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Household and community-based transmission of Mycobacterium tuberculosis in Harare, Zimbabwe

M Chipinduro(1,2) V Dreyer(3,4) J Mutsvangwa(1) E Marambire(1) K Madziva(1) C Calderwood(1,5) L S Larsson(1) U Panzner(6) S Niemann(3,4) N Heinrich(6) K Kranzer(1,5,6)

1:Biomedical Research and Training Institute, Harare, Zimbabwe; 2:Midlands State University, Gweru, Zimbabwe; 3:Molecular and Experimental Mycobacteriology, Research Center Borstel, Borstel, Germany; 4:German Center for Infection Research, Partner Site Hamburg-Lübeck-Borstel-Riems, Borstel, Germany; 5:Department of Clinical Research, Faculty of Infectious & Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom; 6:Department of Infectious Diseases and Tropical Medicine, Ludwig-Maximilian University, Munich, Germany

Tuberculosis is a public health concern. While household transmission of Mycobacterium tuberculosis complex (Mtbc) strains is the main rationale for tuberculosis screening among household contacts (HHC), Mtbc transmission also occurs outside households, in some settings.  We investigated community and household transmission among people with tuberculosis (index cases and their HHC) in Harare, Zimbabwe. Whole genome sequencing (WGS) was performed on Illumina NextSeq 500. MTBseq-based WGS data analysis was used for phylogenetic strain classification and cluster analysis based on a ≤5 single nucleotide polymorphisms (SNPs) difference. Two-hundred tuberculosis patients were investigated of which 63% (n=126) were men and the median age was 35.1 years (IQR: 26.8-42.7). Out of a total of 200 sequenced Mtbc strains, 92.5% (n=185) were from index cases and 7.5% (n=15) from HHC. The majority of Mtbc strains belonged to the Latin America/Mediterranean lineage (57%, n=114), followed by the Beijing lineage (9.5%, n=19). Overall, 17 clusters were identified with the largest cluster having six members. Of these, 11 (65%) clusters comprised index cases, only. Among 15 HHC strains, six (40%) were clustered with strains from their corresponding index cases and two (13%) with non-household index cases. The remaining seven (47%) sequences were ungrouped of which one became independently clustered with non-household index cases when clusters of ≤12 SNPs difference were considered. Our data indicate, that in Zimbabwe tuberculosis transmission occurs within households and in the community. HHC studies to validate early diagnostic tests must confirm that secondary tuberculosis cases are due to transmission within the household.

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