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Influenza activity low during summer season
There were low levels of seasonal influenza in the United States this summer, according to a CDC report, including sporadic cases of influenza A(H1N1)pdm09, influenza A(H3N2) and influenza B.
From May 19 to Sept. 28, there were 52,150 respiratory specimens tested for influenza, of which 2,013 (3.9%) were positive. Among those, 1,403 (70%) were influenza A viruses. From mid-June to September, influenza A(H1N1)pdm09 was more common than influenza A(H3N2).
The number of outpatient visits due to influenza-like illness was below the national baseline, and the percentage of deaths attributed to pneumonia and influenza was below the epidemic threshold. There were two influenza-related pediatric deaths reported during this time frame.
In June, influenza A(H3N2) variant viruses were first detected in Indiana. From June 18 to Sept. 28, there were 20 cases of influenza A(H3N2) variant and influenza A(H1N1) variant. There was one hospitalization related to influenza A(H3N2) variant, and no deaths related to either variant virus. Fourteen of the cases (70%) were in Indiana. All 20 cases reported contact with swine in the week before illness onset.
Worldwide, the seasonal patterns of influenza activity were typical in countries of the Southern Hemisphere.
“Although neither the influenza viruses that will predominate nor the severity of influenza-related disease during the 2013-14 season in the United States can be predicted, antigenic characterization of viral isolates submitted during the summer demonstrated that the majority of influenza viruses were antigenically similar to the influenza vaccine strains contained in the 2013-14 Northern Hemisphere vaccine,” the researchers wrote.