Might spitting in a tube be the solution to finding out who is infected with SARS-CoV-2? The results of a recent study suggest that might be the case.
To diagnose someone who is infected with SARS-CoV-2, a long swab is inserted deep into the nasal sinus to provide samples of the nasopharyngeal mucosa, a site of virus reproduction. The material collected is then subjected to RT-PCR to determine the number of copies of viral RNA. This procedure is not ideal: it is difficult to do properly, and may cause extreme discomfort to the patient. The sampling could induce coughing or sneezing, placing the healthcare worker at risk. Comparing serial samples is unreliable because different quantities of mucus can be sampled each time.
Saliva sampling has great appeal because it is not only non-invasive, but can provide consistent sample sizes and can be self administered (who hasn’t spit into a tube?). However we do not know whether assaying SARS-CoV-2 RNA in saliva is better than a nasopharyngeal swab.
To answer this question, the detection of SARS-CoV-2 RNA by nasopharyngeal swabs administered by healthcare workers was compared with self-collected saliva from 44 COVID-19 patients. Higher levels of viral RNA were found in saliva samples compared with nasopharyngeal swabs.
In another study of 22 participants administered multiple nasopharyngeal swabs or who provided multiple saliva samples, there were 5 cases in which a negative nasopharyngeal swab was followed by a positive result during the next collection. In contrast, there were no cases where saliva samples were first negative and then positive.
Finally, saliva was positive for SARS-CoV-2 in two healthcare workers who were asymptomatic and had tested negative by nasopharyngeal swab.
While these observations should be confirmed in a larger study, they suggest that saliva sampling for SARS-CoV-2 could be a sensitive, reproducible self-administered test for identifying both active and subclinical infections.
If the results of larger studies show that the saliva assay is a sensitive and reliable assay for detecting active infection with SARS-CoV-2, it could simplify testing in countries that lack nasopharyngeal swabs, personal protective equipment, and trained health care personnel.
If I were the COVID-19 Czar, I would have the saliva test sent to every individual in the US at the cost of the US government. Everyone would receive a kit consisting of a bar-coded tube into which they would spit, then record the barcode via cell phone to CDC. The tube of saliva would be mailed or dropped off at local collection boxes. The results of the RT-PCR assay would indicate who is currently infected in the US. This information will help to understand what fraction of the population might have immunity to infection.