Smallpox surveillance in Bangladesh: II - Smallpox facial scar survey assessment of surveillance effectiveness.

A smallpox facial scar survey of 465 892 persons aged 0-19 years was carried out in Bangladesh in 1976, covering approximately 1% of the 0-19 year old population. Of the 4 306 persons found with facial scarring consistent with previous smallpox infection, none had a history of smallpox with onset after the last reported case on October 16, 1975. Histories taken from persons with facial scars allowed smallpox incidence to be estimated for each year from 1972 to 1975. These estimates indicate that completeness of reporting increased steadily from 11.8% in 1972 to 83.0% in 1975, reflecting the increasing effectiveness of surveillance.