A neutralization test survey for Lassa Fever activity in Lassa, Nigeria.

5-8% of 434 sera collected in Lassa village, Nigeria, in August 1970 were positive by neutralization test for Lassa fever (LF) virus. A second survey in March 1971 found 15 of 47 complete compounds tested in Lassa, Dille and Yuba villages had at least one peron with serologically demonstrable experience with LF virus. 67% of positive compounds had more than one infected member. Four of 17 hospital staff sero-converted between August 1970 and March 1971 without symptoms, evidence that subclinical infections of LF occr.