Black, Hispanic and Latino pregnant women in Philadelphia are five times as likely as their white counterparts to have been exposed to the coronavirus, according to data collected from nearly 1,300 women between April and June.
The findings, which have not been published in a scientific journal, were based on tests for coronavirus antibodies, which reveal a person’s past exposure to the virus even if it did not cause any symptoms.
The study bolsters other research showing that the coronavirus disproportionately affects Black and Latino people.
“The racial disparities are striking, and important to bring out,” said Whitney Robinson, a social epidemiologist at the University of North Carolina, who was not involved in the study. “This reinforces what we’ve already seen, and adds more certainty that the racial differences are real.”
The study’s numbers dwarf previous estimates of the virus’s skewed impact on racial and ethnic minorities. Across the United States, Black and Latino people have been reported to be about three times as likely to contract the coronavirus as white people — a trend roughly mirrored by data collected by the city of Philadelphia. But these patterns have largely been based on tests for active infections, which have struggled to accurately capture where and how the virus has spread.
Although there is increasing awareness that many coronavirus infections cause few to no symptoms, many diagnostic testing centers — stymied by a lack of equipment and trained personnel — have rationed their tests to only people who are noticeably sick. And people who have reliable access to health care and insurance, often white and well-off, are more likely to seek out tests than others.
Diagnostic testing sites in many cities, including Philadelphia, have also been cordoned off by ZIP code, said Carmen Guerra, a health disparities researcher at the University of Pennsylvania who was not involved with the study, but is collaborating with the research team on others. Residents who do not own cars or cannot afford public transportation, she said, must surmount enormous barriers to determining their health status.
Tests that look for coronavirus genes also can’t find people who were previously infected and are now virus free. To fill that gap, several health centers in the area are now offering antibody tests in addition to those for active infections, said Dr. Karen Puopolo, a neonatologist at Pennsylvania Hospital and an author of the study, which was posted to the website medRxiv on Friday. But many people decide not to get antibody tests, painting an incomplete picture of exposure throughout the city.
Keeping tabs on pregnant women, who have continued to seek medical care amid the pandemic, could offer a less biased glimpse into what is going on in the population at large, said Scott Hensley, a virologist at the University of Pennsylvania who also was an author of the study.
Dr. Hensley, Dr. Puopolo and their colleagues searched for coronavirus antibodies in anonymized blood samples from 1,293 women who gave birth at Pennsylvania Hospital or the Hospital of the University of Pennsylvania between April 4 and June 3. These two medical centers see about half of Philadelphia’s live births, Dr. Hensley said.
Unlike diagnostic tests that search for stretches of genetic material specific to the coronavirus, antibody tests hunt for immune molecules produced in response to the virus and can thus detect infections that have already resolved, even if they did not result in overt symptoms. That potentially gives researchers a window into the past — and a chance to catalog infections that diagnostic tests miss.
The researchers found that just over 6 percent of all the women they tested carried coronavirus antibodies.
But once teased apart by race and ethnicity, the numbers revealed striking differences. About 10 percent of the study’s Black, Hispanic and Latino participants had been exposed to the coronavirus, compared with 2 percent of the white women and 1 percent of the Asian women, the study found.
“When I saw the data, I almost fell out of my chair,” Dr. Hensley said.
Some have questioned the accuracy of certain antibody tests, which sometimes mistakenly detect coronavirus antibodies in a person who has never been infected. But Dr. Hensley said the team confirmed that its laboratory test had a false positive rate of just 1 percent, on par with some of the best commercial tests.
Mounting evidence shows that the pandemic’s outsize effects on Black, Hispanic and Latino people have been driven in large part by a long list of social factors that increase their risk of exposure to the virus, Dr. Guerra said.
Black, Hispanic and Latino individuals are more likely to work essential jobs that cannot be done from home. Many live in multigenerational households and rely on public transportation, and have struggled for access to reliable sources of information about Covid-19, the disease caused by the coronavirus.
Toxic and chronic stress, born out by decades of persistent racism, have also taken a toll on the health and well-being of Black, Hispanic and Latino people, Rachel Hardeman, a reproductive health equity researcher at the University of Minnesota who was not involved in the study, said in an email.
As health workers and researchers try to ramp up testing efforts nationwide, pregnant women could play a larger role in helping experts track the spread of disease, Dr. Robinson said.
“We also need more targeted research on pregnant populations” in general, she added.
Recent analyses have found that pregnant women infected by the coronavirus may be at higher risk of worse outcomes, Dr. Hardeman said. Pregnant women are also thought to be more vulnerable to certain infections because carrying a fetus tamps down the immune system.
The study was not designed to assess whether pregnant women are at higher risk of contracting the coronavirus than other groups. But if evidence of that emerges, it would be “concerning,” given the other known racial disparities among pregnant women, said Dr. Ibukun Akinboyo, a pediatrician and infectious disease specialist at Duke University. For instance, Black women are three to four times more likely than white women to die during or soon after childbirth.
Pregnant women — who tend to be young and healthy members of the work force — do not represent the population as a whole, Dr. Robinson added. “We still need to have samples like this from kids and older people, and unpartnered people.”
Still, these patterns “reflect the structural inequities in the United States,” and underscore the need to address the factors that underlie them, Dr. Akinboyo said. That is powerful for those trying to curb disease transmission, but it can also help identify and protect those in need.
“Highlighting the groups that are more likely to get infected,” she said, “means we can get resources to the right groups.”