Dr Maxens Decavèle
email: maxens.decavele@aphp.fr

A,B,D,E,F Nathalie Gault

PhD Jean Denis Moyer

Maël Gennequin

Moyer: A,D,F Maël Gennequin: A,D,F Pierre-Antoine Allain

Arnaud Foucrier

A,B,D, E,F Jean Denis

A,B,C, D F Arnaud

Prediction models of methicillin sensitive staphylococcus aureus ventilator associated pneumonia relapse in trauma and brain injury patients: a retrospective analysis

Keywords:

Purpose: To describe the incidence and risk factors of methicillin sensitive staphylococcus aureus ventilator associated pneumonia (MSSA-VAP) relapse in trauma and non-traumatic brain injury patients.

Materials and Methods

: Retrospective observational monocentric cohort study of consecutive ICU patients who developed a first episode of MSSA-VAP after trauma and nontraumatic brain injury. MSSA-VAP relapse encompass MSSA-VAP treatment failure (persistence or recurrence of MSSA) or other pathogen -VAP. Results: A total of 165 patients (71% of trauma and 29% of non-traumatic brain injury) with MSSA-VAP were included. MSSA-VAP relapse occurred in 54 (33%) patients, including 28 (17%) MSSA-VAP treatment failure and 46 (28%) other pathogen-VAP. Empirical first-line antibiotic therapy was appropriate in 96% of cases. In multivariate analysis, the presence of Streptococcus species (Odds ratio [OR] 7.37) and oropharyngeal flora (OR 3.64) as initial MSSA co-pathogen, suggested aspiration at the time of admission and independently predicted MSSA-VAP treatment failure. Initial Glasgow coma scale (OR 0.89), need for emergent surgery (OR 5.71) and the presence of an acute respiratory distress syndrome at the time of the first MSSA-VAP (3.99), independently predicted the onset of other pathogen -VAP. Conclusion: Early and simple factors may help to identify patients with high-risk of MSSA-VAP relapse.

Running title

Predictive factors of MSSA-VAP relapse

Ethics approval

The data file was declared to the French Data Protection Agency (CNIL, N° 1925005) and the study was approved by the institutional review board (IRB 00006477) of Bichat hospital, Paris 7 University, AP-HP.

Invitation

This paper is not an invited paper.

Total word count

Introduction

Ventilator associated pneumonia (VAP), defined by an intensive care unit (ICU) acquired pneumonia that develops in patients mechanically ventilated for at least 48 h [START_REF] Torres | International ERS/ESICM/ESCMID/ALAT guidelines for the management of hospitalacquired pneumonia and ventilator-associated pneumonia: Guidelines for the management of hospital-acquired pneumonia (HAP)/ventilator-associated pneumonia (VAP) of the European Respiratory Society (ERS), European Society of Intensive Care Medicine (ESICM), European Society of Clinical Microbiology and Infectious Diseases (ESCMID) and Asociación Latinoamericana del Tórax (ALAT)[END_REF], is the most common complication in patients receiving invasive mechanical ventilation.

Although VAP incidence have significantly decreased in the general ICU population and currently concerns around 10% of intubated ICU patients [START_REF] Ferrer | Epidemiology of ICU-acquired pneumonia[END_REF], its incidence remains very high in trauma and non-traumatic brain injury (NTBI) patients (around 50%) [START_REF] Asehnoune | Hydrocortisone and fludrocortisone for prevention of hospital-acquired pneumonia in patients with severe brain injury (Corti-TC): a double blind multicenter phase 3, randomised placebo-controlled trial[END_REF][START_REF] Cavalcanti | Risk and prognostic factors of ventilator-associated pneumonia in trauma patients[END_REF][START_REF] Bronchard | Early onset pneumonia: risk factors and consequences in head trauma patients[END_REF][START_REF] Seguin | Study of Povidone Iodine to Reduce Pulmonary Infection in Head Trauma and Cerebral Hemorrhage Patients (SPIRIT) ICU Study Group; AtlanRéa Group. Effect of oropharyngeal povidoneiodine preventive oral care on ventilator-associated pneumonia in severely brain-injured or cerebral hemorrhage patients: a multicenter, randomized controlled trial[END_REF]. Consciousness disorders and subsequent aspiration at the time of brain injury, inflammatory response [START_REF] Giannoudis | Current concepts of the inflammatory response after major trauma: an update[END_REF] and prolonged mechanical ventilation, especially in case of severe brain injury, could explain this finding. Whereas gram-negative bacterial strains are prevalent in VAP of non-trauma patients [START_REF] Torres | International ERS/ESICM/ESCMID/ALAT guidelines for the management of hospitalacquired pneumonia and ventilator-associated pneumonia: Guidelines for the management of hospital-acquired pneumonia (HAP)/ventilator-associated pneumonia (VAP) of the European Respiratory Society (ERS), European Society of Intensive Care Medicine (ESICM), European Society of Clinical Microbiology and Infectious Diseases (ESCMID) and Asociación Latinoamericana del Tórax (ALAT)[END_REF][START_REF] Ferrer | Epidemiology of ICU-acquired pneumonia[END_REF][START_REF] Restrepo | Comparison of the Bacterial Etiology of Early-Onset and Late-Onset Ventilator-Associated Pneumonia in Subjects Enrolled in 2 Large Clinical Studies[END_REF], methicillin-sensible Staphylococcus aureus (MSSA) is the pathogen the most frequently encountered in VAP of trauma and NTBI patients, accounting for up to 40-50% of VAP [START_REF] Asehnoune | Hydrocortisone and fludrocortisone for prevention of hospital-acquired pneumonia in patients with severe brain injury (Corti-TC): a double blind multicenter phase 3, randomised placebo-controlled trial[END_REF][START_REF] Cavalcanti | Risk and prognostic factors of ventilator-associated pneumonia in trauma patients[END_REF][START_REF] Bronchard | Early onset pneumonia: risk factors and consequences in head trauma patients[END_REF][START_REF] Seguin | Study of Povidone Iodine to Reduce Pulmonary Infection in Head Trauma and Cerebral Hemorrhage Patients (SPIRIT) ICU Study Group; AtlanRéa Group. Effect of oropharyngeal povidoneiodine preventive oral care on ventilator-associated pneumonia in severely brain-injured or cerebral hemorrhage patients: a multicenter, randomized controlled trial[END_REF][START_REF] Launey | Risk factors for ventilator-associated pneumonia due to Staphylococcus aureus in patients with severe brain injury: A multicentre retrospective cohort study[END_REF][START_REF] Lepelletier | Retrospective analysis of the risk factors and pathogens associated with early-onset ventilatorassociated pneumonia in surgical-ICU head-trauma patients[END_REF][START_REF] Roquilly | ATLANREA group. Empiric antimicrobial therapy for ventilator-associated pneumonia after brain injury[END_REF].

If, the physiological mechanism that leads to the development of a first VAP in general ICU population has been extensively described, the VAP relapse, that yet concern 25% of patients [START_REF] Combes | Early predictors for infection recurrence and death in patients with ventilator-associated pneumonia[END_REF], have unfortunately not been fully addressed. The few published reports focused mainly on nonfermenting Gram-negative bacilli (GNB) and non-trauma patients [START_REF] Siempos | Frequency and predictors of ventilator-associated pneumonia recurrence: a meta-analysis[END_REF][START_REF] Rello | Recurrent Pseudomonas aeruginosa pneumonia in ventilated patients: Relapse or reinfection?[END_REF][START_REF] Silver | Recurrent Pseudomonas aeruginosa pneumonia in an intensive care unit[END_REF][START_REF] Planquette | Pseudomonas aeruginosa Ventilator-associated Pneumonia. Predictive Factors of Treatment Failure[END_REF][START_REF] Nseir | Risk factors for relapse of ventilator-associated pneumonia related to nonfermenting Gram negative bacilli: A case-control study[END_REF][START_REF] Rangel | Risk Factors for Relapse of Ventilator-Associated Pneumonia in Trauma Patients[END_REF][START_REF] Combes | Early predictors for infection recurrence and death in patients with ventilator-associated pneumonia[END_REF][START_REF] Combes | Factors predicting ventilator-associated pneumonia recurrence[END_REF][START_REF] Zahar | Outcomerea Study Group. Is methicillin resistance associated with a worse prognosis in Staphylococcus aureus ventilator-associated pneumonia?[END_REF]. Up-to-date, there is no data on MSSA-VAP relapse in trauma and NTBI patients. However, given the high incidence of MSSA-VAP in trauma and NTBI patients and the negative impact of VAP on weaning from mechanical ventilation outcomes [START_REF] Torres | International ERS/ESICM/ESCMID/ALAT guidelines for the management of hospitalacquired pneumonia and ventilator-associated pneumonia: Guidelines for the management of hospital-acquired pneumonia (HAP)/ventilator-associated pneumonia (VAP) of the European Respiratory Society (ERS), European Society of Intensive Care Medicine (ESICM), European Society of Clinical Microbiology and Infectious Diseases (ESCMID) and Asociación Latinoamericana del Tórax (ALAT)[END_REF][START_REF] Safdar | Clinical and economic consequences of ventilator-associated pneumonia: a systematic review[END_REF], a better understanding of the incidence, the risk factors and the consequences of MSSA-VAP relapse on outcomes, is of high clinical importance.

We hypothesized that factors associated with MSSA-VAP relapse could be identified and that MSSA-VAP relapse was associated with longer duration of mechanical ventilation.

We thus conducted a retrospective study to measure the incidence and risk factors of MSSA-VAP relapse and analyse its relationship with mechanical ventilation withdrawal in trauma and NTBI patients who developed a first episode of MSSA-VAP.

Materials and Methods

Study design and settings

This was a monocentric retrospective study. The data were collected from adults hospitalized in a 17-bed surgical ICU from January 2009 to January 2015. The data file was declared to the French Data Protection Agency (CNIL, N° 1925005) and the study was approved by the institutional review board (IRB 00006477) of Bichat hospital, Paris 7 University, AP-HP. In accordance with the French law, written informed consent was not required. Results were reported according to guidelines (Table S1).

Patients

Any ICU trauma or NTBI patients requiring intubation and who developed a first episode of VAP documented to MSSA was considered for inclusion. Patient with history of infectious pneumonia prior to the intubation or an infection related to methicillin-resistant Staphylococcus aureus were not eligible. Patients discharged from the ICU during the 48h following the MSSA-VAP diagnostic were also excluded.

Definitions and follow up

According to current guidelines [START_REF] Torres | International ERS/ESICM/ESCMID/ALAT guidelines for the management of hospitalacquired pneumonia and ventilator-associated pneumonia: Guidelines for the management of hospital-acquired pneumonia (HAP)/ventilator-associated pneumonia (VAP) of the European Respiratory Society (ERS), European Society of Intensive Care Medicine (ESICM), European Society of Clinical Microbiology and Infectious Diseases (ESCMID) and Asociación Latinoamericana del Tórax (ALAT)[END_REF], MSSA-VAP was defined by the presence in an intubated patient of 1) a new or persistent infiltrates on chest X-ray 48 hours after intubation and mechanical ventilation 2) at least 2 of the following criteria: purulent tracheal secretions, fever greater than or equal to 38.5°C or hypothermia less than or equal to 36.5°C, leucocytosis greater than 10 9 /L or lower leukopenia, 3) a positive quantitative culture of lower respiratory tract (LRT) samples: either bronchoalveolar lavage with a threshold > 10 4 colony forming unit (cfu)/ml or either plugged telescopic catheter with a threshold > 10 3 cfu/ml, showing MSSA alone or in association with other bacteria and 4) a decision was made to initiate antibiotic therapy. Same criteria applied also for VAP related to other pathogens.

The onset of MSSA-VAP relapse was then observed during a period that extend from the first day of antibiotic therapy until either the end of ICU stay or the death in the ICU or until 28 days after the initiation of antibiotics, depending on which occurred first. MSSA-VAP relapse was defined by new or persistent clinical, biological and radiological signs compatible with pneumonia, that conducted physicians to performed a second LRT sample, confirmed by significant growth in quantitative culture with the same thresholds as described above. MSSA-VAP relapse definitions were adapted from a recent randomized control trial [START_REF] Kollef | Ceftolozane-tazobactam versus meropenem for treatment of nosocomial pneumonia (ASPECT-NP): a randomised, controlled, double-blind, phase 3, non-inferiority trial[END_REF] and included (Figure 1): MSSA-VAP treatment failure that encompassed:

1. Persistent MSSA-VAP in case of isolation of at least MSSA in a second LRT sample performed between four days after the initiation and two days after the end of the firstline antibiotic therapy.

2. Recurrent MSSA-VAP in case of isolation of at least MSSA, from a second LRT samples performed two full days after the end of first-line antibiotics. The LRT sample performed during the four days after antibiotics initiation was not considered for the definition of persistent or recurrent MSSA-VAP.

Other pathogen -VAP that encompassed: 3. Superinfection in case of isolation of at least a pathogen other than the initial causative pathogens from LRT sample obtained at any time during the first-line antibiotic therapy.

4. New infection in case of isolation of at least a pathogen different from the initial causative pathogens from LRT culture obtained after completion of the first-line antibiotic therapy.

In case of both presence of MSSA and another pathogen in the second LRT sample, the patient could be classified as both, Persistent MSSA-VAP and Superinfection, or both Recurrent MSSA-VAP and New infection (Figure S1).

According to our local procedure, the decision to perform a second lower respiratory tract sample was left to the discretion of the physician in charge of the patient.

Endpoints

Our first primary endpoint was the occurrence of MSSA-VAP treatment failure defined by the presence of the criteria 1 or 2.

Our second primary outcome was the occurrence of an other pathogen-VAP defined by the presence the criteria 3 or 4.

Secondary outcome was the mechanical ventilation withdrawal across the study period (28 days).

Data collection

The following data were collected for every included patient: age, gender, main comorbidities, prehospital clinical variables (eg. Glasgow coma scale, the need for prehospital intubation), type of trauma, causes of NTBI, duration of mechanical ventilation. The microbiological characteristics of the first episode of pneumonia (cfu count of MSSA, presence and type of associated pathogens) and of the antibiotic therapy (type of antibiotics, appropriate empirical treatment regarding the antibiogram) were also collected. The Simplified Acute Physiology Score (SAPS II) and Injury Severity Score (ISS) and the presence of an acute respiratory distress syndrome (ARDS) at the time of the first MSSA-VAP diagnostic, were also recorded.

Statistical analysis

Continuous variables are expressed as median (0.25-0.75 interquartile range) and categorical variables are expressed as absolute and relative frequency. Factors associated with MSSA-VAP treatment failure and other pathogen -VAP were investigated using univariate logistic regression models, and those associated with p-value less than 0.20, or clinically relevant were proposed in a multivariate logistic regression model. Variable selection was performed using the stepwise procedure based on the Akaike criterion (both forward and backward procedures). Results were reported as adjusted Odds-ratios (OR), with their 95% confidence interval (95%CI). The performance of the models was explored using the Area under the ROC (discrimination) and the Hosmer and Lemeshow goodness of fit test (calibration). To assess the association of MSSA-VAP treatment failure, on the one hand, and other pathogen-VAP, on the other hand, with mechanical ventilation withdrawal, we performed a Landmark analysis whereby the exposure status (either treatment failure or other pathogen-VAP) is defined before the Landmark time point (any exposure occurring after that time point is ignored) and the outcome of interest (end of mechanical ventilation) is measured after that time point (patients with the outcome of interest before that time point are excluded from the analysis). The method is suitable to account for reverse causality. We defined the Landmark time at 12 days, since the median time of each exposure was 8 and 9 days respectively, and the median duration of mechanical ventilation was 16 days in patients with VAP relapse, and 23 days in patients with no relapse. Adjusted hazard ratios of mechanical ventilation withdrawal associated with MSSA-VAP treatment failure, on the one hand, and other pathogen-VAP, on the other hand, were estimated using multivariate Cox proportional hazard models. Missing data imputation was not necessary (less than 0.1% of missing data).

Analyses were performed using R version 3.6.1.

RESULTS

Characteristics of the patients

The study flowchart is represented in the figure 2. One hundred and sixty-five patients with MSSA-VAP patients were included. The characteristics of the patients are described in the table 1. Among them, 117 (71%) were admitted for trauma and 48 (29%) for NTBI. The characteristics between trauma and NTBI patients are compared in Table S2. Duration of mechanical ventilation prior to the diagnostic of MSSA-VAP first episode was 4 (3-6) days. ICU-mortality rate was 8% (n=13) and length of ICU stay was 21 (14-33) days. MSSA-VAP relapse was observed in 54 (33%) patients. Table 1 depicts the characteristics of patients with and without MSSA-VAP relapse. Empirical antibiotic therapy appropriateness was confirmed in 158 (96%) patients and did not differ between patients with (92%) or without MSSA-VAP relapse (97%).

First primary endpoint -MSSA-VAP treatment failure

Twenty-eight (17%) patients presented an MSSA-VAP treatment failure, among them, 11 (7%) had persistent MSSA-VAP and 17 (10%) had recurrent MSSA-VAP. Univariate analysis of factors associated with MSSA-VAP treatment failure is reported in the table S3. In multivariate analysis, the presence of oropharyngeal flora (OR 3.64 95%CI 1.14 -11.47, p=0.026) and the presence of Streptococcus in the initial respiratory sample (OR 7.37 95%CI 1.15 -51.75, p=0.036) were associated with MSSA-VAP treatment failure (Table 2). More details about the variables selected, and the performance of the models are available in Supplemental (Figure S2 andS3).

Among the whole population, antibiotics were more frequently secondarily adapted into amoxicillin-clavulanic acid in patients with oropharyngeal flora or Streptococcus present in association with MSSA than their counterparts (63% vs. 30%, p<0.001). Same results was observed in the sub-group of the 28 MSSA-VAP treatment failure patients, with higher rate of amoxicillin-clavulanic acid use in patients with MSSA-associated oropharyngeal flora or Streptococcus (62% vs. 13%, p=0.016).

Second primary endpointother pathogen -VAP

Forty-six (28%) patients developed an other pathogen -VAP. Among them, 14 (8%) were superinfections and 32 (19%) were new infections. Univariate analysis of factors associated with other pathogen -VAP is reported in the table S4. Multivariate analysis showed that two factors were independently associated with a higher risk of other pathogen -VAP, the need for emergent surgery (OR 5.71 95%CI 1.48-37.97, p=0.027) and the presence of ARDS at the time of the first MSSA-VAP (OR 3.99 95%CI 1.53-10.83, p=0.005). One factor, the Glasgow coma score was independently associated with a lower risk of newpathogen VAP (OR: 0.89 95%CI 0.81-0.97, p= 0.019) (Table 2).

Weaning from mechanical ventilation outcome

In the Landmark analysis no relationship could be demonstrated between MSSA-VAP relapse and duration of mechanical ventilation (Figure 3).

Discussion

To the best of our knowledge, this is the largest published study of trauma and NTBI patients with MSSA-VAP and the first that focused specifically on factors associated with its relapse.

Main results can be summarized as follows: in intubated trauma and NTBI patients, 1) MSSA-VAP relapse is frequent (on third of patients) despite appropriate empirical antibiotics, 2) MSSA-treatment failure (17% of patients) is predicted by the microbiological association with Streptococcus species or oropharyngeal flora, 3) other pathogen -VAP (28% of patients) is independently predicted by the severity of the disease (Glasgow coma scale, ARDS, emergent surgery) and 4) both, MSSA-VAP treatment failure and other pathogen -VAP, did not significantly prolonged the duration of mechanical ventilation.

MSSA-VAP relapse

The 33% rate of MSSA-VAP relapse observed in our study is in line with the around 30% rate observed in other population (non-surgical ICU patients) and with other pathogens such as nonfermenting GNB [START_REF] Siempos | Frequency and predictors of ventilator-associated pneumonia recurrence: a meta-analysis[END_REF][START_REF] Rello | Recurrent Pseudomonas aeruginosa pneumonia in ventilated patients: Relapse or reinfection?[END_REF][START_REF] Silver | Recurrent Pseudomonas aeruginosa pneumonia in an intensive care unit[END_REF][START_REF] Planquette | Pseudomonas aeruginosa Ventilator-associated Pneumonia. Predictive Factors of Treatment Failure[END_REF][START_REF] Nseir | Risk factors for relapse of ventilator-associated pneumonia related to nonfermenting Gram negative bacilli: A case-control study[END_REF][START_REF] Rangel | Risk Factors for Relapse of Ventilator-Associated Pneumonia in Trauma Patients[END_REF][START_REF] Combes | Early predictors for infection recurrence and death in patients with ventilator-associated pneumonia[END_REF][START_REF] Combes | Factors predicting ventilator-associated pneumonia recurrence[END_REF][START_REF] Zahar | Outcomerea Study Group. Is methicillin resistance associated with a worse prognosis in Staphylococcus aureus ventilator-associated pneumonia?[END_REF]. In non-surgical patients, one study reported a 14% rate of MSSA-VAP recurrence [START_REF] Zahar | Outcomerea Study Group. Is methicillin resistance associated with a worse prognosis in Staphylococcus aureus ventilator-associated pneumonia?[END_REF], which was also similar to the 10% of MSA-VAP recurrence observed in our study. Thus, VAP-relapse seems neither to depend on the type of patient (surgical or medical) or on the initial causative pathogen [START_REF] Siempos | Frequency and predictors of ventilator-associated pneumonia recurrence: a meta-analysis[END_REF]. Moreover, the absence of association between the appropriateness of the empirical antibiotic therapy and VAP relapse has also been observed by others [START_REF] Silver | Recurrent Pseudomonas aeruginosa pneumonia in an intensive care unit[END_REF][START_REF] Combes | Early predictors for infection recurrence and death in patients with ventilator-associated pneumonia[END_REF][START_REF] Combes | Factors predicting ventilator-associated pneumonia recurrence[END_REF].

MSSA-VAP treatment failure

In this study we reported, for the first time, an independent association between the presence of Streptococcus species or oropharyngeal flora as co-infection and the risk of MSSA-VAP treatment failure. Permanent naso-pharyngeal carriage of MSSA is common in general population (around 20%) [START_REF] Wertheim | The role of nasal carriage in Staphylococcus aureus infections[END_REF], and encountering Streptococcus species, oropharyngeal flora or MSSA in LRT samples, especially after brain injury, is highly suggestive of aspiration. We first hypothesized that the presence of oropharyngeal flora or Streptococcus reflects the volume of the aspirate, the MSSA inoculum, and thus the subsequent treatment failure. In our study, quantity of MSSA was two-fold higher in patients with MSSA-VAP treatment failure (even non significant). Moreover, the association between Glasgow coma scale and the onset of other pathogen -VAP reinforce the aspiration hypothesis (e.g. Enterobacteriaceae not covered by empirical antibiotics), also in line with data from similar settings, showing that neurological failure at admission is associated with the onset of MSSA-VAP [START_REF] Zahar | Outcomerea Study Group. Is methicillin resistance associated with a worse prognosis in Staphylococcus aureus ventilator-associated pneumonia?[END_REF].

Our second hypothesis is that amoxicillin-clavulanic acid, which was more frequently used in case of oropharyngeal flora or Streptococcus identification, was less effective than antistaphylococcal beta-lactam (e.g. oxacillin or cloxacillin) for the treatment of MSSA, even both empirical choices judged appropriate. Indeed, despite the lack of randomized control trial, it has been demonstrated in retrospective [START_REF] Paul | Are all beta-lactams similarly effective in the treatment of methicillin-sensitive Staphylococcus aureus bacteraemia?[END_REF] and prospective [START_REF] Braquet | VIRSTA-AEPEI study group. Factors associated with 12 week case-fatality in Staphylococcus aureus bacteraemia: a prospective cohort study[END_REF] studies that using specific antistaphylococcal antibiotics, rather than amoxicillin-clavulanic acid or other betalactam-beta-lactamase, as first-line treatment of MSSA bacteraemia, was associated with higher treatment success and survival. In addition, in vitro data, showed that amoxicillinclavulanic acid, was more resistant to the inoculum effect and staphylococcal beta-lactamase than other antistaphylococcal antibiotics [START_REF] Sabath | Effect of inoculum and of beta-lactamase on the anti-staphylococcal activity of thirteen penicillins and cephalosporins[END_REF]. This hypothesis may challenges the choice of having preferred amoxicillin-clavulanic, as definitive antibiotic monotherapy, in case of oropharyngeal flora or Streptococcus co-infection.

Other pathogen -VAP

The main independent predictive factor of VAP relapse observed in the literature is the presence of an ARDS at the time of the first VAP diagnosis. Our results support also this finding, especially for the prediction of other pathogen -VAP. If longer duration of mechanical ventilation during ARDS could simply explain this result, other immunological explanations could be proposed. Indeed, alveolar neutrophils dysfunction during ARDS [START_REF] Matute-Bello | Neutrophil apoptosis in the acute respiratory distress syndrome[END_REF] may favour treatment failure or new infections. Moreover, adapting the two-hit inflammatory response model in major trauma, first hit (trauma) survivors, who underwent a second insult (e.g. ARDS), enter in an immunosuppressive state called Compensatory Anti-inflammatory Response Syndrome (CARS) [START_REF] Van Der Poll | Systemic inflammatory response syndrome and compensatory anti-inflammatory response syndrome in sepsis[END_REF]. This CARS is proportional to the initial inflammatory response [START_REF] Giannoudis | Current concepts of the inflammatory response after major trauma: an update[END_REF] and associated with the development of secondary infection [START_REF] Monneret | Persisting low monocyte human leukocyte antigen-DR expression predicts mortality in septic shock[END_REF]. As an illustration, it has been observed that Interleukine 6 plasma level of trauma patients at admission was associated with subsequent VAP treatment failure [START_REF] Cavalcanti | Risk and prognostic factors of ventilator-associated pneumonia in trauma patients[END_REF].

In this study, the need for emergent surgery was also an independent predictor of other pathogen -VAP and could be explained by the fact that intraoperative prophylactic antibiotic exposure may favour the emergence of MSSA [START_REF] Karaman | Effect of septoplasty and peroperative antibiotic prophylaxis on nasal flora[END_REF], and induce antibiotic resistance. In a cohort of patient with VAP caused by Pseudomonas aeruginosa, previous exposure to fluoroquinolone was associated with treatment failure [START_REF] Planquette | Pseudomonas aeruginosa Ventilator-associated Pneumonia. Predictive Factors of Treatment Failure[END_REF].

Finally, and after adjustments on variables associated with longer duration of mechanical ventilation (e.g. SAPS 2, initial Glasgow coma scale, presence of ARDS, need for emergent surgery) no causal relationship between MSSA-VAP relapse and duration of mechanical ventilation could have been demonstrated. This could be put in parallel with the fact that obvious reverse causality exists between MSSA-VAP relapse and duration of mechanical ventilation (one can favor the other reciprocally).

Limitations

Firstly, it was a retrospective study, which involves a potential bias in patient selection or data collection. Secondly, the lack of consensual definition of VAP-relapse in Guidelines [START_REF] Torres | International ERS/ESICM/ESCMID/ALAT guidelines for the management of hospitalacquired pneumonia and ventilator-associated pneumonia: Guidelines for the management of hospital-acquired pneumonia (HAP)/ventilator-associated pneumonia (VAP) of the European Respiratory Society (ERS), European Society of Intensive Care Medicine (ESICM), European Society of Clinical Microbiology and Infectious Diseases (ESCMID) and Asociación Latinoamericana del Tórax (ALAT)[END_REF] led us to establish specific definitions for our purpose adapted from those retained in recent international trial [START_REF] Kollef | Ceftolozane-tazobactam versus meropenem for treatment of nosocomial pneumonia (ASPECT-NP): a randomised, controlled, double-blind, phase 3, non-inferiority trial[END_REF] and other [START_REF] Combes | Early predictors for infection recurrence and death in patients with ventilator-associated pneumonia[END_REF][START_REF] Combes | Factors predicting ventilator-associated pneumonia recurrence[END_REF]. Thirdly, given the low ICU mortality rate observed in this study (8%), we decided to not analyse the association between MSSA-VAP relapse and mortality. Fourthly, we did not perform any assessment of nasal carriage of MSSA at ICU admission, which could have reinforced the aspiration hypothesis. Finally, there was no molecular typing of MSSA culture, no patient biological inflammatory response assessment and no antibiotic dosing. Thus, we could not exactly determine whether MSSA-VAP relapse observed was also eventually linked to specific patient factors (e.g. immunological response), treatment factors (e.g. appropriate antibiotics dosing), or bacterial factors (e.g. enhanced virulence).

Conclusion

Early and simply identifiable factors predict MSSA-VAP relapse and may prompt clinicians for optimized antibiotic administration and surveillance. Above all, these new findings pave the way for further studies that should clarify the pathophysiological mechanisms of MSSA-VAP relapse and may suggest to test new strategies in the choice of beta-lactam when facing MSSA-VAP associated with oropharyngeal flora or Streptococcus species.

Tables and Figures

Introduction

Background and objectives 3a

Explain the medical context (including whether diagnostic or prognostic) and rationale for developing or validating the multivariable prediction model, including references to existing models.

3b

Specify the objectives, including whether the study describes the development or validation of the model or both.

6-7

Methods

Source of data 4a

Describe the study design or source of data (e.g., randomized trial, cohort, or registry data), separately for the development and validation data sets, if applicable.

4b

Specify the key study dates, including start of accrual; end of accrual; and, if applicable, end of follow-up.

7-8

Participants 5a

Specify key elements of the study setting (e.g., primary care, secondary care, general population) including number and location of centres.

5b

Describe eligibility criteria for participants.

7-8 5c

Give details of treatments received, if relevant (antibiotics) 10

Outcome 6a

Clearly define the outcome that is predicted by the prediction model, including how and when assessed. 10 6b Report any actions to blind assessment of the outcome to be predicted. NA

Predictors 7a

Clearly define all predictors used in developing or validating the multivariable prediction model, including how and when they were measured.

9-10 7b

Report any actions to blind assessment of predictors for the outcome and other predictors. NA

Sample size 8

Explain how the study size was arrived at. NA

Missing data 9

Describe how missing data were handled (e.g., complete-case analysis, single imputation, multiple imputation) with details of any imputation method.

Participants 13a

Describe the flow of participants through the study, including the number of participants with and without the outcome and, if applicable, a summary of the follow-up time. A diagram may be helpful.

Fig 2 13b

Describe the characteristics of the participants (basic demographics, clinical features, available predictors), including the number of participants with missing data for predictors and outcome.

11

Model development 14a

Specify the number of participants and outcome events in each analysis.

11-12 14b

If done, report the unadjusted association between each candidate predictor and outcome. Table S3/S4

Model specification 15a

Present the full prediction model to allow predictions for individuals (i.e., all regression coefficients, and model intercept or baseline survival at a given time point). Discuss any limitations of the study (such as nonrepresentative sample, few events per predictor, missing data). 16

Interpretation 19b

Give an overall interpretation of the results, considering objectives, limitations, and results from similar studies, and other relevant evidence.

14-15

Implications 20 Discuss the potential clinical use of the model and implications for future research.

Figure 1 . 22 ]Figure 2 .Figure 3 .Figure 3 .

 122233 Figure 1. Definitions of methicillin sensitive staphylococcus aureus ventilator associated pneumonia (MSSA-VAP) treatment failure and Other pathogen -VAP, adapted from [22]

Fig S2/ 3 15b 10 Fig S2/ 3

 3103 Fig S2/3

  Figure S2. Area under the ROC (discrimination) of the multivariate logistic regression model for the prediction of methicillin sensitive Staphylococcus aureus -ventilator associated pneumonia (MSSA-VAP) treatment failure

Figure S3 .

 S3 Figure S3. Area under the ROC (discrimination) of the multivariate logistic regression model for the prediction of other pathogenventilator associtaed pneumonia (other pathogen -VAP).

Table 1 . Characteristics of the patients with and without methicillin sensitive staphylococcus aureus -ventilator associated pneumonia (MSSA-VAP) relapse

 1 Continuous variables are expressed as median (inter-quartile range) and categorical data as n (%). SAPS II, Simplified Acute Physiology Score II; ISS, Injury Severity Score; CGS, Coma Glasgow Score. MSSA-VAP, methicillin sensitive staphylococcus aureusventilator associated pneumonia

		Whole	MSSA-VAP relapse
	Variables	population n = 165	YES n = 54	NO n = 111
	Age, years	37 [23-53]	29 [22-49]	42 [24-55]
	Gender (male), %	126 (76)	46 (85)	80 (72)
	Comorbidities
	Chronic respiratory disease, n (%)	6 (4)	2 (4)	4 (4)
	Arterial hypertension, n (%)	30 (18)	7 (13)	25 (21)
	Diabetes, n (%)	10 (6)	1 (2)	9 (8)
	Admission for trauma	117 (71)	41 (76)	76 (68)
	Injury severity score	25 (18-29)	25 [18-29]	26 (19-41)
	Injury severity score >15, n (%)	113 (97)	38 (93)	75 (99)
	Brain trauma, n (%)	97 (83)	35 (85)	62 (82)
	Thoracic trauma, n (%)	56 (48)	21 (51)	35 (46)
	Abdominal and pelvic trauma, n (%)	44 (38)	15 (37)	29 (38)
	Spine trauma, n (%)	39 (33)	15 (37)	24 (32)
	Multiple trauma, n (%)	72 (62)	28 (68)	44 (58)
	Admission for non-traumatic brain injury, n (%)	48 (29)	13 (24)	35 (32)
	Subarachnoid haemorrhage, n (%)	22 (46)	4 (30)	18 (51)
	Intraparenchymal haemorrhage, n (%)	19 (40)	5 (38)	14 (40)
	Other, n (%)	7 (15)	3 (23)	4 (11)
	Severity at admission
	Simplified acute physiology score 2	37 (29-51)	35 [29-51]	35 (25-48)
	Acute respiratory failure, n (%)	26 (16)	7 (13)	19 (17)
	Glasgow coma scale, n (%)	11 (6-14)	9 (5-14)	14 (8-15)
	Need for vasopressors, n (%)	41 (25)	12 (22)	29 (26)
	Need for prehospital intubation, n (%)	118 (72)	40 (74)	78 (70)
	Need for emergent surgery, n (%)	137 (83)	52 (96)	85 (77)
	Characteristics of the first MSSA-VAP
	Time between intubation and MSSA-VAP, days	5 (3-7)	5 (3-5)	5 (3-7)
	Presence of ARDS, n (%)	28 (17)	16 (30)	12 (11)
	Quantity of MSSA in LRT (CFU/mL)	3.10 4 (4.10 3 -10 5 ) 3.10 4 (3.10 3 -10 5 ) 2.10 4 (2.10 3 -10 5 )
	Presence of other pathogens, n (%)	96 (58)	28 (52)	68 (61)
	Streptococcus species	22 (13)	10 (19)	11 (11)
	Oropharyngeal flora	22 (13)	7 (13)	15 (14)
	Enterobactericeae species	30 (18)	5 (9)	25 (23)
	Pseudomonas aeruginosa	9 (5)	0 (0)	9 (8)
	Initial antibiotic therapy
	Amoxicillin-clavulanic acid	75 (45)	30 (56)	45 (41)
	Cefepim	70 (42)	12 (43)	58 (42)
	Piperacillin-tazobactam	4 (2)	0 (0)	4 (4)
	Association of 2 antibiotic agents	101 (61)	30 (56)	71 (64)
	Aminosid	105 (64)	34 (63)	71 (64%)

Table 2 . Multivariable analysis of factors associated with methicillin sensitive staphylococcus aureus -ventilator associated pneumonia (MSSA-VAP) treatment failure and other pathogen VAP.

 2

		Prediction model of	Prediction model of
		MSSA-VAP treatment failure	Other pathogen -VAP
	Variables	OR (95%CI)	P value	OR (95%CI)	P value
	Age > 40 years-old	0.98 (0.95-1.01)	0.156	-	-
	Initial Glasgow coma scale	-	-	0.89 (0,81-0.97)	0.019
	Enterobacteriaceae in the MSSA-VAP	0.24 (0.03-1.01)	0.091	0.36 (0.09-1.06)	0.085
	Streptococcus in the MSSA-VAP	7.37 (1.15-51.75)	0.036	-	-
	Oropharyngeal flora in the MSSA-VAP	3.64 (1.14-11.47)	0.026	-	-
	Quantity of MSSA in the MSSA-VAP			0.99 (0.99-1)	0.299
	Need for emergent surgery	10.49 (1.56-247.19)	0.052	5.71 (1.48-37,97)	0.027
	ARDS associated with first MSSA-VAP	-	-	3.99 (1.53-10.83)	0.005
	Prehospital shock	0.27 (0.01-1.49)	0.222	-	-
	OR, odds ratio; CI, confidence interval; ARDS, acute respiratory distress syndrome

Acknowledgments

No specific acknowledgments

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflicts of interest/Competing interests disclosure

Maxens Decavèle, Nathalie Gault, Jean Denis Moyer, Maël Gennequin, Pierre-Antoine Allain and Arnaud Foucrier had no conflicts of interest to declare.