Routine use of Staphylococcus aureus rapid diagnostic test in patients with suspected ventilator-associated pneumonia

In patients with ventilator-associated pneumonia (VAP), administration of an appropriate empirical antimicrobial treatment is associated with improved outcomes, leading to the prescription of broad-spectrum antibiotics, including a drug active against methicillin resistant Staphylococcus aureus (MRSA). In order to avoid the overuse of antibiotics, the present study aimed to evaluate the technical characteristics of a rapid diagnostic test (Cepheid Xpert assay) in patients with suspected VAP.

From June 2011 to June 2012, in patients with suspected VAP, a sample from the bronchialalveolar lavage (BAL) or miniBAL was tested in a point-of-care laboratory for a rapid diagnostic test of methicillin susceptible Staphylococcus aureus (MSSA) and MRSA. Then, the result was compared to the quantitative culture with a threshold at 10⁴ colony-forming units per milliliter for bronchoalveolar lavage and 10³ colony-forming units per milliliter for minibronchoalveolar lavage. The study was performed in three intensive care units at two institutions.

Four hundred, twenty-two samples from 328 patients were analyzed. The culture of 6 (1.1%) and 28 (6.5%) samples were positive for MRSA and MSSA. The test was not interpretable in 41 (9.3%) patients. The negative predictive values of the rapid detection test were 99.7% (98.1 to 99.9%) and 99.8% (98.7 to 99.9%) for MSSA and MRSA, respectively.

The rapid diagnostic test is reliable in excluding the presence of MSSA and MRSA in the samples of patients with suspected VAP. Its utility should be regarded depending on the prevalence of MRSA.