The Chinese city of Wuhan, the epicenter of the novel coronavirus outbreak, had a viral homecoming of sorts when a few new cases, described as a "handful," were discovered at a housing compound. The city’s response was an attempt to test each one of the 11 million people who call Wuhan home.

Medical authorities report that they fell a bit short of testing everyone but still managed to run coronavirus swab tests on more than 9 million people in the past 10 days. On Friday (May 22), the test count was 1.47 million, more than triple the number of tests performed on a single day in the U.S., going by the data from Atlantic’s COVID Tracking Project.

The results were optimistic with only 180 people testing positive as asymptomatic carriers of the coronavirus. They were put under quarantine and observed for symptoms with only one case being reclassified as a confirmed case.

To test that many people in less than two weeks required a technique called “sample pooling” that dates to World War II in the early 1940s when the U.S. military pooled GI’s urine sample to test for syphilis.

For sample pooling to work, the assumption is that the number of people infected is relatively low. Instead of individual testing, the samples taken are combined and tested in groups.

For example, if the infection rate is 1 in 1000 (or 0.1%) and the samples are divided into groups of 10, then 100 tests will be run. The people in the one positive batch of 10 will be re-tested individually to single out the one infected person. Instead of 1000 tests, only 110 tests are needed which is a significant test and time saver, if accurate records are kept.

The Wuhan infection rate of 180 positive out of nine million is significantly less than 0.1% meaning that future sample pooling may be able to use larger groups to further reduce the number of tests.

Modern technologies as well as old-fashioned footwork were used in the effort. Mobile-phone apps to quickly check results and the use of a health-status code to allow people to show their uninfected status was on display as were the use of megaphones and knocking on doors to reach untested stragglers and holdouts.

An official notice circulated in newspapers and on social media sites Monday (May 25) encouraging Wuhan citizens who hadn’t yet, to register for testing before 5:00 p.m., Tuesday. The only regret over the testing is that it was not done earlier before the coronavirus left its 'home' in January.

Fresh tests for Wuhan as cluster sparks mass virus screening
Fresh tests for Wuhan as cluster sparks mass virus screening AFPTV / Lillian DING