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14 Dec 2012

2012-2013 Influenza Season Week 49 ending December 8, 2012 (US CDC, December 14 2012, edited)

[Source: US Centers for Disease Control and Prevention, FluView, full text: (LINK). Extract, edited.]

2012-2013 Influenza Season Week 49 ending December 8, 2012

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



During week 49 (December 2-8), influenza activity increased in the U.S.

  • Viral Surveillance: Of 7,663 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 49, 2,172 (28.3%) were positive for influenza.
  • Novel Influenza A Virus: One human infection with a novel influenza A virus was reported.
  • Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.
  • Influenza-Associated Pediatric Deaths: One influenza-associated pediatric death was reported and was associated with an influenza B virus.
  • Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 2.8%, which is above the national baseline of 2.2%. Seven of ten regions reported ILI above region-specific baseline levels. Eight states experienced high ILI activity, 2 states experienced moderate ILI activity; New York City and 9 states experienced low ILI activity; 31 states experienced minimal ILI activity, and the District of Columbia had insufficient data.
  • Geographic Spread of Influenza: The geographic spread of influenza in 18 states was reported as widespread; 17 states reported regional activity; the District of Columbia and 11 states reported local activity; Guam and 4 states reported sporadic activity, and Puerto Rico and the U.S. Virgin Islands did not report.

A description of surveillance methods is available at:


National and Regional Summary of Select Surveillance Components

[HHS Surveillance Regions* - Data for current week: Out-patient ILI† - % positive for flu‡ - Number of jurisdictions reporting regional or widespread activity§ - Data cumulative since September 30, 2012 (Week 40): 2009 H1N1 - A (H3) - A(Subtyping not  performed) – B - Pediatric Deaths]

  • Nation – Elevated - 28.3% - 35 of 54 – 66 - 3,284 - 2,299 - 2,372 -  6
  • Region 1 -  Elevated -  17.6% -  4 of 6 -  0 -  121 -  22 -  18 -  0
  • Region 2 -  Elevated -  16.6% -  2 of 4 -  7 -  196 -  133 -  112 – 0
  • Region 3 – Elevated -  24.0% -  3 of 6 -  13 -  336 -  48 -  46 -  0
  • Region 4 -  Elevated -  28.5% -  8 of 8 -  13 -  627 -  1,692 -  700 -  3
  • Region 5 -  Elevated -  47.3% -  6 of 6 -  19 -  489 -  52 -  182 -  1
  • Region 6 -  Elevated -  17.1% -  3 of 5 -  3 -  195 -  200 -  443  - 2
  • Region 7 -  Elevated -  24.3% -  3 of 4 -  0 -  389 -  62 -  255 -  0
  • Region 8 -  Normal - 19.1%  -  4 of 6 -  6 -  249 -  53 -  515 -  0
  • Region 9 -  Normal -  7.9% -  0 of 5 -  4 -  194 -  34 -  50 -  0
  • Region 10 -  Normal -  22.9% -  2 of 4 -  1 -  488 -  3 -  51 -  0

*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 Puerto Rico report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza virus type and influenza A virus subtype. Region specific data can be found at The results of tests performed during the current week are summarized in the table below.


Week 49

  • No. of specimens tested - 7,663
    • No. of positive specimens (%) - 2,172 (28.3%)
      • Positive specimens by type/subtype
        • Influenza A - 1,655 (76.2%)
          • 2009 H1N1 - 14 (0.8%)
          • Subtyping not performed - 850 (51.4%)
          • H3 - 791 (47.8%)
        • Influenza B - 517 (23.8%)


View National and Regional Level Graphs and Data

Since the start of the season, the predominant circulating influenza virus nationally has been influenza A (H3N2), followed by influenza B viruses. 2009 H1N1 viruses have been identified rarely so far this season. The predominant type and subtype has varied by region and even between states within the same region.


Antigenic Characterization:

CDC has antigenically characterized 287 influenza viruses [10 2009 H1N1 viruses, 182 influenza A (H3N2) viruses, and 95 influenza B viruses] collected by U.S. laboratories since October 1, 2012.

2009 H1N1 [10]:

  • All 10 2009 H1N1 viruses tested were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2012-2013 influenza vaccine for the Northern Hemisphere.

Influenza A (H3N2) [182]:

  • 180 (98.9%) of the 182 H3N2 influenza viruses tested have been characterized as A/Victoria/361/2011-like, the influenza A (H3N2) component of the 2012-2013 Northern Hemisphere influenza vaccine.
  • 2 (1.1%) of the 182 H3N2 viruses tested showed reduced titers with antiserum produced against A/Victoria/361/2011.

Influenza B (B/Yamagata/16/88 and B/Victoria/02/87 lineages) [95]:

  • Yamagata Lineage [63]: 63 (66.3%) of the 95 influenza B viruses tested so far this season have been characterized as B/Wisconsin/1/2010-like, the influenza B component of the 2012-2013 Northern Hemisphere influenza vaccine.
  • Victoria Lineage [32]: 32 (33.7%) of 95 influenza B viruses tested have been from the B/Victoria lineage of viruses.


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, 2012

[Oseltamivir: Virus Samples tested (n) - Resistant Viruses, Number (%) – Zanamivir: Virus Samples tested (n) - Resistant Viruses, Number (%)]

  • Influenza A (H3N2)  - 257  0 (0.0) – 257  0 (0.0)
  • Influenza B – 118  0 (0.0) -  118  0 (0.0)
  • 2009 H1N1 – 17  0 (0.0) -  14  0 (0.0)

The majority of currently circulating influenza viruses are susceptible to the neuraminidase inhibitor antiviral medications oseltamivir and zanamivir; 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 serious influenza-related complications. Additional information on recommendations for treatment and chemoprophylaxis of influenza virus infection with antiviral agents is available at


Novel Influenza A Virus:

One infection with an influenza A (H3N2) variant virus (H3N2v) was reported to CDC during week 49 by Minnesota. Close contact between the case patient and swine in the week preceding illness was reported. The patient has fully recovered and no further cases have been identified in contacts of the case patient. This is the second H3N2v infection reported for the 2012-13 influenza season, which began on September 30, 2012.

A total of 312 infections with variant influenza viruses (308 H3N2v viruses, 3 H1N2v viruses, and 1 H1N1v virus) have been reported from 11 states since July 2012. More information about H3N2v infections can be found at


Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 49, 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 6.9% for week 49.


View Full Screen


Influenza-Associated Pediatric Mortality:

One influenza-associated pediatric death was reported to CDC during week 49 and was associated with an influenza B virus. This death occurred during the week ending December 1 (week 48). This brings the total number of influenza-associated pediatric deaths reported during the 2012-2013 season to 6. Additional data can be found at


View Interactive Application


Influenza-Associated Hospitalizations:

The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in children younger than 18 years of age (since the 2003-2004 influenza season) and adults (since the 2005-2006 influenza season).

The FluSurv-NET covers more than 80 counties in the 10 Emerging Infections Program (EIP) states (CA, CO, CT, GA, MD, MN, NM, NY, OR, TN) and additional Influenza Hospitalization Surveillance Project (IHSP) states. The IHSP began during the 2009-2010 season to enhance surveillance during the 2009 H1N1 pandemic. IHSP sites included IA, ID, MI, OK and SD during the 2009-2010 season; ID, MI, OH, OK, RI, and UT during the 2010-2011 season; MI, OH, RI, and UT during the 2011-2012 season; and IA, MI, OH, RI, and UT during the 2012-2013 season.

Data gathered are used to estimate age-specific hospitalization rates on a weekly basis, and describe characteristics of persons hospitalized with severe influenza illness. The rates provided are likely to be an underestimate as influenza-related hospitalizations can be missed, either because testing is not performed, or because cases may be attributed to other causes of pneumonia or other common influenza-related complications.

Between October 1, 2012 and December 8, 2012, 677 laboratory-confirmed influenza-associated hospitalizations were reported. This is a rate of 2.4 per 100,000 population.

Among all hospitalizations, 524 (77.4%) were associated with influenza A and 145 (21.4%) with influenza B. There was no virus type information for 7 (1.0%) hospitalizations.

Among hospitalizations with influenza A subtype information, 123 (96.9%) were attributed to H3 and 4 (3.1%) were attributed to 2009 H1N1.

The most commonly reported underlying medical conditions among hospitalized adults were metabolic conditions, cardiovascular disease, obesity, and chronic lung disease (excluding asthma).

Among 15 hospitalized women of childbearing age (15-44 years), four were pregnant.

The most commonly reported underlying medical conditions in hospitalized children were asthma, cardiovascular disease, immune suppression and neurologic disorders. Forty percent of hospitalized children had no identified underlying medical conditions.

Additional FluSurv-NET data can be found at: and


View Interactive Application


View Interactive Application


Outpatient Illness Surveillance:

Nationwide during week 49, 2.8% 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 above the national baseline of 2.2%. (ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and cough and/or sore throat.) Region specific data is available at


View National and Regional Level Graphs and Data

On a regional level, the percentage of outpatient visits for ILI ranged from 1.2% to 4.8% during week 49. Seven regions (Regions 1, 2, 3, 4, 5, 6, and 7) reported a proportion of outpatient visits for ILI above their region-specific baseline levels.


ILINet 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 average.

During week 49, the following ILI activity levels were experienced:

  • Eight states experienced high ILI activity (Alabama, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, and Texas).
  • Two states experienced moderate ILI activity (Missouri and Virginia).
  • New York City and nine states experienced low ILI activity (Colorado, Delaware, Florida, Illinois, Kansas, New York, Ohio, Utah, and Wyoming).
  • Thirty-one states experienced minimal ILI activity (Alaska, Arizona, Arkansas, California, Connecticut, Hawaii, Idaho, Indiana, Iowa, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, North Dakota, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Dakota, Vermont, Washington, West Virginia, and Wisconsin).
  • Data were insufficient to calculate an ILI activity level from the District of Columbia.



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 49, the following influenza activity was reported:

  • Widespread influenza activity was reported by 18 states (Alabama, Alaska, Arkansas, Connecticut, Florida, Kentucky, Iowa, Massachusetts, Mississippi, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Texas, Utah, and Wyoming).
  • Regional influenza activity was reported by 17 states (Georgia, Idaho, Illinois, Indiana, Kansas, Louisiana, Maine, Michigan, Minnesota, Missouri, New Jersey, North Dakota, South Dakota, Tennessee, Virginia, West Virginia, and Wisconsin).
  • Local influenza activity was reported by the District of Columbia and 11 states (Arizona, Colorado, Maryland, Montana, Nebraska, Nevada, New Hampshire, New Mexico, Oklahoma, Oregon, and Washington).
  • Sporadic influenza activity was reported by Guam and 4 states (California, Delaware, Hawaii, and Vermont).
  • Puerto Rico and the U.S. Virgin Islands did not report.

Flu Activity data in XML Format