Current forecasts of the burden of antibiotic resistance could be significant underestimates in the face of a growing population and climate change, according to a team from the US and Canada.

The researchers found that the common bacterial strains Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus showed a higher degree of antibiotic resistance where local temperature and population density were higher.

“The effects of climate are increasingly being recognized in a variety of infectious diseases, but so far as we know this is the first time it has been implicated in the distribution of antibiotic resistance over geographies,” said Derek MacFadden of Boston Children’s Hospital, US. “We also found a signal that the associations between antibiotic resistance and temperature could be increasing over time.”

MacFadden and colleagues looked at antibiotic resistance data from 2013–2015 for a total of 1.6 million bacterial pathogens. Areas with higher antibiotic prescription rates tended to exhibit increased antibiotic resistance.

“Estimates outside of our study have already told us that there will already be a drastic and deadly rise in antibiotic resistance in coming years,” said John Brownstein of Boston Children’s Hospital and Harvard Medical School. “But with our findings that climate change could be compounding and accelerating an increase in antibiotic resistance, the future prospects could be significantly worse than previously thought.”

A local average minimum temperature increase of 10°C was associated with a 4.2% increase in antibiotic resistant strains of E. coli, a 2.2% rise in antibiotic resistant K. pneumoniae and a 3.6% rise in S. aureus, the team found.

What’s more, the study linked an increase of 10,000 people per square mile to a 3% increase in antibiotic resistance in E. coli and a 6% increase in K. pneumoniae. The antibiotic resistance of S. aureus did not appear to change with population.

“As transmission of antibiotic resistant organisms increases from one host to another, so does the opportunity for ongoing evolutionary selection of resistance due to antibiotic use,” said MacFadden. “We hypothesize that temperature and population density could act to facilitate transmission and thus increases in antibiotic resistance.”

The team published the study in Nature Climate Change.