Validation of a New PCR-Based Screening Method for Prevention of <b><i>Serratia marcescens</i></b> Outbreaks in the Neonatal Intensive Care Unit

<b><i>Background:</i></b> <i>Serratia marcescens</i> may cause severe nosocomial infections, mostly in very low birth weight infants. Since <i>S. marcescens</i> exhibits by far the highest adjusted incidence rate for horizontal transmission, it can cause complex outbreak situations in neonatal intensive care units. <b><i>Objective:</i></b> The aim of this study was to establish a fast and highly sensitive colonization screening for prompt cohorting and barrier nursing strategies. <b><i>Methods:</i></b> A probe-based duplex PCR assay targeting the 16S <i>rRNA</i> gene of <i>S. marcescens</i> was developed and validated by using 36 reference strains, 14 <i>S. marcescens</i> outbreak- and nonoutbreak isolates, defined by epidemiological linkage and molecular typing, and applied in 1,347 clinical specimens from 505 patients. <b><i>Results and Conclusions:</i></b> The novel PCR assay proved to be highly specific and had an in vitro sensitivity of 100 gene copies per reaction (∼15 bacteria). It showed a similar (in laryngeal/tracheal specimens) or even higher (in rectal/stoma swabs) in vivo sensitivity in comparison to routine microbial culture and was much quicker (&#x3c;24 h vs. 2 days). By combining different oligonucleotide primers, there was robust detection of genetic variants of <i>S. marcescens</i> strains. PCR inhibition was low (1.6%) and observed with rectal swabs only. Cohort analysis illustrated applicability of the PCR assay as a quick tool to prevent outbreak scenarios by allowing rapid decisions on cohorting and barrier nursing. In summary, this novel molecular screening for colonization by <i>S. marcescens</i> is specific, highly sensitive, and substantially accelerates detection.