Article

Transmissibility of seasonal and pandemic influenza in a cohort of households in Hong Kong in 2009.

School of Public Health, The University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, China.
Epidemiology (Cambridge, Mass.) (impact factor: 5.51). 08/2011; 22(6):793-6. DOI:10.1097/EDE.0b013e3182302e8e pp.793-6
Source: PubMed

ABSTRACT The household secondary attack proportion (SAP) is commonly used to measure the transmissibility of an infectious disease.
We analyzed the final outbreak size distributions of pandemic A(H1N1), seasonal A(H1N1), and A(H3N2) infections identified in paired sera collected from members of 117 Hong Kong households in April and in August-October 2009.
The estimated community probability of infection overall was higher for children than adults; the probability was similar for pandemic A(H1N1) and seasonal A(H3N2) influenza. The household SAP for pandemic A(H1N1) was higher in children than in adults, whereas for seasonal A(H3N2), it was similar in children and adults. The estimated SAPs were similar for seasonal A(H3N2) and pandemic A(H1N1) after excluding persons with higher baseline antibody titers from analysis.
Pandemic and seasonal influenza A viruses had similar age-specific transmissibility in a cohort of initially uninfected households, after adjustment for baseline immunity.

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    Article: The feasibility of age-specific travel restrictions during influenza pandemics.
    Elson H Y Lam, Benjamin J Cowling, Alex R Cook, Jessica Y T Wong, Max S Y Lau, Hiroshi Nishiura
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    ABSTRACT: Epidemiological studies have shown that imposing travel restrictions to prevent or delay an influenza pandemic may not be feasible. To delay an epidemic substantially, an extremely high proportion of trips (~99%) would have to be restricted in a homogeneously mixing population. Influenza is, however, strongly influenced by age-dependent transmission dynamics, and the effectiveness of age-specific travel restrictions, such as the selective restriction of travel by children, has yet to be examined. A simple stochastic model was developed to describe the importation of infectious cases into a population and to model local chains of transmission seeded by imported cases. The probability of a local epidemic, and the time period until a major epidemic takes off, were used as outcome measures, and travel restriction policies in which children or adults were preferentially restricted were compared to age-blind restriction policies using an age-dependent next generation matrix parameterized for influenza H1N1-2009. Restricting children from travelling would yield greater reductions to the short-term risk of the epidemic being established locally than other policy options considered, and potentially could delay an epidemic for a few weeks. However, given a scenario with a total of 500 imported cases over a period of a few months, a substantial reduction in the probability of an epidemic in this time period is possible only if the transmission potential were low and assortativity (i.e. the proportion of contacts within-group) were unrealistically high. In all other scenarios considered, age-structured travel restrictions would not prevent an epidemic and would not delay the epidemic for longer than a few weeks. Selectively restricting children from traveling overseas during a pandemic may potentially delay its arrival for a few weeks, depending on the characteristics of the pandemic strain, but could have less of an impact on the economy compared to restricting adult travelers. However, as long as adults have at least a moderate potential to trigger an epidemic, selectively restricting the higher risk group (children) may not be a practical option to delay the arrival of an epidemic substantially.
    Theoretical Biology and Medical Modelling 11/2011; 8:44. · 1.86 Impact Factor
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Keywords

117 Hong Kong households
 
August-October 2009
 
children
 
estimated community probability
 
estimated SAPs
 
final outbreak size distributions
 
higher baseline antibody titers
 
household SAP
 
household secondary attack proportion
 
paired sera
 
SAP
 
seasonal influenza
 
transmissibility
 
uninfected households
 
viruses