Refined tuberculosis contact tracing in a low incidence area

Our aim was to evaluate the efficacy of a revised tuberculosis (TB) contact tracing procedure in South Glamorgan whereby routine annual radiological surveillance was abandoned and contacts were either discharged or referred to chest clinic following their initial screening. We reviewed and evaluated data from the TB contact tracing clinic, the Public Health Service Mycobacterium Reference Unit, Cardiff and the Consultant in Communicable Diseases Control, South Glamorgan Health Authority and compared these results with those of our previous study. One hundred and three index cases and 732 contacts were identified. Seven hundred and seven contacts, 526 close and 181 casual, were screened, of whom 102 casuals should not have been. One hundred and sixty-one contacts were given BCG vaccination. Fifty-four contacts were referred to the chest clinic. Seven cases of TB were detected, all in young, unvaccinated, close contacts of pulmonary disease. Twenty-one contacts were given chemoprophylaxis, 20 of whom were close contacts of pulmonary TB and one of extrapulmonary disease. Five contacts who were screened and initially discharged developed TB later: in two the protocol had not been followed and three presented with extrapulmonary TB. Compared with the results of the previous protocol fewer contacts were unnecessarily screened and referrals to the chest clinic increased, as did the number given chemoprophylaxis. The case finding rate is similar to that found prior to the revision of the protocol. The yield from tracing casual contacts continues to be nil. It is very low in contacts of extrapulmonary disease. When the protocol was followed no case of pulmonary TB was missed. The revised protocol seems to be as effective as the previous, more complex protocol. In our area, one of low incidence of TB, screening of casual contacts and of contacts of extrapulmonary TB is not cost-effective. We will concentrate even more on screening close contacts of pulmonary TB.