Age and sex associated with likelihood of antimicrobial resistance

A study of nearly one million people across 29 European countries found distinct patterns of resistance for different bloodstream infections
"Our findings suggest there may be value in considering interventions to reduce antimicrobial resistance burden that take into account important variations with age and sex." Gwen Knight, Associate Professor & co-Director, AMR Centre, LSHTM

A person’s age and sex are correlated with the chance that they have a bloodstream infection caused by a bacterium that is resistant to antibiotics, according to a new study published in PLOS Medicine.

Antimicrobial resistance (AMR), which encompasses infections that cannot be treated with antibiotics, is a major global public health threat. Little has been known about how the prevalence of resistance varies with patient’s age and sex, despite both factors being linked to variation in antibiotic usage, changes in immune function and exposure to high-risk settings.

In the new study, led by researchers from the London School of Hygiene & Tropical Medicine (LSHTM), data collected as part of routine surveillance between 2015 and 2019 on bloodstream infections in 944,520 individuals across 29 European countries were analysed. The team looked at which bacterial species were isolated and sent to the surveillance service, and which antibiotics were used to treat the infections.

Distinct patterns in the prevalence of resistance by age were observed throughout Europe but varied across bacterial species. For most but not all bacteria, peaks in resistance were seen at the youngest and oldest ages.

The occurrence of methicillin-resistant Staphylococcus aureus (MRSA) increased with age and the occurrence of aminopenicillin resistance in Escherichia coli decreased with age. Some antimicrobial resistance profiles peaked in middle-age; Pseudomonas aeruginosa was most likely to be resistant to several antibiotics around 30 years of age and, for women, the incidence of bloodstream infections due to E. coli peaked between ages 15 and 40.

There were other important differences between sexes; in general, men had a higher risk of antimicrobial resistance than women.

Dr Gwen Knight, Associate Professor and co-Director of the AMR Centre at LSHTM, said:

“Our findings highlight important gaps in our knowledge of the spread and selection of antimicrobial resistance (AMR) and may help us understand why the epidemiology has been difficult to explain through known patterns of antibiotic exposure and healthcare contact.

“They also suggest there may be value in considering interventions to reduce antimicrobial resistance burden that take into account important variations in antimicrobial resistance prevalence with age and sex.

“In order for us to address this growing threat to public health, we now need data from a wider range of sources to determine the contribution that cultural versus natural history differences have in driving these patterns globally and the role that they play in the increasing rates of antimicrobial resistance being seen.”


Naomi R. Waterlow, Ben S. Cooper, Julie V. Robotham, Gwenan Mary Knight (2024). Antimicrobial resistance prevalence in bloodstream infection in 29 European countries by age and sex: An observational study. PLoS Med.

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