Epidemiology and Clinical Outcomes of Serratia marcescens Infections in Adults with Cystic Fibrosis

Background:

Cystic fibrosis (CF) airway infections are often viewed as being confined to a few classical pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus, Burkholderia cepacia complex, and Stenotrophomonas maltophilia. However, a range of other organisms are commonly observed in CF; organisms where the epidemiology, natural history and clinical consequences are not understood. Herein we sought to characterize Serratia marcescens infections in adults with CF.

Methods:

We retrospectively audited the Calgary Adult CF program clinical records to identify patients with a history of sputum S. marcescens isolation. Baseline demographics were assessed. We compared those with sustained infection to patients with only transient isolation, as well as to age and time-matched patients with no history of S. marcescens infection to identify risk factors for infection and various outcomes such as lung function decline, mortality and lung transplantation.

Results:

Over the study period 9.4% of patients (29/318) had sputum positive on at least one occasion for S. marcescens. While 18 patients had transient infections clearing immediately, 11 patients had sustained infection (median 9.1 months, IQR 5-30 months). Pulmonary exacerbation was only observed in 48% of cases at incident isolation and did not differ significantly between incident transient and sustained infections. From the time of incident isolation, the number of pulmonary exacerbations was significantly increased in the following year in only those with transient infection. Compared to matched controls without S. marcescens, patients with sustained infection did not differ significantly in 5-year mortality (45% vs. 23%, p=0.64) or lung transplantation (18% vs. 0%, p=0.11).

Conclusion:

S. marcescens was identified as a relatively common organism from sputum culture in patients with CF. Approximately one third of patients experienced prolonged carriage of the organisms in their lower airways, but none persisted indefinitely with all eventually clearing infection. No evidence of short or long-term deleterious consequences were noted in our cohort.