快猫短视频

Covid-19 could already be circulating in the US, according to similar genetic sequences in viruses from two people who contracted the disease several weeks apart. One comes from a recent case in Snohomish County, Washington, in which the infected person had no contact with another case or outbreak location. Despite this, the sequence of the virus in their sample closely matches that in the first infection detected in the US, on 21 January, in a man in the same county who had visited Wuhan.

Both sequences, which were posted to GISAID, a public database initially designed for flu viruses, share a rare single mutation.

鈥淭his strongly suggests that there has been cryptic transmission in Washington State for the past 6 weeks,鈥� with perhaps several hundred cases, tweeted Trevor Bedford at Fred Hutchinson Cancer Research Center in Seattle, who belongs to a scientific collaboration using genetic analysis to track covid-19.

The US has reported only 86 cases of covid-19 so far, but there could be more. Testing for the virus has been limited 鈥� partly because a test can cost more than $3000, and in some cases even people with private insurance may have to pay half of that.

But there have been other problems. Bedford suspects that the outbreak in Washington wasn鈥檛 detected until now because of narrow rules governing testing. Under guidelines issued on 1 February, a person needed to have had contact with mainland China or a known case to be tested for covid-19, and tests could only be processed at the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.

This led to a backlog of tests and the exclusion of cases infected elsewhere, including by local spread. Last month, the CDC initially refused to test the first locally acquired infection in the US for four days, because it didn鈥檛 meet the criteria for testing.

One problem was that in test kits the CDC sent to state labs, one of three components was faulty. China is now doing 1.6 million covid-19 tests a week, and South Korea is testing upwards of 10,000 people a day 鈥� some at drive-through windows 鈥� while the UK had tested about 13,000 suspected cases by 28 February.

By that same date, the US had tested only 500 people who met the test criteria, and some 2000 repatriated Americans.

Then on 28 February, the CDC issued new guidelines. These allow tests of people who have had contact with other places with covid-19 transmission, and the tests can be done at local public health labs using just the two working test components.

Three new locally acquired covid-19 cases were quickly reported from California, Oregon and Washington, including the Snohomish case. Caitlin Rivers at Johns Hopkins University in Maryland warns that the US should now test hospitalised patients with severe respiratory disease of unknown cause, to see if they have covid-19.

If there is substantial local transmission in the US, it could be hard to slow. Eric Toner at Johns Hopkins University warns that US hospitals 鈥渞outinely operate at or near full capacity鈥�, with worker shortages and overcrowded emergency rooms. The FluSurge model, which predicts hospital requirements in flu pandemics, estimates that a covid-19 pandemic could see 1 million Americans needing to be hospitalised, 200,000 in intensive care.

The US has only about 46,500 intensive care beds, which might be doubled in a crisis. 鈥淓ven spread out over several months, the mismatch between demand and resources is clear,鈥� says Toner. He warns hospitals to start preparing. 鈥淚n the event of a pandemic, the predictable costs of not preparing, in human, societal and political terms, would be huge,鈥� he says.

Sign up to our free Health Check newsletter for a weekly round-up of all the health and fitness news you need to know about