Due to the scarcity of tests across the country, hospitals usually only test those cases that they need to admit to the hospital. The hospitals are not testing the majority of people complaining of symptoms, nor the many possibly infected asymptomatic people. We need to keep this fact in mind when looking at the statistics being tracked by Johns Hopkins University, The New York Times, and Worldometers.
Let us focus on the statistics for New York state, because that is one geographical entity where we know testing only the sick is the policy. This region is the origin of the largest number of cases in the U.S. As of today, April 6, 2020, there are 130,000 cases of COVID19 confirmed in NY state. Those numbers came from about one-third of the 302,000 administered tests that came back positive. It is more interesting to consider these numbers on a per capita basis, to learn how widely the virus is spread in the community. About 1.5% of the population has been tested, and about 0.67% of the population has shown a positive result from the tests.
Now let’s step back and ask the real question: how many infected patients become candidates for admission to the hospital? Only a few places in the world are not being strictly reactive to the crisis and have tested enough people to have a handle on the overall retrospective distribution of outcomes. Reports from the outbreak in China suggest that about 15% to 20% of those infected eventually need hospitalization.
The point is, if we are only testing patients imminently needing hospitalization, then we are missing the other 80 to 85% of the cases that are milder. Since those milder cases are not tested, they are not even counted. If we go back to hard-hit New York and make a correction for the case numbers based on this information, then we can expect that the real case prevalence in the community is likely 5 times higher than what is reported, about 3% of the population; that is to say, one in 30 people are sick.
My concern is that once you reach this level of infection, it becomes very difficult to tamp it back down. There are just too many opportunities for the infection to spread further. I hope I’m wrong on this, and that social distancing will do its job. But if the infection rate continues to run, there are only a few more doublings possible before everyone has it. The reported case rate is still doubling in New York every 6 or 7 days, so one could expect half of the people in the city to have contracted it in four more doublings or about 25 days – by the end of the month. Only then will the infection really run out of steam, because there will be no more virgin immune systems of which to take advantage. Until we have a vaccine, the only thing really fighting this virus are the immune systems of the victims it infects.
In the early days before social distancing, an infected individual would spread the infection to, on average, another 2.4 people. To bring the pandemic under control, that number needs to be reduced to less than one.
There are two possible outcomes for this first round of infection from COVID-19. We could be effective with social distancing and reduce the infection rate to something that is manageable, where individual cases are few enough that communities can trace all contacts and isolate them to prevent further infection. The second option is for the virus to run through the community until it has infected at least half of us. When an infected individual, while still infectious, no longer manages to infect another person (because there just aren’t that many susceptible people to come in contact with anymore), the epidemic will end. By the end of the summer, different parts of the country could have these very different outcomes.