Despite three weeks of assurances, most Americans who have symptoms of Covid-19 still can’t get tested for SARS-CoV-2, the coronavirus that causes the disease. Last Friday, Sen. Brian Schatz (D-Hawaii) tweeted succinctly, “Hey where are the tests.”
The hardest-hit states are rationing tests to health workers and those who have Covid-19 symptoms. The Trump administration, meanwhile, continuously reassures us that we are getting more and more testing out there.
While increasing the number of tests is absolutely necessary, it is not sufficient. If we want to stop Covid-19, we must also focus on gathering other essential information as these tests are administered. There’s little value to getting a bunch of positive test results without being able to understand the clinical conditions of the individuals they came from, how they were exposed to SARS-CoV-2, and, perhaps most importantly, how they compare to people who test negative.
Even South Korea, which has tested more than 250,000 people, has failed to do this effectively.
Based simply on the number of positive cases, young adults would appear to be at highest risk of Covid-19 in South Korea. But is that due to higher testing rates among this age group? We don’t know.
We need more than data — we need insights. That’s why we need “smart testing” to address four fundamental public health questions.
The first two questions, which will be key to guiding policymakers on whether the extreme measures taken to suppress the outbreak are working, are these: Is the Covid-19 outbreak in a city or state getting better or worse? And how fast?
The answers to these questions cannot be determined just by looking at how many people test positive, especially as more testing capacity comes online. What we really need to look at is the percentage of people in the population who are testing positive each day. This requires knowing not just the number of positive tests, but how many tests of people in the overall population were performed — the numerator and denominator.
Epidemiology is a bit like baseball. Knowing that a ball player has gotten 134 hits isn’t that informative. What is informative is knowing that those 134 hits were made during 335 at-bats, which translates into a batting average of .400. But we can only know the batting average if we know the player’s total number of at bats and hits. It’s the same thing for the coronavirus: We need to know the number of all tests in in each age group and each locale, as well as the number of positive ones.
To know if Covid-19 is getting better or worse, we need to know how the percentage of positive cases — not the number — changes day by day, accounting for delays in testing and reporting and how the percentages change in response to public health measures such as sheltering-in-place or suppression. This will tell us how effective these measures are in curtailing the spread of SARS-CoV-2 and thus whether when social restrictions could be relaxed or additional policies might need to be implemented.
The other two questions that need answers are essential for guiding doctors in their medical decision making: Who is getting Covid-19? And what are their outcomes?
Consider the CDC’s latest study on the first 4,226 coronavirus cases in the United States. For one-third of these cases, no information was available about whether the patient had to be hospitalized. More than half lacked information on whether the patient required treatment in an intensive care unit. For just under half, it was unclear if the patient survived the infection or died. And, vitally important for a disease that has such disparate impacts on different segments of the population, there wasn’t even the most basic demographic data — age, sex, race— for 10% of the cases.
If we are going to get a handle on this fearsome disease, we need to stop emphasizing the sheer number of tests and whether any citizen can walk up and get tested. Instead, we need to insist on four basic groups of information gathering as we expand testing.
First, as a condition of receiving approval and test kits, laboratories should be required to submit basic information like age, county of residence, and testing site on every person tested — not just the positives.
Second, we need a sero survey of multiple communities. Such studies test blood samples from randomly chosen individuals in a defined population. This is the way to assess the real percentage of people in a community who test positive for recent coronavirus infection. This gives a picture that is wider than just the individuals who are bringing themselves in for testing. Right now we simply have no idea how many Americans are infected with the coronavirus. This will be a key input to models trying to predict when herd immunity can begin to blunt the outbreak.
That means we need to do random testing of people in communities like New Rochelle or Seattle that have been hard-hit by the outbreak. When one of us (F.M.) worked in New York City leading the fight against West Nile virus, health workers went door to door, testing and surveying households in the epicenter of the outbreak to understand the true case-fatality rate and the true infection rate of the virus.
Third, the CDC needs to rapidly help state and local public health agencies set up what is known as sentinel testing for Covid-19. This means they need money and technical support to collect comprehensive clinical and exposure information on a systematic sample of patients. That could be through existing sentinel clinics set up for influenza surveillance, drive-through coronavirus testing sites, or having select hospitals volunteer to systematically collect key information and test results for a sample of patients with cough and fever or severe acute respiratory illness.
Fourth, we need to look deeply into the information we already have. We should investigate data being collected daily in nearly every state on what are known as syndromic surveillance clusters. One of us helped design and build such a system for monitoring emergency room visits in New York City, which are now showing unprecedented increases in respiratory and flu-like complaints since March 1. By last Thursday, there had been 4,663 emergency visits with these complaints in 2020, while last year there were only 1,603. We need to look at the data of these patients to understand how much of this increase in emergency room visits is actually related to Covid-19 and how much is due to worried people imagining they are infected. This could be a key way to understand just how much we have undercounted the severity of the spread of Covid-19, and a tool that other communities can use to detect when the outbreak is spreading rapidly.
As our nation wrestles with the challenge of Covid-19, we should take heart from history. This is not the first major public health challenge our nation has faced, and we will overcome it. But we need to remember, as Tom Frieden, former director of the Centers for Disease Control and Prevention, recently said, “testing is not a panacea” but intelligent application of testing will provide vital public health information needed to effectively fight this pandemic.
Farzad Mostashari, M.D., is the CEO of Aledade Inc., the former assistant commissioner of the New York City Department of Public Health, and a former senior official in the U.S. Department of Health and Human Services. Ezekiel J. Emanuel, M.D., is the chairman of the department of medical ethics and health policy at the University of Pennsylvania and serves on former Vice President Joe Biden’s public health advisory committee addressing the coronavirus outbreak.