A dry cough. Loss of smell. Diarrhea. Fever. All of these have been considered possible symptoms associated with SARS-CoV-2 infection, along with the complete absence of symptoms at all. In the absence of a sufficient testing capacity, many areas in the United States are being compelled to allocate their limited tests to only those who seem to have COVID-19 symptoms. But, given the difficulty of determining which symptoms actually indicate a likely infection, those are difficult decisions to make.

The bewildering array of symptoms also raises questions about why people respond so differently to the same virus.

Figuring out what’s going on in the midst of a pandemic is an incredible challenge. We’re going to take a look at some preliminary reports about one way doing so—not because the results are likely to hold up as more research comes in, but because it reveals some of the ways that researchers are using to try to understand the virus’ infection.