Air pollution may contribute to rising threat of antimicrobial resistance, study says

By Jen Christensen, CNN

(CNN) — Antibiotic resistance is on the rise around the world, and there may be a surprising reason why: air pollution.

In a study published Monday in the journal Lancet Planetary Health, scientists saw a connection between these two seemingly different phenomena.

The researchers created a model to look at levels of air pollution called PM2.5 – also sometimes called particle pollution or particulate matter pollution – and levels of antibiotic resistance in 166 countries. The research detected a correlation between high levels of PM2.5 air pollution and high levels of antibiotic resistance that became even stronger over time. As the levels of particle pollution rose, so did levels of antibiotic resistance.

Particle pollution is the mix of solid and liquid droplets floating in the air, according to the US Environmental Protection Agency. It can come in the form of dirt, dust, soot or smoke. Particulate pollution comes from coal- and natural gas-fired plants. Cars, agriculture, unpaved roads, construction sites and wildfires can also create it.

Antibiotic resistance, also known as antimicrobial resistance or AMR, happens when a particular pathogen – a bacteria, parasite or fungi – develops a tolerance to a certain kind of medicine so that it will no longer work to fight those infections.

Antibiotic resistance has become a significant problem around the world, accelerating at what some scientists call “an alarming pace” and causing an estimated 700,000 additional deaths each year. The UN considers antibiotic resistance a “fundamental threat” to the entire planet’s health and safety.

Scientists say that most antibiotic resistance is caused by overprescribing or misusing antibiotics, poor infection control in hospitals and overuse in farm animals, along with poor sanitation. But these activities can’t account for the entire problem, the new study’s authors say.

Their model shows that particle pollution is to blame for 11% of changes in average antibiotic resistance levels around the world, making particle pollution potentially one of the leading drivers of antibiotic resistance.

The study, which looked at nine bacterial pathogens and 43 types of antibiotics, suggests that every 1% rise in air pollution is linked to increases in antibiotic resistance between 0.5 and 1.9%, depending on the pathogen.

The researchers say that their work will have to be further tested, but if this analysis is accurate and if particle pollution levels continue at about the same level, the level of antibiotic resistance worldwide in 2050 will be about 17% higher than now. This might not sound like much, but it means about 840,000 additional people could die prematurely due to diseases that are unable to be treated by antibiotics.

The study is observational, so it can’t prove a connection between particle pollution and antibiotic resistance, nor can it explain what the connection may be.

One possibility is that particle pollution may be helping spread antibiotic-resistant bacteria. Earlier studies have shown that particulate matter pollution can act as an energy source that carries bacteria along with it. Resistance genes have been found in airborne microorganisms in areas where antibiotics would normally be found, like around hospitals, wastewater treatment plants and farms, but they also show up in unexpected areas. A 2018 study found antibiotic resistance genes in the air near city parks in California. Their number grew in concentration on heavy smog days, when there was more particle pollution in the air.

The pollution itself may be changing the bacteria and making them resistant to medicine. When particle pollution and bacteria meet, studies have shown, it can make the bacteria more virulent. Particle pollution can even change genes within the bacteria to make it resistant to medicine.

Policies to reduce particle pollution would be good for the health of every human, scientists say.

“Antibiotic resistance and air pollution are each in their own right among the greatest threats to global health,” said Hong Chen, an author of the new study and a system dynamics and control engineering expert at Zhejiang University in China. “Until now, we didn’t have a clear picture of the possible links between the two, but this work suggests the benefits of controlling air pollution could be twofold: Not only will it reduce the harmful effects of poor air quality, it could also play a major role in combating the rise and spread of antibiotic-resistant bacteria.”

Particle pollution is particularly deadly. PM2.5 is so tiny –- 1/20th of a width of a human hair – that you can’t see it, and it can travel past your body’s usual defenses. Instead of being breathed out when you exhale, it can get stuck in your lungs or go into your bloodstream.

The particles cause irritation and inflammation and can lead to respiratory problems. Long-term exposure to particle pollution can cause cancer, stroke, dementia, depression, and cause heart problems. It can also aggravate asthma, and it has long been associated with a higher risk of depression and anxiety.

Almost the entire global population breathes air that exceeds World Health Organization air quality limits, and the number of “very unhealthy” and “hazardous” air quality days has grown, in part because of the climate crisis. In 2011 in the US alone, exposure to this kind of pollution resulted in 107,000 extra premature deaths, research shows. But the new study suggests that the health risks may be significantly higher.

The study authors say there are several limitations to their research. Not all countries have enough data to understand the true depth of problems of antibiotic resistance, and comparing results between countries is difficult because pollution levels and antibiotic resistance levels may be measured differently. The study also looked at country-wide data, and some regions, like in California in the US, have significantly higher levels of particle pollution than others, so the results may vary significantly from place to place.

Dr. Albert Rizzo, chief medical officer for the American Lung Association, says scientists will need to do a lot more research on the possible connection between pollution and the growth of antibiotic resistance.

He offers a theory that more exposure to pollution means more lung infections, and that may increase the inappropriate use of antibiotics.

“That may be what drives that relationship,” Rizzo said. “It’s interesting, but there are a lot of assumptions being made.”

Even if the theory does not prove to be true, he said, anything that could be done to lower pollution exposure would help our health.

“Decreasing PM2.5 pollution is going to save lives, whether or not it’s due to antibiotic resistance or not,” Rizzo said.

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