PCR testing has also been developed to detect a mutation in the organism that leads to resistance to a specific antimicrobial. It is essential to recognize that while PCR can detect sections of identified genomes, it cannot determine whether there is a live or dead organism (such as a virus) in the sample. It is also unable to decide whether that organism is resistant to an antimicrobial, but only whether it has the genetic capability to be resistant. In addition, other issues can arise when the target sequences chosen for detection are later determined to overlap with different strains or species, causing previously reported positives to be possible false positives. False-negative results can occur due to improper sample collection, collecting too early during infection, or viral mutations in the genome section used to detect the organism. False positives, negatives, sensitivity, and specificity of a specific test can vary between manufacturers and depend on the organisms tested.
When PCR testing protocols are developed, it is also essential to recognize that running amplification cycles more significant than 35 times can increase the likelihood of detecting viral particles too small to cause infection. As with any laboratory test, it is important to remember that results should be used with history and clinical signs and symptoms.
This image shows the amplification cycles in reverse transcription PCR used to evaluate the presence of the mutation in influenza A (H7N9) that causes oseltamivir (Tamiflu) resistance.
