The analysis, using information spanning almost two decades from more than 100 countries, indicates that higher air pollution is linked to increased antibiotic resistance in all countries and continents.

Moreover, the study suggests that the connection between the two has strengthened over time, with higher air pollution coinciding with greater increases in antibiotic resistance.

"Our analysis provides strong evidence that increasing levels of air pollution are associated with an increased risk of antibiotic resistance", wrote researchers from China and the United Kingdom. This analysis is the first to show how air pollution affects antibiotic resistance globally". Their findings are published in the Lancet Planetary Health journal.

Antibiotic resistance is one of the fastest-growing threats to global health. It can affect people of all ages in any country and it already kills 1.3 million people annually, according to estimates.

The primary factors remain the incorrect and excessive use of antibiotics, which are used to treat infections. However, the study suggests that the issue is exacerbated by increased air pollution levels.

The study did not analyze the scientific reasons why the two might be linked. Evidence suggests that PM2.5 particles can contain antibiotic-resistant bacteria and resistance genes, which can be transferred between environments and inhaled directly by humans, the authors say.

Air pollution is already the largest environmental risk to public health. Long-term exposure to air pollution is associated with chronic conditions such as heart disease, asthma and lung cancer, reducing life expectancy.

Short-term exposure to high levels of pollution can cause coughing, shortness of breath, and asthma attacks, leading to an increase in hospital and family doctor visits worldwide.

Reducing air pollution could contribute to reducing antibiotic resistance, according to the study, the first in-depth global analysis of possible links between the two. Furthermore, it suggests that controlling air pollution could significantly reduce deaths and economic costs resulting from antibiotic-resistant infections.

Lead author Professor Hong Chen from Zhejiang University in China stated: "Antibiotic resistance and air pollution are among the biggest threats to global health, each on its own".

"Until now, we didn't have a clear picture of the possible links between the two, but this study suggests that the benefits of air pollution control could be twofold: not only will it reduce the harmful effects of poor air quality, but it could also play a major role in tackling the growth and spread of antibiotic-resistant bacteria".

While air is recognized as a direct route for the dissemination of antibiotic resistance, there is limited data on the different ways antibiotic-resistant genes are transported through air pollution.

One possible scenario indicates that if current air pollution policies were not altered, global antibiotic resistance levels could increase by 17% by 2050. The annual number of premature deaths related to antibiotic resistance could rise to approximately 840 000.

The authors acknowledged the limitations of their study. It is possible that a lack of data in some countries may have affected the overall analysis, they said.

The study was observational, so it could not prove cause and effect. Future research should focus on investigating the mechanism underlying how air pollution affects antibiotic resistance, they said.

A second study, published in the BMJ Mental Health journal, found that exposure to relatively high levels of air pollution was associated with increased use of community mental health services by individuals with dementia. The long-term study focused on a large area of London with heavy traffic.