Day 79: Cryptic Cases

In world stats, Turkey has surpassed China in cases, and Iran is very close now. In New York (City or state was not specified), two housecats appear to have caught coronavirus from their (respective) sick owners. Here in Massachusetts, our Sunday numbers are depressed as usual, going up only 5%. Note that tomorrow is still a holiday in Massachusetts despite the postponement of the Boston Marathon, and the numbers may continue to reflect the long weekend rather than the medical situation.

According to a somewhat arbitrary standard published in the New York Times, Rhode Island is the only state doing anything like enough testing to reopen.

Several more surveys of asymptomatic cases have come out recently, including a random, anonymous test of 200 people healthy enough to walk the streets of Chelsea (Mass.), of whom 32% proved to have antibodies to coronavirus. The Boston Globe also reports that half of the participants had had symptoms of COVID-19 in the past month, but none had previously tested positive. Chelsea is by far the most infected part of the state per capita, so PlagueBlog recommends not projecting these numbers across the state. Because the subjects were anonymous there was no way to give them their test results, but if they follow the news perhaps they will consider their odds and get tested elsewhere.

LiveScience reports on a similar study in Santa Clara County that "suggested that between 2.5% and 4.2% of people in the county have contracted COVID-19, which is 50 to 85 times greater than the number of cases being reported at the time." The study has been criticized for overestimating the rate, either through massaging the percentage up from its raw value of 1.5%, for the self-selection bias of the volunteers, for potential false positives on the antibody test (which is not yet FDA approved), and also for not being ethnically representative (the only criticism which implies the rate should be higher than the study estimated).

A similar study has been done in Wuhan, where the official infection rate was about half a percent, but more than 2% of hospital employees had antibodies. In Italy, most residents of the small town where their first death occurred (Vò) were tested twice. The preprint results show 43% of cases were asymptomatic, across all age groups, and that several asymptomatic patients spread the disease to others in the same household.

On the pretty picture front, I've updated last week's Massachusetts case rate map with better estimates of case rates in towns with fewer than 5 cases. I don't have the actual population numbers the MDPH seems to be using, so I used numbers from the census' population estimates API: