Testing patience: Results discrepancy eludes easy answers
Everyone in Southern Vermont wants to know: Why did so many positive antigen tests for COVID-19 at Manchester Medical Center result in negative PCR follow-up tests from the state Department of Health?
Dr. Janel Kittredge-Sterling, the co-founder of MMC, joined Dr. Mark Levine, the state's health commissioner, on Vermont Public Radio's "Vermont Edition" on Monday afternoon to address that question.
While the two doctors didn't arrive at an explanation, both pledged cooperation in search of answers — and reminded residents of Manchester and its surrounding mountain towns that regardless, continued vigilance is crucial in preventing spread of the highly communicable virus.
The data remains confounding.
There have been 64 positive antigen tests reported by MMC as of Monday. But of the 35 follow-up PCR tests reported, only two have returned positive.
Overall, Levine said, there have been 1,423 PCR tests taken in the Manchester area in the past week, in pop-up testing conducted in Londonderry and Manchester and in follow-ups to the antigen tests. Of those, three have returned positive, he said.
"I do have empathy for what families are going through. I know this is very stressful. And there's a lot of fear," Kittredge-Sterling said earlier Monday. "There's significant confusion here making it hard for folks to know how to proceed or what to think about themselves.
"We are doing our part and our due diligence to figure out to the best of our ability why this discrepancy is occurring," she added. "But I cannot say that it wasn't because we didn't have [COVID-19] cases. We did."
NEW TEST, NOT NEW EQUIPMENT
Manchester Medical Center has been using testing equipment made by San Diego-based Quidel since the clinic opened in 2019, Kittredge-Sterling said. Like many other private practices, MMC had difficulty obtaining PCR test kits, and began using Quidel's COVID-19 test when it was made available by the U.S. Food and Drug Administration in May.
"We spent a great deal of time researching and receiving data to ensure this was accurate," Kittredge-Sterling said of the equipment. It was routinely calibrated and the staff was trained in its proper use, she said.
What's the difference in tests?
The antigen test looks for the presence of certain proteins that are part of the virus, while the PCR test — which stands for "polymerase chain reaction" — seeks the virus' unique genetic signature. The antigen test's benefits are that it returns results much more quickly than the PCR test, which can take days.
Both tests are considered highly effective in detecting positive results. Their down side, more so for the antigen test, has been the number of false negative results — telling people they're not COVID-positive when they actually are.
But it's worth noting that no medical test is 100 percent effective. Kittredge-Sterling said she's personally aware of coronavirus cases in which the patient returned multiple negative PCR tests for COVID-19, but clearly had most of its debilitating symptoms.
So what's really happening? "This is what makes this extremely unprecedented like every other aspect of this epidemic," Levine said. "I don't think this has been encountered anywhere before."
Levine laid out a number of potential theories, but quickly added reasons why many of them seem unlikely:
- Are the antigen tests correct and the PCR tests incorrect? "It would be unlikely to have such a large number of PCRs if that were true," Levine said.
- Are the antigen tests correct and the PCR tests were taken too late? "That doesn't seem really likely either, because there was a huge number of PCR tests and because the vast majority of followup was within two days of the antigen test," Levine said.
- Could the antigen test have picked up another coronavirus, resulting in false positives from another virus? "That's not supposed to be likely but the FDA is allowing emergency use (of the antigen tests) without a lot of preliminary data," he said.
- Are equipment malfunctions or human error at fault? "The physicians at MMC have assured me they pay very special attention to that," Levine said.
Kittredge-Sterling raised the possibility that the time it takes to get PCR test vials from Southern Vermont to their laboratory destination might play a role. It takes hours, sometimes days, for those vials to reach their destination, she said.
"Is there something with the testing media that's making [COVID-19] undetectable? Is it the delay? Is it the temperature at which vials are being stored in between transport time? I look at all of the possible reasons we have this discrepancy, because the only way to manage the pandemic looking forward is to find where the break in the chain is occurring," she said.
Also appearing on the program was Dr. Trey Dobson, the chief medical officer of Southwestern Vermont Medical Center in Benington. He said the testing dilemma highlights the importance of people following the behaviors that are already proven to reduce spread of the virus.
"Let's all act as if we have this whether or not we have a (positive) test," he said.
Earlier Monday, Kittredge-Sterling said that between May 20 and July 1, the clinic conducted about 700 tests to rule COVID-19 in or out for people who had similar symptoms. The results were all negative for the coronavirus.
"People were coming in with a sore throat, fatigue, nausea, they were here from Brooklyn, they'd been in a wedding party," she said.
That changed July 1 with a single test — a positive from a teenager visiting the area with family.
Fourth of July weekend was quiet, she said. But July 10 brought five positive cases — not all from the same family or social group.
"There were different pockets of positives — it wasn't random. They had symptoms that made sense significant for COVID. A plus B was equaling C," she said.
In many patients, the symptoms being presented included gastrointestinal distress, such as nausea, cramps and diarrhea — all of which were on the list of symptoms for the virus.
As positive test results piled up over the weekend, Kittredge-Sterling had a decision to make about whether to to tell the community that it might have an outbreak on its hands.
"When I can't get a hold of the fire department, do I let the house burn? The wrong thing for me is to think 'these are false positives' and let these people roam," she said.
While experts try to understand the results — Quidel and the U.S. Centers for Disease Control and Prevention are both aware of the situation, Kittredge-Sterling said — she wants to assure patients that the clinic acted appropriately, followed protocols, and made the results public in the interest of protecting public health.
"There's no conspiracy, there's no divisiveness, I'm not telling anybody not to trust the Vermont Department of Health," she said. "We have to work in collaboration ... to figure out why there's a discrepancy. Something happened, somewhere.
"We need to look at all the angles and I am transparent. If there is something that happened on our end, I will own it," Kittredge-Sterling said. "And I want people to know the truth about their health. I have nothing to gain in giving anybody false information. I want to know where does the discrepancy lie and if it's our testing, we will own that."
Reach Greg Sukiennik at email@example.com
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