- Antibody studies are now indicating much higher rates of COVID infection
- A PCR study showed 15% of random NYC woman giving birth were positive for COVID virus by early April
- Given the timing and limitations of the PCR testing, the percent of random NYC COVID-19 infected is now approaching 50%
Last Sunday, for Passover and Easter, I likened the patients already infected with COVID-19 as our “Moses” to lead us out of the pandemic. These patients could do this because of protective immunity (even if only short term!). I also suggested that 20-30% of the US population could be infected by the end of April. I was derided by a few individuals who had much lower patient number projections based on varying hypotheses or observations. My response was we needed to wait for real data to make a final conclusion. This week that data started to arrive.
A small antibody study in Santa Clara California showed that 50 to 85 times as many people had been infected with COVID-19 as the number of confirmed infections. The overall percentage of COVID-19 infected was approximately 4.0-5.0% of the entire population, but this was from early April and is likely higher now. While not surprising, it isn’t clear how representative this county is compared to other areas of the country. In addition, the assay used for antibody testing was not approved by the FDA (a common issue right now).
A second study in NYC, the epicenter of the US pandemic, gave more remarkable results. Between March 22 and April 4, 2020, the investigators sampled a total of 215 pregnant women who 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). 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.
There are several noteworthy findings from this study. Over 15% of randomly selected NYC women with late stage pregnancies were positive for COVID-19 virus by early April. This is not antibody testing, but screening for virus using nasal swab (PCR). The PCR test is only positive for a short time in the course of the infection and is prone to false negative results. It also won’t identify women who had been infected and stopped shedding virus. So, PCR testing is likely to grossly underestimate the number of infected.
Importantly, 29 of the 33 patients who were positive for SARS-CoV-2 at admission (87.9%) had no symptoms of Covid-19. This again suggests that most COVID patients have no symptoms when they are infected and shedding virus (and able to infect others!).
Given the Santa Clara results showing much higher infection rates with antibody testing and the limitations of the NYC swab test, it would not be a stretch to say that 25% of random NYC individuals had been or were actively infected with COVID the last week or March/first week of April. Today, April 19, it is likely that number is doubled; potentially closing in on 50%. We can expect very high rates of infection in other viral “hotspots.”
We should stop thinking of this as a rare disease.