The Trump administration said on April 27 that the United States will soon have enough capacity to double the current number of active infection tests. The country has made nearly 248,000 average daily tests over the past seven days, according to the nonprofit Covid Tracking project. Doubling that would mean making about 496,000 a day.
Will this be enough? What benchmark should states try to meet?
A leading research group, the Global Health Institute at Harvard, is proposing that the United States do more than 900,000 tests a day as a country. This projection, released Thursday, is a big leap from its previous projection of test need, which was between 500,000 and 600,000 per day.
Estimates of Harvard tests have increased, says Ashish Jha, director of the Global Health Institute, as the latest modeling shows that the epidemic in the United States is worse than expected before.
“Just in the past few weeks, all the models have converged on many more infected people and many more people [dying], ” he says.
But each state’s specific need for testing varies depending on the size of its epidemic, says Jha. The larger the epidemic, the more tests are needed.
Jha’s Harvard group released a simulation on Thursday that estimates the amount of testing needed in each state by May 15. In the graph below, we compare these estimates with the average number of daily tests that states currently perform. (Go to graph)
Two ways to assess if the test is adequate
To make its state-by-state estimates, the Harvard Global Health Institute group used a model of future counts. They calculated how many tests would be needed for a state to test all infected people and all close contacts who may have exposed the virus. (The simulation estimates testing 10 contacts on average.)
“The test is controlling epidemics 101, because what the test allows you to do is find out who is infected and who is not,” says Jha. “And that allows you to separate the infected from the uninfected and control the disease. “
This approach is how communities can prevent outbreaks from occurring. First, test all symptomatic people, then contact and test their loved ones, and finally ask those who are infected or exposed to isolate themselves.
Our graph also shows another test criterion for each state: the ratio of tests performed that return positive. Communities that see about 10% or less positive among their test results are probably testing it enough, advises the World Health Organization. If the rate is higher, they are probably missing a lot of active infections.
What emerges from the data we present below is that many states fall short of Harvard estimates and the 10% positive benchmark.
Only nine states are close to or have exceeded the test minima estimated by Harvard; they are mainly larger and less populated states: Alaska, Hawaii, Montana, North Dakota, Oregon, Tennessee, Utah, West Virginia and Wyoming.
Several states with large epidemics – New York, Massachusetts and Connecticut among others – are far from the minimum test target. Some states that are already relaxing their social restrictions, such as Georgia, Texas and Colorado, are also far from being targeted.
Jha offers several caveats regarding his group’s estimates.
Estimates are directional, not literal
Researchers at the Global Health Initiative at Harvard considered three different models of the coronavirus epidemic in the United States as a starting point for their test estimates. They found that, even if there was a significant variation in the outbreak size projections, all models tend to point in the same direction, that is, if a model showed that a State needed many more tests, the others generally did the same.
The model they used to create these estimates is the Youyang Gu COVID-19 Forecasts, which they say followed closely what actually happened in the field. However, the researchers warn, these figures are not meant to be taken literally, but as an indication.
If social isolation is relaxed, testing needs may increase
The Harvard test estimates are built on a model that assumes states continue social distancing until May 15. And about half of the states have already started lifting some of them.
Jha says that without the right measures in place to contain the spread, easing could quickly lead to new cases.
“The moment you relax, the number of cases will start to climb. And so, the number of tests you need to prevent your company, your condition from having large epidemics will also start to climb, “warns Jha.
Tests alone are not enough
A community cannot base the decision to open securely only on test data. States should also see a steady drop in the number of cases, by at least two weeks, according to White House guidelines. If their cases increase, they should assume that the number of tests they need will also increase.
And Jha warns, the test is the first step, but it will not contain an epidemic itself. It must be part of “a much broader set of strategies and plans that states must have in place” when they begin to reopen.
In fact, his group model is built on the assumption that states conduct contact tracing and have plans to support the isolation of infected or exposed people.
“I don’t want anyone to just look at the number and say, we’re meeting it and we’re ready to go,” he says. “What it really means is to test the ability in the context of having a really effective staff of contact tracers. “
Targets are floors, not targets
States that have achieved the estimated target should consider this as a starting point.
“We have always built them as a floor, the bare minimum,” says Jha. More tests would be even better, allowing states to reduce surges more quickly.
In fact, other experts have suggested that the United States do even more testing. Paul Romer, professor of economics at New York University, proposed in a recent white paper that if the United States tests each resident every two weeks, isolating those who are positive, it could stop the pandemic on its traces.
Jha warns that without sufficient testing and the infrastructure in place to locate and isolate contacts, there is a real risk that states – even those with few cases now – will see major new epidemics. “I think what people need to remember is that the virus has not gone away. The disease has not gone away. And it’s going to be with us for a while, ”he says.
Daniel Wood contributed to this report.