Rationale: The lifetime risk of tuberculosis (TB) for infected contacts is often mentioned to be 5-10%, but these estimates are based on studies conducted decades ago, and thus may not reflect current epidemiologic conditions.
Objectives: To estimate the risk of TB among contacts with evidence of infection and to compare this with estimates often stated in the literature.
Methods: A retrospective cohort study was performed using records on contacts of pulmonary TB patients at the Public Health Service Amsterdam, 2002-2011. The Public Health Service Amsterdam TB electronic registration system identified TB cases during follow-up until October 2012; these were defined as coprevalent if diagnosed less than or equal to 180 days and incident if diagnosed greater than 180 days after TB diagnosis of index patient. Cumulative TB risk was estimated with Kaplan-Meier curves.
Measurements and main results: Of 9,332 contacts of pulmonary TB patients, 4,774 were screened for latent TB infection (LTBI) of whom 739 (16%) had evidence of infection. Among these the 5-year Kaplan-Meier TB cumulative risk was 9.5% (95% confidence interval, 7.5-11.9). This varied by age: 33.3% of 36 contacts aged less than 5 years, 19.1% of 84 contacts aged 5-14 years, and 6.7% of 619 contacts aged greater than or equal to 15 years (log rank, P < 0.001). Of 739 contacts with evidence of infection, 57 had coprevalent TB and 14 developed incident TB. Of patients without coprevalent TB but with LTBI diagnosis, 45% received preventive therapy. Five-year risk of incident TB was 2.4% (95% confidence interval, 1.2-4.7) among contacts with LTBI who did not start preventive therapy.
Conclusions: Five-year risk of TB among contacts with evidence of infection was higher compared with older estimates, and differed considerably by age. Incidence of TB among contacts with LTBI was low, suggesting limited impact may be expected of expanding preventive therapy.
Keywords: follow-up; preventive therapy; tuberculosis contact investigation; tuberculosis incidence.