• The WHO has requested more information from China about an illness affecting children.

• Chinese authorities reported an increasing number of respiratory diseases earlier this month.

• Reports of "undiagnosed pneumonia" in children in northern China  circulated on November 21.

The World Health Organization asked China for "detailed information" about a respiratory illness affecting children in the north of the country.

The organization requested "additional epidemiologic and clinical information" following reports of "undiagnosed pneumonia" spreading among children, according to a statement released on Wednesday.

The rise in cases has led to overcrowded clinics and emergency rooms, the South China Morning Post reported, citing social-media posts. Hospitals in northern China appear to be "overwhelmed with sick children," NBC News reported.

The WHO statement said Chinese authorities had attributed the surge in cases to "the lifting of COVID-19 restrictions and the circulation of known pathogens such as influenza, mycoplasma pneumoniae (a common bacterial infection which typically affects younger children), respiratory syncytial virus (RSV), and SARS-CoV-2 (the virus that causes COVID-19)."

The South China Morning Post reported that Chinese authorities have since said that no new or unusual pathogens caused the illnesses.

Memories of COVID-19 outbreak

China faced added scrutiny over the news as it conjured up memories of its handling of the COVID-19 outbreak.

Health experts added that a continuing drug-resistance problem from overusing antibiotics had helped spread the illnesses, which mycoplasma pneumoniae bacteria cause, per the report.

Mycoplasma pneumoniae bacteria usually cause "mild infections of the respiratory system," but they can sometimes lead to more serious problems that may require hospital treatment, according to the CDC.

The agency says good hygiene is key to preventing the bacteria from spreading to others.

The WHO suggested people in China follow specific steps to mitigate the risk of infection, including taking the "recommended vaccination; keeping distance from people who are ill; staying home when ill; getting tested and medical care as needed; wearing masks as appropriate; ensuring good ventilation; and regular handwashing."