2010-2011 Influenza Season Week 47 ending November 27, 2010

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

Synopsis:

During week 47 (November 21-27, 2010), influenza activity in the United States remained relatively low overall, but increased slightly in the Southeast.

• Of the 3,430 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, 366 (10.7%) 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 1.9%, which is below the national baseline of 2.5%. One of the 10 regions (Region 4) reported ILI above region-specific baseline levels; one state experienced high ILI activity; one state experienced low ILI activity, and 48 states experienced minimal ILI activity.
• The geographic spread of influenza in one state was reported as regional, Puerto Rico and nine states reported local activity; the District of Columbia, Guam, the U.S. Virgin Islands, and 33 states reported sporadic activity; and seven states reported no influenza activity.

*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 47
No. of specimens tested	3,430
No. of positive specimens (%)	366 (10.7%)
Positive specimens by type/subtype
Influenza A	181 (49.5%)
A (2009 H1N1)	7 (3.9%)
A (subtyping not performed)	47 (26.0%)
A (H3)	127 (70.2%)
Influenza B	185 (50.5%)

The District of Columbia and 44 states from all 10 surveillance regions have reported laboratory-confirmed influenza this season. Region 4 in the Southeastern United States has accounted for 1,231 (69.7%) of all 1,766 reported influenza viruses this season, including 680 (88.2%) of the 771 influenza B viruses.

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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 11 jurisdictions reported during week 47. From October 3-November 27, 2010, 271 laboratory-confirmed influenza associated hospitalizations and four laboratory-confirmed influenza associated deaths were reported to CDC.

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Antigenic Characterization:

CDC has antigenically characterized 18 influenza viruses [four 2009 influenza A (H1N1) viruses, eight influenza A (H3N2) viruses, and six influenza B viruses] collected by U.S. laboratories since October 1, 2010.

2009 Influenza A (H1N1) [4]

• All four were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2010-11 influenza vaccine for the Northern Hemisphere.

Influenza A (H3N2) [8]

• All eight were characterized as A/Perth/16/2009-like, the influenza A (H3N2) component of the 2010-11 influenza vaccine for the Northern Hemisphere.

Influenza B [6]

• All six viruses belong to the B/Victoria lineage of viruses and was characterized as B/Brisbane/60/2008-like, the recommended influenza B component for the 2010-11 Northern Hemisphere influenza vaccine.

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)	10	0 (0.0)	10	0 (0.0)
Influenza B	13	0 (0.0)	13	0 (0.0)
2009 Influenza A (H1N1)	8	0 (0.0)	8	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 47, 6.0% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 7.2% for week 47.

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Influenza-Associated Pediatric Mortality

No influenza-associated pediatric deaths were reported to CDC during week 47.

One death, associated with an influenza A virus for which the subtype was not determined, occurring during the 2010-2011 season has been reported.

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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 younger 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 47, 1.9% 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 0.4% to 3.2% during week 47. One of the 10 regions (Region 4) reported a proportion of outpatient visits for ILI above 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. Because the clinical definition of ILI is very general, not all ILI is caused by influenza; however, when combined with laboratory data, the information on ILI activity provides a clear picture of influenza activity in the United States.

During week 47, the following ILI activity levels were experienced:

• One state (Georgia) experienced high ILI activity. While influenza-like illness is a non-specific term and may be caused by a variety of organisms, the increase in ILI in Georgia has occurred at the same time as a significant increase in the number of reported influenza B virus infections.
• New York City and one state (Alabama) experienced low ILI activity.
• Forty-eight states experienced minimal ILI activity (Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, 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).
• Data were insufficient to calculate an ILI activity level from the District of Columbia.

*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 47, the following influenza activity was reported:

• Regional influenza activity was reported by one state (Georgia).
• Local influenza activity was reported by Puerto Rico and nine states (Alabama, Connecticut, Hawaii, Louisiana, Mississippi, New York, Oklahoma, Pennsylvania, and South Carolina).
• Sporadic influenza activity was reported by the District of Columbia, Guam, the U.S. Virgin Islands, and 33 states (Alaska, Arizona, Arkansas, California, Colorado, Florida, Idaho, Illinois, Indiana, Kansas, Kentucky, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nevada, New Hampshire, New Jersey, New Mexico, North Carolina, Ohio, Oregon, Rhode Island, Tennessee, Texas, Utah, Virginia, Washington, West Virginia, Wisconsin, and Wyoming).
• No influenza activity was reported by seven states (Delaware, Iowa, Maine, Nebraska, North Dakota, South Dakota, and Vermont).