2010-2011 Influenza Season Week 42 ending October 23, 2010

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

Synopsis:

During week 42 (October 17-23, 2010), influenza activity remained low in the United States.

• Forty-eight (3.0%) specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division were positive for influenza.
• The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.
• No influenza-associated pediatric deaths were reported.
• The proportion of outpatient visits for influenza-like illness (ILI) was below the national baseline. All 10 regions reported ILI below region-specific baseline levels, and all 50 states experienced minimal ILI activity.
• Geographic spread of influenza in Guam and the U.S. Virgin Islands was assessed as regional; two states reported local influenza activity; the District of Columbia and 22 states were assessed as sporadic; 26 states reported no influenza activity, and Puerto Rico did not report.

*HHS regions (Region 1 CT, ME, MA, NH, RI, VT; Region 2: NJ, NY, Puerto Rico, US Virgin Islands; Region 3: DE, DC, MD, PA, VA, WV; Region 4: AL, FL, GA, KY, MS, NC, SC, TN; Region 5: IL, IN, MI, MN, OH, WI; Region 6: AR, LA, NM, OK, TX; Region 7: IA, KS, MO, NE; Region 8: CO, MT, ND, SD, UT, WY; Region 9: AZ, CA, Guam, HI, NV; and Region 10: AK, ID, OR, WA).
† Elevated means the % of visits for ILI is at or above the national or region-specific baseline
‡ National data are for current week; regional data are for the most recent three weeks
§ Includes all 50 states, the District of Columbia, Guam, Puerto Rico, and U.S. Virgin Islands

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. The results of tests performed during the current week are summarized in the table below.

	Week 42
No. of specimens tested	1,594
No. of positive specimens (%)	48 (3.0%)
Positive specimens by type/subtype
Influenza A	33 (68.8%)
A (2009 H1N1)	4 (12.1%)
A (subtyping not performed)	7 (21.2%)
A (H3)	22 (66.7%)
Influenza B	15 (31.3%)

View WHO-NREVSS Regional Bar Charts | View Chart Data | View Full Screen | View PowerPoint Presentation

Aggregate Hospitalization and Death Reporting Activity (AHDRA):

This system tracks weekly counts of laboratory-confirmed influenza-associated hospitalizations and deaths and was implemented on August 30, 2009, during the 2009 pandemic, and ended on April 4, 2010. AHDRA surveillance during the 2010-11 season is being continued on a voluntary basis and 19 jurisdictions reported during week 42. From October 3-23, 2010, 54 laboratory-confirmed influenza associated hospitalizations and two laboratory-confirmed influenza associated deaths were reported to CDC.

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Antigenic Characterization:

CDC has antigenically characterized one 2009 influenza A (H1N1) collected by U.S. laboratories since October 1, 2010.

This virus was characterized as A/California/7/2009-like, the 2009 influenza A (H1N1) component of the 2010-11 influenza vaccine for the Northern Hemisphere.

Antiviral Resistance:

Testing of 2009 influenza A (H1N1), influenza A (H3N2), and influenza B virus isolates for resistance to neuraminidase inhibitors (oseltamivir and zanamivir) is performed at CDC using a functional assay. Additional 2009 influenza A (H1N1) clinical samples are tested for a single known mutation in the neuraminidase protein of the virus that confers oseltamivir resistance (H275Y). The data summarized below combine the results of both test methods and includes samples that were tested as part of routine surveillance purposes; it does not include diagnostic testing specifically done because of clinical suspicion of antiviral resistance.

High levels of resistance to the adamantanes (amantadine and rimantadine) persist among 2009 influenza A (H1N1) and A (H3N2) viruses (the adamantanes are not effective against influenza B viruses) circulating globally. As a result of the sustained high levels of resistance, data from adamantane resistance testing are not presented weekly in the table below.

	Samples tested (n)	Resistant Viruses, Number (%)	Samples tested (n)	Resistant Viruses, Number (%)
		Oseltamivir		Zanamivir
Seasonal Influenza A (H1N1)	0	0 (0.0)	0	0 (0.0)
Influenza A (H3N2)	0	0 (0.0)	0	0 (0.0)
Influenza B	0	0 (0.0)	0	0 (0.0)
2009 Influenza A (H1N1)	4	0 (0.0)	1	0 (0.0)

To prevent the spread of antiviral resistant virus strains, CDC reminds clinicians and the public of the need to continue hand and cough hygiene measures for the duration of any symptoms of influenza, even while taking antiviral medications. Additional information on antiviral recommendations for treatment and chemoprophylaxis of influenza virus infection is available at http://www.cy118119.com/flu/antivirals/index.htm.

Pneumonia and Influenza (P&I) Mortality Surveillance

During week 42, 6.4% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 6.7% for week 42.

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Influenza-Associated Pediatric Mortality

No influenza-associated pediatric deaths were reported to CDC during week 42.

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Influenza-Associated Hospitalizations

The Influenza Hospitalization Network (FluSurv-NET) conducts surveillance for population-based, laboratory-confirmed influenza related hospitalizations in children (persons less than 18 years) and adults. The network covers over 80 counties in the 10 Emerging Infections Program (EIP) states (CA, CO, CT, GA, MD, MN, NM, NY, OR, and TN) and six additional states (ID, MI, OH, OK, RI and UT). FluSurv-NET estimated hospitalization rates will be updated every two weeks starting later this season.

Outpatient Illness Surveillance:

Nationwide during week 42, 1.2% 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%.

View ILINet Regional Charts | View Chart Data | View Full Screen | View PowerPoint Presentation

On a regional level, the percentage of outpatient visits for ILI ranged from 0.3% to 2.1% during week 42. All 10 regions reported a proportion of outpatient visits for ILI below their region-specific baseline levels.

ILINet State Activity Indicator Map:

Data collected in ILINet are used to produce a measure of ILI activity* by state. Activity levels are based on the percent of outpatient visits in a state due to ILI and are compared to the average percent of ILI visits that occur during spring and fall weeks with little or no influenza virus circulation. Activity levels range from minimal, which would correspond to ILI activity from outpatient clinics being below the average, to high, which would correspond to ILI activity from outpatient clinics being much higher than the average.

During week 42, the following influenza activity levels were experienced:

• All 50 states, New York City, and the District of Columbia were experiencing minimal ILI activity (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming).

*This map uses the proportion of outpatient visits to health care providers for influenza-like illness to measure the ILI activity level within a state. It does not, however, measure the extent of geographic spread of flu within a state. Therefore, outbreaks occurring in a single city could cause the state to display high activity levels.
Data collected in ILINet may disproportionately represent certain populations within a state, and therefore, may not accurately depict the full picture of influenza activity for the whole state.
Data displayed in this map are based on data collected in ILINet, whereas the State and Territorial flu activity map are based on reports from state and territorial epidemiologists. The data presented in this map is preliminary and may change as more data is received.
Differences in the data presented by CDC and state health departments likely represent differing levels of data completeness with data presented by the state likely being the more complete .

Geographic Spread of Influenza as Assessed by State and Territorial Epidemiologists:

The influenza activity reported by state and territorial epidemiologists indicates geographic spread of influenza viruses, but does not measure the severity of influenza activity.

During week 42, the following influenza activity was reported:

• Regional influenza activity was reported by Guam and the U.S. Virgin Islands.
• Local influenza activity was reported by two states (Hawaii and Texas).
• Sporadic influenza activity was reported by the District of Columbia and 22 states (Alabama, Arizona, California, Connecticut, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Maryland, Michigan, Mississippi, Nevada, New Jersey, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Virginia, and Washington).
• No influenza activity was reported by 26 states (Alaska, Arkansas, Colorado, Delaware, Idaho, Iowa, Kansas, Maine, Massachusetts, Minnesota, Missouri, Montana, Nebraska, New Hampshire, New Mexico, North Dakota, Oklahoma, Oregon, Rhode Island, South Dakota, Tennessee, Utah, Vermont, West Virginia, Wisconsin, and Wyoming).
• Puerto Rico did not report.