(NEXSTAR) — Health officials are investigating the death of an Iowa resident believed to have contracted Lassa fever, a viral disease rarely seen in the U.S.

The resident, who has not been identified, had recently returned to the U.S. after visiting West Africa earlier this month. They were not sick while traveling, making the risk to fellow airplane passengers "extremely low," according to the Centers for Disease Control and Prevention.

The patient had been hospitalized in isolation at the University of Iowa Health Care Medical Center and testing done by the Nebraska Laboratory Response Network early Monday showed that the patient was presumptively positive for Lassa fever.

While the disease is uncommon in the U.S., should the test results be confirmed, this would mark the country's ninth known case of Lassa fever since 1969 among people returning from areas where the disease is found.

Here's what to know about the potentially deadly disease.

What is Lassa fever?

Lassa fever is a viral illness........

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