How saliva can predict COVID-19

Recent studies from Yale University in the United States have detected how crucial saliva is to prevent complications in those infected with covid-19, through the viral load in the mouth of patients that could even help to personalize treatments and leave behind the swab test.

It has been just over a year since COVID-19 appeared in the Chinese city of Wuhan, without being able to predict by then that it would become a global pandemic. Most of the patients began with mild symptoms, similar to those of a cold, but 15% required oxygen, while 5% needed to be admitted to the Intensive Care Unit (ICU) and in 1% of those infected, the infection progressed fatally, leading patients to death, according to data from the first wave in Spain, one of the countries most affected by the coronavirus at the beginning of last year.

After a year of fighting, the scientific community is learning to anticipate the movements of the virus. One of the latest advances has been studied by the laboratory of immunologist Akiko Iwasaki, at Yale University in the United States. Their preliminary results suggest that the amount of virus in saliva is used to predict the outcome of the disease.

“The viral load in saliva in the first moments is correlated with the severity of the disease and with mortality”, sustains the Iwasaki team, which has exhaustively analyzed 154 patients with COVID-19 at the university hospital in the city of New Haven.

The data found in the study show that virus levels progressively increase from a minimum in mild patients to a maximum in seriously ill patients and in people who died from the coronavirus.

The higher viral load in saliva is associated with known risk factors, such as advanced age, male sex, cancer, heart failure, hypertension, and chronic lung diseases.

“If we took samples of saliva and analyzed the viral load – especially at the beginning of the infection, when the person arrives at the hospital – it could help doctors a lot to predict the patient’s prognosis and choose the treatments”, points out the Spanish microbiologist Arnau Casanovas, who after seven years at Yale University and now hired in August by the American biotechnologist Tangen Biosciences, dedicated to designing new diagnostic methods, has participated in the new study, which still It is a draft that requires a final pending revision for publication in a specialized journal.

The team led by Iwasaki maintains that saliva helps predict disease progression much better than samples taken by the now popular nasal swab.

One of their hypotheses is that the swab test in the nose only reflects the multiplication of the virus in the upper respiratory tract, while the saliva also shows the situation in the lungs. The mucociliary system – a defense mechanism to expel germs – would carry coronaviruses from the lower respiratory tract to the mouth, reported the Spanish newspaper The country.

Research shows that the higher viral load in saliva is also associated with a higher amount of biomarkers in the blood of the inflammatory reaction characteristic of severe cases of COVID-19. That higher viral load, on the contrary, is linked to lower levels of platelets, white blood cells and specific antibodies against the coronavirus.

Elisabet Pujadas, a pathologist and researcher at the Icahn School of Medicine at Mount Sinai Hospital in New York, applauds the new study. “It provides a valuable perspective: that saliva may have a greater value than previously thought for diagnosis and prognosis”. His team had already published in August the relationship between the highest viral load analyzed in nasal samples and mortality from covid-19. “It is possible that saliva may better reflect lower respiratory tract infection,” Pujadas pointed out on that occasion.

Because the study so far only includes 154 patients, Pujadas considers that it may be premature to conclude that saliva should be used instead of swabs. “However, these promising results justify more resources being devoted to collecting and studying saliva samples.”

For the pathologist, the main lesson is that it would no longer be necessary to classify only covid-19 patients with a simple positive or negative. Additionally, your viral load must be measured. “For certain viruses, such as HIV, the quality standard is viral load, because years of research have shown that it has important implications for patient risk and affects our treatment strategy. It should also be the same with covid ”, said.

A systematic review of 37 investigations has just shown that saliva samples can replace swabs to diagnose COVID-19, with the same precision and lower price.

“We have been saying for quite some time that it would be better to use saliva as a priority sample. It is much easier to collect saliva than a nasopharyngeal swab. You don’t need a nursing staff. Each person can spit at home in a small boat. And you avoid the risk by taking the sample with the swab, because sometimes people sneeze or cough and aerosols are generated “, argued Casanovas.

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