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Nearly 80% of coronavirus patients in Japan have not infected others: experts

A girl receives masks from her homeroom teacher at Hirata Elementary School in Asago, Hyogo Prefecture, on March 2, 2020. (Mainichi/Manabu Matsuda)

TOKYO -- Nearly 80% of patients with the new coronavirus in Japan have not passed on the infection to others regardless of the degree of their symptoms, a government panel of experts announced on March 2.

At the same time, the panel considering countermeasures against infections with the new coronavirus pointed to the possibility that one person could spread the virus to multiple people in closed indoor spaces, forming clusters of patients.

Bearing in mind the increasing number of infections in the northernmost prefecture of Hokkaido, where the largest number of patients in Japan has been reported, the panel has warned that even those with slight symptoms are believed to be playing a key role in the spread of infections without realizing it.

The panel has summarized its views on the spread of infections after the Ministry of Health, Labor and Welfare analyzed specific cases of 110 people, who had been confirmed to have contracted the pneumonia-causing coronavirus, up to Feb. 26.

According to the outcome, 83 of them, or 75.4%, have not passed on the virus to anybody else. Moreover, at least 50% of 27 people who are victims of secondary infections have not transmitted the virus to more than one person.

Citing cases in which infections spread in closed indoor spaces such as live music clubs and buffet parties, the panel pointed to the possibility that clusters of those infected with the virus are formed if people have close contact with others over a certain period of time.

The panel said that 80% of those confirmed to have been infected with the virus have shown slight symptoms and 14% have developed serious symptoms, while 6% have been in critical condition. Half of those who suffered serious symptoms have since recovered.

The conditions of those who show serious symptoms of pneumonia caused by the new coronavirus typically worsen rapidly after they experience cold-like symptoms, such as a slight fever and coughing, for five to seven days. Therefore, experts say it is difficult to determine whether the conditions of such patients will worsen based on their initial symptoms.

Tohoku University professor Hitoshi Oshitani, a member of the government's panel, pointed to the possibility that many clusters of patients have been formed in Hokkaido where the prefectural government declared a state of emergency on Feb. 28.

"There is a high probability that a considerable number of clusters of patients have been formed. There may be connections between clusters of younger patients who don't interact with middle-aged and elderly people," he said.

Hokkaido University professor Hiroshi Nishiura released the panel's estimate that some 940 people in Hokkaido had contracted the virus as of Feb. 25 based on the number of people from Japan and overseas who were confirmed infected with the virus after traveling in Japan's northernmost prefecture.

Nishiura suggested the confirmed cases of coronavirus infections in Hokkaido is just the tip of the iceberg. "There is a wide gap between the number of confirmed cases and the estimated figure. The only explanation is that there are people with slight symptoms who haven't been diagnosed with the disease," he said.

Moreover, warning that those in their teens to 30s who are at low risk of getting extremely ill from the virus may be spreading it, the panel said, "If you avoid going to poorly ventilated places where many people gather, you can help prevent the conditions of many patients from worsening and save lives."

(Japanese original by Sooryeon Kim and Go Kumagai, Lifestyle and Medical News Department)

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