2012-2013 Influenza Season Week 3 ending January 19, 2013

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

Synopsis:

During week 3 (January 13-19), influenza activity remained elevated in the United States, but decreased in some areas.

• Viral Surveillance: Of 11,984 specimens tested and reported by collaborating laboratories, 3,129 (26.1%) were positive for influenza.
• Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was above the epidemic threshold.
• Influenza-Associated Pediatric Deaths: Eight influenza-associated pediatric deaths were reported.
• Influenza-Associated Hospitalizations: A cumulative rate for the season of 22.2 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. Of all hospitalizations, 50% were among adults 65 years and older.
• Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 4.3%; this is above the national baseline of 2.2%. All 10 regions reported ILI above region-specific baseline levels. Twenty-six states and New York City experienced high ILI activity; 14 states experienced moderate activity; 9 states experienced low activity; 1 state experienced minimal activity, and the District of Columbia had insufficient data.
• Geographic Spread of Influenza: Forty-seven states reported widespread geographic influenza activity; 2 states reported regional activity; the District of Columbia and one state reported local activity; Guam reported sporadic influenza 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:

U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (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 3
No. of specimens tested	11,984
No. of positive specimens (%)	3,129 (26.1%)
Positive specimens by type/subtype
Influenza A	2,515 (80.4%)
2009 H1N1	57 (2.3%)
Subtyping not performed	879 (35.0%)
H3	1,579 (62.8%)
Influenza B	614 (19.6%)

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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 less frequently. Over the course of the season the predominant circulating virus has varied by state and by region.

Antigenic Characterization:

CDC has antigenically characterized 751 influenza viruses [Fifty-four 2009 H1N1 viruses, 465 influenza A (H3N2) viruses, and 232 influenza B viruses] collected by U.S. laboratories since October 1, 2012.

2009 H1N1 [54]:

• All fifty-four 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) [465]:

• 463 (99.6%) of the 465 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 (0.4%) of the 465 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) [232]:

• Yamagata Lineage [160]: 160 (69.0%) of the 232 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 [72]: 72 (31.0%) of 232 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		Zanamivir
	Virus Samples tested (n)	Resistant Viruses, Number (%)	Virus Samples tested (n)	Resistant Viruses, Number (%)
Influenza A (H3N2)	762*	0 (0.0)	762*	0 (0.0)
Influenza B	274	0 (0.0)	274	0 (0.0)
2009 H1N1	119*	1 (0.8)	58	0 (0.0)

*Includes specimens tested in national surveillance and additional specimens tested at public health laboratories in six states (AZ, ME, MD, MI, NY, and PA) who share testing results with CDC.

The first oseltamivir-resistant 2009 H1N1 virus detected in the U.S. during the 2012-2013 influenza season is being reported this week. 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 as early as possible is recommended 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 3.

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 3, 9.8% of all deaths reported through the 122 Cities Mortality Reporting System were due to P&I. This percentage was above the epidemic threshold of 7.3% for week 3.

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Influenza-Associated Pediatric Mortality:

Eight influenza-associated pediatric deaths were reported to CDC during week 3. Two were associated with influenza A viruses for which the subtype was not determined and occurred during week 1 (week ending January 5, 2013), and six were associated with influenza B viruses and occurred during weeks 43, 46, 50, 52, and 3 (weeks ending October 27, November 17, December 15 and 29, 2012 and January 19, 2013).

A total of 37 influenza-associated pediatric deaths have been reported during the 2012-2013 season from New York City [1] and 18 states (Arkansas [1], Colorado [4], Florida [4], Indiana [1], Kansas [1], Maine [1], Massachusetts [1], Michigan [4], Minnesota [1], Nebraska [1], New Jersey [2], New York [3], Ohio [1], South Carolina [1], Tennessee [1], Texas [7], Washington [1], and Wisconsin [1]). 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 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 January 19, 2013, 6,191 laboratory-confirmed influenza-associated hospitalizations were reported. This is a rate of 22.2 per 100,000 population. The most affected group is those ≥65 years, accounting for 50% of reported cases. Among all hospitalizations, 5,403 (87.3%) were associated with influenza A and 739 (11.9%) with influenza B. There was no virus type information for 37 (0.6%) hospitalizations. Among hospitalizations with influenza A subtype information, 1,255 (97.8%) were attributed to H3 and 28 (2.2%) were attributed to 2009 H1N1. The most commonly reported underlying medical conditions among hospitalized adults were cardiovascular disease, metabolic disorders, obesity, and chronic lung disease (excluding asthma). Among 120 hospitalized women of childbearing age (15-44 years), 27 were pregnant. The most commonly reported underlying medical conditions in hospitalized children were asthma, neurologic disorders, chronic lung disease and immune suppression. Forty-three percent 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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Outpatient Illness Surveillance:

Nationwide during week 3, 4.3% 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%. Similar to what has been observed in previous seasons, the increase observed in week 52 may be attributed in part to a reduced number of routine health care visits during the end of year holidays. (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 2.9% to 7.0% during week 3. All 10 regions 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 3, the following ILI activity levels were experienced:

• Twenty-six states and New York City experienced high ILI activity (Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Indiana, Kansas, Louisiana, Maryland, Michigan, Missouri, Nevada, New Jersey, North Carolina, North Dakota, Oklahoma, Oregon, Pennsylvania, Texas, Utah, Virginia, and West Virginia).
• Fourteen states experienced moderate ILI activity (Georgia, Idaho, Iowa, Minnesota, Mississippi, Nebraska, New Mexico, New York, Ohio, Rhode Island, Vermont, Washington, Wisconsin, and Wyoming).
• Nine states experienced low ILI activity (Alaska, Florida, Kentucky, Massachusetts, Montana, New Hampshire, South Carolina, South Dakota, and Tennessee).
• One state experienced minimal ILI activity (Maine).
• Data were insufficient to calculate an ILI activity level for 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 3, the following influenza activity was reported:

• Widespread influenza activity was reported by 47 states (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Kentucky, Idaho, Illinois, Indiana, Iowa, Kansas, Louisiana, 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, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming).
• Regional influenza activity was reported by 2 states (Georgia and Tennessee).
• The District of Columbia and one state (Hawaii) reported local influenza activity.
• Guam reported sporadic influenza activity.
• Puerto Rico and the U.S. Virgin Islands did not report.