Abstract
We aimed to model the incidence of infection with Mycobacterium tuberculosis among adults using data on infection incidence in children, disease prevalence in adults, and social contact patterns. We conducted a cross-sectional face-to-face survey of adults in 2011, enumerating “close” (shared conversation) and “casual” (shared indoor space) social contacts in 16 Zambian communities and 8 South African communities. We modeled the incidence of M. tuberculosis infection in all age groups using these contact patterns, as well as the observed incidence of M. tuberculosis infection in children and the prevalence of tuberculosis disease in adults. A total of 3,528 adults participated in the study. The reported rates of close and casual contact were 4.9 per adult per day (95% confidence interval: 4.6, 5.2) and 10.4 per adult per day (95% confidence interval: 9.3, 11.6), respectively. Rates of close contact were higher for adults in larger households and rural areas. There was preferential mixing of close contacts within age groups and within sexes. The estimated incidence of M. tuberculosis infection in adults was 1.5–6 times higher (2.5%–10% per year) than that in children. More than 50% of infections in men, women, and children were estimated to be due to contact with adult men. We conclude that estimates of infection incidence based on surveys in children might underestimate incidence in adults. Most infections may be due to contact with adult men. Treatment and control of tuberculosis in men is critical to protecting men, women, and children from tuberculosis.
Highlights
Tuberculosis remains a major global public health problem
Interviewees in Zambia reported larger households than did those in South Africa (mean number of people per household = 4.6, 95% confidence interval (CI): 4.5, 4.7, and 3.6, 95% CI: 3.5, 3.7, respectively), and fewer South African households than Zambian households included a 5–12-year-old child (40% versus 60%; P < 0.001)
The incidence was 1.5–6 times higher than what was empirically measured in children
Summary
Tuberculosis remains a major global public health problem. Approximately 1 in 3 people globally might be infected with Mycobacterium tuberculosis and at risk of progressing to tuberculosis disease [1]. Mathematical models of the transmission of acute respiratory infections are sensitive to assumptions about contact patterns between different age groups [22,23,24] This has led to diary and interview-based attempts to empirically measure and analyze social mixing patterns in Europe [25,26,27,28,29,30,31,32], Asia [33], and more recently, South Africa [34]. In the absence of reliable estimates of M. tuberculosis infection incidence among adults, we performed a survey of social contact patterns and modeled the age- and sex-specific M. tuberculosis infection incidence and the sexes of source cases. We combined social contact data, data on the incidence M. tuberculosis infection among schoolchildren, and data on the prevalence of adult tuberculosis from 24 communities in Zambia and South Africa [35,36,37]
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