A dying patient in Utah with a staggering level of circulating Zika virus apparently infected a family caregiver in what may be the first case of non-sexual person-to-person transmission of the emerging virus.

The family member who cared for the patient completely recovered from the Zika infection, but the strange Utah case opens up a whole new area of concern for a virus that is proving highly unpredictable. In addition, as this issue went to press, the first 15 cases of mosquito transmission were reported in Miami. That was a feared, but expected, milestone, but the Utah case is yet another departure from the projected Zika characteristics.

The case began with the first reported Zika-related death of a person in the continental U.S., in late June near Salt Lake City.

“The deceased patient had traveled to an area with Zika and lab tests showed he had uniquely high amounts of virus — more than 100,000 times higher than seen in other samples of infected people — in his blood,” the CDC reported.

That certainly suggests how the patient was able to transmit the virus to a family contact who provided care, as any exposure to blood or body fluid could have contained high levels of virus. Zika virus has been recovered in a variety of bodily fluids in past research, including semen, vaginal fluid, urine, blood, and saliva. Transmission by one of these fluids is merely supposition at this point, but public health investigators are not ruling anything out. Asked about airborne transmission, a CDC epidemiologist said at a recent press conference that was “extremely unlikely,” particularly in the absence of a medical procedure that could generate aerosols.

“In our line of work, nothing is truly off the table,” said Michael Bell, MD, deputy director of CDC’s Division of Healthcare Quality Promotion. “The table is vast. We never want to underestimate possibilities; however, it would be extremely unlikely for something like that to occur.”

Here’s what is known: The caregiver had not traveled to a Zika transmission area, had no sexual risk factors, and the Aedes mosquitoes that transmit the virus have not been seen in Utah. Culex mosquitoes that typically feed on birds in the state are being periodically tested for Zika virus, and thus far all are negative. The CDC and state health officials are testing other family members of the index case, and healthcare workers who may have provided care.

Again, the secondary case recovered and did not have the high viral titers of Zika like the index case. The question of why the first patient had such an off-the-charts viral load raises the issue of whether Zika proliferated due to the patient’s reported underlying medical condition.

“From the infection control perspective, I think it is too early to make a clear statement about what we think could have happened,” Bell said at the press conference. “Certainly a high viral load is something we take very seriously, and as it is not something about which we have a very long experience [with Zika]. So you are asking sort of a chicken-or-the-egg question. Someone who is extremely ill and debilitated from another disease process could have a diminished immune system that does not fight the virus as well and that might allow more virus to proliferate in the bloodstream. On the other hand, someone with a high viral load could be sick with the viral infection. I personally cannot tell you which way that went.”

Given the lack of information, the CDC is not changing any guidelines for PPE use by healthcare workers treating Zika patients.

“Make sure that healthcare personnel don’t have any direct contact with blood or bodily fluid, through broken skin, needlesticks, or splashes to the mucous membranes,” Bell said. “I think this highlights the fact that with an infection like Zika virus, a good percentage of patients don’t have symptoms. It means that it is as important as ever to stick with good precautions. Just like we assume anybody might carry hepatitis or HIV, we don’t wait for a positive diagnosis in order to prevent blood or bodily fluid exposure. The same thing is true with Zika virus, and this is a great example of why we should never take chances, but always adhere to standard precautions.”