Spectrum of pathogens associated with foot infections: review of 178 episodes from a rural hospital

Authors:
Hugo Bonatti, Krupesh Patel, Manuel Linarte, Rachel Tuer

Body of Abstract:
Background: The spectrum of pathogens associated with foot infections seems to be expanding due to changes in demographics, more invasive medical therapy, spread of multidrug resistant pathogens and improved microbiologic test systems.
Patients and Methods: Our institutional database was searched for all cases of foot infection treated by a single podiatrist during a 4-year period in which a pathogen was identified. Identification of organisms was done using biochemical assays until 2020 and in 2021 matrix assisted laser desorption/ionization – time of flight (MALDI-TOF) mass spectrometry was introduced. All patients underwent incision and drainage of abscesses, wound debridement or minor amputation as indicated during which the specimens for microbiology were retrieved.
Results: A total of 310 isolates in 178 patients (1.7 isolates/patient) were analyzed. Only 1st isolates were considered. There were 124 men and 54 women with a median age of 58.3 (range 10.1 to 91.6) years) including 13 pediatric cases (7%). Median BMI was 30.9 (range 18.6 – 85.7) kg/m2 with an obesity rate of 56%. Rate of DM was 51%, 20% of patients were active smokers. 33% of specimens consisted of tissue biopsies, 25% came from drained abscesses, 22% from drained fluid collections, and 20% from wounds. In 177 cases microscopy was done showing WBC in 67%, Gram positive cocci in 68%, Gram negative rods in 29% and Gram positive rods in 15%. 45% of pathogens were diagnosed using MALDI-TOF, 36% of infections were polymicrobial and in 58% in addition to pathogens, “normal flora” was reported. Staphylococci were isolated in 112 cases (63%) with MSSA accounting for 32% and MRSA for 24%; streptococci were reported in 50 cases (22%) with Streptococcus agalactiae (23 isolates) being the most common; enterococci were found only in 3 patients. In 31% of patients Gram negative rods were reported and Pseudomonas aeruginosa was the most common with 11 isolates followed by Citrobacter spp (8), Proteus spp (7) and E. coli (6). Anaerobes were also found in 31% of patients with Bacteroides spp and Prevotella spp accounting for 12 and 6 isolates, respectively, however, Gram positive anaerobic cocci including Finegoldia magna (10), Parvimonas micra (1), Anaerococcus prevotii (6), Peptostreptococcus anaerobius (4) and Peptoniphilus asaccharolyticus (9) outnumbered Gram negative rods.
Conclusion: Whereas staphylococci remain the most common pathogens causing foot infections requiring treatment by podiatry, many other pathogens must be considered. Empiric treatment should cover MRSA, Gram negative rods including Pseudomonas aeruginosa as well as anaerobes and appropriate specimens for microbiology should be sent during surgery in order to tailor treatment.