Preventable and non-preventable risk factors for influenza transmission and hygiene behavior in German influenza households, pandemic season (H1N1) 2009/2010.

Background: To date, little is known about the role of behavioral risk factors for influenza transmission as well as hygiene behavior in the household setting during the influenza pandemic (H1N1) 2009. In a household-based study conducted during 2008/2009, we identified several behavioral risk factors for influenza transmission; 30% of index patients and 30% of household contacts reported increased hand cleaning frequency in the week after symptom onset of the index patient. We conducted another household-based study during the pandemic season 2009/2010.

Methods: We identified index patients with laboratory confirmed influenza infection and interviewed household members after illness day 8 of the index patient. Outcome was influenza-like illness (ILI) in a household contact.

Results: We included 108 households. Overall secondary attack rate was 10·1% (27/267) and decreased with increasing age. Apart from being in close daily proximity with the index patient for at least 9 hours, no other behavioral risk factor was associated with secondary ILI. Of all index patients and household contacts, 49% and 55%, respectively, cleaned their hands more often in the week after symptom onset of the index patient (in comparison with 2008/2009 P-value for both <0·01).

Conclusions: While the study was hampered by its relatively limited size, data suggest that a significantly larger proportion of influenza households practiced good hand hygiene compared to the last pre-pandemic season. This may have led to a different risk factor profile and a delay of the time threshold necessary for transmission among household members with close contact.