A few days ago, on December 1st, the World Health Organization sent China a request for more information on a surge in respiratory illnesses. There seemed to be big clusters of pneumonia in children emerging in China and the WHO wanted to know more.

Pediatric clinics in China were reportedly overwhelmed, and similar cases appear to have spread to different countries as well. But it’s not a new pathogen this time. At least not from the information that’s currently available.

The rise in infections is caused by a bacterium called Mycoplasma pneumoniae. This is a fairly well-known bacterium and it usually causes mild symptoms.

So what’s going on?

Walking pneumonia

The pathogen is known to primarily cause mild respiratory symptoms, although it sometimes also causes infections of the middle ear. Even when it causes pneumonia, the cases are typically mild. In fact, they’re so mild that it’s even called “walking pneumonia” because you can just walk it off.

But this is not what we’re seeing now.

The social media images from China are a heart-rending déjà vu with photos of young children connected to intravenous lines receiving fluids in overcrowded hospital waiting rooms.

It’s always hard to gauge reality on the ground in China due to internet censorship but many people are understandably spooked. Cases seem to be on the rise in other places as well. In Denmark, the State Serum Institute says rates are at “epidemic levels,” with 541 cases last week — a 300% increase from 6 weeks ago. In the Netherlands and parts of the US, cases are also on the rise.

Ironically, researchers say, once again, COVID-19 may be to blame.

Not a different bug

Maria Van Kerkhove, acting director of the WHO’s department of epidemic and pandemic preparedness and prevention, said the overall number of infections is not as high as pre-pandemic levels.

“We asked about comparisons prior to the pandemic. And the waves that they’re seeing now, the peak is not as high as what they saw in 2018-2019,” Van Kerkhove told health news outlet STAT in an interview on Friday.

“This is not an indication of a novel pathogen. This is expected. This is what most countries dealt with a year or two ago,” she added.

The increase in problems appears to stem from a surge in the number of children catching pathogens that they had previously evaded during two years of lockdown measures.

“There are no differences in expected viral infections this year, and the known culprits were reported in expected waves based on pre-pandemic levels, according to the World Health Organization. Mycoplasma pneumoniae flares are also as expected. However, waning mycoplasma-specific herd immunity has been flagged up with a warning to watch out for the resurgence of severe cases following the pandemic restrictions,” writes Zania Stamataki, Associate Professor in Viral Immunology, University of Birmingham.

In China, this is particularly impactful as the country experiences its first winter without strict COVID-19 restrictions since three years ago.

But there may be other factors at play.

Co-infections and drug resistance

Co-infections occur when an individual is simultaneously infected with two or more different pathogens, such as viruses, bacteria, or parasites. These pathogens could be a combination of multiple viruses, multiple bacteria, a virus and a bacterium, or some other combination. Co-infections are concerning for several reasons. They can increase the severity of illness, they make it harder to diagnose and treat conditions, and they can compromise the immune system.

So, it’s possible that another pathogen, perhaps even an inconspicuous one that wouldn’t normally cause major issues, is causing co-infections along with Mycoplasma pneumoniae.

Another problem is that the bacterium is developing resistance to common treatments. The pathogen is usually treated with antibiotics known as macrolides. However, an overreliance on such treatments has enabled M. pneumoniae in Beijing to achieve between 70% and 90% resistance rates. This resistance may also be playing a role in the surge in pneumonia cases.

The situation underscores the complexities of infectious diseases in a post-pandemic world. While the immediate response focuses on managing the current outbreak, it’s also a stark reminder of the importance of long-term strategies in public health. These strategies involve not just addressing immediate threats but also preparing for future challenges through robust healthcare systems, ongoing research, and public education.

One critical aspect is the need for global collaboration. If there’s one thing we’ve learned recently it’s that outbreaks know no borders, and international cooperation is essential for effective surveillance, data sharing, and coordinated responses.

In addition, public health authorities are stressing the importance of flu vaccination (where available) and other preventive measures. These include good hygiene practices and public awareness campaigns to inform people about how to recognize symptoms early and seek timely medical care.