The risk and timing of tuberculosis (TB) among recently exposed close contacts of patients with infectious TB is not well established.
We prospectively enrolled culture-confirmed pulmonary TB patients ≥15 years of age and their close contacts at nine health departments in the United States and Canada. Close contacts were screened and cross-matched with TB registries to identify those who developed TB.
TB was diagnosed in 158 (4%) of 4490 contacts to 718 index TB patients. Of those with TB, cumulative totals of 81 (51%), 119 (75%), 128 (81%) and 145 (92%) were diagnosed by 1, 3, 6, and 12 months after index case diagnosis, respectively. TB rates among contacts were 2644, 115, 46, 69, and 25 per 100,000 persons, respectively, in the five consecutive years after index patient diagnosis. Of the TB cases among contacts, 121 (77%) were identified by contact investigation and 37 (23%) by TB registry cross-match.
Close contacts to infectious TB patients had high rates of TB, with most disease diagnosed before or within 3 months after index patient diagnosis. Contact investigations need to be prompt to detect TB and maximize the opportunity to identify and treat latent infection in order to prevent disease.