Pneumonia in China: Everything we know so far about mystery illness

A rise in cases of an unknown illness in China is being investigated by health officials, with children being hospitalised with pneumonia. While the situation remains unclear, it appears most likely that these outbreaks are due to a resurgence of common respiratory pathogens after the country’s strict coronavirus lockdowns, rather than being the result of a new infection. Here’s what we know so far.

What is pneumonia?

Pneumonia is a general term for inflammation of the lungs, which is usually as a result of an infection. Symptoms can include coughing, shortness of breath, fever and chest pain. Most people recover in a few weeks, but those who are particularly vulnerable, such as babies, older people and those with certain health conditions, may require hospitalisation.

When and where were the cases first seen?

On 21 November, the infectious disease monitoring network ProMED summarised a news report from China saying that hospitals in Beijing and elsewhere were “overwhelmed with sick children” with undiagnosed pneumonia. This has caused concern about a potential new pandemic and led the World Health Organization to request more information from China on 22 November.

What are the symptoms being seen in China?

The first of two ProMED posts on the topic cites “a Beijing citizen” as saying fever is the main symptom they have seen in children, with no coughing, but many developing what are known as pulmonary nodules. Neither of the ProMED posts mentions any deaths.

What is a pulmonary nodule?

It is a small lump in a lung, revealed by an X-ray or CT scan. They are found in a third of people whose lungs are scanned and are usually a result of ongoing or past infections. According to Paul Hunter at the University of East Anglia, UK, they are typically a sign of bacterial rather than viral infection and could be a result of people developing a bacterial infection after having the flu virus, for instance.

Is a bacterial infection less of a worry than a viral one?

While bacterial infections can be just as dangerous as viral ones, when it comes to pandemic potential, they are regarded as less of a threat. This is because bacteria replicate and evolve much more slowly than viruses. They can usually also be treated with broad-spectrum antibiotics. In other words, it is usually easier to control outbreaks caused by bacterial infections.

What bacterium could be responsible for the pneumonia?

The second ProMED post states that there have been reports over the past two months of outbreaks due to a common bacterium called Mycoplasma pneumoniae. This usually causes mild infections of the throat and windpipe, but is also the main cause of pneumonia in children hospitalised with the condition in the US.

However, the pulmonary nodules described in China aren’t typical of Mycoplasma, according to a ProMED moderator. Mycoplasma typically causes “patchy infiltrates”, as seen on X-rays, rather than pulmonary nodules, though atypical cases are possible, the moderator notes.

Has the pneumonia spread elsewhere?

Amid a similar outbreak in South Korea, more than 200 cases of pneumonia have been reported in children across the country. These are all due to Mycoplasma, so either this is separate from the China outbreaks or the China cases are also due to Mycoplasma.

A South Korean newspaper quotes a hospital doctor, Ma Sang-hyuk, as saying the country is confident it can deal with the outbreak. During a Mycoplasma outbreak in South Korea in 2019, 13,500 people were hospitalised, the newspaper says.

Why is this happening now?

It is normal for respiratory infections to rise during winter. What’s more, this is China’s first winter since its strict lockdowns to prevent covid-19. That means there will be a much larger number of children than usual who haven’t been exposed to certain viruses and bacteria before, and therefore have no immunity.

Furthermore, the immunity of people who have previously been infected by these viruses and bacteria will have faded somewhat. That means a big wave of infections is probable, as occurred in other countries after lockdowns.

That, in turn, means that cases of pneumonia that would usually be spread over years may be happening all at once. This is thought to be why there were more than 1000 reports of acute hepatitis in children globally in 2022, as a rare complication of exposure to a common virus that rebounded after lockdowns.

So it isn’t going to cause another pandemic?

There will definitely be another pandemic, due to some infection, eventually, given the number of pathogens evolving away. But as Hunter points out, if these cases in China were being caused by a new pathogen, lots of adults should be getting ill too, as they would also have no previous exposure.

“My feeling is that it won’t lead to a public health emergency of international concern, but I would not totally rule out that possibility until we have a definitive diagnosis,” he said in a statement put out by the Science Media Centre in the UK.