To the Editor—Surgical-site infections (SSIs) are common healthcare-associated infections that increase patient morbidity and mortality and cost the US healthcare system billions of dollars annually.Reference Zimlichman, Henderson and Tamir 1 The 1999 Centers for Disease Control and Prevention (CDC) SSI prevention guidelines define a set of recommendations based on relative pathogen frequency and patient- and procedure-based SSI risk known at that time.Reference Mangram, Horan, Pearson, Silver and Jarvis 2 Most of the effort in SSI prevention has been built around these guidelines since their publication.Reference Schaffzin, Harte and Marquette 3 , Reference Stulberg, Delaney, Neuhauser, Aron, Fu and Koroukian 4 Additional recommendations have been published to direct specific aspects of SSI prevention, such as antimicrobial prophylaxis, in addition to their implementation and tracking.Reference Bratzler, Dellinger and Olsen 5 , Reference Yokoe, Anderson and Berenholtz 6 While these updated guidelines have included new data, they are built upon the foundation of the 1999 CDC guidelines. Despite SSI rate improvement, SSIs remain the most common and costly healthcare-acquired infection in the United States.Reference Zimlichman, Henderson and Tamir 1
We hypothesized that targeted SSI prevention efforts based on the 1999 guidelines could have changed the relative pathogen frequency, possibly indicating a need to refine our approach to SSI prevention. We used SSI data from our medical center over 2 decades to study trends in SSI pathogen frequency.
METHODS
Pathogens associated with SSIs in incision class I and II surgical proceduresReference Mangram, Horan, Pearson, Silver and Jarvis 2 performed between January 1, 1994, and December 31, 2015, were obtained through the Infection Prevention and Control Program at Cincinnati Children’s Hospital Medical Center. All SSIs were identified prospectively and met the CDC’s National Nosocomial Infection Surveillance System (NNISS) or National Healthcare Safety Network (NHSN) criteria for SSIs at the time they occurred. 7
Multiple reports of single pathogens from the same procedure were considered to represent a polymicrobial infection and were consolidated and counted as a single SSI. Cases were excluded from the final analysis if the associated surgery occurred prior to January 1, 1994, the SSI had no culture obtained or no pathogen identified, the result was reported as mixed flora, or if the SSI was associated with an incision class III or IV surgical procedure. 7 Cases were subsequently divided by the year in which the surgery was performed.
Procedures were stratified into 4 periods: 1994–1999, 2000–2005, 2006–2011, and 2012–2015. The organisms of single-pathogen and polymicrobial infections were determined for each period for SSIs meeting the inclusion criteria. Linear trends were analyzed for pathogen prevalence among single-pathogen SSIs and among polymicrobial SSIs utilizing variance-weighted least-squares regression, with P<.05 considered statically significant. Analyses were performed using STATA version 14.0 software (StataCorp, College Station, TX).
RESULTS
In total, 1,278 unique SSIs were reported at CCHMC during the study period, of which 953 were single or polymicrobial SSIs. Pathogens identified for single and polymicrobial SSIs are listed in Table 1.
TABLE 1 Prevalence of Pathogens Associated With Single-Pathogen and Polymicrobial SSIs
NOTE. Each value is expressed as the number of SSIs associated with that pathogen and the percentage of SSIs in which the pathogen was recovered. MSSA, methicillin-sensitive Staphylococcus aureus; MRSA, methicillin-resistant S. aureus.
a Other gram-positive isolates: Actinomyces spp., Bacillus spp., Clostridium spp., Corynebacterium spp., Eubacterium spp., Gemella spp., Lactobacillus spp., Propionibacterium spp., Peptostreptococcus spp, unidentified gram-positive cocci.
b Other gram-negative isolates: Acinetobacter spp., Aeromonas spp., Argobacterium spp, Alcaligenes spp, Bacteroides spp, Capnocytophagia spp., Citrobacter spp., E coli, Eikenella spp., Flavobacterium spp., Fusobacterium spp., Hafnia spp, Haemophilus spp, Klebsiella spp, Moraxella spp., Morganella spp., Neisseria spp., Proteus spp., other Pseudomonas spp., Pantoea spp., Providencia spp., Prevotella spp., Serratia spp., Sphingobacteria spp., Xanthomonas spp., unidentified gram-negative rods.
Staphylococci were the predominant pathogens for single-pathogen SSIs. Among single-pathogen SSIs, the proportion of both methicillin-resistant and methicillin-susceptible S. aureus (MRSA and MSSA, respectively) increased during the study period. MRSA increased from 0.6% to 19.7% (P<.01), while MSSA increased from 28.1% to 36.1% (P=.03) (Table 1). The proportion of most other pathogens declined steadily, with the exception of Enterococcus spp., Streptococcus spp., and Pseudomonas aeruginosa, for which no change was detected (Table 1). Among polymicrobial infections, >50% included a gram-negative organism. No significant change was noted for most pathogens associated with polymicrobial SSIs.
DISCUSSION
Our study demonstrates that the pathogens most commonly associated with SSIs in pediatric surgical cases are similar to those in adults.Reference Mangram, Horan, Pearson, Silver and Jarvis 2 Current interventions are designed to prevent infections caused by skin flora. However, their ongoing prevalence despite these interventions suggests that additional interventions are needed to prevent SSIs caused by these organisms.
Staphylococcus spp. were the most prevalent species identified, and the proportion of both MSSA and MRSA increased over time. The increase in MRSA is not particularly surprising given its emergence as a major community pathogen nationally.Reference Klevens, Morrison and Nadle 8 The concurrent increase in cases of SSIs caused by MSSA, however, was unexpected. This finding suggests that despite the increase in MRSA, MSSA still plays a large role in causing SSIs. Therefore, preoperative screening for Staphylococcus spp., not just MRSA, may help guide preoperative antibiotic selection, skin preparation, and postoperative wound care to minimize the risk of infection with either of these organisms.Reference Vitale, Riedel and Glotzbecker 9
The predominance of gram-negative organisms in polymicrobial SSIs suggests that external contamination of the wound, (eg, with fecal matter) plays a major role in polymicrobial SSI pathogenesis. This finding highlights the ongoing importance of postoperative wound management and the need for protective barriers to prevent contamination of the wound.Reference Vitale, Riedel and Glotzbecker 9
Our conclusions are limited by our inability to account for potential correlations between patient-level characteristics, such as comorbidities, with particular organisms causing SSIs. Reference Subramanyam, Schaffzin, Cudilo and Varughese 10 Another limitation was our inability to assess the direct influence of specific interventions that occurred in our medical center over the study period.Reference Schaffzin, Harte and Marquette 3 Further study is planned to examine such interactions.
Our study findings indicate that among pediatric patients, skin and bowel flora play a significant role in SSIs. Future interventions to target aspects such as preoperative screening and management of MSSA and MRSA colonization and postoperative wound management to prevent fecal contamination may reduce pediatric SSIs. Further study is planned to assess the effect of patient and procedure factors as well as interventions on both the incidence of and the type of pathogens associated with SSIs.
ACKNOWLEDGMENTS
We would like to thank Lou Fitzner for assistance with extraction of SSI data.
Financial support: This study was conducted as part of institutional quality improvement efforts. No external funding was used.
Potential conflicts of interest: All authors report no conflicts of interest relevant to this article.
