4 Jan 2013

2012-2013 Influenza Season Week 52 ending December 29, 2012 (US CDC, FluView, January 4 2013, edited)

[Source: US Centers for Disease Control and Prevention, FluView, full page: (LINK). Edited.]

2012-2013 Influenza Season Week 52 ending December 29, 2012

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



During week 52 (December 23-29), influenza activity increased in the U.S.

  • Viral Surveillance: Of 9,363 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories, 2,961 (31.6%) were positive for influenza.
  • Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.
  • Influenza-Associated Pediatric Deaths: Two influenza-associated pediatric deaths were reported and were associated with influenza B viruses.
  • Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 5.6%; above the national baseline of 2.2%. Nine of 10 regions reported ILI above region-specific baseline levels. New York City and 29 states experienced high ILI activity; 9 states experienced moderate ILI activity; 4 states experienced low ILI activity; 6 states experienced minimal ILI activity, and the District of Columbia and 2 states had insufficient data.
  • Geographic Spread of Influenza: Forty-one states reported widespread geographic influenza activity; 7 states reported regional activity; the District of Columbia reported local activity; 1 state reported sporadic activity; Guam reported no influenza activity, and Puerto Rico, the U.S. Virgin Islands, and 1 state did not report.

A description of surveillance methods is available at: http://www.cdc.gov/flu/weekly/overview.htm


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 - 31.6% -  48 of 54 -  194 -  10,612 -  5,621 -  5,621 -  18
  • Region 1 -  Elevated -  45.3% -  6 of 6 -  18 -  850 -  204 -  59 – 1
  • Region 2 -  Elevated -  36.6% -  2 of 4 -  21 -  722 -  683 -  161 -  3
  • Region 3 -  Elevated -  43.3% -  4 of 6 -  37 -  1,688 -  105 -  171 -  0
  • Region 4 -  Elevated -  28.3% -  8 of 8 -  20 -  1,410 -  3,368 -  1,058 -  4
  • Region 5 -  Elevated -  58.4% -  6 of 6 -  29 -  1,985 -  174 -  417 -  5
  • Region 6 -  Elevated -  24.7% -  5 of 5 -  7 -  599 -  529 -  971 -  4
  • Region 7 -  Elevated -  33.9% -  4 of 4 -  2 -  868 -  173 -  422 -  0
  • Region 8 -  Elevated -  30.3% -  6 of 6 -  25 -  940 -  297 -  1,174 -  0
  • Region 9 -  Normal -  22.9% -  3 of 5 -  32 -  599 -  58 -  137 -  0
  • Region 10 -  Elevated -  31.5% -  4 of 4 -  3 -  951 -  30 -  138 -  1

*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 http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.


Week 52

  • No. of specimens tested - 9,363
    • No. of positive specimens (%) - 2,961 (31.6%)
      • Positive specimens by type/subtype:
        • Influenza A - 2,346 (79.2%)
          • 2009 H1N1 - 25 (1.1%)
          • Subtyping not performed  -  1,112 (47.4%)
          • H3 - 1,209 (51.5%)
        • Influenza B - 615 (20.8%)


View National and Regional Level Graphs and Data

Since the start of the season, influenza A (H3N2) viruses have predominated nationally, followed by influenza B viruses, while 2009 H1N1 viruses have been identified rarely. The predominant circulating virus has varied by state and by region.


Antigenic Characterization:

CDC has antigenically characterized 413 influenza viruses [17 2009 H1N1 viruses, 281 influenza A (H3N2) viruses, and 115 influenza B viruses] collected by U.S. laboratories since October 1, 2012.

2009 H1N1 [17]:

  • All 17 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) [281]:

  • 279 (99.3%) of the 281 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 (0.7%) of the 281 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) [115]:

  • Yamagata Lineage [79]: 79 (68.7%) of the 115 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 [36]: 36 (31.3%) of 115 influenza B viruses tested have been from the B/Victoria lineage of viruses.


Antiviral Resistance:

Testing of 2009 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, data from adamantane resistance testing are not presented 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) – 526 - 0 (0.0) – 526 -  0 (0.0)
  • Influenza B -  226 -  0 (0.0) -  226 -  0 (0.0)
  • 2009 H1N1 -  39 -  0 (0.0) -  30 -  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 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 http://www.cdc.gov/flu/antivirals/index.htm.


Novel Influenza A Virus:

No new human infections with novel influenza A viruses were reported to CDC during week 52.

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 http://www.cdc.gov/flu/swineflu/h3n2v-cases.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 7.1% for week 52.


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Influenza-Associated Pediatric Mortality:

Two influenza-associated pediatric deaths were reported to CDC during week 52 and were associated with influenza B viruses. One death occurred during week 48 (week ending December 1) and one death occurred during week 52 (week ending December 29). This brings the total number of influenza-associated pediatric deaths reported during the 2012-2013 season to 18. Additional data can be found at http://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.


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 29, 2012, 2,257 laboratory-confirmed influenza-associated hospitalizations were reported. This is a rate of 8.1 per 100,000 population. Among all hospitalizations, 1,924 (85.2%) were associated with influenza A and 312 (13.8%) with influenza B. There was no virus type information for 19 (0.8%) hospitalizations. Among hospitalizations with influenza A subtype information, 475 (98.1%) were attributed to H3 and 9 (1.9%) 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 36 hospitalized women of childbearing age (15-44 years), seven were pregnant. The most commonly reported underlying medical conditions in hospitalized children were asthma, neurologic disorders, and immune suppression. Approximately 40% of hospitalized children had no identified underlying medical conditions. Additional FluSurv-NET data can be found at: http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.


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View Interactive Application


Outpatient Illness Surveillance:

Nationwide during week 52, 5.6% 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%. This increase may be attributed in part to a reduced number of routine health care visits during the Christmas holidays, which has been observed in previous seasons. (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 http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.


View National and Regional Level Graphs and Data

On a regional level, the percentage of outpatient visits for ILI ranged from 2.0% to 9.1% during week 52. Nine regions (Regions 1-8 and 10) 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 52, the following ILI activity levels were experienced:

  • New York City and 29 states experienced high ILI activity (Alabama, Arkansas, Colorado, Florida, Georgia, Illinois, Indiana, Kansas, Louisiana, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Utah, Vermont, Virginia, and Wyoming).
  • Nine states experienced moderate ILI activity (Alaska, Arizona, Delaware, Iowa, Nebraska, North Dakota, Oregon, Washington, and West Virginia).
  • Four states experienced low ILI activity (Kentucky, New Hampshire, South Dakota, and Wisconsin).
  • Six states experienced minimal ILI activity (California, Connecticut, Hawaii, Maine, Montana, and Nevada).
  • Data were insufficient to calculate an ILI activity level for the District of Columbia and 2 states (Idaho and Maryland).


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 severity of influenza activity.

During week 52, the following influenza activity was reported:

  • Widespread influenza activity was reported by 41 states (Alabama, Alaska, Arkansas, Colorado, Connecticut, Florida, Georgia, Kentucky, Idaho, Illinois, Indiana, Iowa, Kansas, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, South Carolina, Rhode Island, Tennessee, Texas, Utah, Vermont, Virginia, West Virginia, Wisconsin, and Wyoming).
  • Regional influenza activity was reported by 7 states (Arizona, California, Missouri, Montana, Oregon, South Dakota, and Washington).
  • The District of Columbia reported local influenza activity.
  • Sporadic influenza activity was reported by 1 state (Hawaii).
  • Guam reported no influenza activity.
  • Puerto Rico, the U.S. Virgin Islands, and 1 state (Delaware) did not report.

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