Coronavirus: Nine million tested for COVID-19 in Wuhan

A staggering nine million people in Wuhan have been tested for COVID-19 over the past 10 days, according to Chinese officials.

A guard checks the temperature of a customer as he enters a shop in Wuhan on Tuesday. Picture: AFP

The central Chinese city of Wuhan says it has collected coronavirus swab tests from more than nine million of its 11 million people over the past 10 days.

Most of those nine million samples have already been processed, according to a daily record of nucleic-acid tests by Wuhan health authorities, who said the mass testing identified 180 asymptomatic carriers of the coronavirus, who were put under quarantine and monitored for symptoms. Just one of those cases was later recategorised as a confirmed case.

On Friday alone, the city said it tested 1.47 million people — more than three times the number on the busiest day of testing in the US.

The aggressive mass-testing regimen was ordered after authorities said a handful of coronavirus cases had been discovered earlier this month. The plan to test all of the city’s 11 million people was greeted with doubt from some sceptics, who questioned the ability and necessity of testing so many people in such a short period.

While falling slightly short of its ambitious target of testing everyone, Wuhan was nonetheless able to test so many people so quickly by adopting an approach known as “sample pooling”, used earlier in the US and Germany to track COVID-19, albeit on a much smaller scale.

Using sample pooling, Wuhan authorities collected samples one by one from citizens, and then processed five to 10 of them at once in a single nucleic-acid test.

By bundling multiple samples, Wuhan was able to immediately clear all of the citizens included in one test — as long as the test came out as negative — thereby significantly cutting the number of total nucleic-acid tests required.

Sample pooling has been used to identify blood-borne infectious diseases. The practice of group testing dates back to World War II, when the US military pooled service members’ urine samples to screen for syphilis.

During the coronavirus pandemic, researchers in the San Francisco Bay area employed sample pooling to track early community transmission in a retrospective screening of routine respiratory patients, identifying two individual infections among nearly 3000 people, whose samples had been divided into groups of nine or 10.

Using a similar approach, scientists from Germany’s Saarland University pooled up to 30 samples in tests that resulted in “sufficient diagnostic accuracy”, according to their paper published in The Lancet medical journal.

The approach works only when the results of the pools are largely negative. That appears to be the case in Wuhan. Within the past 10 days, as it rolled out near-blanket testing, it added no more than three dozen asymptomatic cases from the hundreds of thousands of tests conducted each day.

Wuhan public-health experts said jurisdictions facing active cases of large-scale transmission could benefit from the kind of mass-scale testing in which the city has just engaged.

Wuhan citizens were able to check results in mobile phone apps within days of testing, and many presented it alongside another health-status code to get around, making it harder for the city’s infection reports to be fudged. Wuhan said earlier that the testing campaign could help cut off transmissions and reassure residents.

In one neighbourhood, according to the city’s official newspaper, only 946 of the community’s 210,000 people hadn’t been tested, as of Saturday. Social workers knocked on doors and used megaphones to reach the remaining holdouts, the report said.

The Wall Street Journal