A health worker takes a nasal sample for the COVID-19 rapid antigen test in New Delhi, India, Friday, June 19, 2020. Credit: Manish Swarup / AP

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A relatively new method of testing for the coronavirus has come under scrutiny in recent weeks after two cases across northern New England in which people initially shown to have the virus later tested negative using a more reliable technology.

In Maine, 19 people from a summer camp were initially presumed to have the virus earlier this month after they received positive results from that newer technique, which is known as antigen testing and has been designed to offer rapid results at a relatively low price.

But as state health officials announced last week, those results soon turned out to be false when the 19 people received negative results from a different method, the polymerase chain reaction, or PCR, test, which is considered the gold standard for identifying active cases. Officials declined to identify the summer camp, which administered the antigen tests as part of a plan to ensure the virus wasn’t circulating.

Around the same time, 48 people who had initially received positive antigen tests from a clinic in Manchester, Vermont, were given additional PCR tests that showed they too did not have the virus, according to the Boston Globe.

It’s still unclear what caused the discrepancies in those particular antigen tests. Maine officials said they are still determining what happened to the testing system at the camp.

A representative for the company that made the testing system used in both places, San Diego-based Quidel, did not respond to an email seeking comment. But the company told the Globe that it’s investigating what went wrong in Vermont. “At this time, there is nothing to indicate a failure of the Quidel test system,” the company said.

But the two cases demonstrate the confusion that has arisen as relatively unproven technologies have received federal authorization and quickly been adopted by groups that are struggling to detect, contain and keep out COVID-19, the disease caused by the virus. In general, quick and widespread testing is seen as critical to recognizing and blunting new outbreaks as the pandemic continues to surge in states across the South and West.

The producers of antigen tests have said that their systems can deliver quick test results by collecting nasal samples so that they can be placed in cassettes and processed within 20 minutes in portable machines. The technology looks for proteins on the surface of the coronavirus.

By comparison, PCR tests often look for genetic samples of the virus and must be sent to labs for analysis, which in some parts of the country has resulted in long delays that render the results effectively meaningless.

But while antigen tests may have some value, they are overall considered to be less accurate than PCR tests, and the two companies that market them, Quidel and Becton Dickinson, have only received temporary approval to do so from the U.S. Food and Drug Administration based on a limited amount of research, according to the Globe.

Antigen testing does not appear to be in widespread use across Maine, according to Robert Long, a spokesperson for the Maine Center for Disease Control and Prevention.

But at least a few of the state’s summer camps have adopted it as part of a multi-pronged strategy to ensure that campers and staff do not have COVID-19, said Howard Salzberg, executive director of Camp Modin in Belgrade.

At Camp Modin, staff and campers were required to receive negative PCR tests before arriving for the single five-week session the camp is offering this year, in addition to a number of other new precautions the overnight camp has implemented. They then received a second test using a Quidel machine when they arrived at camp, followed by at least one more PCR test later on, Salzberg said.

He acknowledged the Quidel tests are not as accurate as the PCR tests, but said they have provided an added degree of security at less expense. Each antigen test costs the camp $38 — on top of the price of the machine — compared to $150 for the PCR tests. Salzberg said the camp has not had any false positive cases or actual positive cases.

“The PCR testing is much more accurate. There is no question,” he said. “Ultimately we made the decision to add antigen testing because it’s another layer. I’d rather have one test that’s 99 percent accurate and have another test that’s 89 percent, then go back to 99. The more testing you do, the more accurate it is.”

“I think campers in Maine are more tested than anybody else who is from the state of Maine,” he added.

While Maine health officials say there is value in offering antigen testing to people who show symptoms of COVID-19, they do not currently endorse it for large groups of seemingly healthy people, as the summer camps have been doing.

But the state has not gone as far as two other New England states, New Hampshire and Vermont, to require that all positive antigen tests be confirmed with a PCR test before they can be added to the state’s case totals, according to the Boston Globe. Rather, Maine only calls for retesting when the result of the antigen test seems to conflict with other evidence, Long said.

In the case of the summer camp, that was because people tested positive despite previously testing negative multiple times and not having been in any situations where they could have been exposed to COVID-19. Maine would also call for retesting if, for example, someone with a fever and shortness of breath — common coronavirus symptoms — received a negative result from an antigen test.

“To date, antigen tests have proved to be a useful tool for confirming that people with symptoms have COVID-19,” Long said. But he added the “caveat” that “COVID-19 testing technology continues to evolve rapidly on multiple fronts, which means that new information becomes available all the time.”