Lassa fever: response to an imported case.

In February, 1976, a Peace Corps worker returned to the United States from Sierra Leone with an undiagnosed illness later recognized as Lassa fever. To assess the risk of transmission and to contain a potential outbreak, we identified 552 contacts as having had exposure to the patient before the start of strict isolation procedures, and maintained intensive surveillance on these contacts for 21 days. At the end of the surveillance period, no illness had developed in contacts. One month later, a serologic survey among 29 of the contacts judged to be at high risk gave no evidence of infection. In response to the importation of this communicable and highly fatal disease, procedures for the isolation of the patient, the identification, surveillance and management of contacts and the handling of laboratory specimens were developed and implemented. These procedures could be adapted to future introductions of highly contagious diseases.