P aeruginosa is found in 11.6% of diabetic foot infection cultures from hot, humid climates.
Kari A Mergenhagen, PharmD, BCPS, BCIDP
Infectious Disease Clinical Pharmacy Specialist at US Department of Veterans Affairs
Image credits: Unsplash
A national study examining the prevalence of Pseudomonas aeruginosa in diabetic foot infections (DFIs) found significant regional variation based on United States climate zones. The study underscores the potential of using climate data to guide antibiotic treatment for P aeruginosa in DFIs.1
Multivariable logistic regression showed that P. aeruginosa was more likely to be present in hot, humid climates, as well as in hot, dry and humid climates. A history of P. aeruginosa infection was strongly associated with an increased likelihood of the pathogen. Factors such as a lower Charlson Comorbidity Index and recent inpatient admission also influenced prevalence.1 Kari A Mergenhagen, PharmD, BCPS, BCIDP, lead author of the study, discussed how climate zones influence infection risk and the potential for climate-informed treatment protocols.
“Even accounting for various risk factors for P aeruginosa, warmer and more humid environments had a higher odds of P aeruginosa,” Mergenhagen explained. “In the multivariable logistic regression model, hot and humid climates were associated with an odds of P aeruginosa of 1.92 (97.5% CI, 1.69-2.20). A hot, dry climate was associated with an odds of P aeruginosa of 1.65 (97.5% CI, 1.44–1.90). A humid climate zone was associated with an odds of P aeruginosa of 1.65 (97.5% CI, 1.45–1.89).”
Mergenhagen noted that recommendations based on climate and local prevalence patterns could be more applicable to clinicians than those based on general climate categories. The study, conducted on veterans with diabetes mellitus between January 2010 and March 2024, categorized P aeruginosa prevalence based on climate zones defined by the International Energy Conservation Code. P aeruginosa was most common in hot, humid climates, isolated in 11.6% of DFI cultures. It was least common in very cold climates, where it was found in 6.2% of cultures.
These infections can affect the bloodstream, lungs (pneumonia), urinary tract, or surgical wounds, and symptoms may include fever, chills, difficulty breathing, pain or redness at the infection site, and urinary symptoms like pain or urgency. Patients most at risk include those with weakened immune systems, those on ventilators or with catheters, and individuals with open wounds from surgery or burns. Treatment typically involves antibiotics, but some strains of P aeruginosa are resistant to many antibiotics, making infections more difficult to manage.
P aeruginosa infections are a significant concern in the US, particularly in healthcare settings. In fact, the CDC tracks infections caused by this bacterium. It is a leading cause of hospital-acquired infections, especially among patients with compromised immune systems or those using medical devices like ventilators or catheters. Multidrug-resistant (MDR) strains of P aeruginosa are also a growing problem in the US, contributing to a substantial number of infections and associated deaths each year.2
P aeruginosa is commonly found in soil, seawater, and fresh water. This exposure increases the risk of acquiring the bacterium. “In general, Pseudomonas species primarily live in soil, seawater, and fresh water,” Mergenhagen said. “This correlates to greater water exposure, increasing a patient’s risk of acquiring P aeruginosa.” The study also highlights the role of temperature in P aeruginosa’s pathogenicity. “The genes that encode for P aeruginosa’s virulence mechanisms are upregulated at 37°C, increasing P aeruginosa’s pathogenicity in warmer environments,” Mergenhagen added.
The study also examined whether climate data could inform antimicrobial selection for DFIs. Mergenhagen noted that while the International Working Group on the Diabetic Foot (IWGDF)/Infectious Diseases Society of America (IDSA) guidelines suggest P aeruginosa is less common in North America and Europe compared to tropical or subtropical regions, their study provides relevant data for United States-based clinicians. “The IWGDF/IDSA guidelines indicate that P aeruginosa is not as prevalent in North America or Europe but is more common in tropical or subtropical climates. This recommendation is based on a study that prospectively examined the bacteriology profile of DFI specimens from 522 patients in Turkey,” Mergenhagen said. “This is the reason we chose to do this study.”
United States-based data gives clinicians an opportunity to target their antimicrobial use with greater precision, accounting for local rates of P aeruginosa. “Our study includes United States data, which allows clinicians to target their antimicrobial use with full knowledge of rates of P aeruginosa,” Mergenhagen said.
P aeruginosa is most prevalent in hot, humid climates and least common in very cold climates, with climate zones significantly influencing infection risk.
A history of P aeruginosa infection and recent inpatient admission were key factors associated with increased odds of the pathogen in DFIs.
The study's findings support the use of climate-informed treatment protocols to improve the accuracy of empiric antibiotic selection for DFIs.
Mergenhagen recommends clinicians take climate and individual patient histories into account when making treatment decisions, such as recent antibiotic use, prior P aeruginosa infections, and the severity of the diabetic foot infection. “We think that climate as well as prior and current culture data is important in making treatment decisions for those patients with diabetic foot infections,” Mergenhagen said. “The severity of illness is also an important consideration in determining initial antimicrobial therapy.”
Mergenhagen provided a clinical example: while a local P aeruginosa prevalence of 6% might not warrant empiric coverage, a prevalence of 11% or 12% could be more clinically significant depending on the severity of the infection. “While a local P aeruginosa rate of 6% may not warrant empiric coverage, a local prevalence of 11 or 12% may be more clinically significant, depending on the severity of illness,” Mergenhagen said.
The study’s findings emphasize the need for further research into the regional factors influencing P aeruginosa prevalence and its impact on treatment. Mergenhagen highlighted the importance of local data in formulating effective, climate-informed treatment protocols for diabetic foot infections. By integrating climate zone data into clinical decision-making, healthcare providers can offer more targeted care, improving outcomes for patients with DFIs.
