Changes in sampling for influenza viruses before and after the 2009 A/H1N1 outbreak

Background: In Pennsylvania, monitoring of circulating influenza viruses is primarily done using specimens submitted to the State Public Health Laboratory (BOL) by a network of sentinel physicians. Participating providers are encouraged to voluntarily submit up to 3 clinical specimens per week for influenza confirmatory testing.

Objective: We examined changes in specimen submission patterns in the season before and after the 2009 A/H1N1 pandemic.

Methods: Specimen submission patterns in the six months before 2009 A/H1N1 was recognized (October 1, 2008 to March 31, 2009) were compared to submissions after the pandemic period (October 1, 2010 to March 2011). The number of enrolled providers submitting specimens and the yield of submitted specimens were also examined. Results : The number of participating providers more than doubled after the pandemic (60 vs. 148, p<0.05). Although the proportion of enrolled providers who submitted specimens was similar before (32/53%) and afterwards (67/45%) the absolute number of providers submitting specimens doubled (32 vs. 67). There was a fourfold increase in the number of specimen submissions after the outbreak (486 vs. 1, 852, p<0.05), and the number of specimens that yielded a virus also quadrupled (128 vs. 588, p > 0.05). Conclusions: The 2009 H1N1 pandemic resulted in a marked increase in the number of sentinel providers and the number of samples submitted for testing. The large increase in positive specimens markedly enhances the ability to detect the emergence of unusual virus types or antiviral resistance.