TY - JOUR T1 - Risk factors of influenza transmission in households JF - British Journal of General Practice JO - Br J Gen Pract SP - 684 LP - 689 VL - 54 IS - 506 AU - Cécile Viboud AU - Pierre-Yves Boëlle AU - Simon Cauchemez AU - Audrey Lavenu AU - Alain-Jacques Valleron AU - Antoine Flahault AU - Fabrice Carrat Y1 - 2004/09/01 UR - http://bjgp.org/content/54/506/684.abstract N2 - Background: Influenza transmission in households is a subject of renewed interest, as the vaccination of children is currently under debate and antiviral treatments have been approved for prophylactic use.Aims: To quantify the risk factors of influenza transmission in households.Design of study: A prospective study conducted during the 1999 to 2000 winter season in France.Setting: Nine hundred and forty-six households where a member, the index patient, had visited their general practitioner (GP) because of an influenza-like illness were enrolled in the study. Five hundred and ten of the index patients tested positive for influenza A (subtype H3N2). A standardised daily questionnaire allowed for identification of secondary cases of influenza among their household contacts, who were followed-up for 15 days. Of the 395 (77%) households that completed the questionnaire, we selected 279 where no additional cases had occurred on the day of the index patient's visit to the GP.Methods: Secondary cases of influenza were those household contacts who had developed clinical influenza within 5 days of the disease onset in the index patient. Hazard ratios for individual clinical and demographic characteristics of the contact and their index patient were derived from a Cox regression model.Results: Overall in the 279 households, 131 (24.1%) secondary cases occurred among the 543 household contacts. There was an increased risk of influenza transmission in preschool contacts (hazard ratio [HR] = 1.85, 95% confidence interval [CI] = 1.09 to 3.26) as compared with school-age and adult contacts. There was also an increased risk in contacts exposed to preschool index patients (HR = 1.93, 95% CI = 1.09 to 3.42) and school-age index patients (HR = 1.68, 95% CI = 1.07 to 2.65), compared with those exposed to adult index cases. No other factor was associated with transmission of the disease.Conclusion: Our results support the major role of children in the dissemination of influenza in households. Vaccination of children or prophylaxis with neuraminidase inhibitors would prevent, respectively, 32–38% and 21–41% of secondary cases caused by exposure to a sick child in the household. ER -