2011-2012 Influenza Season Week 52 ending December 31, 2011

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

Synopsis:

During week 52 (December 25-31, 2011), influenza activity increased in the United States, but remains relatively low.

• U.S. Virologic Surveillance: Of the 3,310 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, 95 (2.9%) were positive for influenza.
• Pneumonia and Influenza (P&I) Mortality Surveillance: The proportion of deaths attributed to P&I was below the epidemic threshold.
• Influenza-associated Pediatric Mortality: No influenza-associated pediatric deaths were reported.
• Outpatient Illness Surveillance: : The proportion of outpatient visits for influenza-like illness (ILI) was 1.7%, which is below the national baseline of 2.4%. Three of the 10 regions (Regions 1, 5, and 10) reported ILI at or above region-specific baseline levels. One state experienced moderate ILI activity, New York City and six states experienced low ILI activity, 42 states experienced minimal ILI activity, and the District of Columbia and one state had insufficient data.
• Geographic Spread of Influenza: The geographic spread of influenza in one state was reported as regional; four states reported local activity; Guam and 40 states reported sporadic activity; the District of Columbia, the U.S. Virgin Islands and five 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 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 52
No. of specimens tested	3,310
No. of positive specimens (%)	95 (2.9%)
Positive specimens by type/subtype
Influenza A	85 (89.5%)
A (2009 H1N1)	0 (0.0%)
A (subtyping not performed)	40 (52.9%)
A (H3)	45 (47.1%)
Influenza B	10 (10.5%)

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Antigenic Characterization:

CDC has antigenically characterized 129 influenza viruses [14 2009 influenza A (H1N1), 104 influenza A (H3N2) viruses, and 11 influenza B viruses] collected by U.S. laboratories since October 1, 2011.

2009 Influenza A (H1N1) [14]

• All 14 viruses were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2011-12 influenza vaccine for the Northern Hemisphere.

Influenza A (H3N2) [104]

• One hundred three (99.0%) of the 104 viruses were characterized as A/Perth/16/2009-like, the influenza A (H3N2) component of the 2011-12 influenza vaccine for the Northern Hemisphere.
• One virus (1.0%) tested showed reduced titers with antiserum produced against A/Perth/16/2009.

Influenza B (B/Victoria/02/87 and B/Yamagata/16/88 lineages) [11]:

• Victoria Lineage [7]: Seven (64%) of the 11 influenza B viruses tested belong to the B/Victoria lineage of viruses and were characterized as B/Brisbane/60/2008-like, the recommended influenza B component for the 2011-12 Northern Hemisphere influenza vaccine.
• Yamagata Lineage [4]: Four (36%) of the 11 influenza B viruses tested belong to the B/Yamagata lineage of viruses.

It is too early in the influenza season to determine how well the seasonal influenza vaccine strains and circulating strains will match.

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 mutation in the neuraminidase of the virus known to confer oseltamivir resistance (H275Y). The data summarized below combine the results of both testing methods. These samples are routinely obtained for surveillance purposes rather than for diagnostic testing of patients suspected to be infected with antiviral resistant virus.

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). As a result of the sustained high levels of resistance, data from adamantane resistance testing are not presented in the table below.

Neuraminidase Inhibitor Resistance Testing Results on Samples Collected Since October 1, 2011

	Oseltamivir		Zanamivir
	Virus Samples Tested (n)	Resistant Viruses, Number (%)	Virus Samples Tested (n)	Resistant Viruses, Number (%)
Influenza A (H3N2)	103	0 (0.0)	103	0 (0.0)
Influenza B	14	0 (0.0)	14	0 (0.0)
Influenza A (2009 H1N1)	15	0 (0.0)	15	0 (0.0)

All viruses tested for the 2011-2012 season since October 1, 2011 have been susceptible to the neuraminidase inhibitor antiviral medications oseltamivir and zanamivir as were the majority of viruses tested last season; however, rare sporadic cases of oseltamivir resistant 2009 influenza A (H1N1) and A (H3N2) viruses have been detected worldwide. Antiviral treatment with oseltamivir or zanamivir is recommended as early as possible for patients with confirmed or suspected influenza who have severe, complicated, or progressive illness; who require hospitalization; or who are at greater risk for influenza-related complications. Additional information on recommendations for treatment and chemoprophylaxis of influenza virus infection with antiviral agents is available at (http://www.cy118119.com/flu/antivirals/index.htm).

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 52, 7.0% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 7.5% for week 52.

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Influenza-Associated Pediatric Mortality:

No influenza-associated pediatric deaths were reported to CDC during week 52 and no influenza-associated pediatric deaths have been reported to CDC so far for the 2011-12 season.

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Influenza-Associated Hospitalizations:

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

Outpatient Illness Surveillance:

Nationwide during week 52, 1.7% 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 2.4%.(ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and cough and/or sore throat.)

View National and Regional Level Graphs and Data | View Chart Data | View Full Screen | View PowerPoint Presentation

On a regional level, the percentage of outpatient visits for ILI ranged from 1.1% to 2.7% during week 52. Three of the 10 regions (Regions 1, 5, and 10) reported a proportion of outpatient visits for ILI at or 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 being below the average, to intense, which would correspond to ILI activity being much higher than 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 52, the following ILI activity levels were experienced:

• One state experienced moderate ILI activity (Alabama).
• New York City and six states (Georgia, Illinois, Louisiana, Minnesota, Mississippi, and Nebraska) experienced low ILI activity.
• Forty-two states experienced minimal ILI activity (Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Hawaii, Idaho, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Missouri, Montana, 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, Washington, West Virginia, Wisconsin, and Wyoming).
• Data were insufficient to calculate an ILI activity level from the District of Columbia and one state (Virginia).

*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 here by CDC and independently by some 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 intensity of influenza activity.

During week 52, the following influenza activity was reported:

• Regional influenza activity was reported by one state (Colorado).
• Local influenza activity was reported by four states (Massachusetts, New Hampshire, Texas, and Virginia).
• Sporadic influenza activity was reported by Guam, and 40 states (Alabama, Arizona, Arkansas, California, Connecticut, Florida, Georgia, Hawaii, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, New York, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Utah, Vermont, Washington, West Virginia, Wisconsin, and Wyoming).
• No influenza activity was reported by the District of Columbia, the U.S. Virgin Islands, and five states (Alaska, Delaware, Idaho, New Jersey, and North Dakota).
• Puerto Rico did not report.