(Bloomberg Opinion) -- Of the 215 women who delivered babies at New York-Presbyterian Allen Hospital and Columbia University Irving Medical Center in Upper Manhattan from March 22 through April 4, 214 were tested for the coronavirus that causes Covid-19. Thirty-three of them, or more than 15%, tested positive, even though only a few had symptoms. In Gangelt, a German town that makes a big deal out of Karneval (aka Mardi Gras) and had a major coronavirus outbreak after this February’s festivities, 500 residents were tested for evidence of either the virus or the antibodies that indicate one has recovered from it, and 15% of them tested positive as well.

Meanwhile, in Iceland, randomized testing of the population found 0.6% of those tested in late March and early April to have the disease. In San Miguel County in the mountains of Colorado (the ski town of Telluride is the county seat) widespread testing for coronavirus antibodies had as of Tuesday afternoon delivered a 0.6% positive ratio and an additional 1.5% of “borderline” results.

What these preliminary findings (those from New York and Iceland were published in the peer-reviewed New England Journal of Medicine, the German data are from an as-yet-incomplete University of Bonn study and the Colorado numbers are simply posted daily on the county website) seem to show is that in places hit very hard by Covid-19, a surprisingly large number of people have been infected with it, and that in the rest of the world, very few have.

This means that the occasional hopeful suggestions that the coronavirus is already widespread globally and herd immunity will be putting an end to the pandemic any minute now are most likely bunk. But it also means — and this was already the view of pretty much every epidemiologist whose work I have consulted — that the confirmed coronavirus cases reported by governments and tabulated in places like the Johns Hopkins University coronavirus map represent only the tip of the iceberg of actual infections, especially in disease hot spots. Another way of putting it is that if you live in rural Colorado and had a fever in February, that wasn’t the coronavirus. If you live in New York City and had a fever in late March, it probably was.

Out of a population of 8.4 million, New York City had 111,424 confirmed Covid-19 cases as of Tuesday evening. If those pregnant women in Upper Manhattan are representative of the city as a whole, though, nearly 1.3 million New Yorkers have or have had the disease. That in turn implies a ratio of fatalities to infections of about 1% so far, not the 9.8% one gets dividing deaths by confirmed cases.

A fatality rate of about 1% happens to be the estimate arrived at in the first major disease-severity study published back in February by the much-cited Covid-19 modeling team at Imperial College London, and is still used widely in projections of the disease’s potential impact. A more recent study by the same group puts the infection fatality rate in China at a slightly lower 0.66%, but New York City has a higher percentage of people 65 and older than China does, which given the disease’s much greater severity among senior citizens should drive the rate higher. In other words, my guesstimate that the actual number of Covid-19 cases in New York City is more than 10 times the number of confirmed cases squares with expert guesstimates of the severity of the disease. It also squares with my personal experience in the city over the past few weeks, with multiple friends and family members displaying symptoms of Covid-19, and hardly any of them getting tested.

This should make us more confident about how to adjust official coronavirus data that, as Cathy O’Neil detailed here at Bloomberg Opinion a couple of days ago and Faye Flam did last month, is obviously quite incomplete. In places where the disease seems to be overwhelming the health-care system, like New York City over the past few weeks and Iran, Italy and Spain before that, it seems safe to assume that there are at least 10 times more actual Covid-19 infections than confirmed cases. There probably aren’t 100 times more (which in New York City would imply more infections than there are people), and in areas where either testing is more widespread or the spread of the disease better under control (or both) the ratio of infections to confirmed cases may be well below 10.

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