The value of contact procedures for tuberculosis in Edinburgh

Abstract

We have reviewed the value of routine contact procedures (CP) in screening for tuberculosis in the Edinburgh area. Nine hundred and forty-seven index cases were notified during the 5-year period 1977-81; of these, 131 (14%) were detected by CP, 78 had previously undetected tuberculous disease and a further 53 required chemoprophylaxis (CPX). None had presented with symptoms, and disease was consequently detected at an earlier stage with fewer being sputum smear positive (10% vs 29% P less than 0.01). The 131 cases were found by CP during the screening of 4445 contacts, an overall yield of 2.9%. The highest yield was 18% for close contacts of sputum smear positive index cases, the yield for the casual contact being only 3%. The overall yield for contacts of smear negative respiratory and non-respiratory index cases was less than 2% in each group. Young contacts were particularly vulnerable and the yield in Asian children was 10.2%, twice that of the 4.9% in non-Asian children (P less than 0.001). The incidence of new cases in contacts who had previous BCG vaccination was significantly lower than that in non-vaccinated contacts (1.15% vs 3.06% P less than 0.001) suggesting a protective effect of 62%. One hundred and twenty-five (95%) of the 131 new cases were diagnosed within 3 months of first attendance, the remaining 5% at 6 months. The workload involved in screening contacts in this series could have been halved by restricting CP to all contacts of sputum smear positive index cases and only the close contacts of all other index cases. This would have resulted in missing 18% of the new cases, or three cases of tuberculosis and two cases requiring CPX per year, in a population of 608 000. Seventy-two (7.6%) of the 947 index cases were of Asian origin. Their disease occurred more in young adults, especially women, and was more frequently extrapulmonary in site (25% vs 12% in non-Asians P less than 0.01). We conclude that contact procedures remain valuable in the detection of new, asymptomatic cases of tuberculosis in Edinburgh and, by implication, in other urban areas of the United Kingdom. Particular efforts should be directed towards children, Asians and those without BCG vaccination, especially if they have been in contact with sputum smear positive index cases.