Aedes aegypti mosquitoes are seen at the Laboratory of Entomology and Ecology of the Dengue Branch of the Centers for Disease Control and Prevention in San Juan. (Alvin Baez/Reuters)

U.S. health officials confirmed Friday that a Utah resident's death late last month was the first Zika-related death in the continental United States.

The Salt Lake County health department said the elderly person had an underlying health condition. The individual, who had traveled to a Zika-affected region this year, tested positive for the virus, the department said in a statement. The exact cause of death has not been determined, however.

"We know [Zika] contributed to the death, but we don't know if it was the sole cause," medical officer Dagmar Vitek said in a news conference.

Gary Edwards, the department's executive director, said officials learned of the case while reviewing death certificates. Laboratory tests conducted in Utah were positive for Zika, but the results "did not come back until the individual had died," he said.

Citing health privacy concerns, the local officials provided no other details.

The Centers for Disease Control and Prevention said Friday that it had been notified of the death. In April, the CDC reported the first U.S. death from Zika in a patient in Puerto Rico. That man, who was in his 70s, died from internal bleeding after developing severe thrombocytopenia -- a rare immune reaction to his infection that cause low levels of platelets that help blood clot.

Zika is spread primarily through the bite of an infected Aedes aegypti or Aedes albopictus mosquito. Salt Lake County officials said neither species is present in their area. The virus can also spread through sex. About 80 percent of people who get infected have no symptoms, while the rest tend to only have mild symptoms that last for several days to a week.

In rare cases, though, the virus has been linked to a nervous system disorder that can cause muscle weakness and sometimes paralysis. It poses its biggest danger during pregnancy, when infection can cause a range of severe fetal abnormalities.

As of July 7, no cases of locally transmitted, mosquito-borne Zika have been reported in the continental United States. As of July 6, a total of 1,132 cases of travel-associated Zika have been reported in the 50 states and District of Columbia. Federal, state and local officials are preparing for the possibility of local spread of Zika.

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