2010-2011 Influenza Season Week 36 ending September 10, 2011

All data are preliminary and may change as more reports are received.

U.S. Virologic Surveillance:

WHO and NREVSS collaborating laboratories located in all 50 states and Washington, D.C. report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza type and subtype.

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Novel Influenza A Virus:

As a result of intensive surveillance after the identification of two cases of human infection with a novel influenza A virus, one in Indiana and one in Pennsylvania, reported in August MMWR, two additional human infections with novel influenza A virus were identified in Pennsylvania. Both patients were infected with swine-origin influenza A (H3N2) viruses, with illness onset dates of August 18 and August 21, 2011. One patient was hospitalized, but was discharged home and both patients have fully recovered. All three Pennsylvania patients reported contact with pigs at the same agricultural fair in the week preceding symptom onset and enhanced surveillance for human illness continues. Although these additional cases have been detected, exposure to pigs was reported in both cases and no evidence of ongoing transmission of this virus in the community has been identified.

Pneumonia and Influenza (P&I) Mortality Surveillance

During week 36, 6.1% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 6.4% for week 36.

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Influenza-Associated Pediatric Mortality

One influenza-associated pediatric death was reported to CDC during week 36 and was associated with an influenza B virus.

This season, 116 laboratory-confirmed influenza-associated pediatric deaths from 34 states, Chicago, and New York City have been reported. Forty-five of the 116 deaths reported were associated with influenza B viruses; 30 were associated with 2009 influenza A (H1N1) viruses; 21 deaths reported were associated with influenza A (H3N2) viruses, and 20 were associated with an influenza A virus for which the subtype was not determined.

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Outpatient Illness Surveillance:

Nationwide during week 36, 1.0% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) were due to influenza-like illness (ILI). This percentage is below the national baseline of 2.5%.

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