Polymerase chain reaction testing (PCR) detects tiny amounts of DNA. The procedure uses a technique for doubling the amount of DNA present in the sample, called cycling. In the case of coronavirus, they first have to use reverse transcription to convert the virus’s RNA to DNA, so the sample is even more tiny. Many people know the folktale of the Chinese man who, when offered any reward by the Emperor, asked for a single grain of rice on the first square of the chessboard, two grains on the second, and doubling the number of grains to the 64th square. The Emperor agreed. By the twentieth square, the emperor was out of rice, with twice as much due on the 21st square. The Emperor had the man executed. PCR cycles double in the same way. So, by the 38th cycle, there would be a truly vast amount of any DNA originally present. Most labs use 38 cycles as the cutoff for a positive result for a coronavirus infection. They used 40 cycles, or four times as much DNA, as the cutoff for a negative result. These are called cycle thresholds.
Nearly all positive results appear at fewer than 20 cycles, which is the point where the Chinese man died.
Mr. Emmerich has written that every test is positive over 40 cycles. I have found no such statement in all my reading on this matter. It is an odd thing to say, since no lab does more than 40 cycles. He also wrote that since everybody has the virus in their bodies, efforts to avoid infection are pointless. Actually, the chance of illness depends on the number of viruses in your system. A robust immune system helps a lot toward keeping that number down, but the fewer viruses it has to fight, the better job it is likely to do. Breathing in virus-laden aerosols makes that task vastly harder.
I am fully vaccinated. I still wear a mask in public. This is such a trivial inconvenience that I am horrified that anyone would refuse to do it.
Bill Gillmore, Columbus
