Non-aeruginosa Pseudomonas spp: a critical analysis of 29 surgical and blood stream infections

Authors:
Hugo Bonatti, Saron Araya, Pooja Ajith, Sridha Gona, Aaron George

Body of Abstract:
Background: Pseudomonas aeruginosa is by far the most common non-fermentative Gram-negative rod causing human diseases. Due to new microbiology techniques recently re-classifications in this group of organisms were undertaken, and an increasing number of infections caused by other Pseudomonas strains have been reported, many in immuno-compromised individuals.

Methods: Our institutional database was searched for all surgical and blood stream infections caused by non-aeruginosa Pseudomonas spp. during a 4-year period. 

Results: In total 35 isolates of non-aeruginosa Pseudomonas spp. in 29 patients were identified. Median age of the cohort was 65.3 (range 0.1-88.2) years with 58.6% being male. Rates of comorbid conditions were DM 34%, hypertension 31%, hyperlipidemia 17%, COPD 7%, CAD 7%, and malignancies 10%; 61% of individuals were obese and 24% were active smokers. Demographic, clinical, and microbiology data are shown in table 1. Isolated strains included Ps. species       (14%), Ps. fluorescence (10%), Ps. putida (31%), Ps. fluorescence/putida (24%), Ps. luteola (10%), Ps. stutzeri (7%) and Ps. oleovorans (3%); 55% of infections were polymicrobial with staphylococci in 37%, streptococci in 13%, Gram-negative rods in 20%, anaerobes in 27% and yeast in 3% as co-pathogens. Blood cultures accounted for 28% of specimens, drainage fluids/tissue specimens for 31% and wound cultures for 38% of specimens, 3% came from drained abscesses. The specimens were sent in 31% by surgical services, 28% by medical services including critical care and infectious diseases, 21% by primary care physicians and 21% by the emergency department. Lower extremity soft tissue infections accounted for 62% of infections, upper extremities were involved in 3%, and 7% were intraabdominal infections. Treatment for surgical infections included incision and drainage, debridement and amputation as indicated together with antibiotics according to sensitivity testing, which showed great variability between strains. 

Conclusion: Non-aeruginosa Pseudomonas spp. are a diverse group of pathogens.  During the same time period 850 isolates of Ps aeruginosa in 572 patients were identified. Whereas most non-aeruginosa Pseudomonas infectious episodes were successfully treated, during a 2 year follow up 24% of patients died reflecting their severe chronic co-morbid conditions.

One of These Things Is Not Like the Others: Consideration of Healthcare-Associated Infection Risk in Burn Patients and Other Critically Ill Populations

Authors:
Megan Yoerg, Laura Johnson, Lauren Nosanov

Body of Abstract:
Introduction: Healthcare-associated infections (HAI) are a significant source of preventable morbidity, with the Centers for Disease Control and Prevention (CDC) estimating a prevalence of 3.2% in patients receiving inpatient care. Reporting and benchmarking common HAI is crucial to efforts in prevention and quality improvement. Risk for HAI is elevated in critically ill populations, but the variance based on specific illness and injury patterns is underappreciated. The pathophysiology of severe burn injury induces profound immunocompromise; coupled with loss of the barrier function provided by intact integumentary, this results in uniquely elevated infection risk. Prolonged hospitalization, persistent open wound burden, device days, and frequent surgical interventions additionally contribute. Broadly accepted HAI surveillance definitions may therefore be insufficient and under-stratified when applied to burn patients, with subsequent implications on reimbursement and quality benchmarking.

 

Methods: An in-depth review was conducted of the 2024 CDC National Healthcare and Safety Network (NHSN) Patient Safety Component Manual (PSCM). NHSN is the largest and most widely used tracking system for HAI in the United States, accounting for approximately 25,000 medical facilities, with the Patient Safety Component Manual serving as the prevailing document outlining surveillance definitions and standardization. Populations used to define HAI surveillance and case definitions were identified, with specific attention paid to representation of the burn patient population. Central Line-associate Bloodstream Infections (CLABSI) and Catheter-associated Urinary Tract Infections (CAUTI) were specifically reviewed due to their common and pervasive risk profiles across critically ill patients.  

 

Results: The PSCM explicitly mentions burn units throughout, they are generally grouped based on number of device days and length of stay. Referent groups included units specializing in labor and delivery, neurology, telemetry, and medical surgical, with care provided to patients with vastly different pathophysiology, critical illness, and immunocompromise.

 

Conclusions: Improved understanding of HAI risk in disparate patient populations is crucial. Beyond optimization of patient outcomes, HAI risk identification and mitigation has implication on resource utilization, insurance reimbursement, and reporting of hospital outcomes data. The value of benchmarking can only aid quality improvement efforts when patient populations are considered in comparison to others sharing equivalent risk profiles. As currently structured, the NHSN PSCM may be unfairly penalizing facilities providing the required specialized care to save and rehabilitate critically ill burn patients. Evidence-based re-evaluation of the PSCM referent groups is needed, however efforts will likely be hindered by the paucity of burn-specific HAI literature currently available.

Optimizing HAP Therapy: Launch of a New Antibiotic Protocol

Authors:
Marianna Frazee, Jennifer Beavers, Robel Beyene, Jill Streams, Elizabeth Krebs

Body of Abstract:
Background: Hospital-acquired pneumonia (HAP) is common in trauma patients, making appropriate empiric antibiotic selection and de-escalation important for outcomes and resource use. Evidence suggests that per oral (PO) linezolid offers similar MRSA coverage to intravenous vancomycin with potential reductions in cost and medication-related complications. In August 2025, our Level 1 trauma center revised our practice management guideline (PMG) for antibiotic choice for patients with presumed HAP, recommending PO linezolid in place of IV vancomycin for empiric MRSA coverage. The new protocol also provided designated antibiotic de-escalation strategies based on clinical improvement metrics and respiratory culture results.

Aim: This study aimed to evaluate both protocol implementation and the impact of this new guideline on antibiotic stewardship, hypothesizing that the use of vancomycin and cefepime (as a marker of antipseudomonal antibiotic use) would decrease following protocol change.

Methods: A multidisciplinary team including surgeons, advanced practice providers, and pharmacists developed the new PMG. Education was provided at team-wide meetings and daily morning reports, with the guideline publicly available on our trauma website per our center’s standard practice. This study retrospectively compared patients treated for presumed HAP in the 3 months before and after protocol implementation. Demographics, antibiotic data, and outcomes were obtained via chart review and institutional trauma and infection registries. Data were compared using Wilcoxon rank sum and Chi-square analysis.  Changes in vancomycin and cefepime utilization were also evaluated using a statistical process control (SPC) c-chart to detect variation over time and identify shifts following the intervention.

Results: A total of 82 trauma patients were treated for 102 episodes of presumed pneumonia, 55 before and 47 after guideline implementation. Protocol adherence exceeded 75% within three months of rollout. The SPC c-chart for vancomycin use demonstrated special cause variation after implementation, indicating a statistically meaningful shift in the process (Figure). Median days of vancomycin per pneumonia episode decreased in the post-implementation period (3 vs. 0, p<.01), while median days of cefepime prescribed were similar (4 vs. 5, p=0.18). There was no difference in rate of antibiotic de-escalation (54% vs. 63%, p=0.37.) Importantly, there were no adverse drug reactions noted during this early implementation period, and rates of antibiotic re-escalation remained similar (37% vs. 27%, p=0.43).  Conclusions: Transitioning empiric HAP therapy from IV vancomycin/cefepime to PO linezolid/cefepime resulted in sustained reduction in vancomycin use, while the new de-escalation protocol did not significantly impact cefepime prescribing or de-escalation rates. This change in antibiotic regimen led to cost savings of approximately $6,200 in drug and lab costs over a 3-month period.

Outcomes of Pediatric Patients with Perforated Appendicitis After Implementation of a Delayed Post-operative Imaging Protocol

Authors:
Jill Knepprath, Eiichi Miyaska

Body of Abstract:
Background:

Post-operative management of pediatric perforated appendicitis is highly variable with no clear guidelines for the timing of post-operative imaging. Some studies suggest that delayed imaging may decrease both unnecessary radiation and invasive procedures, while other authors found that delayed imaging was associated with prolonged hospital stays. In this study we investigated changes in outcomes at a single institution after the implementation of a protocol recommending imaging on post-operative day (POD) 7.  

Methods:

This was a single institution retrospective chart review of pediatric patients who underwent an appendectomy for perforated acute appendicitis between January 2021 and June 2025. A modification to the protocol occurred in January 2024, with post-operative imaging recommendations changing from POD 5 to POD 7. No other changes to the protocol were made between January 2021 and June 2025. Patients were divided into two cohorts, Group 1 included patients before protocol modifications (January 2021-December 2023) and Group 2 included patients after protocol modifications (January 2024-June 2025). Categorical data between both groups were compared using the Chi-Square test and medians were compared using the Mann-Whitney U test.

Results:

There were 105 patients in Group 1 and 49 patients in Group 2. There was no difference in length of stay between groups. There was no difference in imaging use (CT or ultrasound) between perforated patients in either group. Group 2 perforated patients had imaging done on a later POD than Group 1. Neither group was more likely to alter their treatment plan based on imaging. There was no difference in post-operative interventions. There was no significant difference in overall complications or in post-operative abscess formation. However, Group 2 perforated patients were more likely to be readmitted (10.2% vs 5.7%, p= 0.0054) or have an emergency room visit after discharge (18.4% vs 5.7%, p= 0.0136). (Table) Of patients with emergency room visits in both groups, the proportion of patients with imaging during their index admission was no different.

Conclusions:

This study suggests that later imaging does not change length of stay, does not decrease imaging or interventions, and does not impact abscess rates. However, patients that undergo delayed imaging may be more likely to be readmitted or present to the emergency room after discharge.

Parabacteroides merdae: a rare Gram-negative anaerobic rod

Authors:
Aprill Park, Rebecca Kowalski, Sridha Gona, Aaron George, Stephen Kavic, Hugo Bonatti

Body of Abstract:
Introduction: Parabacteroides spp were previously listed under Bacteroides spp but refined microbiology testing led to the creation of the new genus with Parabacteroides distasonis being common than Parabacteroides merdae. They are Gram-negative obligate anaerobic rods and part of the normal microbiome. Isolation of the organisms within the microbiome has been associated with inflammatory bowel disease, metabolic syndrome, and most notable obesity. Parabacteroides merdae has been recovered from drained abscesses, wound infections, and blood. Resistance rates to clindamycin, cefoxitin, and moxifloxacin are high, which may lead to treatment failure.

Patients and Methods: Following an index case of a patient with perirectal abscess, in which Parabacteroides merdae was isolated, the institutional database of a rural hospital in the Appalachian region of Western Maryland was searched for all infections caused by the pathogen during a 4-year period. Also, all cases of Parabacteroides distasonis the more common relative were reviewed.

Results: Two patients (3 isolates) with surgical infections associated with Parabacteroides merdae were identified including a 50-year-old woman and a 74-year-old man. The morbidly obese female with poorly controlled DM underwent incision and drainage of an ischiorectal abscess which grew the pathogen together with Eggerthella lenta and Fusobacterium necrophorum and the male patient had an infected tunneled dialysis catheter, which was removed growing Parabacteroides merdae, Enterobacter cloacae and Peptostreptococcus anaerobius. Both infections were successfully managed with surgical intervention and antibiotics. Parabacteroides distasonis was isolated in 42 patients (54 isolates) and intraabdominal infections accounted for 74% of cases including diverticulitis in 11 and appendicitis in 9 patients. No sensitivity testing is done at our hospital for anaerobic bacteria such as Parabacteroides merdae or distasonis.

Conclusion: Parabacteroides merdae is an extremely rare pathogen and much less common than Parabacteroides distasonis. These infections are usually polymicrobial and whereas the exact role of these anaerobes is unknown, they should be considered true pathogens and not contaminants or innocent bystanders.