Information about gargling
In a press conference recently, Governor Yoshimura of Osaka Prefecture began by saying that
“This is a true story that sounds like fiction,” and then introduced the idea of “gargling with
mouthwash” involving mouthwashes using povidone-iodine (such as “isozine”). He said “By
gargling with it, the number of patients with coronavirus and the number of people who test
positive for coronavirus will decrease.”
After that, there was a huge reaction, such as the mouthwash being sold out at drugstores.
Many experts commented on the lack of evidence, and Governor Yoshimura himself said the
next day at the regular meeting, “Mouthwash using povidone iodine can’t prevent coronavirus,”
explaining that the protective effect against new coronavirus infections had not been proven.
So, what was the gist of the research submitted by Governor Yoshimura? And, above all, has
the protective effect of gargling against infectious diseases been confirmed?
What is the conclusion of the study on “gargling with povidone-iodine combination
First, the substance of the research submitted by Governor Yoshimura was as follows:
Forty-one patients (mild or asymptomatic) who underwent medical treatment at an outpatient
medical treatment lodging facility in Osaka Prefecture were divided into two groups: a group that
gargled four times a day with a mouthwash containing povidone iodine, and a group that did not
gargle. When compared separately, the group who gargled with a mouthwash had a lower
percentage of positive saliva PCR tests.
Specifically, when a saliva PCR test was performed every day, the positive rate of “other
patients (meaning patients who did not gargle)” was 40.0% on the 4th day, whereas the
positivity rate of “patients who gargled with mouthwash” was 9.5%.
Does it reduce infection and severity in others?
If you read these results by themselves, you may ask, “Does gargling with a mouthwash
eliminate the virus?” or “Is it possible to prevent infection?”
However, this study has a small sample size of 41 people, and it compares the “group gargling
using mouthwash” with the “group not gargling” as to whether the mouthwash is effective or not.
I’m not sure it works.
Furthermore, Dr. Akifumi Matsuyama of the Osaka Habikino Medical Center, who was present
at the press conference, said, “At this time, I am looking only at saliva. COVID-19 (new
coronavirus) builds up in the back of the nose and throat. It’s impossible to cure this,” he said,
and verified that “reducing the virus in the mouth will reduce the transmission to other people
and the severity of pneumonia.”
In addition, he said “Some of the patients who tested negative can turn positive after a few
minutes, and although the virus in saliva can be killed, the virus in the nose is still dripping.
Sometimes it turns positive.”
There is evidence about gargling
On the other hand, in response to this research result, it is logical that the use of mouthwash
reduces the virus in the mouth; however, “it may eradicate the native bacteria in the mouth,
significantly reducing the preventative ability.” There is also a discussion among experts as to
whether that is also feasible.
There is a well-known paper about mouthwash with povidone iodine.
This is a research essay by Professor Takashi Kawamura of Kyoto University, which was
published in the medical journal “American Journal of Preventive Medicine” in 2005.
In this study, 387 men and women were divided into three groups: (1) those who gargled with
povidone-iodine mouthwash, (2) those who gargled with water, and (3) those who did not
gargle. They were observed for 60 days. As a result, compared to the group who did not gargle,
the group who gargled with water had a 36% less chance of catching a cold, but there was no
apparent effect in the group who gargled with povidone iodine.
Why is gargling with only water more protective?
Regarding this, the paper asserts that povidone-iodine kills the indigenous bacteria in the
mouth, making it impossible to prevent the intrusion of pathogens.
In other words, it’s not as simple as killing a virus.
Therefore, although the preventive effect of mouthwash against colds has been proven, further
verification is needed to determine whether or not the mouthwash using povidone iodine is
really an effective countermeasure against the new coronavirus infection.