Doctors and epidemiologists have traced the origins of a mysterious Zika case in Utah, and it appears that the person acquired the infection through another person’s tears or sweat. The person had not traveled to a Zika-affected area, nor did they have sex with an infected person. Instead, they helped a nurse reposition a hospitalized Zika patient and had also wiped that patient’s eyes, according to a new paper in the New England Journal of Medicine authored by a team led by Sankar Swaminathan, the chief of infections disease at University of Utah Health Care. At no point did the person—“Patient 2”—come into contact with the first patient’s blood or other bodily fluids.

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This is the first documented case of Zika being transmitted through nonsexual contact, though Swaminathan and his team write that it’s unlikely the virus passed through Patient 2’s intact skin. More likely, they had an open wound or touched their eyes or another mucous membrane like the nose or mouth. It’s tempting to believe that this is the result of a troubling new mutation, but that doesn’t appear to be the case, at least not yet. Here’s Julie Beck, reporting for The Atlantic:

It’s very rare for people to die of Zika—in this outbreak so far, there have been only 13 fatal cases in adults (not counting deaths from Zika-related Guillain-Barré). When Zika patients die, Swaminathan says, in many cases they also have a preexisting condition like leukemia that compromises the immune system. In this case, the first patient, while elderly, was not immunocompromised. But his infection was extremely severe. His blood had 200 million copies of the virus per milliliter—with a typical infection, Swaminathan says, you’d expect to see hundreds of thousands, and one million would be considered high.

Swaminanthan goes on to speculate that the person may have had a previous dengue infection—which can make subsequent dengue infections worse by triggering related antibodies, and dengue and Zika share the same genus—or that they may have had a specific genetic profile that made the uniquely susceptible. What’s more, while Patient 2 contracted Zika, it appears to be a relatively normal infection with normal viral loads, hinting that Patient 1’s infection was out of the ordinary.

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Photo credit: Jim Gathany/CDC