiae studies. Isolates from both countries also had high susceptibility to amikacin. However, the isolates from Reunion Island were more likely than the isolates in our study to be susceptible to moxifloxacin (92% versus 30%) and were not as resistant to antituberculous medications as the isolates in our study. Our results were more in accordance with the susceptibility profile of the isolates found by Van Ingen et al. (7). Finally unlike our study, Coolen-Allou et al. focused solely on the outcomes of patients meeting ATS criteria who received treatment (1).

The differences in epidemiology, clinical manifestations, radiographic findings, and drug susceptibility patterns of M. simiae between the 2 studies highlight the importance of conducting research on this emerging pathogen in different parts of the world where the infection is being described. This would offer a better understanding of the local epidemiology and, consequently, better patient care.

Ed. Note: The authors of the published article did not feel that a response was necessary.