Covid-19 in Japan: Numbers vs. Testing

Every day Tokyoites are anxiously waiting for the latest daily count of new confirmed Covid cases: Is it less than 200 or more than 200? It was a big thing when it first exceeded 100. On April 11, it barely missed the next big number with 197 cases. But what does it really mean?

“Cases of Covid-19 confirmed with PCR tests” depends as much on the number of tests conducted as the actual number of people newly infected. Anyone not tested is by definition not included in the count. Until now, anyone testing positive has been sent to a hospital, which supposedly is legally required (only recently have light cases been moved out to specially rented hotel rooms). Therefore hospitals have been reserving tests to people with the most severe symptoms or with pre-existing conditions so that the most deserving patients will occupy the limited hospital beds they can take up.

It may seem counter-intuitive, but the primary purpose of testing has not been to track the growth of infections but to allocate hospital beds. The number does not reflect reality as it is artificially throttled. As long as this policy continues, new confirmed cases will basically only be allowed to grow at a rate at which hospital beds are found for them, which is becoming increasingly difficult, as more and more hospitals are turning away new patients to avoid healthcare associated infections (HAI). There have been a number of cases of infection hotspots in hospitals.

An article in the The Atlantic discusses positivity, the rate of confirmed infections found as a share of tests conducted in different states and countries (please don’t confuse this with prevalence, the rate of infected people as a percentage of the population).

Basically, the higher the percentage of tests that come out positive, the more likely a country or region is to be undercounting infections, for example because of limited lab capacities or limited access to hospitals that can do testing:

“[W]hile the U.S. has a 20 percent positivity rate, South Korea’s is only about 2 percent—a full order of magnitude smaller.

South Korea is not alone in bringing its positivity rate down: America’s figure dwarfs that of almost every other developed country. Canada, Germany and Denmark have positivity rates from 6 to 8 percent. Australia and New Zealand have 2 percent positivity rates. Even Italy—which faced one of the world’s most ravaging outbreaks—has a 15 percent rate. It has found nearly 160,000 cases and conducted more than a million tests. Virtually the only wealthy country with a larger positivity rate than the U.S. is the United Kingdom, where more than 30 percent of people tested for the virus have been positive.

Comparing American states to regions in other countries results in the same general pattern. In Lombardy, the hardest hit part of Italy, the positive rate today stands at about 28 percent. That’s comparable to the rate in Connecticut. But New York, so far the hardest hit state in the U.S., has an even higher rate of 41 percent. And in New Jersey, an astounding one in two people tested for the virus are found to have it.”

(The Atlantic, 2020-04-16)

So what this tells us is that a high positive rate in the tests conducted indicates a higher rate of uncounted cases that the system can’t keep up with.

What does that mean about the potential undercounting of explosive infection growth in Japan and specifically in Tokyo? According to statistics published by the Tokyo Metropolitan government on its website, by yesterday (April 16) Tokyo had 2,595 confirmed Covid-19 cases out of 7,244 cases tested. That’s a positivity of 36%, higher than the positivity for the UK (30%), Lombardy and Connecticut (28%), the US overall (20%), Italy (15%) and Canada, Germany or Denmark (6-8%). Only New York and New Jersey are worse.

Recently, Germany has been running 350,000 tests per week and is capable of running up to 500,000 tests per week. Tests are analyzed 7 days a week, 24 hours a day using shift work in the labs. Japan, with a population 52% larger, has averaged 22,000 tested individuals per week over the past two weeks (Apr 2-15).

Don’t take any comfort from numbers staying flat or growing moderately unless testing is also expanded exponentially to keep up with and exceed the growth rate of virus cases. Without greatly expanded testing, we’re like a pilot flying blind in a cloud without radar. Beware of the mountains ahead.

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