60 Serratia marcescens: An emerging pathogen or innocent bystander?

Objective Serratia marcescens (SM) is a Gram-negative organism which is known to cause hospital-acquired infections. Its incidence in CF lung infections is low and as such determining its effect on CF disease is difficult. This study aimed to examine risk factors for acquisition of SM and the clinical effect of infection. Methods A retrospective review of case notes of all patients who isolated SM in the years 2008–14 was made in a single adult CF centre. Data was compared with controls matched for age, sex and lung function. Results 14 patients had at least one isolate of SM over the study period. Five were single isolates, 3 had intermittent isolates and 6 were chronically infected. Median age (IQR) at isolation was 24 yrs (16.8–32.5). Eight were male. Median FEV 1 at isolation was 2.1 L (1.3–2.6), median FEV 1 % predicted was 52% (30–81). No significant differences between cases and controls(n = 28) at first isolation were seen for the rates of pancreatic insufficiency, CF-related diabetes, ABPA or CF-related diabetes. Equally no differences were seen in the rates of use of mucolytics, inhaled/oral antibiotics or steroid use. A comparison of spirometry revealed no differences in FEV 1 between controls, single isolates and intermittent/chronic infection in the 2 years following infection. Conclusion In this small single-centre study, no significant risk factors for the isolation of SM were seen. Furthermore, isolation of SM had no significant effect on lung function. Specific inclusion of SM infection in CF registries will allow larger studies to determine whether this organism is truly pathogenic.