Fractions are taught in elementary school, but adults sometimes still manage to misunderstand how they work in everyday life. I was reminded of that after President Trump's Saturday press conference, which focused on the federal government's response to the Wuhan coronavirus (formally SARS-CoV-2, with the illness it causes designated COVID-19). Let me explain.
Dr. Anthony Fauci, the articulate, veteran director of the National Institute of Allergy and Infectious Diseases, described at the presser how the efforts to prevent the spread—or "contain" the virus—would continue, but warned that we should expect the number of coronavirus cases in the United States to increase.
Fauci emphasized that the chance of becoming infected remains low and that the majority of those who contract the virus—75 to 80 percent—will experience it like a "bad flu or a cold." The other 15 to 20 percent, he said, may need "advanced medical care."
"For the most part, the people who get in trouble and ultimately tragically would die from this are people who are elderly and or have underlying conditions . . . heart disease, chronic lung disease, diabetes, obesity," Fauci said.
Some of the "if it bleeds, it leads" media immediately jumped on the 15 to 20 percent figure, multiplied it by the entire U.S. population of about 330 million, and concluded that we might need 50-60 million hospital beds, for which we are unprepared.
Not so fast. Recall the old quip that "figures lie, and liars figure."
What Fauci didn't explain, and the pundits failed to clarify, is that the 15 to 20 percent figure is based on the official number of confirmed cases of COVID-19 in China, as reported by the country's public health officials.
And that's where the need to understand fractions comes in.
The 15 to 20 percent figure refers to the fraction of "serious" illnesses requiring advanced medical care, such as the administration of oxygen or hospitalizations, divided by the number of confirmed cases of infection. But here's the rub: In China, there have undoubtedly been many—possibly very many—illnesses that were never confirmed, both because of a shortage of test kits and because people with asymptomatic or mild infections didn't seek medical attention at all.
In other words, the denominator of the fraction is higher than the official number of cases and, therefore, the 15 to 20 percent figure is unquestionably an overestimate of how many people need "advanced medical care."
A similar distortion occurs in estimates of the case fatality rate, the fraction of people who are infected and die. Estimates of the coronavirus death rate from Wuhan, China, the epicenter of the outbreak, have been around 2 percent. But again, we have the problem of the uncertain denominator, which includes only confirmed cases. The true denominator is unquestionably much larger, which would make the true case fatality rate lower.
As Fauci and two colleagues put it, in a just-published editorial in the New England Journal of Medicine:
If one assumes that the number of asymptomatic or minimally symptomatic cases is several times as high as the number of reported cases, the case fatality rate may be considerably less than 1%. This suggests that the overall clinical consequences of Covid-19 may ultimately be more akin to those of a severe seasonal influenza (which has a case fatality rate of approximately 0.1%) or a pandemic influenza (similar to those in 1957 and 1968) rather than a disease similar to SARS or MERS, which have had case fatality rates of 9 to 10% and 36%, respectively.
The purpose of this slightly pedantic discussion is not to minimize the significance of the new coronavirus, but rather to put into perspective some of the media's warnings of apocalypse.
U.S. public health officials are currently taking appropriate actions to prevent outbreaks from expanding, including isolation of patients and contacts, in order to prevent secondary infections.
Community spread, however, could require a shift from containment to mitigation. Social distancing strategies in order to reduce transmission could include isolating ill persons (including voluntary isolation at home), school closures, and telecommuting where possible.
We would do well to heed the British government's message to the populace during the Second World War: "Keep Calm and Carry On."
Henry I. Miller, a physician and molecular biologist, was the founding director of the Office of Biotechnology at the FDA. Please follow him on Twitter: @henryimiller