What we know about China's mystery pneumonia outbreak hospitalizing children

Clusters of an ‘undiagnosed pneumonia’ in children in China are now under investigation by the World Health Organization

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Clusters of “undiagnosed pneumonia” in children in China, now under investigation by the World Health Organization, may have eerie echoes of the early days of the COVID-19 pandemic. But the situation in China also resembles the early crush of overlapping respiratory viral infections among children that overwhelmed hospitals across Canada last year, after masking, school closures and other interventions to thwart COVID’s spread were lifted, experts here said.

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A similar “tripledemic” surge of known pathogens is likely occurring in China, they said.

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Earlier this month, Chinese authorities reported an increase in influenzas, mycoplasma pneumoniae (a common bacterial infection that typically affects younger children), respiratory syncytial virus (RSV) and COVID-19. Authorities attributed the surge to the lifting of COVID restrictions in China, which exited pandemic lockdowns far later than other countries.

This week, media and ProMED, a global reporting system for emerging diseases and outbreaks, reported clusters of undiagnosed pneumonia in children in northern China. “It is unclear if these are associated with the overall increase in respiratory infections previously reported by Chinese authorities, or separate events,” WHO said in a media statement.

The agency has formally requested China provide detailed information on the reported clusters among children, as well as more data about recent trends in SARS-CoV-2, RSV and other viruses.

On Dec. 31, 2019, WHO’s China Country Office was informed of cases of “pneumonia of unknown etiology,” meaning unknown cause, detected in Wuhan.

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“I think we have to save our worry for when we need to worry,” said McMaster University immunologist and university scholar Dawn Bowdish, Canada Research Chair in aging and immunity.

“If you had asked Canada last year, when we were having all those pediatric admissions, we would have had all sorts of undiagnosed pneumonia as well that were causing hospitalization in children,” she said.

Not all pneumonias have a definitive diagnosis, she said, even though it’s clear the lungs are filled with fluid.

“However, should (the reported clusters in China) end up being clinically different than the pneumonias the Chinese doctors are used to, or it looks like it’s spreading, then we might start to worry that it’s some new pathogen,” Bowdish said.

Children and parents in a Beijing hospital
Children and their parents wait at an outpatient area at a children hospital in Beijing on Nov. 23, 2023. Photo by Jade Gao / AFP

On Tuesday,

ProMED shared a Chinese news report

that hospitals in Beijing, Liaoning and other areas were “overwhelmed’ with sick children and that “schools and classes were on the verge of suspension.”

While the report suggested a widespread outbreak, it’s not clear when the outbreak started, “as it would be unusual for so many children to be affected so quickly,” said an editor’s note from ProMED

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“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.”

Other scientists agreed that there are too little data to make any definitive diagnosis.

“The illness in children is fever with no cough or other symptoms, but in some cases, pulmonary nodules can be seen on chest X-ray,” Paul Hunter, a professor of medicine at the University of East Anglia, in England, said in expert comment released by the Science Media Centre.

It’s possible the children have pneumococcal pneumonia, he said. Influenza can also cause “patchy changes” on chest X-rays, often because of secondary bacterial infections.

“Overall, this does not sound to me like an epidemic due to a novel virus,” Hunter said. “If it was, I would expect to see many more infections in adults. The few infections reported in adults suggest existing immunity from a prior exposure.”

This is also China’s first full winter after lengthy COVID-19 lockdowns that slowed normal circulation of respiratory bugs. China could be experiencing a “lockdown exit” wave of respiratory infections that countries like Canada and the U.K. experienced last year, other scientists said.

“There is currently no evidence that the increase in paediatric pneumonia cases in China may be due to a new virus,” said Dr. Zania Stamataki, an association professor in viral immunology at the University of Birmingham.

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