J Infect Dis. 2012 Jul 26. [Epub ahead of print]
Longitudinal Study of Influenza Molecular Viral Shedding in Hutterite Communities.
Loeb M, Singh PK, Fox J, Russell ML, Pabbaraju K, Zarra D, Wong S, Neupane B, Singh P, Webby R, Fonseca K.

Department of Pathology and Molecular Medicine, University of Calgary, Calgary, Alberta.

Background. The nature of influenza viral shedding during naturally acquired infection is not well understood.Methods. A cohort study was conducted in Hutterite colonies in Alberta where flocked nasal swabs were collected over three influenza seasons (2007/2008 to 2009/2010) from both symptomatic and asymptomatic individuals infected with influenza. Samples were tested by real-time RT-PCR for Influenza A and Influenza B and the viral load was determined for Influenza A positive samples.Results. 839 participants were included in the cohort and 25% (208) tested positive for influenza viruses. They experienced 238 episodes of viral shedding, of which 23 (10%) were not accompanied by symptoms. For seasonal and pandemic H1N1, the viral load peaked at or before onset of acute respiratory infection. For H3N2, viral load peaked two days after the onset of acute respiratory infection, which corresponded to the peaks in systemic and respiratory symptom scores. Although the duration of shedding was shorter, the peak level of viral load shedding for asymptomatic participants was similar to those who were symptomatic. Viral loads for children and adults revealed similar patterns.Conclusions.  Molecular viral shedding values follow symptom scores but timing of peak viral load varies by subtype. Asymptomatic infections are infrequent.

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