Risk and Timing of Tuberculosis Among Close Contacts of Persons with Infectious Tuberculosis

Abstract

Background: The risk and timing of tuberculosis among recently exposed close contacts of patients with infectious tuberculosis are not well established.

Methods: We prospectively enrolled patients ≥15 years of age with culture-confirmed pulmonary tuberculosis and their close contacts at 9 health departments in the United States and Canada. Close contacts were screened and cross-matched with tuberculosis registries to identify those who developed tuberculosis.

Results: Tuberculosis was diagnosed in 158 of 4490 contacts (4%) of 718 index patients with tuberculosis. Of tuberculosis cases among contacts, cumulative totals of 81 (51%), 119 (75%), 128 (81%), and 145 (92%) were diagnosed by 1, 3, 6, and 12 months, respectively, after the index patients' diagnosis. Tuberculosis rates among contacts were 2644, 115, 46, 69, and 25 cases per 100000 persons, respectively, in the 5 consecutive years after the index patients' diagnosis. Of the tuberculosis cases among contacts, 121 (77%) were identified by contact investigation and 37 (23%) by tuberculosis registry cross-match.

Conclusions: Close contacts to infectious patients with tuberculosis had high rates of tuberculosis, with most disease diagnosed before or within 3 months after the index patient' diagnosis. Contact investigations need to be prompt to detect tuberculosis and maximize the opportunity to identify and treat latent infection, to prevent disease.

Figure 1.

Timing of tuberculosis (defined as the interval from index case treatment initiation to contact treatment initiation) among 131 contacts, by interval from index case treatment initiation; the 27 contacts in whom tuberculosis was diagnosed before the index cases received a diagnosis are excluded. Of note, tuberculosis registry matches were used to identify the diagnosis of tuberculosis among enrolled contacts after contact investigations were completed; tuberculosis registry matches were performed annually for 4 years after last site enrollment at 8 sites and annually for 2 years at one site. Since enrollment occurred over a 4-year period, contacts enrolled earlier in the study had a longer tuberculosis registry match observation period, with 100%, 94%, 76%, 55%, and 34% observed for 4, 5, 6, 7, and 8 years, respectively, after enrollment.

Figure 2.

Disease-free survival for 4490 contacts (158 with and 4332 without tuberculosis), by age group (A), screening tuberculin skin test (TST) result (B), and receipt of treatment for latent Mycobacterium tuberculosis infection (C). Tuberculosis registry matches were performed annually for 4 years after last site enrollment at 8 sites and annually for 2 years at 1 site. Since enrollment occurred over a 4-year period, contacts enrolled earlier in the study had a longer tuberculosis registry match observation period, with 100% and 94% observed for 4 and 5 years, respectively. Neg, negative; pos, positive; PT, preventive therapy.