Fact check: Trump wrong about testing causing rise in cases

President Donald Trump’s explanation for rising counts of U.S. coronavirus cases is that we’re testing more people for the virus.

On June 23, Trump tweeted, "Cases up only because of our big number testing. Mortality rate way down!!!"

PolitiFact looked at his statement on mortality in a separate fact check. In this article we’ll focus on his mistaken connection between increased testing and increased cases.

While the number of coronavirus tests being conducted is rising over time, the positivity rate — which is the percentage of tests that come up positive for the virus — has also been rising since early June. And that undermines Trump’s argument.

The following chart shows that the number of tests across the country has risen steadily since late March. The orange line shows how the positivity rate has changed over time.

Initially, the rise in tests did show the pattern Trump touted: As more tests were conducted, the percentage of positive results declined. After peaking above 20% positive in early April, the positivity rate fell to about 4% in early June.

A likely reason for this pattern is that early in the pandemic, tests were scarce and were reserved for people who showed visible symptoms. As testing kits became more widely accessible for people without obvious symptoms, a wider cross-section of the population was tested, with a resulting decline in tests showing the patient was infected.

Fact check: Trump says the COVID-19 death rate is 'way down'

The problem for Trump’s assertion is that the decline in the positive rate reversed itself in early June. The positivity rate bottomed out around June 10 at about 4.3%. By June 22, it had risen to about 5.3%.

That may not sound like a big increase, but if more infections are being tallied simply because more tests are being given, as Trump suggested, the positivity rate should be going down, or at least staying about the same, not rising.

"The up-turn in positive rate is sufficient to debunk" what Trump said about testing, "particularly given that the total number tests conducted is at its highest yet, and still we see an increase in the seven-day rolling positive rate," said Brooke Nichols, an infectious disease modeler at the Boston University School of Public Health.

The rise in the positivity rate appears to be driven by a handful of states.

Early coronavirus hot spots, notably New York, have seen a decline in new infections despite widespread testing. But other states are seeing both an increase in infections and an increase in the percentage of positive tests.

In Arizona, Florida, South Carolina, and Texas, the positivity rate has increased consistently since late May.

The White House told PolitiFact that anecdotally, the increased testing has uncovered a growing number of people who are asymptomatic or who have mild or moderate cases than earlier in the pandemic, when tests were hard to get.

However, an increase in the number of infections also means the potential for accelerated spread.

Trump said that the coronavirus case count is "up only because of our big number testing."

Testing has increased nationally, but epidemiologists say that if this were the only reason that new cases were rising, the percentage of positive tests should be dropping or at least remaining about the same.

That pattern did occur from early April to early June, a period when the availability of testing expanded significantly. However, that’s no longer the case. Since early June, the amount of testing being conducted has continued to reach new highs, yet the positivity rate has risen by a full percentage point.

We rate the statement False.