Abstract
BackgroundLittle is known about the impact of growing migration on the pattern of tuberculosis (TB) transmission in middle-income countries. We estimated TB recent transmission and its associated factors and investigated the presence of cross-transmission between South American migrants and Brazilians.MethodsWe studied a convenient sample of cases of people with pulmonary TB in a central area of São Paulo, Brazil, diagnosed between 2013 and 2014. Cases with similar restriction fragment length polymorphism (IS6110-RFLP) patterns of their Mycobacterium tuberculosis complex isolates were grouped in clusters (recent transmission). Clusters with both Brazilian and South American migrants were considered mixed (cross-transmission). Risk factors for recent transmission were studied using logistic regression.ResultsIsolates from 347 cases were included, 76.7% from Brazilians and 23.3% from South American migrants. Fifty clusters were identified, which included 43% South American migrants and 60.2% Brazilians (odds ratio = 0.50, 95% confidence interval = 0.30–0.83). Twelve cross-transmission clusters were identified, involving 24.6% of all clustered cases and 13.8% of all genotyped cases, with migrants accounting for either an equal part or fewer cases in 11/12 mixed clusters.ConclusionsOur results suggest that TB disease following recent transmission is more common among Brazilians, especially among those belonging to high-risk groups, such as drug users. Cross-transmission between migrants and Brazilians was present, but we found limited contributions from migrants to Brazilians in central areas of São Paulo and vice versa.
Highlights
Little is known about the impact of growing migration on the pattern of tuberculosis (TB) transmission in middle-income countries
We described the socio-demographic and epidemiological characteristics of all the TB cases in the studied area and in the studied sample, stratified by origin (Brazilians or other South American migrants), in order to characterize Brazilians and migrants with pulmonary TB (PTB) in our sample and to identify potential selection bias resulting from overrepresentation of potential high-risk populations for recent transmission within the sample
Sensitivity analysis When we considered only identical patterns as clustered, we found a lower proportion clustered in both populations, but the odds ratio (OR) for belonging to a cluster in South American migrants vs Brazilians remained consistent with the main analysis (OR = 0.56, 95% confidence interval (95% CI) 0.33–0.94; Table 3, rows for Clusters)
Summary
Little is known about the impact of growing migration on the pattern of tuberculosis (TB) transmission in middle-income countries. Molecular research from high-income countries has shown that transmission from migrants to the local-. Molecular epidemiology studies can estimate the number of TB cases due to recent transmission between local-born and migrant populations (cross-transmission) [6]. There is little evidence available from middleincome countries [10, 11], where Mycobacterium tuberculosis complex (Mtbc) transmission between migrants and local-born people, in the South-South migration context, Pescarini et al BMC Medicine (2018) 16:62 might be more pronounced because of increased mixing through cultural proximity and social integration [12]. The vulnerability of the local-born population and the contexts in which migrants find themselves might contribute to more TB cross-transmission than what is evidenced in highincome countries [4, 12, 13]
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