Concordance between superficial swab and deep sampling in post-sternotomy mediastinitis: Single center experience

Deep sampling (DS) is the gold standard for microbiological diagnosis of post-sternotomy mediastinitis (PSM), however superficial swab (SS) are frequently performed in some centers and antibiotherapy initiated base on their results. We analysed the concordance between superficial swab and deep sampling in PSM.

We analysed retrospectively patients with a PSM between 2010 and 2014 at Saint-Luc University hospital (Belgium). We considered that there was a concordance between SS and DS when the same microorganism was found in the two sampling method in each patient. Patients were stratified in six groups according to microbiology results as Staphylococcus Aureus (SA) sensitive or resistant, coagulase negative Staphylococcus (CoNS), Gram negative bacilli (GNB), other Gram positive bacteria (GPB) and fungi.

Thirty-six patients were included. Twenty-five men (69%) and a mean age of 66 years old. The overall concordance between SS and DS was 57%. SA and GNB showed high concordance (100% and 85.7% respectively). For the other groups the concordance was low. The sensitivity and specificity of SS was 97% and 33% respectively. The PPV and NPV of superficial swab was 96% and 50% respectively.

Microbiological results from SS, even with flocked swabs, except for SA and GNB have low concordance with those obtained from deep sampling. Our data confirm that in PSM, deep sampling is the gold standard for microbiological assessment.