People in China should wear masks, socially distance and stay home if unwell amid an outbreak of a mystery respiratory illness, global health chiefs have warned.
Cases of 'undiagnosed pneumonia' have been detected at hospitals in Beijing and in Liaoning, a province 500 miles northeast of the capital.
Health facilities are 'overwhelmed with sick children' and classes are on the verge of being suspended according to local news reports.
Infected children are presenting with lung inflammation and a high fever, but not a cough or other symptoms that signal flu, RSV or another respiratory illnesses.
The situation prompted an alert from ProMed — a disease surveillance system which similarly sounded the alarm of a mystery infection in Wuhan in the closing days of 2019, which would later emerge as the global Covid pandemic.
The World Health Organization (WHO) has urged residents to don face coverings, stay away from ill people and remain at home if unwell. It has also called for the famously opaque nation to share 'detailed information' on the outbreak.
Chinese officials first reported an increase in respiratory diseases at a press conference on November 13, which they attributed to lifting lockdown restrictions.
Similar patterns had been seen worldwide as measures brought in to reduce the spread of Covid — such as face masks, social distancing and lockdowns — interrupted the spread of typical seasonal viruses, such as flu and RSV.
As a result, immunity against these bugs dropped across populations meaning people were more vulnerable to bugs as measures were lifted.
Officials blamed mycoplasma pneumoniae — a bacteria that causes lung infections — as well as respiratory syncytial virus (RSV) and Covid for the spike in illness.
Then ProMed this week reported clusters of undiagnosed pneumonia in children.
An editor's note on the alert reads: 'This report suggests a widespread outbreak of an undiagnosed respiratory illness… It is not at all clear when this outbreak started, as it would be unusual for so many children to be affected so quickly.
'The report does not say that any adults were affected, suggesting some exposure at the schools.
'ProMed awaits more definitive information about the etiology and scope of this concerning illness in China.'
It is unclear if these cases are linked to the overall increase in respiratory infections already reported by Chinese officials, or separate and potentially caused by a new virus.
The WHO said it has now called on China to share data on these patients, recent trends in the circulation of viruses and pressures on hospitals.
The UN health agency said it is also in contact with medics and scientists in a bid to understand the situation.
In the meantime, it urged people in China to 'follow measures to reduce the risk of respiratory illness'.
These include '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 hand-washing', the WHO said.
The source for the ProMed alert was a report by the Taiwanese outlet FTV News, which added that 'parents questioned whether the authorities were covering up the epidemic.'
China has previously been criticised for downplaying the original SARS epidemic in 2003 and the Covid pandemic in late 2019 — which were both novel viruses that caused pneumonia.
WHO China, the regional branch of the United Nations backed health body, has already sought to downplay the wider WHO's request for information, calling it a 'routine' procedure.
British infectious disease experts said that, while data was still emerging, China must 'get a grip' on the outbreak and do so in 'transparent' fashion.
Dr Simon Clarke, a cellular microbiologist at the University of Reading, told MailOnline that experts were waiting on further analysis of the outbreak.
'There are lots of germs which can cause a patient's lungs to become inflamed and as the northern hemisphere moves towards winter, they are likely to become more prevalent,' he said.
'We don't yet have confirmation of what is causing this outbreak in China, it may be something new or it may be a new version of something we've encountered before.'
However, he added that Chinese public health experts must uncover the source of the infection and, if necessary, contain the spread.
A news clip taken from FTV News appears to show a busy hospital waiting room in China with children receiving intravenous drips
A news clip taken from FTV News appears to show a busy hospital waiting room in China with children receiving intravenous drips
'It's important that medical science in China gets a grip on what is causing this outbreak and whether there is any person-to-person spread,' he said.
'It was failure to contain Covid-19 and an overall lack of transparency that caused so much damage four years ago.
