Another day, another potentially revised timeline in the U.S. chapter of this pandemic. The latest one comes from a Northeastern University estimate of how the coronavirus began spreading undetected in several major American cities in February.
As the New York Times reports today, the Northeastern model is an inherently inexact way of attempting to understand how many asymptomatic and otherwise undetected infections may have been occurring at a time when very little testing was happening in the U.S. and there were only a handful of confirmed cases in each city. Alessandro Vespignani, the director of the Network Science Institute at Boston's Northeastern University, suggests that this silent spreading had to have been occurring simply based on the number of daily flights that were arriving from Europe and China during the first two months of the year.
Vespignani and his team take into account the movements of people in a city, whether or not schools and workplaces were locked down, and extrapolates how a contagion may have multiplied in a given area based on the average number of daily contacts a person may have.
This model puts the March 1 infection total in New York City at 10,700 and in San Francisco at 9,200, when the official, confirmed coronavirus case totals in the two cities were under 10. (It's unclear from the Times piece whether the SF total was for the entire metro area, or the city proper, but it's likely the former.) Similarly, in Seattle, the model suggests there were 2,300 cases, and another 3,300 going undetected in Chicago.
Dr. Donald Burke, a professor of epidemiology at the University of Pittsburgh Graduate School of Public Health, counters to the Times that this model's estimates seem "on the high side." But other infectious disease experts say that such numbers might be completely plausible — because often when a locality has confirmed just a few cases, the reality is that there are thousands out there.
The Northeastern model adds further support to those who have hypothesized in recent weeks that SARS CoV-2 made it to the United States — most likely the West Coast anyway — far earlier than has been believed. Earlier this week we learned that a 57-year-old woman who died in Santa Clara County on February 6 may actually have been the first COVID-19 death in the U.S. — unless an earlier case gets found through posthumous testing. That case suggests the virus was spreading in the county at least a few weeks earlier, in January, but experts who have been sequencing the genome of the virus caution that the evidence points to very limited spread at that point in time in the U.S.
Another newly discovered death, which occurred weeks before the first official COVID-19 death was recorded in the Bay Area, happened in Santa Clara County on February 17.
George Rutherford, an infectious disease expert at UCSF, is one of those. He tells the Chronicle that the CDC is currently investigating all of these threads, and what is more likely than December or January community spreading in California is that the virus made a few failed entry points into the U.S. and claimed just a few victims. Rutherford believes these early cases were part of identifiable clusters with specific lines back to a traveler from China, and not the result of so-called "community spread."
"We need to figure out what went on and what the chains of transmission were, now that we have some antibody testing," Rutherford says. "You might be able to put it together and understand why it died out — and I think these clusters must have died out."
Charles Chiu, the director of the UCSF-Abbott Viral Diagnostics and Discovery Center, tells the Chronicle that he will be sequencing the genome of the virus samples found in these early Santa Clara County victims, but he expects to find the same strain — with the same single mutation from the original Wuhan strain — that was found in other early victims in the county.
"Based on sequencing, we can tell it came into the country sometime in February when all of this began," Chiu tells the paper. "What probably happened is that there was either one or multiple introductions in Santa Clara County, but there is no evidence that it had been circulating widely prior to that time."
But Chiu's confidence is undermined somewhat by the fact that this woman's infection almost certainly occurred in January.
The conflicts between these various scientific efforts will likely continue for months if not years — but Dr. Chiu at least has data on his side, where as the above-mentioned modeling is mostly conjecture.
Genetic scientists can say with some certainty that the virus appears to be mutating about twice a month, with the greater number of mutations indicating further distance in time and carriers from the original Chinese strain. Chiu's team previously surmised that the COVID-19 victims who were passengers on the Grand Princess cruise ship in mid-February were infected with the same strain that appeared in the Seattle area about a month earlier.
As the Times reports, that unique strain from Washington State has now been identified in 14 other states and accounts for a quarter of the confirmed COVID cases in U.S. And the same strain has been found in Australia, Mexico, Canada, and the U.K.
Researchers earlier found that the majority of cases in the New York outbreak came from the unique strain found in Italy.
Photo: Daniel H. Tong
