title: Evaluation of the impact of the source (patient versus staff) on nosocomial norovirus outbreak severity.
abstract: OBJECTIVE
  To study the dependence of infection risk and outbreak size on the type of index case (i.e., patient or staff).
  
  
  METHODS
  Nosocomial outbreaks were reviewed and categorized into those started by patients and those started by staff. Infection risks and outbreak sizes were evaluated taking into account the index case category.
  
  
  RESULTS
  Of the 30 nosocomial outbreaks of norovirus with person-to-person transmission, 20 (67%) involved patients as the index cases. Patient-indexed outbreaks affected significantly more patients than did staff-indexed outbreaks (difference in means, 16.25; 95% confidence interval [CI95], 5.1 to 27.0). For the numbers of affected staff, no dependence on the index case category was detectable (difference in means, -1.05; CI95, -9.0 to 6.9). For patients exposed during patient-indexed outbreaks, the risk of acquiring a norovirus infection was approximately 4.8 times as high as the corresponding risk for patients exposed during staff-indexed outbreaks (odds ratio [OR], 4.79; CI95, 1.82 to 8.28). The infection risk for exposed staff during patient-indexed outbreaks was approximately 1.5 times as high as the corresponding risk during staff-indexed outbreaks (OR, 1.51; CI95, 0.92 to 2.49).
  
  
  CONCLUSIONS
  Patient-indexed norovirus outbreaks generally affect more patients than do staff-indexed outbreaks. Staff appear to be similarly affected by both outbreak index category groups. This study demonstrates the importance of obtaining complete outbreak data, including the index case classification as staff or patient, during norovirus outbreak investigations. Such information may be useful for further targeting prevention measures
authors.affiliation: Institut für Medizinische Mikrobiologie und Krankenhaushygiene, Medizinische Hochschule Hannover, Hannover, Germany. mattner.frauke@mh-hannover.de
authors.forename: Frauke
authors.initials: F
authors.lastname: Mattner
authors.forename: Lutz
authors.initials: L
authors.lastname: Mattner
authors.forename: Hans Ulrich
authors.initials: HU
authors.lastname: Borck
authors.forename: Petra
authors.initials: P
authors.lastname: Gastmeier
mesh_terms: D001315:Australia / Q000453:epidemiology; D017250:Caliciviridae Infections / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission; D002170:Canada / Q000453:epidemiology; D003428:Cross Infection / Q000517:prevention & control / Q000821:virology*; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D005060:Europe / Q000453:epidemiology; D005759:Gastroenteritis / Q000453:epidemiology / Q000517:prevention & control; D006801:Humans; D017758:Infectious Disease Transmission, Patient-to-Professional / Q000517:prevention & control / Q000706:statistics & numerical data; D029322:Norovirus / Q000302:isolation & purification*; D014481:United States / Q000453:epidemiology