2012-2013 Influenza Season Week 48 ending December 1, 2012

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

Synopsis:

During week 48 (November 25-December 1), influenza activity increased in the U.S.

• Viral Surveillance: Of 5,511 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 48, 1,139 (20.7%) 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: Three influenza-associated pediatric deaths were reported. One of these deaths was associated with an influenza B virus and two were associated with influenza A viruses for which the subtype was not determined.
• Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 1.9%, which is below the national baseline of 2.2%. Three regions reported ILI above region-specific baseline levels. Four states experienced high ILI activity, three states experienced moderate ILI activity; 6 states experienced low ILI activity; New York City and 37 states experienced minimal ILI activity, and the District of Columbia had insufficient data.
• Geographic Spread of Influenza: The geographic spread of influenza in 8 states was reported as widespread; 15 states reported regional activity; 15 states reported local activity; the District of Columbia, Guam, and 12 states reported sporadic activity, and Puerto Rico and the U.S. Virgin Islands did not report.

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

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

	Week 48
No. of specimens tested	5,511
No. of positive specimens (%)	1,139 (20.7%)
Positive specimens by type/subtype
Influenza A	854 (75.0%)
2009 H1N1	4 (0.5%)
Subtyping not performed	444 (52.0%)
H3	406 (47.5%)
Influenza B	285 (25.0%)

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

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 249 influenza viruses [Ten 2009 H1N1 viruses, 155 influenza A (H3N2) viruses, and 84 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) [155]:

• 153 (98.7%) of the 155 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 (1.3%) of the 155 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) [84]:

• Yamagata Lineage [57]: 57 (67.9%) of the 84 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 [27]: 27 (32.1%) of 84 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		Zanamivir
	Virus Samples tested (n)	Resistant Viruses, Number (%)	Virus Samples tested (n)	Resistant Viruses, Number (%)
Influenza A (H3N2)	190	0 (0.0)	190	0 (0.0)
Influenza B	98	0 (0.0)	98	0 (0.0)
2009 H1N1	4	0 (0.0)	4	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 http://www.cdc.gov/flu/antivirals/index.htm.

Novel Influenza A Virus:

No new human infections with novel influenza viruses were reported during week 48.

A total of 311 infections with variant influenza viruses (307 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-outbreak.htm.

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 48, 6.5% of all deaths reported through the 122 Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 6.8% for week 48.

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Influenza-Associated Pediatric Mortality:

Three influenza-associated pediatric deaths were reported to CDC during week 48. One of these deaths was associated with an influenza B virus and two were associated with influenza A viruses for which the subtype was not determined. One death occurred during the week ending November 24 (week 47) and two deaths 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 5. Additional data can be found at: http://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.

View Interactive Application | View Full Screen | View PowerPoint Presentation

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 1, 2012, 417 laboratory-confirmed influenza-associated hospitalizations were reported. This is a rate of 1.5 per 100,000 population. Among all hospitalizations, 319 (76.5%) were associated with influenza A, 90 (21.6%) with influenza B; there was no virus type information for 8 (1.9%) hospitalizations. Among hospitalizations with influenza A subtype information, 85 (96.6%) were attributed to H3 and 3 (3.4%) 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 11 hospitalized women of childbearing age (15-44 years), one was pregnant. The most commonly reported underlying medical conditions in hospitalized children were asthma, cardiovascular disease, neurologic disorders and obesity. More than 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.

This week, a second application displaying data from FluSurvNET that focuses on the characteristics (such as virus type, demographic, and clinical information) of these hospitalizations is available.

View Interactive Application | View Full Screen | View PowerPoint Presentation

View Interactive Application | View Full Screen | View PowerPoint Presentation

Outpatient Illness Surveillance:

Nationwide during week 48, 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 2.2%, and is lower than reported during the previous week. This fluctuation may be attributed in part to a reduced number of routine health visits during the Thanksgiving holidays, as 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 | View Chart Data | View Full Screen | View PowerPoint Presentation

On a regional level, the percentage of outpatient visits for ILI ranged from 0.9% to 3.9% during week 48. Three regions (Regions 2, 4, and 6) 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 intense, which would correspond to ILI activity from outpatient clinics being much higher than average.

During week 48, the following ILI activity levels were experienced:

• Four states experienced high ILI activity (Alabama, Louisiana, Mississippi, and Texas).
• Three states experienced moderate ILI activity (Georgia, Missouri and Tennessee).
• Six states experienced low ILI activity (Illinois, North Carolina, Ohio, South Carolina, Utah, and Virginia).
• New York City and 37 states experienced minimal ILI activity (Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Hawaii, Idaho, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Dakota, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Dakota, Vermont, 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 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 48, the following influenza activity was reported:

• Widespread influenza activity was reported by 8 states (Alabama, Alaska, Mississippi, New York, North Carolina, Ohio, Rhode Island, and South Carolina).
• Regional influenza activity was reported by 15 states (Arkansas, Connecticut, Florida, Georgia, Idaho, Illinois, Iowa, Kentucky, Louisiana, Maine, Pennsylvania, Tennessee, Texas, Utah, and Wyoming).
• Local influenza activity was reported by 15 states (Arizona, Colorado, Kansas, Massachusetts, Michigan, Minnesota, Missouri, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Virginia, Washington, and Wisconsin).
• Sporadic influenza activity was reported by the District of Columbia, Guam, and 12 states (California, Delaware, Hawaii, Indiana, Maryland, Montana, Nebraska, Nevada, New Hampshire, New Jersey, Vermont, and West Virginia).
• Puerto Rico and the U.S. Virgin Islands did not report.