Lassa fever may be underdetected after cases reported in the U.S.

Experts say Lassa fever is underdetected in parts of West Africa and testing remains limited, and more than 32 imported cases — including some in the United States — have been reported.

Lassa fever is a viral illness found in parts of West Africa that experts say is often missed by routine clinical screening and has been linked to imported cases in other countries, including the United States. The World Health Organization lists Lassa fever among pathogens of pandemic concern. Researchers note that access to testing is limited in endemic areas and that the full range of symptoms is not fully understood. A multi-year study in Liberia examined hospitalized patients and aimed to clarify viral dynamics and diagnosis. Key findings: - A prospective study in central Liberia (July 2018–August 2024) tested 435 patients and found that 11 percent of those admitted with a fever but not suspected of Lassa were PCR-confirmed cases. - Children aged 5 to 17 accounted for 43 percent of confirmed infections in the study sample. - The World Health Organization has designated Lassa fever as among top pandemic threats; more than 32 imported cases have been reported globally, including in the U.S., with about one-third reported fatal. - Testing is limited in many endemic areas; UNC Project-Liberia has implemented real-time PCR testing in rural settings, but clinicians generally need to suspect Lassa to order tests. Summary: Limited routine testing and overlapping symptoms appear to allow Lassa virus infections to be missed, with implications for patient outcomes and potential spread beyond endemic regions. Study authors note that earlier detection is important for reducing deaths and limiting exposure of health workers. Specific broader policy or programmatic actions were not detailed in the report; these remain undetermined at this time.