A new analysis of surveillance data from Europe shows "substantial interactions" between age, sex, and antimicrobial resistance (AMR).
In a study published on Thursday in PLOS Medicine, a team of researchers from the United Kingdom analyzed data on bloodstream infections (BSIs) collected from nearly one million patients in 29 European Union/European Economic Area (EU/EEA) countries over 5 years. They found that the prevalence of resistance varied by bacteria and antibiotic by the age and sex of the patient, with distinct patterns in resistance prevalence by age observed across Europe for different bacteria.
While sex was only weakly associated with resistance in most cases, the incidence of BSIs, with one exception, was higher in men.
The authors of the study say the findings illuminate important gaps in knowledge of the epidemiology of AMR that aren't explained by antibiotic exposure and healthcare contact.
"These new findings about differences by age and sex should now be considered in AMR research, as they have the potential to yield new insights into AMR epidemiology and may inform the design of control measures," they wrote.
For the study, researchers from the London School of Hygiene & Tropical Medicine and the University of Oxford analyzed data on patients with BSIs routinely collected by the European Antimicrobial Resistance Surveillance Network (EARS-Net) from 2015 through 2019. Looking at eight bacterial species and 38 bacteria-antibiotic combinations, they used the data to explore how age and sex might be connected with trends in resistance, BSI incidence, and the proportion of infections caused by resistant bacteria.
At the European level, the analysis found distinct patterns in resistance prevalence by age. For most bacterial species, resistance was highest at the youngest and oldest ages. But in species like Acinetobacter baumannii and Pseudomonas aeruginosa, resistance to several antibiotics appeared to increase with patient age, peak between the ages of 30 and 50, and then decline. Stronger age-related trends for resistance were observed in Southern and Eastern Europe, where the prevalence of resistance was generally higher.
These new findings about differences by age and sex should now be considered in AMR research, as they have the potential to yield new insights into AMR epidemiology and may inform the design of control measures.
BSI incidence was higher among the youngest and oldest patients across Europe, with substantial increases seen in older patients and men having a higher incidence from age 35 onward. The exception to that was for BSIs caused by Escherichia coli, which were higher in women between the ages of 15 and 40. That observation could be explained by the fact that women in that age range have a higher incidence of urinary tract infections, which are common source of BSI.
When the researchers focused their modeling analysis on two of the most clinically significant bacteria-antibiotic combinations seen in BSIs globally—aminopenicillin-resistant E coli and methicillin-resistant Staphylococcus aureus (MRSA) —they found significant national and subnational variations but clear age- and sex-related trends across countries. For MRSA, 72% of countries saw an increase in resistance in boys and men from age 1 to 100 and a greater change in resistance in men. For aminopenicillin-resistant E coli, the opposite was true, with 93% of countries seeing a decrease in resistance with age among male patients and a smaller change in resistance in girls and women.
The study authors say the differences in AMR burden by age and sex could be explained by "cultural differences between countries as well as variation in pathways to infection between bacteria." And understanding how those cultural factors interact with biological factors across age and sex could lead to more targeted antibiotic stewardship interventions and infection prevention and control strategies.
"Our findings suggest that there may be value in considering interventions to reduce antimicrobial resistance burden that take into account important variations with age and sex," senior author Gwen Knight, PhD, co-director the AMR Centre at the London School of Hygiene & Tropical Medicine, said in a university press release.
Knight and her colleagues say that while risk factors such as previous prescribing and contact healthcare settings will always influence the individual-level risk of a resistant infection, future research estimating the burden of AMR and the impact of interventions will need to account for trends in resistance by age and sex to accurately capture the burden.
