Transmissibility and Disease Progression of Asymptomatic <i>Mycobacterium</i> <i>tuberculosis</i> Infection, Lima, Peru

Estimating the transmissibility of asymptomatic Mycobacterium tuberculosis infection can clarify its contribution to tuberculosis (TB) spread. We conducted a prospective cohort study in Lima, Peru, enrolling index TB patients and their household contacts (HHCs) and classifying patients by the presence of symptoms including cough, night sweats, weight loss, or fever. We followed HHCs with serial tuberculin skin testing and clinical evaluations. Among 4,296 child HHCs, adjusted estimates for baseline infection (prevalence ratio 0.62 [95% CI 0.37-1.03]), incident infection at 6 months (hazard ratio (aHR) 0.63 [95% CI 0.27-1.49]), and TB disease during 1 year of follow-up (aHR 0.74 [95% CI 0.35-1.56]) were all consistent with lower risk for infection and disease progression among HHCs of asymptomatic compared with symptomatic index patients. Although asymptomatic infections may be less transmissible than symptomatic infections, the high prevalence of asymptomatic patients in national surveys suggest that they may contribute substantially to transmission.