Landfills and incinerators for treating municipal waste are releasing antibiotic-resistant bacteria into the surrounding air in the eastern Chinese city of Changzhou, according to a study published Wednesday in the journal Environmental Science & Technology.

The researchers said that breathing in contaminated air could potentially lead to antibiotic-resistant infections in humans that are difficult to treat.

Antibiotic resistance is a global public health threat, and China is especially vulnerable as one of the world’s largest consumers of antibiotics. Extensive antibiotics use has allowed some bacteria to evolve to the point that drugs are no longer effective. As a result, doctors are left with fewer treatment options.

As early as 2015, China had identified superbug genes in humans and pigs that were resistant to almost all available antibiotics. According to the World Health Organization, over 700,000 people worldwide die each year from drug-resistant infections.

Previous studies have found that antibiotics leach into the environment from human sources like agricultural runoff, sewage, and medical and household waste. Drug-resistant bacteria have been detected in the soil, water, and air around the globe.

Luo Yi of Nankai University and her colleagues aimed to investigate how municipal solid waste treatment systems might be contributing to antibiotic resistance genes in the air. The research team collected air samples from several locations near a waste treatment site in Changzhou, Jiangsu province. The plant consists of a landfill, an incinerator, and two stations for storing and transferring garbage.

The team identified 17 different types of antibiotic resistance genes (ARG) in the air samples, with each potentially conferring resistance to a different type of antibiotic. The genes matched with ARGs found in garbage and runoff at the treatment site, which was determined to be the source.

These genetic pieces, although not infectious, can still spread, Luo told Sixth Tone. “When they encounter a human pathogen in our respiratory tract, for example, these genes could become incorporated into the germ and make it antibiotic-resistant,” she said.

One gene conferring resistance to beta-lactam antibiotics was ubiquitous and highly concentrated in all of the air and waste samples. Beta-lactams, which include penicillin and cephalosporins, are the most commonly used category of antibiotics for treatments in humans, according to Luo.

“What we found suggests that medical waste — either from hospitals or just medicines people throw away — could be a major source of ARGs,” she said.

Although ARGs could, in theory, lead to antibiotic-resistant infections by mutating other pathogens, experts say that whether there is a direct link between these genes and human health requires further study.

“There might be risks for immunocompromised people from antibiotic-resistant bacteria,” Antti Karkman, a microbiologist at the University of Helsinki, told Sixth Tone.

“But for healthy people just breathing, these most likely won’t cause any direct health problems,” said Karkman, who is not affiliated with the study. “The risks associated with antibiotic resistance genes alone are not clear.”

According to Luo, most waste treatment plants in China are similar to the one she and her colleagues studied in Changzhou, and landfills and incinerators are common means of waste disposal in other parts of the world.

“Most importantly, these genes can easily spread with the wind to distant areas and countries. The air is not bound by borders,” she said.

Editor: David Paulk.

(Header image: A worker prepares to dump a container of medical waste into a parking lot near Tongji Hospital in Wuhan, Hubei province, Feb. 18, 2020. Cui Meng/Global Times)