Photo: INDRANIL MUKHERJEE / AFP Via Getty Images
Connecticut has so far conducted 1,392,117 tests for coronavirus — specifically they are “PCR tests.”
What is a PCR test, you ask? Does it have any limitations? Why does the state focus on those tests in particular?
For answers, we turned to the head of the state laboratory, Dr. Jafar Razeq, who literally knows everything there is to know on the subject.
Ready? Here we go…
PCR stands for “polymerase chain reaction.” As Rezeq explained, it’s an “amplification testing methodology.”
“If, in theory, you have one single viral particle in the patient’s specimen, that single viral particle in this polymerase chain reaction technique is amplified into tens of thousands and hundreds of thousands of particles for it to be detected,” he said.
The reaction goes in cycles — one molecule becomes two, two becomes four, and so on, for a predetermined number of iterations. The limit of those iterations is called the cycle threshold, and it’s set by the manufacturer of the test itself (and approved by the FDA).
So, for example, if the cycle threshold is 37, that means if you have no positive identification of a virus after 37 iterations, the test is negative. The fewer cycles needed to detect a virus, the higher the viral load in the patient.
You can also grow a specimen in a culture, but that takes far longer than a PCR test (on the order of weeks, instead of minutes).
Growing a culture does offer one nuance that a PCR test doesn’t: A PCR test cannot distinguish between dead and live virus cells.
This is important, theoretically, because a person infected with dead virus cells is not contagious, and might not actually need to be quarantined. But, considering how much longer a culture takes to grow (and the fact that the CDC does not suggest growing cultures for safety’s sake), it’s practical to use PCR tests and assume that every viral particle is live.
“By the time I come back to you, and tell you, ‘Oh, by the way, two weeks ago I collected a specimen from you and that day showed that you had a live virus. “So, really, you’re talking about practicalities,” Rezeq said.
You can listen to the full interview with Dr. Rezeq here. Please note: The transcription is automatic, so there are significant spelling errors.