One of the persistent questions surrounding this outbreak of the COVID-19 coronavirus is whether all of the people who had a bout of some mysterious flu-like illness in the two months or so before the world really started to pay attention to the disease have already had it. Writing on her Facebook page, Lisa Daft made the excellent observation that Rhode Island saw “a lot of negative flu tests this winter.”
The chart she displays comes from the RI Dept. of Health’s Influenza Surveillance page, which currently offers the following, with the gray sections representing tests that came back negative for the flu, presumably despite flu-like symptoms:
Can the number of those negative results actually be showing us early COVID-19 infections? Possibly, but finding the same chart in the last few years of the Dept. of Health’s annual report suggests these results aren’t actually unusual (2016, 2017, 2018, 2019). Here’s the one from two years ago:
These trends are consistent with national experience. The following chart shows the number of flu-negative tests for the United States from October 2015 through January 2020, as reported by the World Health Organization:
So, while negative tests during this flu season look like they’re going to prove to have been higher than average, they aren’t unusual, and this hasn’t been the worst year on record for negative tests. Of course, that doesn’t mean the strange illnesses so many people have reported were not COVID-19. Every year, the number of negative tests could be accounted for by something different, ranging from the amount of attention the media is paying to the flu to the severity of the flu season (making people more inclined to get tested) to an outbreak of some virus that is never identified.
The next question to answer would be how many deaths occur each year due to mysterious illnesses that initially present as the flu.