Lassa Fever Missed in 11% of Febrile Hospital Admissions in Liberia, Study Finds

A new study led by researchers at the Institute for Global Health and Infectious Diseases at the University of North Carolina School of Medicine shows an urgent need for improved detection and treatment of Lassa fever. The findings were published in The Lancet Infectious Diseases and draw on 6 years of data from Liberia, one of the countries most affected by the disease.

Among patients admitted with fever, 11% were infected with Lassa virus despite not being clinically suspected. The PREPARE (Prevalence, Pathogenesis, and Persistence) study was conducted between July 2018 and August 2024 at Phebe and CB Dunbar Hospitals in central Liberia. Researchers enrolled 435 patients aged five years and older who were admitted with fever or with suspected Lassa fever.

Lassa fever, a severe Ebola-like illness designated by the World Health Organization as being among the world's top pandemic threats, causes thousands of deaths each year, mainly in Nigeria, Liberia, and Sierra Leone. Spread primarily by rodents, the virus can also be transmitted person-to-person through direct contact with blood, body fluids, or secretions of infected individuals. Lassa fever remains a major public health threat in West Africa, with high rates of infection and death—often exceeding 20% in some settings.

All participants in the study underwent plasma LASV RNA RT-PCR testing, and those with confirmed infection were followed longitudinally during hospitalization and for up to one-year post-discharge to assess viral dynamics, immune responses, and clinical outcomes. Mortality was strongly linked to higher viral loads and weaker immune responses. Patients who died had higher viral loads and weaker antibody responses.

Children were disproportionately affected: 43% of confirmed cases were aged 5–17 years. Longitudinal data showing severe Lassa fever correlates with higher viral loads, organ damage, and worse outcomes, underscores the importance of early detection and antiviral treatment. Because complications typically emerge in the second week of illness, the window for effective intervention is narrow.

Beyond West Africa, more than 32 imported cases have been reported globally, including to the US, one-third of which were fatal, highlighting its international significance. Many of these deaths can be prevented with early and increased access to diagnostics, supportive care and potentially initiation of effective therapeutics. Furthermore, with over 30 reported cases of Lassa fever imported into non-endemic countries, one third of which were fatal, the importance of early detection and care extends beyond West Africa.

Currently, testing for Lassa fever even in endemic countries is limited and many cases go undiagnosed. The UNC-Liberia team established real-time PCR testing for the Lassa virus at Phebe Hospital in rural Liberia in collaboration with the hospital and the National Public Health Institute of Liberia as a centerpiece of UNC research operations at the site.

Limited access to PCR testing and overlapping symptoms with other common infectious diseases contribute to underdiagnosis. Clinical suspicion is often low because the symptoms of Lassa fever overlap with those of other common infections. Missed cases not only worsen patient outcomes but also expose healthcare workers to infection and increase the risk of human-to-human transmission in clinical settings.

An editorial review of the study, also published in The Lancet Infectious Diseases, underscores the implications for missed diagnoses while recognizing the need for expanded point-of-care diagnostics, vaccines and therapeutics—to reduce mortality, prevent outbreaks, and ultimately work toward eliminating Lassa fever in Liberia and other endemic regions. The PREPARE study was funded by the U.S. National Institute of Allergy and Infectious Diseases and the National Institutes of Health.