2011-2012 Influenza Season Week 43 ending October 29, 2011

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

Synopsis:

During week 43 (October 23-29, 2011), influenza activity remained low in the United States.

• U.S. Virologic Surveillance: Of the 1,804 specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division, 17 (0.9%) were positive for influenza.
• Novel influenza A Virus: Two human infections with a novel influenza A virus were identified.
• Pneumonia and Influenza (P&I) Mortality Surveillance: The proportion of deaths attributed to P&I was below the epidemic threshold.
• Influenza-associated Pediatric Mortality: 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 2.4%. All 10 regions reported ILI below region-specific baseline levels. Forty-nine states and New York City experienced minimal ILI activity, one state experienced ILI low activity and the District of Columbia had insufficient data.
• Geographic Spread of Influenza: The geographic spread of influenza in the District of Columbia, Puerto Rico, and 20 states was reported as sporadic and Guam, the U.S. Virgin Islands, and 30 states reported no influenza activity.

*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 type and subtype. The results of tests performed during the current week are summarized in the table below.

	Week 43
No. of specimens tested	1,804
No. of positive specimens (%)	17 (0.9%)
Positive specimens by type/subtype
Influenza A	16 (94%)
A (2009 H1N1)	0 (0.0%)
A (subtyping not performed)	13 (81%)
A (H3)	3 (19%)
Influenza B	1 (6%)

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Novel Influenza A Viruses:

Two human infections with novel influenza A viruses were detected in individuals from two states (Indiana and Maine). Both patients were infected with swine-origin influenza A (H3N2) viruses. One patient was hospitalized, but has now been discharged and both continue to recover from their illnesses. Both patients reported close contacts with pigs preceding their illness onset. There is no evidence of an epidemiological link between these two patients and no sustained human-to-human transmission of these viruses has been found in either state. Additional information on these cases is available at http://www.cy118119.com/media/haveyouheard/stories/H3N2_virus2.html

CDC is required to report all cases of human infection with novel influenza viruses – including swine influenza viruses -- to the World Health Organization (WHO) as part of the International Health Regulations (IHR). Domestically, CDC reports these cases in this report and on its website. Early identification and investigation of human infections with novel influenza A viruses is critical to evaluate the extent of the outbreak and possible human-to-human transmission. Additional information on influenza in pigs and swine-origin influenza infection in humans can be found at http://www.cy118119.com/flu/swineflu/

Antigenic Characterization:

CDC has antigenically characterized five influenza viruses [four influenza A (H3N2) viruses and one influenza B virus] collected by U.S. laboratories since October 1, 2011.

Influenza A (H3N2) [4]

• All four were characterized as A/Perth/16/2009-like, the influenza A (H3N2) component of the 2011-12 influenza vaccine for the Northern Hemisphere.

Influenza B [1]:

• The virus tested belongs to the B/Victoria lineage and was characterized as B/Brisbane/60/2008-like, the influenza B component of the 2011-12 influenza vaccine for the Northern Hemisphere.

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, 2011

	Oseltamivir		Zanamivir
	Virus Samples tested (n)	Resistant Viruses, Number (%)	Virus Samples tested (n)	Resistant Viruses, Number (%)
Influenza A (H3N2)	4	0 (0.0)	4	0 (0.0)
Influenza B	1	0 (0.0)	1	0 (0.0)
Influenza A (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 43, 6.5% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 6.7% for week 43.

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Influenza-Associated Pediatric Mortality:

No influenza-associated pediatric deaths were reported to CDC during week 43.

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Influenza-Associated Hospitalizations:

The Influenza Hospitalization Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza related hospitalizations in children (persons younger than 18 years) and adults. The network covers more than 80 counties in the 10 Emerging Infections Program (EIP) states (CA, CO, CT, GA, MD, MN, NM, NY, OR, and TN) and four additional states (MI, OH, RI and UT). FluSurv-NET estimated hospitalization rates will be updated weekly starting later this season.

Outpatient Illness Surveillance:

Nationwide during week 43, 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 2.4%. (ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and cough and/or sore throat.)

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On a regional level, the percentage of outpatient visits for ILI ranged from 0.7% to 1.9% during week 43. 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 43, the following ILI activity levels were experienced:

• Forty-nine states and New York City experienced minimal ILI activity (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, 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).
• One state experienced low ILI activity (Maryland).
• 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 43, the following influenza activity was reported:

• Sporadic influenza activity was reported by the District of Columbia, Puerto Rico, and 19 states (Alaska, California, Colorado, Connecticut, Florida, Hawaii, Idaho, Indiana, Louisiana, Maine, Massachusetts, Minnesota, New Mexico, New York, Ohio, Pennsylvania, Texas, Virginia, Washington, and Wisconsin).
• No influenza activity was reported by Guam, the U.S. Virgin Islands, and 31 states (Alabama, Arizona, Arkansas, Delaware, Georgia, Illinois, Iowa, Kansas, Kentucky, Maryland, Michigan, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, North Carolina, North Dakota, Oklahoma, Oregon, Rhode Island, South Carolina, South Dakota, Tennessee, Utah, Vermont, West Virginia, and Wyoming).