Reduced transmission of <i>Mycobacterium africanum</i> compared to <i>M. tuberculosis</i> in urban West Africa

Abstract Background Understanding transmission dynamics is useful for tuberculosis (TB) control. We conducted a population-based molecular epidemiological study to understand TB transmission in Ghana. Methods Mycobacterium tuberculosis complex (MTBC) isolates obtained from prospectively-sampled pulmonary TB patients between July, 2012 and December, 2015 were confirmed as MTBC using IS 6110 PCR. MTBC lineages were identified by large sequence polymorphism and single nucleotide polymorphism assays and further characterized using spoligotyping and standard 15-loci MIRU-VNTR typing. We used the n-1 method to estimate recent TB transmission and identified associated risk factors using logistic regression analysis. Findings Out of 2,309 MTBC isolates, we identified 1,082 (46·9%) single cases with 1,227 (53·1%) isolates belonging to one of 276 clustered cases (clustering range; 2-35). Recent TB transmission rate was estimated to be 41·2%. While we see no significant difference in the recent transmission rates between lineages of Mycobacterium africanum (lineage-5 (31·8%); lineage-6 (24·7%), p=0·118), we found that lineage-4 belonging to the M. tuberculosis transmitted significantly higher (44·9%, p<0·001). Finally, apart from age being significantly associated with recent TB transmission (p=0·007), we additionally identified a significant departure in the male/female ratio among very large clustered cases compared to the general TB patient population (3:1 vs. 2:1, p=0·022). Interpretations Our findings indicate high recent TB transmission suggesting occurrences of unsuspected outbreaks. The observed reduced transmission rate of M. africanum suggests other factor(s) may be responsible for its continuous presence in West Africa. Funding Wellcome Trust Intermediate Fellowship Grant 097134/Z/11/Z to Dorothy Yeboah-Manu.