[Source: US Centers for Disease Control and Prevention, FluView, full page: (LINK). Edited.]
2012-2013 Influenza Season Week 11 ending March 16, 2013
All data are preliminary and may change as more reports are received.
During week 11 (March 10 – 16, 2013), influenza activity remained elevated in the United States, but decreased in most areas.
- Viral Surveillance: Of 5,526 specimens tested and reported by collaborating laboratories, 899 (16.3%) 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: Six pediatric deaths were reported.
- Influenza-Associated Hospitalizations: A cumulative rate for the season of 40.6 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. Of reported hospitalizations, 51% were among adults 65 years and older.
- Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 2.2%. This is at the national baseline of 2.2%. Three of 10 regions reported ILI above region-specific baseline levels. One state experienced high ILI activity; 5 states experienced moderate activity; 6 states and New York City experienced low activity; 38 states experienced minimal activity, and the District of Columbia had insufficient data.
- Geographic Spread of Influenza: Seven states reported widespread influenza activity; Puerto Rico and 8 states reported regional influenza activity; 26 states reported local influenza activity; 9 states reported sporadic influenza activity; Guam reported no influenza activity, and the U.S. Virgin Islands and the District of Columbia 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 - 16.3% - 16 of 54 - 1,187 - 32,361 - 15,952 - 16,983 – 105
- Region 1 – Elevated - 15.9% - 2 of 6 – 62 - 2,363 – 597 – 304 – 5
- Region 2 – Elevated - 17.9% - 3 of 4 – 164 - 2,365 - 2,101 - 1,077 – 16
- Region 3 – Normal - 25.4% - 2 of 6 – 209 - 6,792 – 487 - 1,883 – 4
- Region 4 – Normal - 18.7% - 1 of 8 – 99 - 2,527 - 6,164 - 3,102 – 16
- Region 5 – Elevated - 23.5% - 2 of 6 – 97 - 4,822 – 475 - 1,264 – 20
- Region 6 – Normal - 14.2% - 1 of 5 – 68 - 2,087 - 3,000 - 3,728 – 22
- Region 7 – Normal - 10.5% - 0 of 4 – 35 - 1,952 – 196 – 966 – 4
- Region 8 – Normal - 12.3% - 2 of 6 – 196 - 2,898 - 1,892 - 2,844 – 10
- Region 9 – Normal - 21.5% - 2 of 5 – 203 - 3,852 – 811 - 1,304 - 7
- Region 10 – Normal - 10.1% - 1 of 4 - 54 - 2,703 - 229 - 511 - 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
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.
- No. of specimens tested - 5,526
- No. of positive specimens (%) - 899 (16.3%)
- Positive specimens by type/subtype:
- Influenza A - 253 (28.1%)
- 2009 H1N1 - 12 (4.7%)
- Subtyping not performed - 154 (60.9%)
- H3 - 87 (34.4%)
- Influenza B - 646 (71.9%)
Since the start of the season, influenza A (H3N2) viruses have predominated nationally, however in recent weeks, the proportion of influenza B viruses has been increasing. During week 11, 72% of all influenza positive specimens reported were influenza B viruses and influenza B viruses were reported more frequently than influenza A viruses in 8 of 10 regions.
CDC has antigenically characterized 1,695 influenza viruses [141 2009 H1N1 viruses, 1,012 influenza A (H3N2) viruses, and 542 influenza B viruses] collected by U.S. laboratories since October 1, 2012.
2009 H1N1 :
- 138 (97.9%) of the 141 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.
- 3 (2.1%) of the 141 2009 H1N1 viruses tested showed reduced titers with antiserum produced against A/California/7/2009.
Influenza A (H3N2) [1,012]:
- 1,008 (99.6%) of the 1,012 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.
- 4 (0.4%) of the 1,012 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) :
- Yamagata Lineage : 383 (70.7%) of the 542 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 : 159 (29.3%) of 542 influenza B viruses tested have been from the B/Victoria lineage of viruses.
Composition of the 2013-2014 Influenza Vaccine
The World Health Organization (WHO) has recommended vaccine viruses for the 2013-2014 Northern Hemisphere vaccines, and the Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) has made recommendations for the composition of the 2013-2014 influenza vaccines to be used in the United States.
Both agencies recommend that trivalent vaccines contain an A/California/7/2009-like (2009 H1N1) virus, an A(H3N2) virus antigenically like the cell-propagated, or cell-grown, virus A/Victoria/361/2011 (A/Texas/50/2012), and a B/Massachusetts/2/2012-like (B/Yamagata lineage) virus. It is recommended that quadrivalent vaccines containing an additional influenza B virus contain a B/Brisbane/60/2008-like (B/Victoria lineage) virus in addition to the viruses recommended for the trivalent vaccines.
These recommendations were based on global influenza virus surveillance data related to epidemiology and antigenic characteristics, serological responses to 2012-2013 seasonal vaccines, and the availability of candidate strains and reagents.
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) - 1,577* - 2 (0.1) - 1,577* - 0 (0.0)
- Influenza B – 608 - 0 (0.0) – 608 - 0 (0.0)
- 2009 H1N1 - 405* - 2 (0.5) – 184 - 0 (0.0)
*Includes specimens tested in national surveillance and additional specimens tested at public health laboratories in 11 states (AZ, DE, HI, ME, MD, MI, MN, NY, PA, WA, and WI) who share testing results with CDC.
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 11.
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 11, 7.6% of all deaths reported through the 122 Cities Mortality Reporting System were due to P&I. This percentage was above the epidemic threshold of 7.5% for week 11.
Influenza-Associated Pediatric Mortality
Six influenza-associated pediatric deaths were reported to CDC during week 11. One death was associated with a 2009 H1N1 virus and occurred during week 9 (week ending March 2, 2013) and five were associated with influenza B viruses and occurred during weeks 48, 52, 6, 10, and 11 (weeks ending December 1, December 29, 2012, February 9, March 9, and March 16, 2013).
A total of 105 influenza-associated pediatric deaths have been reported during the 2012-2013 season from:
- Chicago ,
- New York City  and
- 36 states:
- AL ,
- AR ,
- AZ ,
- CA ,
- CO ,
- FL ,
- HI ,
- IA ,
- IL ,
- IN ,
- KS ,
- KY ,
- LA ,
- MA ,
- MD ,
- ME ,
- MI ,
- MN ,
- MS ,
- NE ,
- NH ,
- NJ ,
- NM ,
- NV ,
- NY ,
- OH ,
- OK ,
- PA ,
- SC ,
- SD ,
- TN ,
- TX ,
- UT ,
- VA ,
- WA , and
- WI 
Additional data can be found at http://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.
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 March 16, 2013, 11,307 laboratory-confirmed influenza-associated hospitalizations were reported. This is a rate of 40.6 per 100,000 population. The most affected group is those ≥65 years, accounting for 51% of reported cases. Among all hospitalizations, 9,387 (83.0%) were associated with influenza A and 1,841 (16.3%) with influenza B. There was no virus type information for 40 (0.4%) hospitalizations. Among hospitalizations with influenza A subtype information, 3,022 (96.5%) were attributed to H3 and 96 (3.1%) 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). The most commonly reported underlying medical conditions in hospitalized children were asthma, neurologic disorders, and immune suppression. Approximately 44% of hospitalized children had no identified underlying medical conditions. Among 394 hospitalized women of childbearing age (15-44 years), 119 were pregnant, including 5 pregnancies among the 24 pediatric cases in this category.
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 11, 2.2% 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 at 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 http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.
On a regional level, the percentage of outpatient visits for ILI ranged from 1.1% to 3.0% during week 11. Three of 10 regions (1, 2, and 5) 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 11, the following ILI activity levels were experienced:
- One state (Michigan) experienced high ILI activity.
- Five states experienced moderate ILI activity (Alabama, Mississippi, Nevada, New Jersey, and Virginia).
- Six states and New York City experienced low ILI activity (Indiana, Louisiana, Minnesota, Montana, South Dakota, and Utah).
- Thirty-eight states experienced minimal ILI activity (Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Missouri, Nebraska, New Hampshire, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Vermont, Washington, West Virginia, Wisconsin, and Wyoming).
- Data were insufficient to calculate an ILI activity level for the District of Columbia.
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 11, the following influenza activity was reported:
- Widespread influenza activity was reported by 7 states (Connecticut, Massachusetts, Nevada, New Jersey, New York, North Carolina, and Ohio).
- Puerto Rico and 8 states reported regional influenza activity (Alaska, California, Michigan, Montana, Oklahoma, Pennsylvania, Utah, and Virginia).
- Twenty-six states reported local influenza activity (Alabama, Arizona, Arkansas, Georgia, Idaho, Illinois, Iowa, Kentucky, Louisiana, Maryland, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Mexico, Oregon, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Washington, West Virginia, Wisconsin, and Wyoming).
- Nine states reported sporadic influenza activity (Colorado, Delaware, Florida, Hawaii, Indiana, Kansas, Maine, North Dakota, and Vermont).
- Guam reported no influenza activity.
- The U.S. Virgin Islands and the District of Columbia did not report.