2010-2011 Influenza Season Week 34 ending August 27, 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:

Two human infections with novel influenza A virus were reported; one case from the Indiana State Department of Health and one case from the Pennsylvania Department of Health. Both patients were infected with swine-origin influenza A (H3N2) viruses. The Indiana case experienced symptom onset on July 23, 2011 and was hospitalized on July 24, 2011 for worsening of chronic health problems. No contact with pigs has been identified in the Indiana case in the week before symptom onset; however the case had contact with individuals who reported swine exposure in the week preceding the patient’s illness onset. The Pennsylvania case reported contact with pigs in the week preceding symptom onset on August 20, 2011. Both patients have fully recovered from their illness. These viruses are genetically related, but different enough to suggest there was not a common source of infection. No epidemiologic link between these two cases has been identified. For additional information on these cases see link to MMWR.

Early identification and investigation of human infections with novel influenza A viruses is critical to evaluate the extent of the outbreak and possible human-to-human transmission. Surveillance for human infections with novel influenza A viruses continues year round.

Pneumonia and Influenza (P&I) Mortality Surveillance

During week 34, 5.8% 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 34.

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Influenza-Associated Pediatric Mortality

No influenza-associated pediatric deaths were reported to CDC during week 34. This season, 114 laboratory-confirmed influenza-associated pediatric deaths from 33 states, Chicago, and New York City have been reported. Forty-three of the 114 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 34, 0.8% 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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