The 1972 smallpox outbreak in Khulna Municipality, Bangladesh. II. Effectiveness of surveillance and containment in urban epidemic control.

Abstract

Between April 28 and June 22, 1972, 1384 smallpox cases and 372 deaths were detected in Khulna Municipality, Bangladesh. Within three weeks of instituting surveillance and containment activities the entire city-wide epidemic was under control. Active surveillance detected over 84% of all new cases, as estimated by dividing the number of cemetery registered “pox” burials by the observed case fatality rate. Ninety per cent of family contacts of detected cases were vaccinated in the course of three home visits. Only 75% were vaccinated at the time of the first visit, but intrafamilial transmission essentially ceased at that time. The secondary attack rate among families first visited within one week of onset of their index case was 1.2%, compared with 22.2% for those first visited after five or more weeks had elapsed. Few if any individuals vaccinated as late as five days into their incubation period developed clinical disease. Vaccination performed after that time still reduced the clinical attack rate, on the average, by 50%. These results suggest that selective epidemiologic control can be highly effective in aborting intense urban smallpox epidemics, and that the search of cemetery burial registers is a useful means of reconstructing the actual course of an epidemic and determining the thoroughness of case detection.