Lassa Fever Confirmed in Death of U.S. Traveler Returning from Liberia

On May 25, 2015, CDC and the New Jersey Department of Health confirmed a death from Lassa fever in a person who traveled to the United States from Liberia. The patient traveled from Liberia to Morocco to JFK International Airport on May 17. The patient did not have a fever on departure from Liberia, did not report symptoms, such as diarrhea, vomiting, or bleeding during the flight, and he did not have a fever upon arrival in the United States. On May 18, the patient went to a hospital in New Jersey with a sore throat, fever, and tiredness. According to the hospital, he was asked on May 18 about his travel history and he did not indicate travel to West Africa. The patient was sent home the same day and reported a normal temperature to the local health department on May 19 and 20.

On May 21, the patient returned to the hospital when symptoms worsened and was transferred to a second hospital prepared to treat viral hemorrhagic fevers. Samples submitted to CDC tested positive for Lassa fever on May 25. Tests for Ebola and other viral hemorrhagic fevers were negative. The patient was in appropriate isolation when he died there the evening of May 25.

CDC has sent a rapid response team of public health specialists to New Jersey to assist state and local officials in the response to this imported case of Lassa fever. CDC will help state and local health departments in finding and assessing the level of risk to everyone who came into direct contact with the patient. The team has obtained the manifest for the flight from Morocco to JFK and is reaching out to passengers sitting within a three feet of the patient. CDC is working with state and local health departments, as well as ministries of health, to reach out to the passengers in question.

Lassa fever is a viral disease common in West Africa but rarely seen in the United States. There has never been person-to-person transmission of Lassa fever documented in the United States. The New Jersey case is the sixth known occurrence of Lassa fever in travelers returning to the United States since 1969, not including two recovering patients. The last case was reported in Minnesota in 2014.

Although Lassa fever can produce bleeding in infected people, the disease is different from Ebola, which is responsible for the current outbreak in West Africa. In general, Lassa fever is less likely to be deadly than Ebola. Lassa has an estimated 1% death rate while that for Ebola is about 70%. Lassa virus is also less likely than Ebola to be spread from person to person.

In West Africa, Lassa virus is carried by rats and spread to humans through contact with urine or droppings of infected rats. In rare cases it can be spread from person to person through direct contact with a sick person’s blood or body fluids. The virus is not transmitted through casual contact, and patients are not believed to be infectious before the onset of symptoms. An estimated 100,000 to 300,000 cases of Lassa fever, and 5,000 deaths related to Lassa fever, occur in West Africa each year.

Updates will be provided as the investigation continues.