A small but notable collection of data was published yesterday in The New Journal of Medicine. One major New York City hospital evaluated and tested every expectant mother who was admitted to the hospital for childbirth. Almost 14% were COVID positive and almost all of lacked any symptoms. This is an early and still very small window into the kind of universal and/or random sample testing that will be necessary to get an accurate understanding of the prevalence of COVID19 in the population at large.
Between March 22 and April 4, 2020, a total of 215 pregnant women delivered infants at the New York–Presbyterian Allen Hospital and Columbia University Irving Medical Center . All the women were screened on admission for symptoms of Covid-19. Four women (1.9%) had fever or other symptoms of Covid-19 on admission, and all 4 women tested positive for SARS-CoV-2 (Figure 1). Of the 211 women without symptoms, all were afebrile on admission. Nasopharyngeal swabs were obtained from 210 of the 211 women (99.5%) who did not have symptoms of Covid-19; of these women, 29 (13.7%) were positive for SARS-CoV-2. Thus, 29 of the 33 patients who were positive for SARS-CoV-2 at admission (87.9%) had no symptoms of Covid-19 at presentation.
This raises a number of questions, most especially how representative these women are of the population as a whole. I’ve seen comments both that near term pregnant women are likely to be the most aware of social distancing and that frequent late term doctors appointments are frequent opportunities for infection. I don’t know which might be more true. There was early data out of China that the expression of COVID19 might be particularly limited among pregnant women. Those datasets were small, but this suggests that this very high percentage of asymptomatic cases may not be representative.
Clearly we can’t assume this is a representative sample of the entire New York City population. But if this percentage were representative this would suggest roughly 1.15 million infections in New York City. If we assumed a 1% mortality rate for COVID19 across all demographic groups, the current confirmed death toll in New York City would suggest 735,000 infections. There are clearly a substantial number of unreported COVID19 fatalities. But since we’re drawing our assumptions about how many people die of COVID19 from other countries which also have underreporting it’s hard to know how much we can draw by stacking this many unknowns on top of each other.
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