Table 2.

Definitions of Infection Endpoints

SSI	SSI was defined according to NHSN criteria: Purulent drainage from the incision; organism(s) identified from culture of an aseptically obtained specimen from the superficial incision or subcutaneous tissue; incision deliberately opened by a physician or physician designee without culture testing in a patient with localized pain or tenderness, localized swelling, erythema, or heat; or diagnosis of an SSI by a physician or physician designee. If documentation was inadequate, but the patient had the wound re-opened and was prescribed antibiotic therapy directed against likely wound pathogens, it was considered an SSI. Minor skin dehiscences or serous drainage documented as such were not counted as SSI. SSIs were characterized as a superficial SSI if it involved the skin and subcutaneous tissue only, or as a deep SSI if the infection extended into the fascia or deeper layers of the abdominal wall. SSI involving the laparotomy incision was counted as a related SSI; SSI at a surgical site for an operation unrelated to trauma laparotomy (such as open reduction and internal fixation of a fracture) was counted as an unrelated SSI.
IAI	IAI was diagnosed based on findings at re-laparotomy, percutaneous drainage, or clinical and radiographic findings if no source control procedure was performed. Purulent fluid identified within the abdominal cavity at the time of reoperation was considered diagnostic of IAI. Patients undergoing percutaneous drainage of postoperative fluid collections were counted as having IAI if abdominal cavity fluid cultures were positive, or in the presence of a negative culture if a gram stain revealed leukocytes and micro-organisms and the patient was receiving antimicrobials that may have inhibited growth of organisms. Fluid collections characterized as urinomas or bilomas were not considered IAI. Patients who had clinical symptoms and signs of infection and had CT findings consistent with IAI but did not undergo any procedure for drainage were counted as having IAI if they were treated with an antibiotic regimen directed against presumed IAI pathogens. Patients who had positive laparotomy findings or a positive abdominal fluid culture were counted as having a confirmed IAI, and those who had negative cultures or did not have cultures obtained were counted as having an unconfirmed IAI.
Empyema	Empyema was identified if the patient had purulent pleural fluid found at the time of an operation or formal drainage procedure and was treated with antimicrobials for the infection. Patients whose pleural fluid cultures were positive were considered to have had a confirmed empyema. Those who had negative cultures but had leukocytes and organisms identified on gram stain were considered to have an unconfirmed empyema, as were patients who did not have cultures sent but who had clinical symptoms and signs consistent with an empyema and had pleural fluid described as purulent. Empyema was considered related to abdominal trauma if the patient had a thoraco-abdominal injury, and had a direct communication between the abdominal and the affected thoracic cavity. Empyema was considered unrelated to abdominal trauma if the thoracic cavity had not been contaminated as a result of the abdominal trauma. For instance, a patient who underwent a laparotomy for blunt trauma but developed an empyema after tube thoracostomy for a hemo- or pneumothorax was counted as having an unrelated infection.
SSTI	SSTI was identified by purulent drainage from a traumatic wound, or by cellulitis associated with a traumatic wound that was treated with anti-infective therapy. Culture confirmation was not required. An SSTI treated with operative drainage, or that resulted in prolongation of the hospital stay or re-admission to the hospital was considered a major SSTI; if managed non-operatively without a new or prolonged hospital admission, it was counted as a minor SSTI. The SSTI was considered a related infection if the infected traumatic wound was in direct continuity with the abdominal cavity or was directly related to the abdominal trauma. An SSTI occurring elsewhere was counted as an unrelated SSTI.
Pneumonia	Pneumonia was diagnosed in patients with a new or worsening chest infiltrate on a routine chest radiograph or CT examination, clinical findings consistent with pneumonia (such as cough, dyspnea, production of purulent sputum, new or worsening fever, or leukocytosis) and a decision by the treating clinicians to prescribe an antibiotic regimen appropriate for treatment of a pneumonia. Patients who had a positive tracheal aspirate or bronchoalveolar lavage culture were considered to have a confirmed pneumonia. Patients who met the criteria for pneumonia but did not have respiratory cultures obtained were considered to have an unconfirmed pneumonia.
UTI	UTI was diagnosed by a urinary culture with >50,000 organisms per milliliter (the criteria reported by the hospital microbiology laboratory at the time of the study). Patients whose cultures revealed coagulase-negative staphylococci or Candida were only diagnosed with a UTI if a subsequent culture confirmed the same organism.
Blood stream infection	Patients who had a positive blood culture were counted as having a blood stream infection; however, if the culture was positive for coagulase-negative staphylococci or other skin potential contaminants, these were only counted as a bloodstream infection if the same organism was obtained from two separate cultures obtained at different times. Blood stream infections were characterized as primary if no other source for the organism(s) was identified. A secondary bloodstream infection was diagnosed if the same organism or organisms were cultured from another source within 72 h before or after the positive blood culture.
Clostridiodes difficile colitis	Clostridiodes difficile colitis was diagnosed by a positive Clostridiodes difficile toxin assay in a patient who had new-onset diarrhea.
Other infections	Patients who had positive cultures from the eye, bone specimens, or cerebrospinal fluid were counted as having an ocular infection, osteomyelitis, or meningitis, all of which were considered as unrelated to the trauma laparotomy.
Uncounted infections	Infections diagnosed within 24 h of admission to the hospital were considered pre-existing, and not included in the infection endpoints. Similarly, patients diagnosed with Helicobacter pylori or a sexually transmitted disease subsequently during hospitalization were considered to also have had a pre-existing illness and were not included in infection endpoints.

SSI = surgical site infection; NHSN = National Healthcare Safety Network; IAI = intra-abdominal infection; SSTI = skin and soft tissue infection; CT = computed tomography; UTI = urinary tract infection.