Nasal or saliva: which test detects COVID-19 faster

COVID-19 tests can detect the coronavirus or antibodies generated by the human body after having the disease or after being vaccinated. Rapid tests are done with a swab in the nose. In contrast, laboratory tests involve a sample that can be taken by swabbing or saliva. A study published in the journal of the American Society for Microbiology, with more than 30,000 experts, showed that tests using saliva are faster than tests that use nasal swabs.

The research was published in the specialized journal Microbiology Spectrum. Genetic testing from saliva samples was found to identify the SARS-CoV-2 virus more quickly than nasal swab tests. The researchers pointed out why it is important to consider that speed.

“This is important because people can spread COVID-19 before they know they have it,” says co-author Dr. Donald Milton, professor of occupational and environmental health at the Institute of Applied Environmental Health at the University of Maryland School of Public Health, College Park. “Earlier detection can reduce the spread of the disease,” he added.

The investigation was motivated by the problem that, at the beginning of the pandemic, the urgent need to increase testing was accompanied by a shortage of supplies. There were times when the inputs for making nasal swabs were lacking, which were then the standard method of collecting samples for testing.

To identify people with COVID-19, researchers began weekly testing of saliva samples from healthy volunteers in May 2020 and continued for the next two years. Of the asymptomatic volunteers who tested positive, Milton and his colleagues found that these patients often showed symptoms a day or two later. “That made us wonder if saliva was better at detecting pre-symptomatic patients than traditional nasal swabs,” he said.

To answer that question, the researchers used data from a complementary study of close contacts of people with confirmed cases of COVID-19. In the study, “we collected saliva and nasal swabs samples from contacts every two to three days during the quarantine period,” he said.

“All samples were analyzed by real-time reverse transcription polymerase chain reaction [RT-PCR] to detect coronavirus and measure the amount of viral RNA in the samples. We then analyzed how these results changed in the days before and after the onset of symptoms,” he said.

“At the beginning of the course of infection, saliva was significantly more sensitive than nasal swabs in the middle part,” especially before the onset of symptoms, according to the study, which noted that previous studies had shown that presymptomatic transmission plays a greater role than the symptomatic of coronavirus.

The results have implications for improving public acceptance of COVID-19 testing, reducing the cost of mass screening for COVID-19, and improving the safety of health personnel conducting the tests. In the latter case, self-diagnosis with saliva avoids the close contact between the patient and the healthcare personnel involved in nasal swabbing and prevents patients from coughing and sneezing, thereby spreading virus particles as a result of swabbing the sensitive nostrils, as well as discomfort for patients.

“Our research supports the use of saliva in large-scale screening in schools and workplaces, as a means to improve screening rates, as well as early detection,” Milton said. “We hope that if rapid saliva tests become available, they could be a breakthrough over current rapid tests based on nasal swabs,” he said.

When asked by Infobae, María Victoria Miranda, director of the Nanobiotec Institute, researcher at Conicet and professor at the Faculty of Pharmacy and Biochemistry of the University of Buenos Aires, commented: “Any method that allows the detection of coronavirus early and reliably is very valuable. If we consider that the virus is first detected in the oral area and then begins to accumulate in the nose, analyzing the presence of viruses in saliva is interesting mainly for variants such as Ómicron that replicate very quickly in the upper respiratory tract and with very short incubation periods. The detection of the virus in saliva would facilitate sampling in addition to allowing the early detection of infections even before the onset of symptoms.”

In addition, the expert stated: “It is important to continue evaluating and comparing both options, both saliva and nasal swabs, because although the virus seems to accumulate early in the saliva, the nose may be a better place to detect it as the infection progresses.”

According to the Centers for Disease Control and Prevention (CDC) in the United States, there are different reasons for testing. This should be done if a person has symptoms of COVID-19 or at least 5 days after close contact with someone with suspected or confirmed COVID-19. It can also be used for evaluation in schools, workplaces, group settings; before and after travel, or when requested by a health care professional or public health official.

After taking a test, there are questions to consider. If the result is positive, the CDC's recommendation today is to isolate yourself for at least 5 days. “Learn more about precautions and periods of isolation. Have a confirmatory and follow-up laboratory test if recommended by a health care professional,” recommends the United States federal agency. In addition, it is advisable to be attentive to the symptoms.

If the test result is negative, it should be taken into account whether vaccination was already available or not. If a person who has already been vaccinated takes the test and tests negative, they can resume their usual activities. “Wear a mask indoors in areas where the level of COVID-19 in the community is high,” they advise.

On the other hand, if the person is not vaccinated, has a negative test but has symptoms or has been exposed to the virus, they should be kept in isolation for at least 5 days. “If you are not up to date on vaccines and have no symptoms or been exposed to the virus: you can resume your normal activities. Take steps to stay up to date with vaccines to protect yourself and others,” the United States CDC advises.

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