Castellanos, Maria Eugenia, Lau-Bonilla, Dalia, Moller, Anneliese, Arathoon, Eduardo, Samayoa, Blanca, Quinn, Frederick D., Ebell, Mark H., Dobbin, Kevin K., and Whalen, Christopher C. (2022) Characterization of the Proportion of Clustered Tuberculosis Cases in Guatemala: Insights from a Molecular Epidemiology Study, 2010–2014. American Journal of Tropical Medicine and Hygiene, 106 (4). pp. 1173-1181.

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Abstract

Currently, the tuberculosis (TB) incidence rate worldwide is decreasing at just around 2% per year. 1 Incident cases in endemic settings are considered to be a result of community-based transmission. 2, 3 Understanding the level of recent transmission in endemic areas is essential to guide TB control policies. 4

Mycobacterium tuberculosis strains are considered clustered when the genotypes between two or more are the same. Clustered strains represent a chain of transmission and may represent ongoing or recent transmission if the initial isolates are collected during a short period of time, such as 1–2 years, within a defined geographic area. It is assumed that these clusters are “epidemiologically linked chains of recently transmitted disease.” 5 Strains with unique genotypes are thought to represent reactivation of an old TB cases and are considered nonclustered. 6 Nevertheless, strains with unique genotypes may also represent recently imported genotypes or incomplete sampling of local circulating lineages. 4, 7 – 10

The distribution of clustered strains is affected by several host and population-level characteristics. 11, 12 Individual host characteristics that influence levels of TB clustering include place of birth, pulmonary TB (rather than extrapulmonary), and alcohol abuse. 12 A few population-level characteristics that affect clustering are age structure of the population, prevalence of latent TB infection and HIV prevalence. 11 Several studies have been performed evaluating levels of TB clustering and potential risk factors for cluster membership. Most of these studies, however, were conducted in low-incidence TB settings and little is known about relevant risk factors for recent transmission in persons living with HIV in areas with a medium TB burden, such as Guatemala (incidence rate of 25 cases per 100,000/year). 13

The main aim of this study was to characterize the proportion of clustered TB cases based on genotypic matching in Guatemala City, Guatemala between 2010 and 2014. As a secondary aim, we explored the potential risk factors associated with clustering in a subset of isolates from participants living with HIV. Knowledge of existing circulating genotypes and the identification of risk factors associated with recent transmission will allow an evidenced-based approach for health policymakers to direct and concentrate targeted TB control measures to high-risk populations.

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