AP Photo/Michael Dwyer
A series of coronavirus tests carried out in Chelsea, Massachusetts, suggested than many more people have been exposed to the coronavirus than official figures show.
The project, carried out by Massachusetts General Hospital, took blood from 200 volunteers and tested it for antibodies produced after exposure. 32% had the antibodies.
The official positive rate for COVID-19 testing in Chelsea is 2%, though officials had already assumed the real figures are much higher.
The study is only a snapshot, and its findings are not necessarily applicable to the rest of the US, or even Massachusetts.
A snapshot test of people in a town just outside of Boston found that around one-third of them had been exposed to the coronavirus, even though none showed symptoms.
The results from Chelsea, Massachusetts, have led some experts to conclude that the coronavirus outbreak there, and potentially elsewhere, had touched many more people than first thought.
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The study was carried out by medics from Massachusetts General Hospital, and was reported by the Boston Globe newspaper.
Chelsea is just outside Boston, and has one of the most severe outbreaks in the state.
The study asked 200 people to provide a drop of blood to be examined by a rapid testing kit, which delivered a result in 10 minutes. The Globe said that the tests are not FDA-approved, but are considered reliable by Massachusetts General.
Subjects were those who volunteered to do a test on April 14 and April 15 in Bellingham Square. The test excluded those who had already tested positive for the virus in a different way.
The test was not a large, controlled scientific study, and it isn't possible to confidently extrapolate to the rest of the US, or indeed even the wider Boston area.
However, it was enough to confirm the fears of local authorities, who renewed calls for people to follow social distancing rules.
64 of those tested — 32% — produced results that said they were carrying antibodies for the coronavirus, which are produced after exposure to it.
Around half of the 64 said they had experienced some symptoms which match COVID-19 in the past four weeks.
The 32% positive rate compares to an official infection figure of 2% in Chelsea, the Globe reported.
Thomas Ambrosino, the city manager in Chelsea, told the Globe: "We've long thought that the reported numbers are vastly under-counting what the actual infection is.. It's all the more reason for everyone to be practicing physical distancing."