Contact examination for tuberculosis in Hong Kong is useful.

SETTING: The tuberculosis programme of the Hong Kong Government Tuberculosis and Chest Service.

OBJECTIVE: To determine the outcome of examination of household contacts in Hong Kong.

DESIGN: A retrospective cohort study of all household contacts of 970 randomly selected index cases from a total of 5757 registered for treatment with the Chest Service.

RESULTS: Of 2678 household contacts (three/index case) identified, 90% were examined; 41 active cases were found, at a rate of 1720/100000 (95%CI 1238-2329). The rate was highest among two extremes of age, 3604/100000 (95%CI 990-3615) in children < or = 5 years and 3347/100000 (95%CI 1456-6489) in those >60 years of age. Contacts of index cases whose sputum smear and culture were positive had the highest rate of disease, 2904/100000 (95%CI 1669-4673); but contacts with negative bacteriology also had a high rate of 1478/100000 (95%CI 678-2789). Active cases identified through contact tracing could be source cases rather than secondary cases. Eight per cent of children aged < or = 5 years had positive tuberculin reactions; as BCG vaccination is given to all newborns, with 99% coverage in Hong Kong in the past 30 years, it was difficult to estimate the rate of infection in these children.

CONCLUSION: In Hong Kong, an area with an intermediate burden of tuberculosis, contact investigation is a very useful procedure for active case finding.