Category: Professional Posters
Purpose: The most recent published pilonidal abscess microbiology data was collected prior to 2010. More recently, bacterial identification using precision diagnostic technology like matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) have been adopted across institutions like the one described in this report. MALDI-TOF bacterial identification is objective and accurate, detecting a wider spectrum of organisms than previous methods. Pilonidal abscess is not a common diagnosis in the emergency department, and not all cases require antibiotic therapy. However, characterization of pilonidal abscess isolates based on results from precision microbiology testing is needed to inform appropriate empiric treatment of this infection as needs arise.
Methods: This is a multi-site retrospective study, within a large health system. Inclusion criteria consisted of patients who presented to an emergency department between 2015 and May 2019 with the term “pilonidal” in their discharge diagnosis and a completed wound culture and stain. Exclusion criteria are patients with a “no growth” result from the wound culture, wound culture results identified as “mixed microbial flora” suggestive of contamination per the microbiology department, or any patient that had a repeat culture within a year that isolated the same pathogen. The primary objective of this study was characterization of pilonidal abscess microbiology and isolates per patient encounter. Secondary objectives include clinical analysis of isolates to determine the most common pathogenic cause of infection, excluding isolates considered to be contaminants and/or non-pathogenic, and corresponding empiric antibiotic recommendation. Isolates clinically determined to be contaminants and/or non-pathogenic were defined as cultures that produced 1+ (few) or fewer bacterial counts on culture for the isolates of Coagulase-negative Staphylococcus, Actinomyces, Corynebacterium, Dermabacter, Bacillus, or Lactobacillus species. Descriptive statistics were utilized to analyze data.
Results: 119 patient encounters were reviewed for inclusion and 22 patient encounters were excluded based on criteria. 97 patient encounters were analyzed for the primary endpoint with 148 total organisms seen. The primary outcome identified 42% (n=41) of encounters to be polymicrobial. The most common organisms were Streptococcus viridans 18.2% (n=27), Coagulase negative staphylococcus 17.6% (n=26), Actinomyces 14.9% (n=22), Corynebacterium 10.8% (n=16), and Beta-hemolytic Streptococci 10.8% (n=16). The secondary outcome further excluded isolates considered to be contaminants or non-pathogenic, leaving 75 patients and 98 total organisms for analysis. Given this adjustment, only 21% of cases considered clinically relevant were identified as polymicrobial. The most common isolates considered to be clinically pathogenic were found to be Streptococcus viridans 27.6% (n=27), Beta-hemolytic Streptococci 16.3% (n=16), Actinomyces 14.3% (n=14), Staphylococcus aureus 8.2% (n=8), and Escherichia coli 8.2% (n=8).
Conclusion: After clinical analysis of all isolates, removing likely contaminant and/or non-pathogenic strains, the most common bacteria identified were Streptococcus viridans, Beta-hemolytic Streptococcus, and Actinomyces. Based on known susceptibility data, recommended empiric oral antibiotic therapy for pilonidal abscess would be amoxicillin/clavulanic acid. Precision microbiology testing, such as MALDI-TOF, is evolving knowledge of causative organisms for infections. Prior to this report, published rates for Actinomyces in pilonidal abscess were less than 2%. As seen in this report, even when excluding certain MALDI-TOF detected isolates with 1+ (few) or less bacterial growth, Actinomyces still emerged as a potential pathogen in pilonidal abscess.