A study of COVID-19 prevalence in Santa Clara County, California, conducted by researchers released last Friday suggests that the spread of coronavirus cases is way more prevalent than previously thought.
The study, which was conducted by researchers from Stanford, USC and a number of private institutions, has not been peer reviewed and its methods have come into question given how the researchers recruited participants. Although its too early to draw conclusions, the study was among the first to examine the prevalence of those with COVID-19 antibodies.
Having COVID-19 antibodies means that a patient likely had the virus and have recovered, some of whom may not have had any coronavirus-related symptoms.
The increased prevalence could suggest that the virus spreads more easily than previously thought. It could also mean that the virus' death rate is not as high as suggested.
The study recruited Facebook users to submit to an antibody test. The authors acknowledge that the study was biased toward those with Facebook accounts and who have access to a car. While the researchers were able to weigh these measurements in their study, the researchers said that a bias favoring those with prior COVID-like illnesses seeking antibody confirmation is also possible.
The tests were conducted from April 3-4 and found that of the 3,300 Facebook users tested, between 2.5% and 4.2% showed possible antibodies to COVID-19.
The results found a prevalence of cases could be 50-85-fold larger than the number of confirmed cases detected in Santa Clara County.
Dr. Neeraj Sood, a USC researcher who also was among those who participated in the Santa Clara County study, joined public health officials in Los Angeles County to conduct a similar study. Their study, which was released on Monday, found a prevalence rate of those with coronavirus antibodies in L.A. County of 2.8% to 5.6%.
The L.A. County study estimated the number of those with COVID-19 antibodies is 28 to 55 times higher than the 7,994 confirmed cases of COVID-19 reported to the county by the time of the study in early April.
"We haven't known the true extent of COVID-19 infections in our community because we have only tested people with symptoms, and the availability of tests has been limited," said Sood, "The estimates also suggest that we might have to recalibrate disease prediction models and rethink public health strategies."
Dr. Debroah Birx, who is leading the White House’s response to the coronavirus addressed the studies.
“Looking at all the studies carefully, I think you will remember over the last three weeks I have been talking about the level of asymptomatic spread,” Dr. Birx said on Monday. “My concern about asymptomatic spread -- with the flu and other diseases, when people are sick, it is easy to contact trace. When people are not sick and shedding virus you have to have a very different approach, a different surveillance approach, a sentinel monitoring approach which we outlined in the guidelines.”
While researchers are trying to pin down how many of those infected with COVID-19 are asymptomatic, scientists have concluded that many of those infected are asymptomatic, and those who are asymptomatic are still able to spread the disease. Tracking asymptomatic adds to the challenge for public health officials.
“We will emphasize to the American people, this is a highly contagious virus,” Dr. Birx said. “We don't know by looking at someone whether they have pre-existing conditions or not, and all of us as far as protecting others must continue to do all of the recommendations to ensure that when we are in an asymptomatic state we are not passing the virus.”
But with 41,000 Americans who have died in the last six weeks from the virus, researchers stress that Americans still need to remain vigilant with social distancing measures.
"Though the results indicate a lower risk of death among those with infection than was previously thought, the number of COVID-related deaths each day continues to mount, highlighting the need for continued vigorous prevention and control efforts," said Dr. Paul Simon, chief science officer at L.A. County Department of Public Health and co-lead on the study.