South Korean health officials are straining to contain a new flare-up of infections traced back to nightclub revelers in Itaewon, central Seoul, earlier this month. Of the 40 new patients confirmed positive Wednesday, 37 were linked to the nightclub cluster, while the other three were travelers from overseas.

Since the first infected nightclub visitor was identified on May 6, an extensive testing of over 41,000 people with possible ties to the nightclubs has been carried out to find 259 positive cases.

As preschoolers and primary school kids headed back to school on Wednesday, special health warnings have been issued over two suspected cases of a children’s inflammatory disease reported at Seoul hospitals Tuesday.

In a press briefing, Korea Centers for Disease Control and Prevention Director Jung Eun-kyeong said that the patients -- a boy, 11, and a girl, 4 -- displayed symptoms of the rare condition known as multisystem inflammatory syndrome in children or MIS-C, which is speculated to be a complication of COVID-19.

The first round of testing revealed both were negative for COVID-19, she said. An antibody survey will be conducted to determine whether they have been exposed to the virus.

Jung said their symptoms such as fever, skin rashes and abdominal pain have improved after receiving anti-inflammatory therapy that is typically used to treat Kawasaki disease. Clinical manifestations of the suspected MIS-C cases were similar to those of Kawasaki’s, she added.

The 11-year-old, who visited the Philippines between January and March, has been released from hospital care, and the 4-year-old was set to be discharged as well.

No additional cases of the pediatric condition have been reported so far, the KCDC director said.

As the disease control agency sounded the alarm over the emerging disease affecting children, Minister of Health and Welfare Park Neung-hoo said disease control efforts at schools were paramount to stop the coronavirus from spreading in communities.

Ahead of the phased reopening of schools last week, the government required students, faculty members and other staffers to wear face masks at all times in classrooms and other indoor school facilities.

But keeping masks on for an extended period of time can be harder for younger children, who may experience breathing difficulties.

Pediatric infectious disease specialist Dr. Eun Byeong-wook of Nowon Eulji University Hospital in northern Seoul said surgical masks, which are thinner and more loose-fitting than face masks with higher filtration capabilities of KF80 or KF90, can be an option for children who complain of discomfort.

“High-filtration face masks sift out more particles, but they may not be efficient if children find them uncomfortable and have to wear them on and off.”

But as the surgical masks worn by dental professionals don’t come in children’s sizes, the straps should be adjusted for proper fitting.

Cloth face coverings, while better than nothing, do not block infections as effectively, he said.

Prime Minister Chung Sye-kyun said in a Central Disaster Management Headquarters meeting that updated coronavirus guidance will be introduced in keeping with the imminent summer season.

Two of the major additions in the protocol outlined Wednesday concern air conditioning and dining practices.

Communal spaces with air conditioning require proper indoor ventilation, which means opening doors and windows every two hours. In places where air flow is restricted, people should wear face masks at all times and no one with symptoms should be allowed in.

Infectious disease specialist Dr. Lee Jacob of Seoul’s Hallym University Hospital said in a Facebook statement posted Sunday that air conditioners can cause respiratory droplets -- which may or may not carry the coronavirus -- to travel farther, in which case more widespread contamination can occur in a given setting.

“Keeping spaces well-ventilated helps reduce the concentration of the potentially infectious droplets,” he said.

Some changes are due in terms of dining customs, which can increase risk of transmission.

The Health Ministry’s safety recommendations at the dining table include serving food in individual portions, and avoiding double dipping when sharing dishes -- a convention that should be replaced by use of designated serving utensils.

Health authorities have yet again cautioned against “silent spread” of the coronavirus among younger demographic in whom the infection can lack apparent symptoms.

“In the past three weeks, people in their 20s accounted for 40 percent of all reported cases,” said Jung of the KCDC. The recently diagnosed 20-something coronavirus carriers had passed on the disease to 16 people aged 60 or older who are at greater danger of falling severely ill.

In an unprecedented move, a court in Uijeongbu in Gyeonggi Province on Tuesday sentenced a man in his 20s to a four-month jail term for breaking home quarantine order last month.

“Violating quarantine with no justifiable motives while the outbreak is still unfolding warrants grave punishment,” the court said.

The prime minister, commenting on the ruling, said young people needed more caution when socializing and urged them to practice physical distancing as they go about their daily routines.

By Kim Arin (arin@heraldcorp.com)