Household Transmission of H1N1 Influenza in Ontario
Author Information
Author(s): Rachel Savage, Michael Whelan, Ian Johnson, Elizabeth Rea, Marie LaFreniere, Laura C Rosella, Freda Lam, Tina Badiani, Anne-Luise Winter, Deborah J Carr, Crystal Frenette, Maureen Horn, Kathleen Dooling, Monali Varia, Anne-Marie Holt, Vidya Sunil, Catherine Grift, Eleanor Paget, Michael King, John Barbaro, Natasha S Crowcroft
Primary Institution: Ontario Agency for Health Protection and Promotion
Hypothesis
What are the secondary attack rates of pandemic influenza A (H1N1) among household contacts?
Conclusion
Secondary attack rates for pandemic influenza A (H1N1) were comparable to seasonal influenza estimates, suggesting similarities in transmission.
Supporting Evidence
- Secondary attack rates were estimated at 10.3% for influenza-like illness and 20.2% for acute respiratory illness.
- Children under 16 years had significantly higher attack rates compared to adults.
- The median time between symptom onset in the primary case and the secondary case was estimated at 3.0 days.
Takeaway
When someone in a household gets the H1N1 flu, there's a good chance others in the house will catch it too, especially kids.
Methodology
The study involved contact tracing of laboratory-confirmed H1N1 cases among household contacts in Ontario, with data collected through interviews and standardized questionnaires.
Potential Biases
Potential bias from case ascertainment and misattribution of secondary cases to household contacts.
Limitations
The study may have underestimated secondary attack rates due to incomplete follow-up and reliance on clinical definitions for case ascertainment.
Participant Demographics
The study included 87 primary cases and 266 household contacts, with a median age of 18 years for cases and 34 years for contacts.
Statistical Information
P-Value
0.005
Confidence Interval
95% CI 6.8-14.7 for ILI; 95% CI 15.4-25.6 for ARI
Statistical Significance
p<0.001
Digital Object Identifier (DOI)
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