Two Snohomish County residents in the state of Washington who say they were sick with a respiratory illness in December have now tested positive for COVID-19 antibodies, calling into question how long the virus was circulating in the U.S. The serology tests for antibodies cannot date the time of the virus, so officials caution that it is possible that they were sick with another ailment in December and then contracted the coronavirus without symptoms later. Health officials in the state, which was one of the earliest hot spots, say they will not count them in the official case tallies. The first official case in Snohomish County was detected on Jan. 21. “There’s a saying in medicine, when you hear hoofbeats think horses, not zebras,” Dr. Chris Spitters, Snohomish County Health Officer told KOMO news. “So, the horse in that scenario would be that they had a non-COVID infection in December and then subsequently got infected with COVID but didn’t know it, developed antibodies and then here we are.”