2012-2013 Influenza Season Week 19 ending May 11, 2013

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

Synopsis:

During week 19 (May 5-11, 2013), influenza activity remained low in the United States.

• Viral Surveillance: Of 2,416 specimens tested and reported by collaborating laboratories, 124 (5.1%) 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: One pediatric death was reported.
• Influenza-Associated Hospitalizations: A cumulative rate for the season of 44.3 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. Of reported hospitalizations, about 50% were among adults 65 years and older.
• Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 0.9%. This is below the national baseline of 2.2%. All 10 regions reported ILI below region-specific baseline levels. One state experienced low activity, 49 states and New York City experienced minimal activity, and the District of Columbia had insufficient data.
• Geographic Spread of Influenza: 1 state reported regional influenza activity; Puerto Rico and 2 states reported local influenza activity; Guam and 35 states reported sporadic influenza activity; 12 states reported no influenza activity, and the District of Columbia 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 19
No. of specimens tested	2,416
No. of positive specimens (%)	124 (5.1%)
Positive specimens by type/subtype
Influenza A	30 (24.2%)
2009 H1N1	3 (10.0%)
Subtyping not performed	23 (76.7%)
H3	4 (13.3%)
Influenza B	94 (75.8%)

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

Antigenic Characterization

CDC has antigenically characterized 2,391 influenza viruses [234 2009 H1N1 viruses, 1,324 influenza A (H3N2) viruses, and 833 influenza B viruses] collected by U.S. laboratories since October 1, 2012.

2009 H1N1 [234]:

• 231 (98.7%) of the 234 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 (1.3%) of the 234 2009 H1N1 viruses tested showed reduced titers with antiserum produced against A/California/7/2009.

Influenza A (H3N2) [1,324]:

• 1,319 (99.6%) of the 1,324 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.
• 5 (0.4%) of the 1,324 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) [833]:

• Yamagata Lineage [554]: 554 (66.5%) of the 833 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 [279]: 279 (33.5%) of 833 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.

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)	2,119*	2 (0.1)	2,119*	1 (0.05)
Influenza B	935	0 (0.0)	935	0 (0.0)
2009 H1N1	540*	2 (0.4)	257	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 in the United States were reported to CDC during week 19.

On April 1, 2013, the World Health Organization (WHO) first reported 3 human infections with a new influenza A (H7N9) virus in China. Since then, additional cases have been reported. Most reported cases have severe respiratory illness and, in some cases, have died. At this time, no cases of H7N9 outside of China have been reported. The new H7N9 virus has not been detected in people or birds in the United States.

Pneumonia and Influenza (P&I) Mortality Surveillance

During week 19, 6.4% 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 19.

View Full Screen | View PowerPoint Presentation

Influenza-Associated Pediatric Mortality

One influenza-associated pediatric death was reported to CDC during week 19. This death was associated with an influenza A virus for which the subtype was not determined and occurred during week 51 (week ending December 22, 2012).

A total of 139 influenza-associated pediatric deaths have been reported during the 2012-2013 season from Chicago [2], New York City [4] and 37 states (AL [1], AR [4], AZ [4], CA [4], CO [5], FL [8], GA [3], HI [2], IA [1], IL [2], IN [4], KS [2], KY [2], LA [2], MA [4], MD [3], ME [1], MI [6], MN [4], MS [1], NE [1], NH [3], NJ [7], NM [3], NV [3], NY [10], OH [4], OK [1], PA [1], SC [5], SD [3], TN [3], TX [17], UT [3], VA [1], WA [1], and WI [4]).

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 May 11, 2013, 12,348 laboratory-confirmed influenza-associated hospitalizations were reported. This is a rate of 44.3 per 100,000 population. The most affected group is those ≥65 years, accounting for about 50% of reported cases. Among all hospitalizations, 9,768 (79.1%) were associated with influenza A and 2,498 (20.2%) with influenza B. There was no virus type information for 47 (0.4%) hospitalizations. Among hospitalizations with influenza A subtype information, 3,757 (95.9%) were attributed to H3 and 151 (3.9%) 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 46% of hospitalized children had no identified underlying medical conditions. Among 702 hospitalized women of childbearing age (15-44 years), 208 were pregnant, including 7 pregnancies among the 38 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.

The current season’s influenza-associated hospitalization data includes patients admitted from October 1, 2012 through April 30, 2013; however, these data will continue to be updated as additional information is received.

View Interactive Application | View Full Screen | View PowerPoint Presentation

View Interactive Application | View Full Screen | View PowerPoint Presentation

Outpatient Illness Surveillance

Nationwide during week 19, 0.9% 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%. (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 0.2% to 1.7% during week 19. All 10 regions reported a proportion of outpatient visits for ILI below 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 19, the following ILI activity levels were experienced:

• One state experienced low ILI activity (Hawaii).
• Forty-nine states and New York City experienced minimal ILI activity (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, 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, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming).
• 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 19, the following influenza activity was reported:

• One state reported regional influenza activity (Hawaii).
• Puerto Rico and two states reported local influenza activity (New Hampshire and Massachusetts).
• Guam and 35 states reported sporadic influenza activity (Alaska, Arizona, California, Connecticut, Florida, Illinois, Indiana, Iowa, Louisiana, Maryland, Michigan, Minnesota, Missouri, Montana, Nevada, 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).
• Twelve states (Alabama, Arkansas, Colorado, Delaware, Georgia, Idaho, Kansas, Kentucky, Maine, Mississippi, Nebraska, and Tennessee) reported no influenza activity.
• The U.S. Virgin Islands and the District of Columbia did not report.