Methods
Study Site, Subjects and Design
The study was conducted in the 18-bed adult ICU of a tertiary university teaching hospital admitting approximately 900 patients per year. This study was approved by our Ethical Committee (Catholic University's Ethics Committee (approval number:14599/13)) that waived the need for informed consent, due to its retrospective design. All patients consecutively admitted to our ICU between 1 June 2009 through 31 May 2012 who received TGC for a microbiologically documented infection were evaluated. TGC treatment should last at least three days including the loading dose (LD). Data were extracted from patients' medical records and computerized hospital databases according to a pre-defined questionnaire. These data included demographic characteristics, medical history, clinical and laboratory findings, the simplified acute physiology score II (SAPS II) and sequential organ failure assessment (SOFA) score, the occurrence of abnormal laboratory measures, type of treatment and outcome. The main outcomes of patients were evaluated according to TGC dosages they received, and type of infections, separately analyzing the subgroup of patients with ventilator-associated pneumonia (VAP).
Definitions
Patients who were treated with TGC 50 mg every 12 hours after a 100-mg LD were defined as the standard dose group (SD). Those ones who received 100 mg every 12 hours after a 200 mg LD were classified as the high dose group (HD).
The diagnosis of VAP was established when a new, persistent, progressive radiographic lung infiltrate was present ≥48 hours following tracheal intubation and when two or more of the following clinical criteria were met: (1) new onset of purulent bronchial secretions; (2) body temperature >38.8°C or <35.5°C; and (3) white blood cell count >10,000/mm or <4,000/mm. All episodes were microbiologically confirmed by quantitative cultures of bronchoalveolar lavage (≥10 cfu/ml). The diagnosis of IAI and cSSTIs and bloodstream infections (BSIs) were made according to current guidelines.
Infection onset coincided with the collection date of the first microbiological sample culture yielding the study isolate (index culture). Septic shock was defined as recommended by the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference Committee. Safety and adverse events (AE) were determined through the biochemical abnormalities documented in medical records according to the Department of Health and Human Services - Common Terminology Criteria for Adverse Events (DHHS-CTCAE v.3.0) classification. The severity of AE was graded from 1 to 5.
Clinical cure was defined as the complete resolution of all signs and symptoms of the infection by the end of TGC therapy. Improvement or lack of progression of all abnormalities on chest radiographs was also required for VAP. Microbiological eradication was defined as the absence of the original pathogens from the culture of the specimens subsequently collected from the original site. Clinical outcomes were independently evaluated by two physicians (GDP, VB) who were blinded to the treatment. When judgments were discordant (about 5% of patients), the reviewers reassessed the data and reached a consensus decision.
The initial antimicrobial regimen (that is, that used before in vitro susceptibility data were available for the isolated bacteria) was classified as inadequate (IIAT) when it did not include any agent displaying in vitro activity against the isolated pathogen/pathogens.
Microbiology Analysis
Strains were identified to the species level with the matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry (MS) (BrukerDaltonik). The antibiotic susceptibility profiling of isolates had been performed with the Vitek 2 system (bioMérieux, Marcy l'Etoile, France). The Clinical and Laboratory Standards Institute (CLSI) criteria were used to interpret the results. TGC minimum inhibitory concentrations (MICs) were identified with the Sensititre broth microdilution method (Trek Diagnostic Systems, Cleveland, OH, USA); isolates were considered susceptible if the MIC was ≤2 mg/L and resistant if the MIC was ≥8 mg/L. Multidrug-resistance was defined as acquired non-susceptibility to at least one agent in three or more antimicrobial categories, extensive drug-resistance (XDR) was defined as non-susceptibility to at least one agent in all but two or fewer antimicrobial categories and pandrug-resistance (PDR) was defined as non-susceptibility to all agents in all antimicrobial categories. The presence of blagenes conferring resistance to carbapenems was determined by polymerase chain reaction (PCR) and sequencing, as previously described.
Statistical Analysis
The Kolmogorov-Smirnov test was used to value the variables distribution. The data with a non-normal distribution were assessed with Mann–Whitney test and the median and selected centiles (25th to 75th) value was given. The data with a normal distribution were assessed with the Student t-test. Categorical variables are presented as proportions and were analyzed with the use of the chi-square test or Fisher exact test, as appropriate. A P-value <0.05 was considered significant. The crude odds ratio (OR) and 95% CI were calculated for each variable. We included all variables in the multivariable logistic regression if they achieved a P-value of less than or equal to 0.2 at the univariate analysis. A stepwise selection procedure was used to select variables for inclusion in the final model. The Hosmer-Lemeshow goodness-of-fit test and the receiver operating characteristic (ROC) curve analysis were used to assess the goodness of the logistic final model. All statistical analyses were performed using the Intercooled Stata program, version 11, for Windows (Stata Corporation, College Station, TX, USA).