Duration of Exposure Among Close Contacts of Patients With Infectious Tuberculosis and Risk of Latent Tuberculosis Infection

• Published in: Clinical infectious diseases Vol. 71; no. 7; pp. 1627 - 1634
• Main Authors: Reichler, Mary R, Khan, Awal, Yuan, Yan, Chen, Bin, McAuley, James, Mangura, Bonita, Sterling, Timothy R
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 23-10-2020
• Subjects: Adult; Canada - epidemiology; Child, Preschool; Contact Tracing; Humans; Latent Tuberculosis - diagnosis; Latent Tuberculosis - epidemiology; Male; Prevalence; Tuberculin Test; Tuberculosis - epidemiology; Tuberculosis, Pulmonary - epidemiology; United States - epidemiology; Canada; United States; exposure hours; latent tuberculosis infection; close contacts; epidemiology; exposure
• ISSN: 1058-4838; 1537-6591
• DOI: 10.1093/cid/ciz1044

Abstract
Background
Predictors of latent tuberculosis infection (LTBI) among close contacts of persons with infectious tuberculosis (TB) are incompletely understood, particularly the number of exposure hours.
Methods
We prospectively enrolled adult patients with culture-confirmed pulmonary TB and their close contacts at 9 health departments in the United States and Canada. Patients with TB were interviewed and close contacts were interviewed and screened for TB and LTBI during contact investigations.
Results
LTBI was diagnosed in 1390 (46%) of 3040 contacts, including 624 (31%) of 2027 US/Canadian-born and 766 (76%) of 1013 non-US/Canadian-born contacts. In multivariable analysis, age ≥5 years, male sex, non-US/Canadian birth, smear-positive index patient, and shared bedroom with an index patient (P < .001 for each), as well as exposure to >1 index patient (P < .05), were associated with LTBI diagnosis. LTBI prevalence increased with increasing exposure duration, with an incremental prevalence increase of 8.2% per 250 exposure hours (P < .0001). For contacts with <250 exposure hours, no difference in prevalence was observed per 50 exposure hours (P = .63).
Conclusions
Hours of exposure to a patient with infectious TB is an important LTBI predictor, with a possible risk threshold of 250 hours. More exposures, closer exposure proximity, and more extensive index patient disease were additional LTBI predictors.
Hours of exposure to an infectious tuberculosis patient is an important predictor of latent tuberculosis infection among close contacts, with an incremental prevalence increase of 8.2% per 250 exposure hours; more exposures, closer exposure proximity, and extensive index patient disease were additional predictors.