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TB rates fourfold higher among US, Canada-born contacts compared with foreign-born contacts
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Tuberculosis rates were four times higher among U.S. and Canada-born contacts than among foreign-born contacts, according to a recent study.
“In the United States, Canada and most countries with low TB incidence, contact investigations are conducted for pulmonary TB patients to identify and treat secondary cases of active TB disease and latent TB infection (LTBI) among exposed contacts, thereby interrupting secondary transmission of Mycobacterium tuberculosis and preventing progression from LTBI to TB disease,” Mary R. Reichler, MD, of the Division of Tuberculosis Elimination at the CDC, and colleagues wrote. “Understanding TB risk factors among exposed contacts is important for determining the optimal timing and expected yield of contact investigations, as well as prioritizing public health prevention efforts among persons at highest TB risk.”
To gain insight, researchers conducted a prospective study of contact investigations by health departments in the U.S. and Canada. According to the study, patients with TB and their contacts were interviewed to identify the potential index patient, contact, and exposure risk factors. Contacts were evaluated for LTBI and active TB, and the researchers also examined the effectiveness of LTBI treatment.
Results of the study revealed that among the 4,490 close contacts evaluated, there was higher risk for TB among those who were aged younger than 5 years, had HIV infection, had a skin test induration greater than 10 mm, shared a bedroom with an index patient and who had exposure to more than one index patient. Additionally, the risk was higher among contacts who were U.S. and Canadian-born compared with foreign-born. Specifically, the study showed that TB was diagnosed in 4.2% of U.S. and Canadian-born contacts compared with 2.3% of foreign-born contacts (P = .002).
The researchers said this finding was “unexpected” because TB case rates in the U.S. are 15 times higher among foreign-born vs. U.S.-born residents.
“A possible explanation is that foreign-born contacts have a higher likelihood of previous TB exposure (and previous infection or disease) than contacts born in low-incidence areas such as the U.S. and Canada, and are thus at lower risk of developing disease from the recent exposure,” they wrote.
Rates of U.S. and Canadian-born and foreign-born contacts who did not initiate treatment were 3,592 and 811 per 100,000 person-years, respectively.
The researchers also determined that LTBI treatment was highly effective in preventing active TB disease. Among 1,406 skin test-positive contacts, TB developed in 49 (9.8%) of the 446 people who did not initiate treatment, eight (1.8%) of the 443 who received partial treatment, and one (0.2%) of the 517 who completed treatment, according to the study. This translates to rates of 1,951, 290 and 31 cases per 100,000 person-years, respectively (P < .001), the researchers said.
“Our study provides important new information on risk factors for TB disease and the effectiveness of LTBI treatment in contacts with recent exposure to infectious TB patients,” the authors concluded. “Our findings underscore the importance of contact investigation as a mechanism for identifying and treating new cases of active TB among contacts and emphasizes the importance of prompt screening and LTBI treatment. These findings have important implications for tuberculosis prevention efforts.” – by Caitlyn Stulpin
Disclosures: The authors report no relevant financial disclosures.
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