ByMAAYAN JAFFE-HOFFMAN

One of the main pillars of fighting the coronavirus pandemic is frequent testing, according to epidemiologists. But the traditional nose and throat swab screening is uncomfortable and expensive, and in some parts of the world, the swab kits are not even available.

As such, Prof. Eli Schwartz, of the Center for Geographic Medicine at Sheba Medical Center in Tel Hashomer, said he decided to look for an alternative.
Coronavirus can be accurately tested in mouthwash samples, according to new Israeli research that will be published Thursday by the European Journal of Clinical Microbiology & Infectious Diseases.

“The method I wanted to test is mouthwash,” he said. “You give the patient a saline solution and he rinses his mouth, gargles in his throat for 10-20 seconds and spits it into a tube. This is very convenient and easy. In the past, there had been a trial like this for testing influenza, so that gave me hope that it may work with coronavirus, too.”

Schwartz noted that others have tried using saliva to test for coronavirus, but that this is more complicated for the lab to process and less convenient to require of the patient.

He said that mouthwash is a noninvasive, simple and inexpensive test that can be easily performed by the patient.

Between July and September 2020, Schwartz carried out his trial on individuals over the age of 18 who were being isolated in state-run coronavirus hotels. His team collected 361 samples from 96 confirmed COVID-19 patients – 137 were collected via swab test, 137 saline mouthwash, 59 with distilled water wash, 12 with commercial mouthwash solution with alcohol and 16 with commercial mouthwash without alcohol.

The same medical staff performed all sampling during the entire trial, and all samples were developed at the Israel Central Virology Laboratory, using the same protocol.

“We did a comparison to see whether the performance of the mouthwash is inferior to the regular swab,” Schwartz explained. “We found that it is not.”

Standard tests identify coronavirus infections by isolating and amplifying viral RNA. In Israel, the samples are put through 40 cycles of amplification to determine if a person is positive or negative – a very high standard, according to Schwartz.

In most of the world, RNA samples are put through 30 to 35 amplification cycles.

The mouthwash detected 84% of the positive cases that the swabs detected when put through 40 cycles. However, when comparing the mouthwash and the swabs at a different positive cutoff – values of 30 and below, meaning samples with a higher viral load – the mouthwash tested 94% to 97% of these cases.

“If we are talking about schools coming back with more frequent examinations, I think if you have something that is more user-friendly, it will be much easier to convince people to do it more frequently,” Schwartz said.

He also noted that the Finance Ministry would likely welcome such a move because Israel is investing, according to Schwartz, around NIS 1 million per day on swab tests. Saline tests would be much less expensive and involve less equipment.

“Gargling with saline costs a few cents,” he said. “If we can offer something cheaper, maybe we can perform many more tests.”