Study design and setting

We conducted a prospective, observational study to describe the epidemiology of SSIs after pediatric ambulatory surgery across the Children’s Hospital of Philadelphia (CHOP) Care Network. At the time of the study, the network, located in southeastern Pennsylvania and southern New Jersey, included 3 freestanding ASFs, 1 hospital-based surgical facility, 29 primary care practices, 8 specialty care centers, a 521-bed acute-care hospital, and an emergency department. All sites used a common electronic health record (EHR, Epic Systems, Verona, WI) except for surgical procedure data prior to May 2013, which were collected and stored in OR Manager (Picis Clinical Solutions, Wakefield, MA). Decisions regarding the location of ambulatory surgical encounters are dictated largely by patient and clinician preferences, which include nonclinical factors such as parental preference and ease of scheduling. The CHOP Institutional Review Board reviewed and approved this study.

Study cohort

The EHR data were extracted biweekly for children <18 years of age who had an ambulatory surgical procedure (ie, with admission, procedure, and discharge on the same calendar day) performed at any of the 4 surgical centers (ie, 3 ASFs and 1 hospital-based facility). A surgical procedure was defined using 2010 National Healthcare Safety Network (NHSN) criteria, which required that the procedure was performed in an operating room and that incision and complete closure of the wound occurred during the same operating room visit. ⁹ Eligible wound class 1 and 2 procedures were identified from the procedure name (free-text field) recorded by the surgeon in the EHR after the procedure was performed. Multiple surgical procedures performed during a single operating room visit were included as long as all procedures met NHSN surgery definitions or the additional procedures that did not meet NHSN surgery definitions did not involve penetration of sterile tissue by an instrument or medical device (eg, ear tubes, cystoscopy, biopsy) or an open wound (eg, debridement, closure). Eligible surgical encounters were identified at the 3 ASFs between June 2012 and December 2015 and at the hospital-based facility between August 2012 and December 2015. Children could be enrolled more than once if they had multiple surgical encounters (ie, OR visits) that met eligibility criteria over the study period.

Data collection

Parents or guardians were contacted by phone between 30 and 45 days after their child’s surgical encounter. At the time of phone contact, non–English-speaking parents or guardians were excluded. The guardian provided verbal informed consent for both the telephone interview and the review of data from the EHR. If consent was obtained, a structured telephone interview was completed. The interview included questions about healing of the surgical site, including the occurrence and details of any healthcare encounters during the initial 30 days after the surgery. Additionally, occurrence and details of any healthcare encounters in the CHOP network were abstracted electronically from the EHR for up to 60 days after surgery for each child.

Manual case reviews of the EHR were conducted by 1 of 2 certified infection preventionists, each of whom had more than 20 years of experience working in infection prevention and control. A manual case review was completed if the interview indicated a potential postsurgical complication or if electronically abstracted EHR data indicated that an antibiotic was prescribed or that the child had an emergency department visit or hospitalization during the surveillance window. For manual case reviews of the EHR, the infection preventionist documented diagnoses (ICD-9 diagnosis codes as well as diagnoses from clinical notes), wound descriptions, culture orders, antibiotic treatment, recommendations for over-the-counter medications, and related follow-up procedures (eg, incision and drainage procedures). The manual case review covered the 60 days after the surgical encounter.

Procedure category

Eligible procedure names (free-text field) were grouped into 50 procedure categories by 2 pediatric infectious diseases specialists with experience in hospital epidemiology/infection prevention and control (S.E.C. and J.S.G). If multiple procedures in the same procedure category were performed in a single surgical encounter (ie, OR visit), the surgical encounter was counted only once for that category. However, if multiple procedures of different categories were performed in a single surgical encounter, the encounter was counted for each category. For example, a single surgical encounter with adjacent tissue transfer or arrangement, chordee correction with circumcision, and repair of concealed penis would be counted in 2 different procedure categories: skin and/or tissue graft (first procedure) and penile reconstruction (second and third procedures).

Outcomes

We used 2 different definitions to identify infectious events associated with surgery. First, we identified SSIs assessed in the 30 days after the surgical procedure by applying 2010 NHSN definitions including superficial, deep, and organ-space infections.Reference Horan, Andrus and Dudeck ¹⁰ Second, we developed and applied a broader definition to describe evidence of possible infection associated with surgery. We developed this “expanded” definition for 2 reasons: First, NHSN SSI criteria require clear documentation of each qualifying element in the EHR; thus, an infection reported by the parent but for which there was no documentation in the EHR (eg, if a patient had been evaluated in a nonnetwork emergency department) would not meet this NHSN definition. Second, NHSN SSI criteria exclude certain infectious events (eg, cellulitis) that may be related to surgery if it occurs at the wound site. Therefore, we aimed to develop an expanded definition that would capture all possible events with high sensitivity. The expanded definition included independent assessments of data obtained from the interview and the EHR review (Fig. 1) and categorized each surgical encounter by the strength of evidence (some or strong) for possible infection reported in the interview or documented in the EHR. The nature of the evidence required varied depending on the source (interview vs EHR). The expanded definition was applied to the interview data for the 30 days after surgery and the EHR data for the 60 days after surgery. The expanded definition was constructed to ensure that any SSI meeting NHSN criteria would also meet the expanded definition criteria for strong evidence of possible infection associated with surgery based on EHR documentation.

Fig. 1

Components of the expanded definition for evidence of possible infection associated with surgery based on data from the telephone interview and data from the electronic health record (EHR). ^aPrescription or over-the-counter medication in the absence of another infection, excluding continuation therapy. ^bPrescription for which the parent could not recall the name or type, in the absence of another infection. ^cParental report of 2 of the following symptoms: fluid, dehiscence, erythema, warmth, tenderness, or edema. ^dEHR documentation of purulent fluid or 2 of the following symptoms: dehiscence, erythema, warmth, tenderness, edema, or nonpurulent fluid. Note: When a category intersects in the grid with itself, this indicates that this category alone was observed. For example, for parental interview, an infection diagnosis alone was considered some evidence; however, abnormal wound description alone was not included.

Comparison of hospital-based facility and ASFs

To compare rates of NHSN SSI between the 2 types of facilities, we restricted the cohort to procedure categories routinely performed at both types of facility. We defined routinely performed procedures as those procedure categories performed >10 times at both facility types in our cohort. Of the 50 procedure categories, 23 categories were routinely performed at both facility types. Because NHSN SSI after ambulatory surgery was rare, we implemented exact conditional logistic regression to compare rates between the 2 types of facilities, conditioning on procedure category. The analysis controlled for patient age (continuous) and the number of surgical procedures completed (ie, 1, 2, or ≥3) during the same surgical encounter.

Risk factors of infection related to surgery

To identify risk factors for infection after ambulatory surgery, we used the restricted cohort of 23 procedure categories routinely completed at both facility types and applied the expanded definition of infection related to surgery (either strong or some). We implemented conditional logistic regression conditioned on procedure category. First, we assessed the association of each potential risk factor with the outcome in univariate analysis. Factors with a P value <.20 in the univariate analysis were included in the final multivariable conditional logistic regression model. We reported odds ratios (OR) and 95% confidence intervals (CI).

Descriptive analyses were completed in SAS version 9.4 software (SAS Institute, Cary, NC), and conditional analyses (commands exlogistic and clogit) were performed using Stata version 15.0 software (StataCorp, College Station, TX). P values were 2-sided, and P values <.05 were considered statistically significant.