Risk of tuberculosis infection according to exposure time and other factors of contacts and their index cases.

BACKGROUND

The time of exposure to an index case of tuberculosis (TB) increases the risk of tuberculosis infection (TI) for contacts. Our aim was to determine the impact of exposure time on the TI risk for contacts of pulmonary TB index cases.

METHODS

We conducted a cross-sectional prevalence study of TI among pulmonary TB contacts in Catalonia notified 1 January 2019-30 June 2021. Contacts with TI or TB were identified by means of the tuberculin skin test and/or interferon gamma release assay. The association of exposure time with TI in contacts was analysed using adjusted OR (aOR) and the 95% confidence interval (CI).

RESULTS

TI prevalence was 25.5% (1670/6537), and was higher in males than in females (28.5% versus 22.6%; p<0.001), all age groups with respect to children <5 years (12.4%; p<0.001), immigrants (37.4% versus 18.1%; p<0.001), and smokers (56.0% versus 29.7%; p<0.001), and increased with exposure time to the index case. Relative to <6h/week exposure, TI risk was greater for exposures of ≥6h/day (aOR=2.0; 95% CI: 1.5-2.6) and <6h/day, but ≥6h/week (aOR=1.8; 95% CI: 1.3-2.4).

CONCLUSIONS

Since the risk of TI increases with time of exposure to the index case, it is necessary to record it in all contacts to advance to TB elimination.