Risk factors for acquisition of Serratia marcescens in a surgical Intensive Care Unit

Between January 1996 and May 1997, a four-fold increased rate of isolation of Serratia marcescens was observed amongst patients admitted to the surgic al Intensive Care Unit (SICU) of the Leiden University Medical Center compa red to the preceding years. Random amplification of polymorphic DNA showed the involvement of genotypically distinct strains, implicating multiple dif ferent sources. After improvement of hygienic measures the frequency of iso lation of S. marcescens returned to baseline. A case-control study was perf ormed to assess patient-related risk factors for acquisition of S. marcesce ns. Nineteen cases and 38 controls were included. Hospital-and SICU-stay we re significantly longer in case patients than in controls. By univariate an alysis, statistically significant differences were found in body weight, th e duration of mechanical ventilatory support, the cumulative use of antimic robial agents, the use of aminoglycosides, parenteral nutrition and tube fe eding. The sum of the number of days per invasive device (deep intravenous lines, arterial lines, wound drains and urinary catheters) was higher in ca ses than in controls (P=0.08). Categorically, a cumulative number of device -days :>25 was a statistically significant risk factor for acquisition of S . marcescens. Multivariable logistic regression analysis showed that body w eight, parenteral feeding and mechanical ventilation were independent predi ctors of acquisition of S. marcescens. As transmission of S. marcescens app ears to be by the hands of personnel, the identified risk factors may act b y necessitating an increased frequency and intensity of direct contacts.