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Subclinical tuberculosis includes disease forms that are detectable by radiographic or microbiological assays but do not cause recognizable symptoms. Population-based prevalence surveys demonstrate that the majority of individuals with culture-positive tuberculosis and corresponding radiographic abnormalities lack recognizable symptoms. Subclinical tuberculosis is often conceptualized as an early stage that generally progresses to recognizable active tuberculosis disease within months. However, many individuals with subclinical tuberculosis likely never develop recognizable symptoms, and consequently are never identified as having tuberculosis. A growing body of evidence indicates that, in high-burden settings, people with tuberculosis spend more time in a subclinical state than they spend with recognizable symptoms, and that people with subclinical tuberculosis may be infectious. As such, the subclinical period may represent a long window of potential Mycobacterium tuberculosis transmission. To appropriately prioritize interventions, there is a need to quantify the amount of transmission that occurs during the subclinical period, including the contribution of those who never develop clinically symptomatic disease. If individuals with subclinical tuberculosis are responsible for a large fraction of M. tuberculosis transmission, then ambitious reductions in tuberculosis incidence cannot be achieved without greater focus on early detection and treatment of subclinical tuberculosis. Novel diagnostic assays, population-based studies, and bioinformatic techniques could be used to better estimate the contribution of individuals with subclinical tuberculosis to overall transmission. This knowledge can help us understand whether finding and treating people with subclinical tuberculosis is essential or extraneous as part of a comprehensive strategy to end the epidemic.
Kendall et al. (Mon,) studied this question.