Background: Mongolia has the fifth highest incidence of tuberculosis (TB) in the Western Pacific Region with high rates of multi-drug resistant tuberculosis (MDR-TB). Numbers of MDR-TB have escalated rapidly since 2006, mainly due to improved case detection. However, the harsh climate and crowded living conditions may facilitate spread. The aim of this study was to examine the molecular epidemiology of Mycobacterium tuberculosis (MTB) in Mongolia.
Materials and methods: Data from the National TB program and 66 MDR-TB isolates from the National Tuberculosis Reference Laboratory in Ulaanbaatar were collected between January and December 2012. All MTB isolates were genotyped by 24-loci mycobacterial interspersed repetitive unit (MIRU) typing and gyrA gene PCR sequencing was performed to identify fluoroquinolone resistance.
Results: Among all MDR-TB cases, 68% were from Ulaanbaatar; most were young males (41% 15-29 years of age, 70% male). The MTB population structure of MDR-TB cases was predominantly Beijing (86%), with smaller numbers of Latin-American Mediterranean (8%), Haarlem (5%) and NEW-1 (2%) lineages. Six MIRU clusters were detected, 5 belonging to Beijing. Two Beijing lineage clusters made up 42% (28/66) of all isolates suggested recent transmission within the community. Alarmingly one isolate of the Beijing clusters was pre-extensively drug resistant TB with a non-synonymous mutation on codon 94 of gyrA. We also identified a potential outbreak in a homeless shelter; 7/10 isolates belonged to a single Beijing cluster and 5/7 isolates shared an identical phenotypic drug resistance profile.
Conclusion: Beijing lineage is overrepresented among MDR-TB cases in Mongolia, particularly among young people, with evidence of recent transmission. A likely homeless shelter outbreak indicates the need for routine TB surveillance in these populations.