Two nosocomial norovirus outbreaks in the neonatal intensive and intermediate care unit

Abstract

Norovirus is one of the major causes of non-bacterialacute gastroenteritis worldwide. Diagnostic methods in-clude electron microscopy, enzyme-linked immunosorbentassay (ELISA) and reverse-transcription polymerase chainreaction (RT-PCR) [1]. Electron microscopy has previous-ly been regarded as the gold standard for the diagnosis ofnorovirus, but RT-PCR appears to be a more sensitiveassay (36 to 58% versus 94 to 98%), with similarspecificity(96to98%and92to100%)[2, 3]. Studieson the sensitivity and specificity of the RIDASCREENenzyme immunoassay reported a broad range of 36 to 59%and73to100%,respectively[4, 5] (CDC, Atlanta, GA,USA). However, data for preterm and term born babies israre. Recent studies of norovirus in very young infantshave presumed many false-positive results and havequestioned the high specificity of enzyme immunoassay[2, 6]. The aim of this report is to characterise twooutbreaks of norovirus in neonatal nurseries by raisingquestions about the performance of diagnostic assays fornorovirus and the clinical presentation of norovirusinfectioninveryyounginfants.Faecal specimens of all tested persons were sent to theInstitute of Hygiene, Microbiology and EnvironmentalMedicine of the Medical University of Graz immediatelyafter collection or on the following day. Analysis wasdone for norovirus, adenovirus and rotavirus using anenzyme immunoassay (RIDASCREEN Norovirus ELISAkit, 3rd Generation) and/or real-time PCR (ANDIATECNorovirus real-time PCR kit, Bioproducts Company,designed to detect norovirus genotypes I and II). There-fore, stool cultures on bacteria and parasites were alsodone. To assess the clinical severity of disease, a 14-pointscoring system by Colomba et al. [7] was used. Duringboth outbreaks, the clinical records of all patients werecarefully documented and strict hygienic measures, in-cluding the cohorting of patients, mandatory use of glovesand gowns, and hand washing with disinfecting agents(Skinman® Soft N, Ecolab, Vienna, Austria), wereimplemented at the particular unit. Approval by theEthical Review Board was not necessary since the studywas performed by means of prospective surveillanceinvolving both outbreaks.First outbreak: January to March 2007In January 2007, a neonatologist on duty developedsymptoms of gastroenteritis, including fever, vomiting anddiarrhoea. The day after, the index patient (see Table 1),hospitalized at the Neonatal Intensive Care Unit (NICU) ofthe Pediatric Department of the Medical University Hospi-tal of Graz, Austria, recalled symptoms of bloody tingedstools for one day (14-point severity score: 6). Faecalspecimens of this infant and of the staff member were testedon virus, bacteria and parasites, and turned out to bepositive for norovirus tested by ELISA. Subsequently,faecal specimens of all neonates admitted to and treated atthe NICU were routinely tested three times a week byELISA and, due to repeatedly positive results, some of thespecimens were additionally tested by RT-PCR.