This month, the US reported 5 million cases of coronavirus, and the domestic outbreak is already quietly close to 6 million. How did this unimaginable catastrophe get so far out of control?
The sad truth, scientists say, is that we probably had no idea how widespread and pervasive COVID-19 infections were already in the early stages of the American outbreak, long before a national state of emergency was declared.
These hidden cases – missed by widespread failures in testing and surveillance – could mean that by the time several U.S. states began declaring and enforcing shutdowns in March, it was too late to contain the growing infection that had not yet was discovered.
According to new estimates, nearly 109,000 people in the U.S. could actually be infected by March 12, at which point only 1,514 cases of local transmission were reported.
One day later, a national emergency class was called, but the findings suggest that health authorities are currently only seeing the tip of a very viral iceberg – completely missing tens of thousands of unobserved infections already circulating in their midst.
“We are not testing enough,” says epidemiologist infectious disease Alex Perkins of the University of Notre Dame.
“The number of unobserved infections seems to be due to very low rates of case detection during a critical time, when the epidemic really started to take hold in this country.”
According to Perkins and his team, the unusual spread of SARS-CoV – 2 is the result of a perfect storm of things you do not really want to see in a virus: high transmissibility combined with both presymptomatic transmission and asymptomatic transmission.
Even with a best-testing and surveillance regime, catching such a virus would be a challenge. And the US did not demonstrate a best-in-class test and oversight regime.
“Unlike other countries where testing and containment measures were aggressively pursued, the rollout of tests in the United States was slow, and widespread social-distancing measures did not take effect until several weeks after the first reported case,” the researchers in their paper.
In addition to a widespread lack of test kits and facilities in the US, strict enforcement rules about who could be allowed to be tested in January and February meant a large number of people with serious, COVID-19-like symptoms were unable to get tested for the virus – creating a massive blind spot in real-time outbreak data.
“Until February 27, test criteria in the United States were limited to close contacts of confirmed cases and those with recent travel to China,” the researchers explain.
“This means that all local infections as a result of an unobserved imported infection would have gone unnoticed. Community transmission occurred without notice, while tests were still being conducted, albeit to an unknown extent.”
To go back in time and try to quantify how many COVID-19 infections may have occurred in this time frame, Perkins and his colleagues modeled the distribution, using a stochastic simulation fed with data from the real world about breaking out.
It is a method that produces inherently uncertain results, as the researchers acknowledge, but nonetheless generates rapid preliminary estimates that help explain how the US got to where it is today.
Overall, estimates suggest that there may have been some 108,689 cumulative infections in the US between the start of the year and March 12, with more than 17,000 infections occurring on March 12 alone – even more than 10 times the official cumulative count known at the time.
The estimates may also differ significantly, though, depending on the parameters of the simulations. Some of the outbreaks on March 12 suggested only about 10,000 cases, but others suggested much more: hundreds of thousands of infections on March 12, than even a million more.
Despite the lack of precision, the researchers say that their findings generally indicate that the US was well beyond the possibility of containment by March 12 – and that at that time, large-scale mitigation efforts would have been necessary to effectively combat the virus, instead of state-by-state response measures.
“I think the fact that there were so many infections in the second half of February speaks to the importance of and what we could have done in terms of containment,” Perkins said, noting that early, aggressive action to kill people testing, isolating cases, and conducting strict contact tracking, could have slowed the spread and ultimately saved lives.
“I think a lot of us hope this would be the situation with this disease. By the time we got to February, the problem had become so big, and contained the virus not possible.”
The findings are reported in PNAS.
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