A recent CDC study suggests COVID-19 arrived in Connecticut at least as early as Jan. 10, almost two full months before the first known coronavirus case was diagnosed in a patient in Danbury in early March last year.
For the study, published in November, researchers gathered 7,389 blood samples collected in routine blood donations by the American Red Cross from donors in nine states, including Connecticut, between Dec. 13, 2019, and Jan. 17, 2020. CDC testing showed anti-SARS-CoV-2 antibodies in 1.4 percent of the samples.
While the findings potentially push up the timeline of the coronavirus’ arrival both in Connecticut and the U.S. overall, such antibody tests do not conclusively prove the donors were infected with the virus that causes COVID-19.
“There could be some antibodies that bind both common coronaviruses and SARS-CoV-2. We cannot tell the difference with antibody testing,” the study’s lead author, Dr. Natalie Thornburg, wrote in an email. “We used several different kinds of tests to try to give us more information. Some of the positive samples were positive by only one test, and maybe those results are more likely to be from common coronaviruses. Some samples are positive by several tests. Those samples could be from SARS-CoV-2, but even still, blood antibody tests are not diagnostic. That is a limitation of the study.”
Thornburg and her co-authors note in the study that antibodies “were identified among donations occurring in early January in Connecticut, Iowa, Massachusetts, Michigan, Rhode Island, and Wisconsin prior to the known introduction of SARS-CoV-2 into those states.” They also found a small percentage of coronavirus antibodies in samples taken from donors in California, Oregon and Washington between Dec. 13-16 in 2019, indicating possible spread in the West earlier than previously known.
“We expected a few samples to have antibodies that bound the virus, but I was surprised by the differences between locations,” Thornburg said via email. “The first people that we know with certainty had SARS-CoV-2 in the United States was mid-January in 2020. Our study suggests a few weeks earlier there could have been cases of COVID-19 but does not suggest widespread community transmission in the United States.”
Since last spring, many Connecticut residents who had respiratory illnesses over the winter of 2019-20 have wondered if they may have been infected with an early case of COVID-19. Thornburg says it is impossible to know for certain. “Unless we have respiratory samples from those persons while they were sick to retest for SARS-CoV-2, we cannot know the answer definitively.”
The overcrowding of Connecticut hospitals and ICUs didn’t occur until after cases were known to be here last spring, which suggests to many experts that the virus was not rampant in the community much earlier than we realized.
Mary Petrone, a doctoral student at the Yale School of Public Health who is researching the coronavirus’ arrival in Connecticut, says there are two important questions to ask. “When was the very first coronavirus [case] introduced in Connecticut? And then, two, when did community transmission really take off?”
She adds, “You could have people coming in and bringing the virus with them but maybe they don’t infect anyone or a lot of people and it kind of doesn’t go anywhere from there, versus when did we really have an epidemic on our hands in the state.”
Last spring, Petrone and her colleagues sequenced viral genomes from nine of the earliest known coronavirus patients in Connecticut. “If there’s a local outbreak going on, you would expect to see these genomes being pretty closely related to each other, either identical or nearly identical,” Petrone says. Only two of the samples were similar, suggesting that there was not widespread spread of the virus within Connecticut, and instead those who had it were catching it out of state and bringing it here.
But because the Yale study only looked at genomes of viruses from nine people, the conclusions that can be drawn from this study are limited. Today, researchers at the Yale School of Public Health have sequenced more than 1,000 genomes, and Petrone is working on further analysis. By studying the way these genome sequences evolve over time, she hopes to learn how the virus moved through Connecticut and hopefully better answer the question of when it first arrived here.
This research does more than satisfy the curiosity of those who want to know whether they might have had it last winter. It can also tell researchers how future viruses might spread through the state and potentially help slow that spread by revealing community transmission patterns.
“Connecticut is such a weird state. Between New Haven in New York, there’s a lot of connection, but then, I’ve never been to Hartford,” Petrone says. “What we’re interested in understanding is how did the virus arrive, where did it come from in Connecticut, is that something we’re going to be seeing over and over again as these variants emerge. And then with that information, can we improve our surveillance and our prevention programs.”
She adds that, if we learn that 90 percent of the time, new strains are entering the state via New York City, we could focus our efforts in blocking that line of transmission, “instead of just sort of having to cover all of your bases and being stretched too thin.”