As the United States exceeds 5 million reported coronavirus cases—the world’s first country to do so—epidemiologists have pinpointed what helped to set the country on this path.
In a new study, researchers estimate that more than 100,000 people were already infected with COVID-19 by early March—when only 1,514 cases and 39 deaths had been officially reported and before a national emergency was declared.
The study provides insight into how limited testing and gaps in surveillance during the initial phase of the epidemic resulted in so many cases going undetected.
The research was conducted by a team from the University of Notre Dame.
According to the Centers for Disease Control and Prevention, the first confirmed case of COVID-19 in the United States was reported in January.
Early guidance on identifying possible infection included respiratory symptoms, and travel to Wuhan, China—where an outbreak occurred in December 2019.
While awareness and concern over COVID-19 grew from January to March, it wasn’t until Feb. 29 that Washington became the first state to declare a state of emergency—closing schools and restaurants and imposing restrictions on large gatherings.
By mid-March, several states followed, but a lack of a coordinated national response created a number of variables as each state decided for itself how to react to a rising number of cases.
By focusing their analysis on the January to March timeframe, when little to no action had been taken on a wide scale, the team was able to incorporate a constant into their models.
While other studies provide a sense of how school closures and lockdowns slowed the spread of the virus, looking at transmission for the first three months of the year gave the epidemiologists a clearer picture of how the virus emerged and spread throughout the country so quickly.
The team looked at the United States now and compare it to other countries like South Korea or Germany, New Zealand or Vietnam, any number of countries that have done a much, much better job controlling transmission.
The key differences really come down to the time period they examined in this study. Those countries had adequate surveillance up and running at that time, whereas throughout most of February the United States missed the vast majority of infections that were already out there.
The study used a simulation model beginning on Jan. 1, using data reported by Johns Hopkins University on confirmed cases and deaths, accounting for asymptomatic infections, case-fatality rates, and local transmission.
The team first generated an estimate of total infections in the U.S. through March 12. They then factored in how the detection of symptomatic infections changed over time and estimated the number of unobserved infections during this time.
A significant aspect of the analysis is the model’s incorporation of many uncertainties that played out in the early days of the epidemic in the U.S.
The number of unobserved and unreported infections also speaks to how critical containment strategies are when battling infectious diseases.
The potential for misdiagnosis and the limitations of surveillance are huge issues across infectious diseases, especially emerging infectious diseases.
As illustrated in the COVID-19 study, while public health officials must work quickly to understand how a new virus functions, without appropriate testing or coordinated response strategies the risk grows for infections to go unreported.
One author of the study is Alex Perkins, an associate professor in the Department of Biological Sciences
The study is published in PNAS.
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