The world's last endemic case of smallpox: surveillance and containment measures.

On 31 October 1977, the world's last known case of endemic smallpox was discovered in Merca, Somalia. The source of infection was quickly identified; 19 days previously, the male patient had been in contact with two other cases for not more than 15 minutes, but the surveillance activities surrounding these cases did not identify him as a contact. The patient was isolated and containment and surveillance activities and a vaccination campaign were rapidly instituted; 161 contacts were identified, 41 of whom had not been vaccinated within the last three years. The patient recovered and fortunately no other cases occurred.