Norovirus Tracing in Environmental and Outbreak Settings - Experiences of waterborne, foodborne and nosocomial transmission
Abstract
Noroviruses (NoV), a major cause of acute gastroenteritis in hospital settings, also occur
as sporadic infections or periodic non-seasonal community outbreaks. Human NoV
replicates to high concentration in the intestinal tract, is readily transmitted by the
faecal-oral route, hand-to-hand contact, contaminated food and water, and by aerosols.
Large numbers of NoV are discharged into wastewaters and, despite sewage treatment,
can cause problems when recycled river waters are used as source of drinking water.
Two major groups of NoV are associated with human infections, genogroups (G) GI and
GII. Epidemiological studies indicate association of GI with non-seasonal food- and
waterborne infections, and GII with person-to-person transmission, particularly
nosocomial spread of NoV.
As NoV detection in filter-feeding bivalves may have a sentinel role in tracing NoV in
environmental waters, molecular tools were used to detect and characterize NoV in
mussels from Fotö near the plume of sewage effluents from Gothenburg wastewater
treatment plant. Sequence analyses of NoV RNA from Fotö mussels revealed GI.1 strains
with high similarity (99%, 3.1kb) to strains detected in patients infected in nonseasonal,
waterborne outbreaks linked to bathing in Lake Delsjö. Comparative sequence
analysis of NoV strains from mussels and patients indicated that human NoV outbreak
strains circulate in wastewaters, and can be traced in bivalves.
Molecular methods were used to characterize NoV detected in oysters implicated in a
gastroenteric outbreak where only those guests who ate oysters were affected. Mixed human
NoV GI and GII strains were found in the oysters, evidence of faecal contamination of the
bivalves, held for several weeks in Strömstad harbour waters. NoV GI.1 strains from the
oysters showed high similarity (≥ 99%, 285 nt) to the GI.1 detected in faeces obtained
from one of the oyster-eating patients. Phylogenetic analyses of GI.1 strains from patient
and oysters indicated the contaminated bivalves as point source of infection.
The similarity (99%, 3.1kb) of NoV GI.1 detected in Fotö mussels, patient samples from
Delsjö waterborne outbreak, and the Strömstad oyster outbreak, was remarkable. High
similarity held also when strains were compared with GenBank references; 96% with
L23828, from an oyster outbreak, Japan 1989; 87% with the original Norwalk strain
M87661, 1968, point source well water. These findings indicate genomic stability of NoV
GI.1 strains over a period greater than 20 years, and dispersal of GI.1 in environmental
waters.
Association of NoV GI strains with outbreaks related to sewage-contaminated water was
emphasized in the molecular epidemiology of a large, non-seasonal waterborne
outbreak affecting Lilla Edet, situated on the River Göta. Molecular studies revealed
marked genomic diversity of NoV GI strains in patient samples. Cloning was used to
confirm mixed GI infections including a new genotype, proposed NoV GI.9. Upstream
sewage contamination of recycled river water and disinfection problems at the
municipal drinking water treatment plant precipitated the outbreak.
In contrast study of NoV infections in hospital settings showed predominance of GII.4
strains in symptomatic patients and their environment. High similarity (≥99.5%, 1040
nt) was found between GII.4 variant strains from patients, and strains from dust, air, and
surfaces in the patient's room. GII.4 strains detected in symptomatic patients in 8 wards
during the 5-month study clustered on 11 sub-branches of the phylogenetic tree. One of
the wards, a control, was not affected by nosocomial spread of NoV GII.4. High similarity
of GII.4 strains from patients and their hospital room environment, in a given ward at a
given time, confirmed nosocomial transmission and indicated the need for
interventional cleaning studies.
To summarize, NoV tracing provided strong evidence of bioaccumulation of outbreakrelated
NoV strains in mussels growing near sewage effluents. High similarity of NoV
strains from oysters implicated in a NoV outbreak and from an infected patient,
indicated transmission of NoV from oysters to humans, confirming high stability of GI.1
strains in oysters, water and mussels. Cloning confirmed mixed NoV GI infections in
patients from a waterborne outbreak, strengthening indices of an outbreak caused by
sewage-contaminated drinking water. High similarity of NoV GII.4 strains detected in
patients and their hospital room environment, confirmed local nosocomial transmission.
Parts of work
I. Nenonen NP, Hannoun C, Horal P, Hernroth B, Bergström T. Tracing of norovirus outbreak strains in mussels collected near sewage effluents. Applied Environmental Microbiology 2008; 74(8): 2544-2549. ::PMID::18310420 II. Nenonen NP, Hannoun C, Olsson MB, Bergström T. Molecular analysis of an oyster-related norovirus outbreak. Journal of Clinical Virology 2009; 45(2): 105-108. ::PMID::19451026 III. Nenonen NP, Hannoun C, Larsson CU, Bergström T. Marked genomic diversity of norovirus genogroup I strains in a waterborne outbreak. Applied Environmental Microbiology 2012; 78(6): 1846-1852. ::PMID::22247153 IV. Nenonen NP, Hannoun C, Svensson L, Torén K, Andersson LM, Westin J. Bergström T. Norovirus GII.4 detection in environmental samples from patient rooms during nosocomial outbreaks. Journal of Clinical Microbiology 2014; 52(7) 2352–2358. ::PMID::24759712
Degree
Doctor of Philosophy (Medicine)
University
University of Gothenburg. Sahlgrenska Academy
Institution
Institute of Biomedicine. Department of Infectious Diseases
Disputation
Fredagen den 22 maj 2015, kl 09.00, Föreläsningssal vån 3, Mikrobiologen, Guldhedsgatan 10b, Göteborg..
Date of defence
2015-05-22
nancy.nenonen@microbio.gu.se
Date
2015-05-04Author
Nenonen, Nancy P.
Keywords
Norovirus
tracing
environment
foodborne
outbreak
waterborne
nosocomial
mussels
GI.1
oysters
GII.4
dust
surfaces
air
molecular epidemiology
Publication type
Doctoral thesis
ISBN
978-91-628-9419-1 (printed)
978-91-628-9420-7 (e-pub)
Language
eng