Because the incubation period ranges from a few days to >2 weeks (1,5) and many symptoms are nonspecific, the potential exists for human carriage of Lassa virus to areas outside those to which it is endemic, putting travel companions, close contacts, and healthcare providers at risk for secondary infection. Before 2010, five instances of imported Lassa virus were recorded in persons from West Africa to the United States. Although early instances involved sick persons who were airlifted to the United States for diagnosis and treatment (7–9), the 2 most recent occurrences (1989 and 2004) involved persons who were not identified as potentially infectious until healthcare was sought in the United States (10,11). Here we report a case in a person who became infected and sick during a trip to Liberia and sought care upon return to the United States.

The patient’s symptoms persisted upon arrival in the United States, prompting him to seek medical attention on day 5 of his illness. When he sought treatment, he had fever of 103°F, pulse of 99 beats/min, respiratory rate of 15 breaths/min, and blood pressure of 120/80 mm Hg (Table A1). His physical examination was notable for posterior cervical adenopathy and a palpable spleen tip (Table). He had no evidence of conjunctival, nasal, or oral petechiae; no skin rashes; and no signs of hemorrhage or other lesions. Initial laboratory data showed leukopenia and thrombocytopenia and minimal transaminase elevations (Table A1). Empiric malaria treatment was initiated upon admission and was subsequently discontinued when Plasmodium spp. antigen testing was negative and thick and thin blood smears showed no evident parasitemia. By the next day, mild pharyngitis with slight tonsillar exudates had developed. On the third hospital day, substernal chest pain and profuse watery diarrhea developed. Increasing transaminases and a slight coagulopathy were noted. Lassa fever was considered in the differential diagnosis; contact precautions and, subsequently, airborne precautions were taken. Because of noted clinical improvement, he was not given empiric intravenous ribavirin.

On day 5 of hospitalization, Lassa virus was identified by real-time PCR by using samples collected 2 days earlier, and sequencing of the amplified fragment yielded a unique sequence similar to sequences from previous Lassa virus isolates from Liberia. Subsequent samples confirmed Lassa fever diagnosis on the basis of real-time PCR, viral culture, and serology (Table).

The patient’s fever resolved by day 16 of his illness. After 2 successive negative blood real-time PCR results, he was discharged from the hospital on day 21 of his illness with instructions to avoid unprotected sexual intercourse for 2 months. No hearing abnormalities were noted at the time of discharge or during telephone conversations 2 weeks and 2 months later.

As in this case, early suspicion of Lassa fever should prompt isolation measures to avoid secondary transmission; laboratory testing should be limited to essential tests, and all laboratory specimens should be handled with appropriate biosafety precautions to avoid aerosolizing the virus (13). Experience in regions where Lassa virus is endemic suggests human-to-human transmission occurs through direct contact with blood and body fluids or large-particle inhalation; transmission through viral aerosolization is not seen; and generally, when universal precautions are undertaken, transmission is unlikely (14). Nonetheless, aerosol in addition to contact precautions were undertaken once Lassa fever was suspected, given the theoretical potential for acquiring infection through inhalation of airborne virus from respiratory secretions or, in this case, copious diarrhea.