Disease Transmission by Patients With Subclinical Tuberculosis

BACKGROUND: Subclinical tuberculosis has been increasingly recognized as a separate state in the spectrum of the disease. However, evidence on the transmissibility of subclinical tuberculosis is still inconclusive. METHODS: We re-analyzed the data from the 2007 combined tuberculosis prevalence and tuberculin surveys in Vietnam. Poisson regression with robust standard errors was conducted to assess the effect of clinical presentation of individuals with tuberculosis in the household on tuberculin skin test (TST) positivity among children aged 6–14 years who participated in the tuberculin survey, adjusting for child's age, smear status of the index patient, and other covariates. RESULTS: In the multivariate analysis, we found significantly increased risks for TST positivity in children living with patients with clinical, smear-positive tuberculosis, compared with those living with individuals without tuberculosis (adjusted risk ratio [aRR]: 3.04; 95% confidence interval [CI]: 2.00–4.63) and with those living with patients with subclinical tuberculosis, adjusting for index smear status (aRR: 2.26; 95% CI: 1.03–4.96). Among children aged 6–10 years, those living with patients with clinical, smear-positive tuberculosis and those living with patients with subclinical, smear-positive tuberculosis had similarly increased risks of TST positivity compared with those living with individuals without tuberculosis (aRRs [95% CI] of 3.56 [1.91–6.62] and 3.11 [1.44–6.72], respectively). CONCLUSIONS: Our findings support the hypothesis that smear-positive subclinical tuberculosis contributes to Mycobacterium tuberculosis transmission. To eliminate tuberculosis in 2035, control strategies need to address subclinical presentations of the disease.