Background: Brazil has a tuberculosis (TB) incidence in prisoners that is over 25-times greater than in the general population. We combined conventional epidemiological methods, detailed contact data, and molecular techniques to understand the transmission network of TB in a high incidence prisoner population in the Brazilian state of Mato Grosso do Sul.
Methods: We performed a population-based study of TB transmission in five state prisons from June 2009 to April 2016. For each TB positive prisoner, we obtained the date of disease notification and a temporal record for prisoner location, intra-prison movement, and transfer between prisons. We genotyped the Mycobacterium tuberculosis isolates from each prisoner with IS6110 restriction fragment length polymorphism (RFLP) analysis, and performed whole genome sequencing on 19 isolates to validate the largest cluster. We defined a cluster as a group of individuals with identical RFLP patterns. For each identical cluster, we created a longitudinal record with each prisoner`s location with relation to other prisoners to infer potential transmission.
Results: During the study period, 178 cases of TB were reported and genotyped in the prisoner population. We identified 24 distinct clusters, with 70.2% of cases being classified within a cluster, suggesting linked transmission. The median cluster size was 3 prisoners (IQR: 2-5.5). The largest cluster included 41 new TB cases over seven years (23% of all cases), and when examined with whole genome sequencing showed a range of 6-30 single nucleotide variants, suggesting close phylogenetic relationship. After assembling the full longitudinal record for prisoners from the largest cluster (Figure 1), we found 63% of new TB cases were exposed to a prisoner in the same block who was later diagnosed with TB, and 7.4% were exposed to a prisoner in the same cell who was later diagnosed with TB.
Conclusion: We found sustained transmission of TB over a seven-year period within a Brazilian prisoner population, validated by molecular and epidemiological data. The majority of cases were clustered, suggesting recent transmission, with a single strain representing 23% of all cases. Efforts to control TB in prisons should focus on reducing transmission to avert new infections.
*Lo and Sacchi are co-first authors
**Andrews and Croda are co-senior authors
N. C. Lo,
E. Lemos, None
M. B. Tatara, None
C. C. De Lima, None
E. Cunha, None
J. R. Andrews, None
J. Croda, None