BEIJING (AP) — A surge in respiratory illnesses across China that has drawn the attention of the World Health Organization is caused by the flu and other known pathogens and not by a novel virus, the country’s health ministry said Sunday.

Recent clusters of respiratory infections are caused by an overlap of common viruses such as the influenza virus, rhinoviruses, the respiratory syncytial virus, or RSV, the adenovirus as well as bacteria such as mycoplasma pneumoniae, which is a common culprit for respiratory tract infections, a National Health Commission spokesperson said.

The ministry called on local authorities to open more fever clinics and promote vaccinations among children and the elderly as the country grapples with a wave of respiratory illnesses in its first full winter since the removal of COVID-19 restrictions.

“Efforts should be made to increase the opening of relevant clinics and treatment areas, extend service hours and increase the supply of medicines,” said ministry spokesman Mi Feng.

He advised people to wear masks and called on local authorities to focus on preventing the spread of illnesses in crowded places such as schools and nursing homes.

The WHO earlier this week formally requested that China provide information about a potentially worrying spike in respiratory illnesses and clusters of pneumonia in children, as mentioned by several media reports and a global infectious disease monitoring service.

The emergence of new flu strains or other viruses capable of triggering pandemics typically starts with undiagnosed clusters of respiratory illness. Both SARS and COVID-19 were first reported as unusual types of pneumonia.

Chinese authorities earlier this month blamed the increase in respiratory diseases on the lifting of COVID-19 lockdown restrictions. Other countries also saw a jump in respiratory diseases such as RSV when pandemic restrictions ended.

The WHO said Chinese health officials on Thursday provided the data it requested during a teleconference. Those showed an increase in hospital admissions of children due to diseases including bacterial infection, RSV, influenza and common cold viruses since October.

Chinese officials maintained the spike in patients had not overloaded the country’s hospitals, according to the WHO.

It is rare for the U.N. health agency to publicly ask for more detailed information from countries, as such requests are typically made internally. WHO said it requested further data from China via an international legal mechanism.

According to internal accounts in China, the outbreaks have swamped some hospitals in northern China, including in Beijing, and health authorities have asked the public to take children with less severe symptoms to clinics and other facilities.

WHO said that there was too little information at the moment to properly assess the risk of these reported cases of respiratory illness in children.

Both Chinese authorities and WHO have been accused of a lack of transparency in their initial reports on the COVID-19 pandemic, which started in the central Chinese city of Wuhan in December 2019.