The newly proposed COVID-19 testing in Wuhan

There is a report that Wuhan plans to test all its 10-11 million residents in ten days (https://news.sina.com.cn/c/2020-05-12/doc-iirczymk1215436.shtml and https://www.businessinsider.com/coronavirus-wuhan-orders-all-residents-tested-six-new-cases-2020-5).  It is impossible to justify this newly announced effort: how much time, money, and manpower it will waste, and how little and useless information it will generate. 

My 4/17/2020 blog and https://news.sina.com.cn/c/2020-04-17/doc-iircuyvh8366932.shtml explained Wuhan has been testing people every day.  According to the daily results, the positive rate is below 1 in 1000, all positives have been asymptomatic, until the most recent 6 confirmed cases.  Altogether Wuhan has tested about 1.8 million since April and got ~1000 asymptomatic.  The rest of China also detected perhaps a few hundred positives in people arriving from Wuhan and Hubei, ~ 10 have had symptoms.  All the results are clear-cut: the positive rate for Wuhan residents is lower than 1 in 1000, and most of whom are not infectious.    

It should be stressed that it is not clear how Wuhan wants to do this new testing: will it include everybody, or exclude those who were tested recently?  In truth, it is only a notice from Wuhan, asking individual districts to devise a plan to do the testing in 10 days.  If the districts find it undoable, the whole thing might be changed beyond recognition.  But with a simplistic understanding, this endeavor, like the Wuhan lockdown, is also unprecedented.  11 million tests in 10 days, no other country has done 11 million in total yet, not the least in a city, in mere 10 days.  How much work it will be, and how much precious resource will be wasted, to find fewer than 10K infections, when maybe only 10-100 will be infectious!  And not counting the false negatives and false positives, which will add 10 times to the unspeakable useless work.  Besides, one tests negative today doesn’t mean he will stay negative tomorrow or the day after.  Which means you need to test everybody everyday, or every other day, which is ridiculous and impossible.

As my May 2, 2020 blog stated, the success of Wuhan lockdown doesn’t mean one should apply it or its principles blindly everywhere or every time.  The current efforts should be better spent on monitoring and tracing.  Because the most likely outbreaks in China now come from importations, Wuhan only the distant second.  This total Wuhan in 10 days thing might not happen, for all its utter absurdity and impracticality.  Does someone in Wuhan really think test kits are cheap like water, and Wuhan has thousands of qPCR machines that run 24 hours a day?  And even if the whole medical staff do nothing but taking samples, they won’t finish it in time.  Because the sensitivity of testing is only about 70%, you will miss many positive anyway. 

This proposed new testing, if undertaken, won’t tell us anything about COVID-19 we don’t already know, except identifying a few hundred people who are positive but not necessarily infectious.  A more interesting question is the percentage of Wuhan residents who are Ab positive, indicative of past infections.  Wuhan started the city-wide 11K Ab sampling on April 11 (https://xueqiu.com/3025835605/147163641).  The preliminary results were supposed to come out on April 22, but so far no official results yet.  There are, however, a few news reports on Ab tests conducted by hospitals (https://www.sohu.com/a/393679225_120162468), with positive rates from 2-10%.  It doesn’t mean anything nefarious, as Ab testing is not foolproof yet.  The reason for the delay is most likely Wuhan got conflicting or non-interpretable data because of inconsistency in the Ab test kit(s).  For example, the kit originally used might have specificity and sensitivity rates not high enough, or maybe Wuhan uses different kits, whose results are not comparable.  There are hundreds of Ab kits in the market, and only in May have verification data coming out.  So Wuhan may be testing the same blood samples with multiple kits, delaying the results.  Or if they use up all the blood samples to find the best kit, then they need to recruit more people.     

In any case, when one has a hammer, don’t think everything is a nail.  If Wuhan follows through with 11 million in 10 days, it will get another unprecedented title, only this time the end results will be absolutely disappointing.  

Note on May 15, 2020: More information has come out according to the news.  1. Some districts in Wuhan have started, earlier than others; 2. It is voluntary; 3. It is free; 4. Wuhan had tested ~ 4 million since Jan until this exercise, and those tested within the last month don't have to do it; 5. Children 6 years or younger don't have to do it.  So the initial, reported goal of 11 million in 10 days, is as expected a simplification.  The most important goal is to cover all susceptible people, although it is still voluntary.  At most Wuhan may test 8 million in weeks, not 10 days.  Another way to lessen the workload is to pool several samples, like 20, into one test.  If it is negative, as expected for the vast majority, then all 20 are negative.  If positive, the 20 will be sampled again.  This will save a lot of time and kits, but reduce sensitivity, leading one to think why even bother?  This whole thing doesn't change the fact it is a folly.  The aim would have been OK except that it is such a big waste.