Aportación del laboratorio de microbiología al diagnóstico de la neumonía asociada a la ventilación mecánica

Colonization of the nasal airways by Staphylococcus aureus on admission to a major heart surgery operating room: A real-world experience

INTRODUCTION

Nasal swab culture is used to identify Staphylococcus aureus colonization, as this is a major risk factor for surgical site infection (SSI) in patients who are going to undergo major heart surgery (MHS). We determined nasal carriage of S. aureus in patients undergoing MHS by comparing the yield of a conventional culture with that of a rapid molecular test (Xpert® SA Nasal Complete, Cepheid).

METHODS

From July 2015 to April 2017, all patients who were to undergo MHS were invited to participate in the study. We obtained two nasal cultures from each patient just before entering the operating room, independently of a previous test for the determination of nasal colonization by this microorganism performed before surgery. One swab was used for conventional culture in the microbiology laboratory, and the other was used for the rapid molecular test. We defined nasal colonization as the presence of a positive culture for S. aureus using either of the two techniques. All patients were followed up until hospital discharge or death.

RESULTS

Overall, 57 out of 200 patients (28.5%) were colonized by S. aureus at the time of surgery. Thirty-three patients had both conventional culture- and PCR-positive results. Twenty-four patients had a negative culture and a positive PCR test. Only twenty-one percent (12/57) of colonized patients had undergone an attempt to decolonise before the surgical intervention.

CONCLUSION

A significant proportion of patients undergoing MHS are colonized by S. aureus in the nostrils on entering the operating room. New strategies to prevent SSI by this microorganism are needed. Rapid molecular tests immediately before MHS, followed by immediate decolonisation, must be evaluated. Trial Registration Clinical Trials.gov NCT02640001.

[Bronchoalveolar lavage for diagnosing pneumonia in mechanically ventilated patients]

OBJECTIVE

To evaluate the diagnostic role of bronchoalveolar lavage (BAL) in mechanically ventilated patients with suspected pneumonia and to describe the clinical outcome in the different kinds of pneumonia in critically ill patients.

DESIGN

Descriptive study.

SETTING

A 17-bed medical and surgical intensive care unit.

PATIENTS

Mechanically ventilated patients admitted to the ICU from November 2003 to March 2006 with suspected pneumonia who underwent bronchoscopy with BAL.

INTERVENTIONS

BAL was performed by fiberoptic bronchoscopy with three aliquots of 50 ml sterile normal saline. Recovered BAL fluid was pro-cessed for microbiologic analysis.

MAIN VARIABLES OF INTEREST

Age, APACHE II score within the first 24 hours of admission, time on mechanical ventilation, ICU length of stay, mortality, and isolated bacteria were analyzed.

RESULTS

A total of 96 cases of suspected pneumonia with BAL were recruited, including 4 groups: community associated pneumonia (CAP), 12 cases, early-onset ventilator-associated pneumonia (VAP), 26 cases, late-onset ventilator-associated pneumonia, 43 cases, and immunocompromised patients, 15 cases. BAL was positive (> 10000 ufc/ml) in 40 (41.7%) patients (2, 16, 17 and 5 patients with CAP, early-onset VAP, late-onset VAP and immunocompromised, respectively). Mortality was 33.3%, 26.9%, 25.6% and 73.3% in CAP, early-onset VAP, late-onset VAP and immunocompromised patients respectively.

CONCLUSIONS

The low incidence of positive BAL in the CAP group supports using BAL only for particularly severe, selected cases. Mortality was very high in the immunocompromised patients. In the light of our personal experience, BAL is most useful in the diagnosis of pneumonia in the group of patients with VAP.

[Microbiological diagnosis of bacterial lower respiratory tract infections]

Microbiological diagnosis of bacterial lower respiratory tract infections has relevant limitations and related controversy, depending on the clinical setting and diagnostic methods used, and its value is contingent on an accurate clinical diagnosis and previous antimicrobial therapy. The limitations reside in a low diagnostic yield of the causative agent and the difficulty of determining the clinical significance of the agents recovered. This report examines the current microbiological diagnostic yield of the main clinical entities and etiological agents, indications for invasive or non-invasive specimen collection procedures, and proper specimen processing and culture in the appropriate media. Criteria regarding specimen suitability and indications for quantitative cultures are established. Criteria for evaluating the results are provided, and the current fast diagnostic techniques are described.