The nasopharyngeal tract likely has (1) active virus replication and (2) enough virus to be detected in test kits. This site is relatively easily accessed, compared to the final site of viral infection: the lower respiratory tract. For diseases that are primarily respiratory in nature, like COVID-19, nasopharyngeal swabs have been the most reliable, as they sample an area of the respiratory tract where the virus appears to first infect an individual. Most samples are collected using nasopharyngeal swabs or a sputum cup, although the virus may also be detected in feces, urine, or blood. These tests require samples from the patient that are likely to contain virus. NAATs include the polymerase chain reaction (PCR) assay in a laboratory to amplify viral genomic material for detection and can provide results in hours to days other techniques include LAMP and next generation sequencing. Molecular tests called nucleic acid amplification tests ( NAAT) rely on amplification of existing genetic material in the sample. These rapid tests detect basic levels of antigen already present in a sample, providing only a simple “yes” or “no,” similar to a pregnancy test. Antigens are found on the surface of the virus particle, which are also shed in patient tissues. The viral genomic material for SARS-CoV-2 is ribonucleic acid (RNA), which remains in the body only while the virus is still replicating, even at very low levels.Īntigen tests detect specific viral proteins ( antigens) present in a patient sample taken using nasal or nasopharyngeal swabs and can provide results in under a half hour.
These tests inform researchers and health providers of the presence of the pathogen, either by amplifying and detecting its genetic material or identifying unique markers of the pathogen itself.
Diagnostics able to detect current, active infections are typically antigen- and molecular-based tests. The diagnostic testing field for COVID-19 is rapidly evolving, with many tests focused on diagnosing patients with active viral infections.
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