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2015-03-05
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INFLUENCE OF SCHOOL YEAR ON
SEASONALITY OF NOROVIRUS OUTBREAKS
IN DEVELOPED COUNTRIES
Roni Kraut MD, Kate Snedeker PHD and
Lance Honish MSc, CPHI(C)
February 26, 2015
Conflict of Interest
Presenter: Roni Kraut
Relationships with commercial interests:
• Grants / Research Support: None
• Speakers Bureau / Honoraria: None
• Consulting Fees: None
• Other: None
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Norovirus
Norovirus
1. Siebenga JJ, et al. Norovirus illness is a global problem: emergence and spread of
norovirus gii.4 variants, 2001-2007. Journal of Infectious Diseases 2009; 200: 802-812.
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Norovirus
1http://www.cdc.gov/norovirus/trends-outbreaks.html#outbreaks
Alberta Norovirus outbreaks 2002-2012
0
50
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450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
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Alberta Norovirus outbreaks 2002-2012
0
50
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450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Alberta Norovirus outbreaks 2002-2012
0
50
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450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
60%
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Alberta Norovirus outbreaks 2002-2012
0
50
100
150
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450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Alberta Norovirus outbreaks 2002-2012
0
50
100
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400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
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Objective
• Is the observed seasonal increase in norovirus
outbreaks in Alberta, Canada and selected nations
temporally correlated with the start of the public school
year.
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Methods
• Search of Medline
• Study selection criteria:
• monthly norovirus outbreak for a minimum of 3 years in a developed country
• included all reported norovirus outbreaks from a specific region, lab, or reporting body
• encompassed all norovirus strains
• outbreaks for each month were extractable
• Alberta outbreaks were obtained from the Alberta Communicable Disease Reporting System (acknowledgement: Alberta Health).
Methods
0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
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Methods
2%6%
18%
23%
18%
8% 7%5% 5%
3% 3% 2%0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Methods
2%6%
18%
POM
18%
8% 7%5% 5%
3% 3% 2%0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
POM: peak outbreak month
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Methods
2%6%
18%
POM
18%
8% 7%5% 5%
3% 3% LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
POM: peak outbreak month
LOM: lowest outbreak month
Methods
2%6%
18%
POM
18%
8% 7%5% 5%
3% 3% LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
: 5.6%
POM: peak outbreak month
LOM: lowest outbreak month
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Methods
2%SMS
18%
POM
18%
8% 7%5% 5%
3% 3% LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
: 5.6%
POM: peak outbreak month
LOM: lowest outbreak month
SMS: start month of seasonality
Results
Medline search June 21, 2014
489 papers
49
3
3
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Results
SMS
POM
LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Results
SMS
POM
LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Median: 2 months
Interquartile range: 2.0 - 3.5 months
Spearman correlation coefficient: 0.67725
P value: 0.0020
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Results
POM
LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Results
POM
LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Median: 4 months
Interquartile range: 3.0 – 4.8 months
Spearman correlation coefficient: 0.65995
P value: 0.0021
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Results
SMSP
POM
LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Results
SMS
POM
LOM0
50
100
150
200
250
300
350
400
450
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Median: 1 month
Interquartile range: 0 – 1 month
Spearman correlation coefficient: 0.54084
P value: 0.0168
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Results: subgroup analysis
All locations besides Oceania
Oceania
sep oct nov dec jan feb march april may june july august
SMS POM LOM
feb march april may june july august sep oct nov dec jan
LOM SMS POM
Results: subgroup analysis
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Results: subgroup analysis
Limitation
• Unclear whether this is a cause and effect
relationship.
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Conclusion
The congregation of children in schools may be a
key factor in the seasonality of norovirus outbreaks
in developed countries.
Acknowledgement
• Larry Svenson, Alberta Health and Dr. Gerry Predy, Alberta Health Services for their support and resources
• Anthony Mounts for clarification of his research methodology
• Dale Storie, medical librarian at University of Alberta, for assistance with the literature search
• Dr. Mike Allan and Dr. Tina Korownyk for help with the presentation
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Questions?
References
Siebenga JJ, et al. Norovirus illness is a global problem: emergence and spread of norovirusgii.4 variants, 2001-2007. Journal of Infectious Diseases 2009; 200: 802-812.
(http://www.cdc.gov/norovirus/trends-outbreaks.html#outbreaks). Accessed 11/01, 2014.
Ahmed SM, Lopman BA, Levy K. A Systematic Review and Meta-Analysis of the Global Seasonality of Norovirus. PLoS ONE. Published online: October 2013. doi:10.1371/journal.pone.0075922
London WP, Yorke JA. Recurrent outbreaks of measles, chickenpox and mumps. I. Seasonal variation in contact rates. American Journal of Epidemiology 1973; 98: 453-468.
Earn DJD, et al. Effects of school closure on incidence of pandemic influenza in Alberta, Canada. Annals of Internal Medicine 2012; 156: 173-181.
Mikolajczyk RT, et al. Social contacts of school children and the transmission of respiratory-spread pathogens. Epidemiology and infection 2008; 136: 813-822.
Chao DL, Halloran ME, Longini Jr. IM. School opening dates predict pandemic influenza A(H1N1) outbreaks in the United States. Journal of Infectious Diseases 2010; 202: 877-880.
Wu JT, et al. School closure and mitigation of pandemic (H1N1) 2009, Hong Kong. Emerging Infectious Diseases 2010; 16: 538-541.
