In just one hour on March 17, the number of confirmed COVID-19 cases in the U.S. increased by ~600. This increase occurred with no widespread testing, so the numbers are likely much greater. If we look at the increase in confirmed cases over the past 15 days, we see the beginning of an exponential curve. The exponential explosion of COVID-19 infections is what creates the public health emergency seen in Italy and Wuhan, China.
To illustrate, let’s consider that each person who gets COVID-19 will, under unrestricted conditions, infect two to three people. Therefore, if one infected person causes two new cases, this results in four more, then eight, 16, 32, 64, 128, 256, 1012, 2048, 5096, 10192 and so forth. The increases start slowly with low numbers that are not alarming. This is where the US has been in past weeks. But then it skyrockets exponentially in a very short time – all of this from 1 infected person. The present number of infected in the US is over 11,000, putting us on the same trajectory for the worst hit areas in the world.
The relatively low numbers of presently reported cases provide a false sense of security. Each day that goes by without testing or taking action results in 10-100 times more infection. The trajectory is sobering.
The history of the 1918 influenza pandemic in Philadelphia and St. Louis teaches us the consequences of delayed action. After a few cases were reported, the Philadelphia city government waited more than 10 days to take action. By then, it was too late to effectively stop the exponential expansion. In a 4-week period, 50,000 cases appeared, overwhelming the hospitals, with an eventual death toll of over 16,000.
In contrast, St. Louis acted immediately, initiated isolation and social distancing immediately upon learning of the first cases. There was no spike in cases and their hospitals were not overwhelmed.
While it is impossible to predict how the disease will progress in specific locations, it is time for Arizona to become prepared for a situation where millions may be sickened in a very short period of time, many requiring significant critical care. It is estimated that if just 20% of the adult population of the Tucson or Phoenix metropolitan areas are infected over a 6-month period, available hospital capacity will get dramatically overwhelmed.
Steps must be taken now to stop the spread. The recent actions of several Arizona municipalities and counties, closing restaurants and bars to slow the spread, is a good start. However, more action will be required to stop exponential expansion of COVID-19.
Food and supply delivery to the isolated must be worked out with local businesses. Hospitals must have treatment protocols and knowledge of the drugs and treatments that showed some success in China and Singapore. Additional hospital space, equipment and protective equipment should be urgently arranged. Negotiations with military bases to use their facilities and land for additional health services and mobile/modular hospitals should be ongoing.
To thwart the spread will require strict shelter-in-place plans enforced by police and National Guard. This worked in China, Taiwan, Singapore and Japan. Peru, which is currently using police to enforce shelter-in-place, has suspended constitutional rights to assembly and movement. Taiwan used soldiers to control mass distribution and production. Malaysia has said it would deploy soldiers. Serbia has instituted a mandatory dawn to dusk curfew. Several Cities in South Carolina – and also LA – are enforcing curfews with police with fines and jail time as penalties.
Finally, we must be prepared to deal with the emotional and psychological toll that will result from prolonged separation and the stress of an unprecedented pandemic.
In addition to public health support measures, we need widespread testing. First, this will determine how widespread the disease is. Second, it will tell us how severe the disease is in Arizona. For example, the percent lethality is the number of dead divided by the number of cases. We cannot accurately determine the fatality risk in areas like Pima and Maricopa Counties without knowing the total number of infections. Just as importantly, testing can define people who have recovered, and allow them to join (or rejoin) the fight against the virus, now possessing what will likely be long-term immunity to this virus.
The predicted trajectory for COVID-19 indicates that exponential expansion is beginning and will result in overwhelming numbers of infected individuals within the next two to three weeks. This is not much time. This pandemic needs to be taken seriously now. Steps must be taken immediately to blunt the magnitude of the expansion.
Felicia Goodrum Sterling is a virologist and professor at the University of Arizona, a fellow of the American Academy for Microbiology and a 2018 Public Voices Fellow. James Alwine is a virologist and professor emeritus at the University of Pennsylvania, a visiting professor at the University of Arizona, a fellow of the American Academy for Microbiology and of the American Association for the Advancement of Science.