Health authorities in Utah are investigating a unique case of Zika found in a person who had been caring for a relative who had an unusually high level of the virus in his blood.

Exactly how the disease was transmitted is still a mystery, though the person has since recovered.

The elderly relative who died after contracting Zika abroad had amounts of the virus in his blood more than 100,000 times higher than other samples of infected people, according to the Centers for Disease Control and Prevention.

Though the tropical mosquito that mainly spreads Zika isn't typically found in Utah, officials haven't ruled out the possibility that the man brought a mosquito back with him from an area where he caught the virus, perhaps in a suitcase, according to the Centers for Disease Control and Prevention.

"The new case in Utah is a surprise, showing that we still have more to learn about Zika," CDC medical epidemiologist Dr. Erin Staples said.

Authorities did not give further details about either patient, citing health privacy laws. The new case was discovered after a doctor noticed the caregiver's Zika-like symptoms, which include rash, fever and pink eye, officials said.

He or she had cared for the older man both at home and in the hospital. That man died in late June and was the first death of a Zika-infected in the continental U.S. His age and another health condition made his exact cause of death unclear. The caregiver did not travel to an affected area.

Health workers are testing other people who had contact with the first patient. Officials are trapping mosquitoes in Utah to test them, though the species that spread the disease don't usually live in the state's high altitude and cold winters.

The CDC did not immediately revise its advice to health care workers or caregivers after the new case emerged.

"Based on what we know so far about this case, there is no evidence that there is any risk of Zika virus transmission among the general public in Utah," said Dr. Angela Dunn, deputy state epidemiologist at the Utah Department of Health.

Signs of Zika have been found in blood, urine, semen and saliva. There's no evidence yet that the Zika infection in this case is an unusual mutation, but researchers are exploring that possibility through genomic analysis.

The virus causes only a mild illness in most people. But during recent outbreaks in Latin America, scientists discovered that infection during pregnancy has led to severe brain-related birth defects.

No cases of mosquito-spread Zika have been reported in the continental United States, according to the CDC. Health experts think mosquito transmission probably will occur in the U.S., but the expectation is that it will be in low-elevation, sweltering places where the insect has been a steady problem — such as southern Florida or southern Texas.

More than 1,300 Zika illnesses have been reported in the 50 states and the District of Columbia, including eight in Utah, according to health officials. Almost all were people who had traveled to Zika outbreak countries and caught the virus there.

Fourteen were people who had not traveled to Zika zones but had sex with someone who had.

The CDC has also been tracking pregnant women infected with Zika, and says they have five reports of pregnancy losses because of miscarriage, stillbirth or abortion.

