title: Contributing and Terminating Factors of a Large RSV Outbreak in an Adult Hematology and Transplant Unit.
abstract: BACKGROUND
  In January 2012, an increase of respiratory syncytial virus (RSV) infections on an adult hematology and transplant unit in a German university hospital was detected. We investigated the outbreak to assess its timing and extent and to identify risk factors for transmission.
  
  
  METHODS
  We tested and typed patient samples pro- and retrospectively for RSV. We conducted a cohort and a case-control study. A confirmed outbreak case had laboratory-diagnosed, nosocomially-acquired RSV infection. Possible outbreak cases had pneumonia but were not laboratory-confirmed.
  
  
  RESULTS
  Of 53 outbreak cases, 36 (68%) were confirmed and 17 (32%) possible. Retrospective testing and chart review dated the beginning of the outbreak to November 2011. Patients with community-acquired RSV infection were identified when the community epidemic began in January 2012. In multivariable analysis (controlling for contact with medical personnel, hygiene behaviour and age) patients with active social behaviour were more at risk for RSV infection (odds ratio 23.8, 95% confidence interval, 1.3 to 434.9; p-value, 0.03). Confirmed outbreak cases were more likely than controls to have been accomodated together with a confirmed or possible case before their onset of illness (OR 9.3, 95%CI: 2.1-85.1; p<0.001). Control measures, including isolation of every patient in the unit, initiated until the end of January terminated the outbreak.
  
  
  CONCLUSIONS
  Epidemiological investigations revealed co-accomodation with a case-patient and active social behaviour as likely risk factors for RSV infection. Awareness of and vigorous testing for respiratory viruses in immunosuppressed hospitalised patients is necessary to timely detect cases with outbreak potential. Isolation of patients with respiratory infectious illnesses is crucial to prevent the continuation or occurrence of outbreaks.