By Ethan Covey
A fatal case of Lassa fever, which occurred in an Iowa resident who returned from travel in Africa, is the first U.S. case since 2016, and only the ninth travel-associated case confirmed in the United States since Lassa fever was discovered in 1969 (MMWR Morb Mortal Wkly Rep 2025;74[11]:194-196).
The person returned to Iowa from Liberia in October 2024, where the patient had been doing construction work, and experienced fever, myalgias and headache eight days later. After care at two different hospitals, the patient died on the 21st day of their illness.
A blood specimen was tested at the Nebraska Public Health Laboratory using the BioFire Global Fever Special Pathogens Panel, and was positive for Lassa virus. The diagnosis was confirmed by the CDC’s Viral Special Pathogens Branch.
A public health response to the case resulted in the identification of 180 contacts. Of these, four household and three community-associated contacts were determined to have had a high risk for exposure. These seven individuals were quarantined until 21 days from last exposure.
The majority of the identified contacts (96%) were healthcare associated. Sixty-seven percent of these exposures were classified as high risk due to one or more omissions of personal protective equipment (PPE); 39% of the healthcare-associated contacts occurred while the patient was clinically stable. Five of the high-risk contacts had skin-to-skin contact with the individual, as well as one or more PPE omission, and were excluded from work until 21 days post-exposure.
No secondary cases of Lassa fever were identified.
“Our report highlights the importance of obtaining a travel history from febrile patients, effective viral hemorrhagic fever planning within public health departments and medical communities, and the importance of having rapid local testing capabilities available,” said Matthew Donahue, MD, the state epidemiologist for the Iowa Department of Health and Human Services. “This response was a multidisciplinary response that reinforces teamwork and makes partners better prepared for the next big response.”
Among laboratorians, 34 contacts were identified across six labs. Of these, 68% were identified as being high risk.
“There’s limited guidance available for understanding the risk of transmission among laboratorians processing specimens from an infected patient,” Dr. Donahue said. “Guidance for understanding risk in a laboratory is a need and should be a focus moving forward.”
Dr. Donahue said future studies will hopefully cast light on why an estimated 80% of Lassa fever cases result in mild symptoms, and some individuals may go undiagnosed. “In the future, we hope to determine if contacts may have had mild/asymptomatic illness through a seroprevalence analysis,” he said.
Dr. Donahue reported no relevant financial disclosures.
