Background: The aim of this study was to examine the rate of transmission of influenza and other respiratory viruses from children attending an Emergency Department to their family members in the household using active surveillance.
Methods: A prospective hospital-based study was conducted over three consecutive winters (2006-2008) in children aged <1-15 years presenting with influenza-like illness (ILI). 168 children with ILI and their healthy families were recruited over three winter seasons.
Results: Respiratory viruses were detected in 101 (60.8%) children with ILI; in 91/166 (54.8%) a single pathogen was detected, and in the remaining 10 children more than one virus was detected concurrently. Influenza was the most common virus detected (34/101), followed by rhinoviruses (22/101) and adenoviruses (14/101). Of influenza viruses, 21/34 were influenza A and 13/34 influenza B. Meeting the clinical definition of ILI did not differentiate between influenza and other viruses. Clinical ILI developed within one week of follow up in 12% (26/205) of the family members who were swabbed. Viral pathogens were detected in 42.3% (11/26) of the symptomatic family members. In 6/11 cases the same virus was detected in the adult and child. The lower estimate of the household risk of transmission of respiratory viruses, based on concordant proven infection in both child and adult, from a single sick child to adult household contacts is therefore 3% per week.
Conclusion: This study provides quantitative, prospective data on rates of household transmission of infection from children to adults.
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