2014-2015 Influenza Season Week 46 ending November 15, 2014

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

Synopsis:

During week 46 (November 9-15, 2014), influenza activity was low in the United States.

• Viral Surveillance: Of 10,304 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 46, 955 (9.3%) 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: No influenza-associated pediatric deaths were reported.
• Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 1.6%, which is below the national baseline of 2.0%. All 10 regions reported ILI below region-specific baseline levels. Puerto Rico experienced high ILI activity; two states experienced low ILI activity; New York City and 48 states experienced minimal ILI activity; and the District of Columbia had insufficient data.
• Geographic Spread of Influenza: The geographic spread of influenza in Puerto Rico and five states was reported as regional; 21 states reported local activity; the District of Columbia, the U.S. Virgin Islands, and 23 states reported sporadic activity; one state reported no influenza activity; and Guam 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, Puerto Rico, and the District of Columbia report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza virus type and influenza A virus subtype. The results of tests performed during the current week are summarized in the table below. Region specific data are available at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.

	Week 46
No. of specimens tested	10,304
No. of positive specimens (%)	955 (9.3%)
Positive specimens by type/subtype
Influenza A	836 (87.5%)
2009 H1N1	0 (0.0%)
H3	257 (30.7%)
Subytping not performed	579 (69.3%)
Influenza B	119 (12.5%)

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

Antigenic Characterization*:

CDC has antigenically characterized 52 influenza viruses (one 2009 H1N1 virus, 34 influenza A (H3N2) viruses, and 17 influenza B viruses) collected by U.S. laboratories since October 1, 2014 by hemagglutination inhibition (HI).

2009 H1N1 [1]:

• The 2009 H1N1 virus tested was characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2014-2015 Northern Hemisphere influenza vaccine.

Influenza A (H3N2) [34]:

• 19 (56%) of the 34 influenza A (H3N2) viruses tested have been characterized as A/Texas/50/2012-like, the influenza A (H3N2) component of the 2014-2015 Northern Hemisphere influenza vaccine. 15 (44%) of the 34 viruses tested showed reduced titers with antiserum produced against A/Texas/50/2012. Among viruses that showed reduced titers with antiserum raised against A/Texas/50/2012, the majority were antigenically similar to A/Switzerland/9715293/2013, the H3N2 virus selected for the 2015 Southern Hemisphere influenza vaccine. A/Switzerland/9715293/2013 is related to, but antigenically and genetically distinguishable, from the A/Texas/50/2012 vaccine virus. A/Switzerland-like H3N2 viruses were first detected in the United States in small numbers in March of 2014 and began to circulate in greater numbers over the spring and summer.

Influenza B [17]: Ten (58.8%) of the influenza B viruses tested belong to B/Yamagata/16/88 lineage and the remaining seven (41.2%) influenza B viruses tested belong to B/Victoria/02/87 lineage.

• Victoria Lineage [10]: All ten B/Yamagata-lineage viruses were characterized as B/Massachusetts/2/2012-like, which is included as an influenza B component of the 2014-2015 Northern Hemisphere trivalent and quadrivalent influenza vaccines.

• Yamagata Lineage [7]: All seven B/Victoria-lineage viruses were characterized as B/Brisbane/60/2008-like, the virus that is included as an influenza B component of the 2014-2015 Northern Hemisphere quadrivalent influenza vaccine.

*CDC conducts antigenic characterization of influenza viruses year-round to compare how similar currently circulating influenza viruses are to those included in the influenza vaccine, and to monitor for changes in circulating influenza 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 H1N1 and influenza A (H3N2) clinical samples are tested for mutations of the virus known to confer oseltamivir resistance. 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). Therefore, data from adamantane resistance testing are not presented below.

Neuraminidase Inhibitor Resistance Testing Results on Samples Collected Since October 1, 2014

	Oseltamivir		Zanamivir
	Virus Samples tested (n)	Resistant Viruses, Number (%)	Virus Samples tested (n)	Resistant Viruses, Number (%)
Influenza A (H3N2)	15	0 (0.0)	15	0 (0.0)
Influenza B	7	0 (0.0)	7	0 (0.0)
2009 H1N1	2	0 (0.0)	2	0 (0.0)

In the United States, all recently circulating influenza viruses have been susceptible to the neuraminidase inhibitor antiviral medications, oseltamivir and zanamivir; however, rare sporadic instances 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 high 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.

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 46, 5.0% of all deaths reported through the 122 Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 6.4% for week 46.

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For the 2014-2015 influenza season, CDC/Influenza Division and the National Center for Health Statistics (NCHS) are collaborating on a pilot project to use NCHS mortality surveillance data for the rapid assessment of pneumonia and influenza (P&I) mortality. To view the data, please click here.

Influenza-Associated Pediatric Mortality:

No influenza-associated pediatric deaths were reported to CDC during week 46. To date, one influenza-associated pediatric death has been reported for the 2014-2015 season.

Additional data can be found at: http://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.

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Influenza-Associated Hospitalizations:

The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts all age population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in the Emerging Infections Program (EIP) states and Influenza Hospitalization Surveillance Project (IHSP) states. FluSurv-NET estimated hospitalization rates will be updated weekly starting later this season. 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.

Outpatient Illness Surveillance:

Nationwide during week 46, 1.6% 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 below the national baseline of 2.0%.

(ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and cough and/or sore throat.)

Additional data are 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 0.8% to 2.3% during week 46. All 10 regions reported a proportion of outpatient visits for ILI below 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 weeks with little or no influenza virus circulation. Activity levels range from minimal, which would correspond to ILI activity from outpatient clinics being below, or only slightly above, the average, to high, which would correspond to ILI activity from outpatient clinics being much higher than average.

During week 46, the following ILI activity levels were experienced:

• Puerto Rico experienced high ILI activity.
• Two states (Alaska and Louisiana) experienced low ILI activity.
• New York City and 48 states (Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, 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) experienced minimal ILI activity.
• 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 disproportionally 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 is 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 46, the following influenza activity was reported:

• Regional influenza activity was reported by Puerto Rico and five states (Alaska, Florida, Louisiana, Massachusetts, and Texas).
• Local influenza activity was reported by 21 states (Alabama, Colorado, Connecticut, Delaware, Georgia, Illinois, Indiana, Kansas, Maine, Maryland, Michigan, Minnesota, New York, North Carolina, Ohio, Oklahoma, Oregon, South Carolina, Utah, Vermont, and Wyoming).
• Sporadic influenza activity was reported by the District of Columbia, U.S. Virgin Islands, and 23 states (Arizona, Arkansas, California, Hawaii, Idaho, Iowa, Kentucky, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, North Dakota, Pennsylvania, South Dakota, Tennessee, Virginia, Washington, West Virginia, and Wisconsin).
• No influenza activity was reported by one state (Rhode Island).
• Guam did not report.