Molecular epidemiology and drug resistance patterns of Mycobacterium tuberculosis complex isolates from university students and the local community in Eastern Ethiopia

Abstract

Background: Previous studies suggest the burden of pulmonary tuberculosis (PTB) in Ethiopia may be greater in university students relative to the overall population. However, little is known about the transmission dynamics of PTB among students and members of the communities surrounding university campuses in Eastern Ethiopia.

Methods: A cross sectional study was conducted in Eastern Ethiopia among prevalent culture-confirmed PTB cases from university students (n = 36) and community members diagnosed at one of four hospitals (n = 152) serving the surrounding area. Drug susceptibility testing (DST) was performed on Mycobacterium tuberculosis complex (MTBC) isolates using BD Bactec MGIT 960 and molecular genotyping was performed using spoligotyping and 24-loci MIRU-VNTR. MTBC strains with Identical genotyping patterns were assigned to molecular clusters as surrogate marker for recent transmission and further contact tracing was initiated among clustered patients.

Results: Among all study participants, four MTBC lineages and 11 sub-lineages were identified, with Ethiopia_3 (Euro-American lineage) being most common sub-lineage (29.4%) in both cohorts and associated with strain clustering (P = 0.016). We further identified 13 (8.1%) strains phylogenetically closely related to Ethiopia_3 but with a distinct Spoligotyping pattern and designated as Ethiopia_4. The clustering rate of MTBC strains was 52.9% for university students and 66.7% for community members with a Recent Transmission Index (RTI) of 17.6% and 48.4%, respectively. Female gender, urban residence, and new TB cases were significantly associated with strain clustering (P<0.05). Forty-eight (30%) of the study participants were resistant to one or more first line anti TB drugs, three patients were classified as multidrug resistant (MDR).

Conclusion: We found evidence for recent transmission of PTB among Ethiopian university students and the local community in Eastern Ethiopia, mainly linked to strains classified as Ethiopia_3 sub lineage. Drug resistance didn't have a major impact on recent transmission but comprehensive molecular surveillance in combination with drug resistance profiling of MTBC strains is desirable to better characterize TB transmission dynamics in high risk congregate living environments such as university campuses and guide regional TB control programs.

Fig 1. Minimum spanning tree based on 24-loci MIRU-VNTR profiles of 160 MTBC isolates from Eastern Ethiopia.

The identified sub-lineages are color-coded. Branch lengths are proportional to number of MIRU-VNTR loci differences between two nodes (<1 locus, solid thick lines; 2–3 loci, solid thin lines; >4 loci, dashed line). Node size is proportional to the number of isolates with identical MIRU-VNTR profiles. EAI: East Africa India, LAM = Latin American Mediterranean.

Fig 2. Visualization of PTB cases using a radial UPGMA tree based on 24-loci MIRU-VNTR data.

Ring 4 shows drug resistance categories per isolate: fully susceptible (pink), at least one first-line drug resistance (dark green). Ring 3 shows whether cases were part of a genetic cluster (orange) or were unique (purple). Ring 2 differentiates students (yellow) from community members (blue).