Saliva tests for SARS-CoV-2 may reveal how a patient develops a coronavirus infection, a new study suggests.
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By Robert F. Service
Science”s The COVID-19 report is supported by the Pulitzer Center and the Heising-Simons Foundation.
To the known risk factors for developing COVID-19 – age, male sex, or any set of underlying conditions – a new study adds one more: high levels of the virus in your saliva. Routine COVID-19 tests sample the nasal passage. But several new tests are looking for SARS-CoV-2, the coronavirus pandemic, in saliva, and the new work finds a striking correlation between high virus levels there and hospitalization or later death. If the results are confirmed, salivary tests may help doctors prioritize which patients in the early stages of the disease should receive medications that lower levels of the virus.
“I thought it was very interesting,” said Shane Crotty, a neurologist at the La Jolla Institute of Immunology, who was not involved in the research. Crotty notes that the results show that virus levels in saliva show deep viral loads in the lungs, where the disease does much of its damage in severe cases. “That’s a valuable foundation,” says Crotty.
The new work is not the first to link the body’s coronavirus weight and disease outcome. Several research groups have found a correlation between high viral levels in the nasal passages at the time of hospital admission and the severity of the infection. But other groups did not find the same connection.
The standard test to detect SARS-CoV-2 is sampling nasal mucus using nasopharyngeal swabs (NP). The procedure is unpleasant, but the usual method is to sample respiratory pathogens. In the past few months, however, several research groups have developed and obtained emergency use authority from the U.S. Food and Drug Administration for testing for SARS-CoV-2 in saliva.
Yale University researchers were among the first, and university hospitals have been using both saliva and NP swab tests. In each case, labs analyze the samples using quantitative transcription polymerase chain reaction tests, which detect genetic material from SARS-CoV-2 and measure the number of viral granules per milliliter of sample. .
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Researchers led by Akiko Iwasaki, an immunologist at Yale, compared viral loads in saliva and NP swabs from 154 patients and 109 people without the virus. They divided the patients into groups with low, medium and high viral loads as determined by both types of test. They then compared these results with the severity of the symptoms that the patients developed later.
They found that patients who developed severe disease, were hospitalized, or died were more likely to have high virus loads in their saliva tests, but not in their NP swabs. The viral load in saliva and nasal mucus decreased over time in patients who recovered, but not in those who died.
When Iwasaki and her colleagues reviewed patients’ electronic medical records for signs of disease in the blood, they found that high saliva viral loads were associated with high levels of immune signals such as cytokines and chemokines, nonspecific molecules that ramp up up in response to viral diseases and has been linked to thin damage. People with more virus in their saliva gradually lost some cells that put up an immune response against viral targets, lower levels of antibodies targeted the spike protein that the virus uses to pass into cells, and were slower to suppress the strong immune response required to suppress the virus in cases where they overcame it. The team’s results on Jan. 10 appeared in an introduction that was not peer-reviewed.
Iwasaki and her colleagues argue that saliva may be a better predictor of disease outcome than nasal mucus because the latter comes from the upper respiratory tract, but severe infection is associated with damage. deep in the lungs. “Saliva may represent better than what is going on in the lower respiratory tract,” Iwasaki says, as cilia lining the respiratory tract naturally ‘moving mucus up from the lungs into the throat, where it mixes with saliva; coughing has the same effect.
The results do not have enough statistical power to show how likely a person with a high saliva viral load is to develop severe COVID-19, Iwasaki says. She also wants other groups to replicate the results, especially since there have been mixed results in efforts to link high NP viral swab loads to disease progression.
If further research confirms the findings, it “cleared much of the smoke” surrounding this disease, Crotty says. Monica Gandhi, an infectious disease expert at the University of California, San Francisco, says if salivary tests are predictive, they could help doctors identify patients for early treatment with antibodies to reduce viral or steroids to suppress inactive immune responses.
Saliva tests are cheaper and easier than NP tests, but much less available. Demonstration of the new results could therefore support efforts to make saliva testing easier, said Sri Kosuri, CEO of Octant, Inc., a biotechnology company. “If this investigation were to take place in March, we would be discussing whether we should be conducting NP tests at all,” Kosuri says.