Abstract
Tuberculosis patients with identical strains of Mycobacterium tuberculosis are described as clustered. Cluster size may depend on patient or strain characteristics. In a 7-year population-based study of tuberculosis in Karonga District, Malawi, clusters were defined by using IS6110 restriction fragment length polymorphism, excluding patterns with <5 bands. Spoligotyping was used to compare strains with an international database. Among 682 clustered patients, cluster size ranged from 2 to 37. Male patients, young adults, and town residents were over-represented in large clusters. Cluster size was not associated with HIV status or death from tuberculosis. Spoligotypes from 9 (90%) of 10 large cluster strains were identical or very similar (1 spacer different) to common spoligotypes found elsewhere, compared with 37 (66%) of 56 of those from nonclustered patients (p = 0.3). Large clusters were associated with factors likely to be related to social mixing, but spoligotypes of common strains in this setting were also common types elsewhere, consistent with strain differences in transmissibility.
Highlights
Tuberculosis patients with identical strains of Mycobacterium tuberculosis are described as clustered
In a population-based study of the molecular epidemiology of tuberculosis in northern Malawi, we found that clustering was associated with young age, female sex, area of residence, and, in older adults, HIV positivity [5]
This study suggests that both epidemiologic and strainrelated factors may contribute to large cluster size
Summary
Tuberculosis patients with identical strains of Mycobacterium tuberculosis are described as clustered. Spoligotypes from 9 (90%) of 10 large cluster strains were identical or very similar (1 spacer different) to common spoligotypes found elsewhere, compared with 37 (66%) of 56 of those from nonclustered patients (p = 0.3). Giordano et al [1] hypothesized that cluster size would be related to duration of symptoms Those researchers found no evidence of this but did find inverse associations with age and HIV status in a population-based study in Texas in the United States. In a population-based study of the molecular epidemiology of tuberculosis in northern Malawi, we found that clustering was associated with young age, female sex, area of residence, and, in older adults, HIV positivity [5]. We explored the determinants of cluster size and the characteristics of the larger clusters
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