2012-2013 Influenza Season Week 42 ending October 20, 2012

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

Synopsis:

During week 42 (October 14-20, 2012), influenza activity remained low in the United States.

• Viral Surveillance: Of 2,891 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 42, 178 (6.2%) 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 1.2%, which is below the national baseline of 2.2%. All 10 regions reported ILI below region-specific baseline levels. All 50 states and New York City experienced minimal ILI activity and the District of Columbia had insufficient data.
• Geographic Spread of Influenza: The geographic spread of influenza in three states was reported as local; the District of Columbia and 34 states reported sporadic activity; Guam and 13 states reported no influenza activity, and Puerto Rico and the U.S. Virgin Islands 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 and Washington D.C. 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 42
No. of specimens tested	2,891
No. of positive specimens (%)	178 (6.2%)
Positive specimens by type/subtype
Influenza A	104 (58%)
2009 H1N1	2 (1.9%)
Subtyping not performed	33 (32%)
H3	69 (66%)
Influenza B	74 (42%)

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Novel Influenza A Virus:

No novel influenza A virus infections were reported to CDC during week 42. A total of 310 infections with variant influenza viruses (306 H3N2v viruses, 3 H1N2v viruses, and one H1N1v virus) have been reported from ten states since July 2012, with September 7, 2012 being the most recent date of illness onset in a confirmed case. The vast majority of cases have occurred after contact with swine, though instances of likely human-to-human transmission have been identified. At this time no ongoing human-to-human transmission has been identified.

More information about the H3N2v outbreaks can be found at http://www.cy118119.com/flu/swineflu/h3n2v-outbreak.htm. Additional information on influenza in swine, variant influenza infection in humans, and precautionary measures recommended during interactions with swine can be found at http://www.cy118119.com/flu/swineflu/index.htm.

Antigenic Characterization:

CDC has antigenically characterized 1 influenza B virus collected by a U.S. laboratory since October 1, 2012.

Influenza B (B/Yamagata/16/88 lineage) [1]:

• Yamagata Lineage [1]: One influenza B virus tested, belonging to the B/Yamagata lineage of viruses, was characterized as B/Wisconsin/1/2010-like, the recommended influenza B component for the 2012-13 Northern Hemisphere influenza vaccine.

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)	0	0 (0.0)	0	0 (0.0)
Influenza B	1	0 (0.0)	1	0 (0.0)
2009 H1N1	0	0 (0.0)	0	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 influenza-related complications. Additional information on recommendations for treatment and chemoprophylaxis of influenza virus infection with antiviral agents is available at http://www.cy118119.com/flu/antivirals/index.htm.

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 42, 5.7% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 6.3% for week 42.

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Influenza-Associated Pediatric Mortality:

No influenza-associated pediatric deaths were reported to CDC during week 42. One influenza-associated pediatric death has been reported during the 2012-13 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.

Outpatient Illness Surveillance:

Nationwide during week 42, 1.2% 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 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.

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On a regional level, the percentage of outpatient visits for ILI ranged from 0.6% to 1.8% during week 42. 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 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 42, the following ILI activity levels were experienced:

• All 50 states and New York City 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 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 intensity of influenza activity.

During week 42, the following influenza activity was reported:

• Local influenza activity was reported by three states (Iowa, Texas, and Wyoming).
• Sporadic influenza activity was reported by the District of Columbia and 34 states (Alabama, Alaska, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Indiana, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Montana, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Vermont, Washington, and Wisconsin).
• No influenza activity was reported by Guam and 13 states (Arizona, Arkansas, Illinois, Kansas, Kentucky, Maine, Missouri, Nebraska, Nevada, New Hampshire, Utah, Virginia, and West Virginia).
• Puerto Rico and the U.S. Virgin Islands did not report.