On norovirus outbreaks and transmission in hospitals

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Noroviruses are now the leading cause of gastroenteritis worldwide. Noroviruses are effectively transmitted due to a low infectious dose, viral shedding in high concentrations, environmental stability, and they induce only a limited immunity after infection. Especially, the norovirus variants of genotype II.4 (GII.4) have seemed greatly adapted for pandemic spread. The high infectivity of noroviruses result in frequent outbreaks, particularly at healthcare facilities. Hospital norovirus outbreaks cause excess morbidity among vulnerable inpatients, ill staff, shortage of beds and economic loss.

In the first study, using two outbreak surveillance methods, based on either clinical reporting or clustering of positive laboratory results, incidence of norovirus outbreaks at all hospital wards in Skåne was estimated to 0.5 to 0.2 per ward and winter season, 2010-2012. In total, 135 outbreaks were detected, 74 with both methods, 18 only by clinical reporting and 43 only with laboratory surveillance. Laboratory surveillance performed better at identifying outbreaks and seem a stable option for continuous surveillance, but the combination of both surveillance methods would be preferred.

In the second study, the first patient in each outbreak (n 65), was compared with patients not involved in any outbreak (n 186), to analyse factors associated with outbreak development. Sharing room with other patients, old age, comorbidities, onset of disease at the ward and vomiting were independently associated with an outbreak outcome. Infection with norovirus GII.4 was associated with outbreak development and vomiting, suggesting a possible explanation for the efficient transmission of GII.4 in hospitals.

In a third study, aspects of possible airborne transmission was investigated, by analysis of air samples collected in the proximity of 26 norovirus patients. Norovirus genome in the air was a common finding during outbreaks, supporting the hypothesis that airborne transmission might be of importance. The size of the norovirus carrying particles and the concentration of norovirus genomes in air allow for the possibility of airborne transmission. A short time period since the last vomiting event in the room was associated with norovirus positive air samples, indicating vomiting as the major source of airborne norovirus.

In the final study, aspects of environmental transmission was explored. Different exposures related to room admission and association to norovirus acquisition at the ward were analysed. A room stay at a room with a prior occupant with norovirus infection was a small but independent risk factor for acquisition of norovirus infection. Norovirus acquisition was not observed in association to sharing room with patients with recently resolved symptoms of norovirus infection.

In conclusion, prevention of hospital outbreaks may be improved by better recognition of factor associated with outbreak development and improved surveillance. Airborne transmission and dissemination of norovirus, originating from vomiting events, may be an important mode of transmission, but further studies are needed. Environmental transmission from prior room occupants stress cleaning and disinfection as important preventive measures.
Original languageEnglish
Awarding Institution
  • Department of Clinical Sciences, Lund
  • Böttiger, Blenda, Supervisor
  • Inghammar, Malin, Assistant supervisor
  • Johansson, Hugo, Assistant supervisor
Award date2019 Oct 25
Place of PublicationLund
ISBN (Print)978-91-7619-827-8
Publication statusPublished - 2019

Bibliographical note

Defence details
Date: 2019-10-25
Time: 13:00
Place: Belfragesalen, BMC D15, Klinikgatan 32 i Lund
External reviewer(s)
Name: Westin, Johan
Title: professor
Affiliation: Department of Infectious Disesese / Clinical Virology, Gothenburg

Subject classification (UKÄ)

  • Infectious Medicine
  • Public Health, Global Health, Social Medicine and Epidemiology
  • Microbiology in the medical area

Free keywords

  • norovirus
  • outbreaks
  • transmission
  • surveillance
  • prevention


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