Larger households contribute to COVID-19 transmission in Fraser Health Region

Household size and family members’ inability to isolate in larger settings can explain why the Fraser Health region has had more COVID-19 cases than the Vancouver Coastal Health region, according to a new pre-print study from Simon Fraser University researchers.

The Fraser Health region, which includes communities from Burnaby and Surrey to the Fraser Canyon, has had the most cases of COVID-19 in British Columbia, far more than even Vancouver Coastal Health (VCH), the other health authority which covers parts of the Lower Mainland. As of Feb. 3, Fraser Health had recorded 41,061 cases of COVID-19, compared to 15,836 in VCH.

The discrepancy in case numbers between the two regions has been a topic of hot conversation throughout the pandemic. One theory has been the prevalence of larger, multi-generational households in the Fraser Health area. According to Canadian census data, there are more large households and fewer single-individual households in the Fraser Health region than there are in VCH. The average household size in Fraser Health is 2.68 persons, compared to 2.31 in VCH.

Pengyu Liu and Caroline Colijn in the department of Mathematics, ran a series of mathematical models that confirmed the difference in household sizes between the two areas can lead to a “substantial difference” in COVID-19 incidence, especially as people stay home and take other steps to limit their risk of community transmission.

According to the modelling, the spread of COVID-19 would decline when 55 per cent of individuals isolate at home if ill under the household settings similar to those within VCH. But with household settings similar to Fraser Health, isolating at home was less effective and incidence would continue to increase.

Researchers also created a scenario where people living in households of four or more individuals were offered a separate place to isolate from the rest of their household if they were ill and would have to isolate at home. With 55 per cent of individuals practicing isolation, the modelling showed the strategy can turn transmission into a decline.

According to the study, which has not yet been peer-reviewed, the current practice in B.C. of requiring people to isolate at home can be effective but applying it uniformly across different demographics may not be optimal. Jurisdictions with larger households would benefit from additional policies, such as offering self-isolation to people in a separated space.

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