Contact investigation for tuberculosis in Taiwan contacts aged under 20 years in 2005.

OBJECTIVE

To measure the tuberculosis (TB) incidence rate and assess the relative risk of TB disease in contacts based on the tuberculin skin test (TST) and sputum status of index cases.

DESIGN

All contacts aged <20 years who were exposed to a TB case in 2005 were cross-matched using an electronic surveillance system to estimate TB incidence over a 24-month follow-up period.

RESULTS

Among 6959 contacts there were 67 secondary cases (1%). The incidence was highest in the first year after exposure and decreased by half in the second year (P = 0.001). The relative risks of developing TB in contacts aged 0-4, 5-9, 10-14 and 15-19 years were respectively 325, 209, 337 and 53 times greater than for the general population. The hazard ratio of developing TB among contacts with a TST ≥ 15 mm induration was 12 times higher than for those with a TST < 5 mm (P = 0.003).

CONCLUSIONS

The relative risk of developing TB disease within 24 months of exposure was approximately 200-300 times greater for contacts aged <15 years. The majority developed TB within 12 months of exposure.