COVID-19 test rates are still low in Pa., and high in N.J. How much is enough?

How much diagnostic testing for the coronavirus is enough to keep COVID-19 at bay so schools and businesses can open — and stay open?

Researchers, state health officials, the Trump administration — and the president himself — give differing answers.

But there is one thing everyone (except Donald Trump) agrees on: Adequate testing, plus basic safeguards such as masking and social distancing, is essential to safely reopening state economies.

After hitting its peak in April, Pennsylvania has seen only a slight uptick in cases so far amid reopening, but its testing rate continues to rank near the bottom of the 50 states. New Jersey, once a national COVID-19 hot spot, has crushed its daily case numbers, and continues to rank near the top in terms of testing.

Many factors, including population density and the ability to do contact tracing, shape how much diagnostic testing needs to be done. Here is an update on the issue that has plagued the U.S. response to the five-month-old pandemic:

On Friday, at the request of Rep. Frank Pallone (D., N.J.), the U.S. Department of Health and Human Services released individual state testing plans for May and June that had to be submitted under new federal laws aimed at pandemic relief.

States were supposed to detail how at least 2% of the state’s population would be tested in each of those months, as well as plans to increase that rate by the fall.

In May, the U.S. Centers for Disease Control and Prevention awarded $10.25 billion to states, territories, and localities to help carry out testing plans.

It is not clear what that 2% monthly testing goal is based on. Nationally, it would mean testing a total of 6.6 million people per month.

“Testing is not just about numbers — it is about targeting testing to the right people at the right time, and incorporation of testing into a comprehensive state plan for COVID-19,” Assistant Secretary for Health Brett P. Giroir said in a statement.

» READ MORE: Parts of Pa. reopened without robust coronavirus contact tracing to keep residents safe

Recently, the United States has been testing way more than 2% of the population per month, according to the COVID Tracking Project — and yet the project says that isn’t nearly enough. As the New York Times reported on Friday, the tracking project uses a methodology developed by researchers at Harvard University Global Health Institute that estimates testing needs for each state. The target for each state varies over time as infection rates change.

An average of 634,000 people per day were tested over the last week, while the target should be 1.6 million a day to keep the coronavirus at bay, according to the tracking project and Harvard.

Since the experts don’t agree on how much testing is enough, it’s hard to assess state numbers.

Pennsylvania, for example, reported 412,000 diagnostic tests in June, far more than its goal of 256,000, or 2% of the population. About 5% of those tests were positive — a relatively low rate that suggests the state is testing broadly and including people without symptoms.

“We have ramped up testing significantly and we will continue to do that,” Pennsylvania Secretary of Health Rachel Levine said Friday.

The COVID Tracking Project has a different take. It says Pennsylvania is doing a daily average of 100 tests per 100,000 residents — just below the Harvard target rate. That makes the Keystone State the 28th worst in state testing rankings. In comparison, New Jersey, where the positive test rate is down to 2%, has a daily testing average of 218 per 100,000 residents, more than the Harvard target rate.

Testing is just a piece of the coronavirus containment challenge, but it is the key to identifying outbreaks quickly and snuffing them out. It goes hand-in-hand with tracing an infected person’s close contacts so they can self-quarantine at home for two weeks, the maximum time between exposure to the virus and symptom onset. Since many infected people never have symptoms, contact tracing and quarantine are important — but these strategies aren’t practical if case numbers are exploding, as they are in numerous states.

To the dismay of federal health officials, the president has been pushing for less testing because the nation’s record-shattering daily numbers make the U.S. “look bad.”

“Cases, Cases, Cases! If we didn’t test so much and so successfully, we would have very few cases,” Trump tweeted last Saturday.

In another tweet last week, he said: “There is a rise in Coronavirus cases because our testing is so massive and so good, far bigger and better than any other country.”

In reality, testing does nothing to affect transmission rates. Nor does testing prevent hospitalizations and deaths — alarming indicators that are also soaring in the U.S., and are worse than in countries with more testing.

As cases surge, especially in Southern and Western states, access to diagnostic testing is once again hampering efforts to contain the pandemic.

Just as we saw locally months ago, drive-through testing sites in surging states report long lines and shortages of swabs and protective gear. Testing labs face backlogs and shortages of needed chemicals.

To be sure, collecting a respiratory sample and doing a molecular analysis to find virus particles is not quick or easy. Some newer molecular tests need only saliva or a nasal swab, and some can deliver results in an hour or so at the “point of care,” usually a hospital. But for the most part, diagnostic testing still relies on an unpleasant sample collection process — a long swab is pushed through the nose to the back of the throat — and a several-day turnaround time for results.

In some large cities with exploding case numbers, testing is again being limited to people showing symptoms, even though asymptomatic spread is one of the drivers of the explosion.

“It’s terrifying, and clearly an evidence of a failure of the system,” Morgan Katz, an infectious-disease expert at Johns Hopkins University School of Medicine, told the New York Times.

Staff writer Stacey Burling contributed to this article.