Molecular detection of Staphylococcus aureus in urine in patients with S. aureus bacteremia: an exploratory study

Staphylococcus aureus bacteremia (SAB) is associated with a 90-day mortality of 28-34%. Many SAB-patients (7.8-39%) have a secondary S. aureus bacteriuria (SABU) mainly without symptoms of a urinary tract infection. Due to high morbidity and mortality, there is an interest in rapid detection of S. aureus bacteremia. Here, we compared a rapid nucleic acid amplification test (NAAT) with conventional culture to detect S. aureus in urine and to identify cases with increased risk for SAB.

In a cross-sectional study, we assessed urine samples (mid-stream, clean catch and catheter urine) of patients with SAB and bacteremia other than SAB (non-SAB). Urine samples were collected ± 3 days to the collection of the positive blood culture and were cultured on a set of selective and non-selective agar plates. NAAT was performed using a commercial test (Xpert^® SA Nasal Complete G3, Cepheid) from a sterile swab soaked in urine.

We included samples from 100 patients (68% male, median age: 67.4 years) with SAB and 20 patients (75% male, median age: 65.84 years) with non-SAB. The sensitivity of detecting SAB from urine samples was 47% (specificity: 90%) for NAAT, when applying a Ct-value of ≤ 37.4 for positive results. Urine culture had a sensitivity of 25% and a specificity of 95%. Molecular and culture methods showed a moderate agreement (80%, Cohens kappa: 0.55).

NAAT from urine has a higher sensitivity than culture in patients with SAB and could potentially identify cases with increased risk for SAB. Future studies should investigate whether this characteristic could translate into a clinical benefit through rapid detection of SAB.