Flu activity is high across most of the country with flu illnesses, hospitalizations and deaths elevated. Flu season will probably continue for several weeks.
While the flu vaccine is not working as well as usual against some H3N2 viruses, vaccination can still protect some people and reduce hospitalizations and deaths, and will protect against other flu viruses.
Influenza antiviral drugs can treat flu illness. CDC recommends these drugs be used to treat people who are very sick or who are at high risk of serious flu complications who have flu symptoms. Early antiviral treatment works best.
2014-2015 Influenza Season Week 1 ending January 10, 2015
All data are preliminary and may change as more reports are received.
During week 1 (January 4-10, 2015), influenza activity remained elevated in the United States.
*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
§ Includes all 50 states, the District of Columbia, Guam, Puerto Rico, and U.S. Virgin Islands
‡ National data are for current week; regional data are for the most recent three weeks
U.S. Virologic Surveillance:
WHO and NREVSS collaborating laboratories located in all 50 states, Puerto Rico, and the District of Columbia report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza virus type and influenza A virus subtype. The results of tests performed during the current week are summarized in the table below. Region specific data are available at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.
Influenza Virus Characterization*:
CDC has characterized 462 influenza viruses [10 A(H1N1)pdm09, 349 A(H3N2), and 103 influenza B viruses] collected by U.S. laboratories since October 1, 2014.
Influenza A Virus 
Influenza B Virus 
Sixty-nine (67.0%) of the influenza B viruses tested belong to B/Yamagata/16/88 lineage and the remaining 34 (33.0%) influenza B viruses tested belong to B/Victoria/02/87 lineage.
*CDC routinely uses hemagglutination inhibition (HI) assays to antigenically characterize influenza viruses year-round to compare how similar currently circulating influenza viruses are to those included in the influenza vaccine, and to monitor for changes in circulating influenza viruses. However, a portion of recent influenza A(H3N2) viruses do not grow to sufficient hemagglutination titers for antigenic characterization by HI. For many of these viruses, CDC is also performing genetic characterization to infer antigenic properties.
Testing of influenza A(H1N1)pdm09, A(H3N2), and influenza B virus isolates for resistance to neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) is performed at CDC using a functional assay. Additional A(H1N1)pdm09 and A(H3N2) clinical samples are tested for mutations of the virus known to confer oseltamivir resistance. 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 A(H1N1)pdm09 and A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, data from adamantane resistance testing are not presented below.
In the United States, all recently circulating influenza viruses have been susceptible to the neuraminidase inhibitor antiviral medications, oseltamivir, zanamivir, and peramivir; however, rare sporadic instances of oseltamivir-resistant A(H1N1)pdm09 and A(H3N2) viruses have been detected worldwide. Antiviral treatment with oseltamivir, zanamivir, or peramivir 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 high risk for serious influenza-related complications. Additional information on recommendations for treatment and chemoprophylaxis of influenza virus infection with antiviral agents is available athttp://www.cdc.gov/flu/antivirals/index.htm.
Pneumonia and Influenza (P&I) Mortality Surveillance:
During week 1, 8.5% of all deaths reported through the 122 Cities Mortality Reporting System were due to P&I. This percentage was above the epidemic threshold of 7.0% for week 1.
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For the 2014-2015 influenza season, CDC/Influenza Division and the National Center for Health Statistics (NCHS) are collaborating on a pilot project to use NCHS mortality surveillance data for the rapid assessment of pneumonia and influenza (P&I) mortality. To view the data, please click here.
Influenza-Associated Pediatric Mortality:
Nineteen influenza-associated pediatric deaths were reported to CDC during week 1. Eight deaths were associated with an influenza A (H3) virus and occurred during weeks 51, 52, 53, and 1 (weeks ending December 20, December 27, 2014, January 3, and January 10, 2015, respectively). Nine deaths were associated with an influenza A virus for which no subtyping was performed and occurred during weeks 50, 52, 53, and 1 (weeks ending December 13, December 27, 2014, and January 3, and January 10, 2015, respectively). One death was associated with an influenza virus for which the type was not determined and occurred during week 53, and one death was associated with an influenza B virus and occurred during week 1.
A total of 45 influenza-associated deaths have been reported during the 2014-2015 season from New York City  and 18 states (Arizona , Colorado , Florida , Georgia , Iowa , Kansas , Kentucky , Louisiana , Minnesota , North Carolina , Nevada , Ohio , Oklahoma , South Carolina , Tennessee , Texas , Virginia , and Wisconsin ).
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 70 counties in the 10 Emerging Infections Program (EIP) states (CA, CO, CT, GA, MD, MN, NM, NY, OR, and 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; IA, MI, OH, RI, and UT during the 2012-2013 season; and MI, OH, and UT during the 2013-2014 and 2014-2015 seasons.
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, 2014 and January 10, 2015, 8,199 laboratory-confirmed influenza-associated hospitalizations were reported. The overall hospitalization rate was 29.9 per 100,000 population. The highest rate of hospitalization was among adults aged ≥65 years (143.3 per 100,000 population), followed by children aged 0-4 years (30.0 per 100,000 population). Among all hospitalizations, 7,934 (96.8%) were associated with influenza A, 200 (2.5%) with influenza B, 21 (0.3%) with influenza A and B co-infection, and 38 (0.4%) had no virus type information. Among those with influenza A subtype information, 2,110 (99.6%) were A(H3N2) virus, seven (0.3%) were A(H1N1)pdm09 and one (0.1%) was A(H1) unspecified.
Clinical findings are preliminary and based on 984 (12%) cases with complete medical chart abstraction. The majority (93.4%) of hospitalized adults had at least one reported underlying medical condition; the most commonly reported were metabolic disorders, cardiovascular disease, and obesity. There were 164 hospitalized children with complete medical chart abstraction, 68 (41%) had no identified underlying medical conditions. The most commonly reported underlying medical conditions among pediatric patients were asthma, obesity, and immune suppression. Among the 95 hospitalized women of childbearing age (15-44 years), 24 were pregnant.
Additional FluSurv-NET data can be found at: http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html andhttp://gis.cdc.gov/grasp/fluview/FluHospChars.html.
Data from the Influenza Hospitalization Surveillance Network (FluSurv-NET), a population-based surveillance for influenza related hospitalizations in children and adults in 13 U.S. states. Incidence rates are calculated using the National Center for Health Statistics’ (NCHS) population estimates for the counties included in the surveillance catchment area.
FluSurv-NET data are preliminary and displayed as they become available. Therefore, figures are based on varying denominators as some variables represent information that may require more time to be collected. Data are refreshed and updated weekly. Asthma includes a medical diagnosis of asthma or reactive airway disease; Cardiovascular diseases include conditions such as coronary heart disease, cardiac valve disorders, congestive heart failure, and pulmonary hypertension; does not include isolated hypertension; Chronic lung diseases include conditions such as chronic obstructive pulmonary disease, bronchiolitis obliterans, chronic aspiration pneumonia, and interstitial lung disease; Immune suppression includes conditions such as immunoglobulin deficiency, leukemia, lymphoma, HIV/AIDS, and individuals taking immunosuppressive medications; Metabolic disorders include conditions such as diabetes mellitus; Neurologic diseases include conditions such as seizure disorders, cerebral palsy, and cognitive dysfunction; Neuromuscular diseasesinclude conditions such as multiple sclerosis and muscular dystrophy; Obesity was assigned if indicated in patient's medical chart or if body mass index (BMI) >30 kg/m2; Pregnancy percentage calculated using number of female cases aged between 15 and 44 years of age as the denominator; Renal diseases include conditions such as acute or chronic renal failure, nephrotic syndrome, glomerulonephritis, and impaired creatinine clearance; No known condition indicates that the case did not have any known high risk medical condition indicated in medical chart at the time of hospitalization.View Interactive Application | View Full Screen | View PowerPoint Presentation
Outpatient Illness Surveillance:
Nationwide during week 1, 4.4% 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 2.0%.
(ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and cough and/or sore throat.)
Additional data are available at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.
On a regional level, the percentage of outpatient visits for ILI ranged from 2.6% to 8.4% during week 1. All 10 regions reported a proportion of outpatient visits for ILI at or above 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 weeks with little or no influenza virus circulation. Activity levels range from minimal, which would correspond to ILI activity from outpatient clinics being below, or only slightly above, the average, to high, which would correspond to ILI activity from outpatient clinics being much higher than average.
During week 1, the following ILI activity levels were experienced:
Click on map to launch interactive tool
*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 disproportionally 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 is 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 1, the following influenza activity was reported:
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics. To access these tools, visithttp://www.cdc.gov/flu/weekly/fluviewinteractive.htm.
U.S. State and local influenza surveillance: Click on a jurisdiction below to access the latest local influenza information.
Google Flu Trends: Google Flu Trends uses aggregated Google search data in a model created in collaboration with CDC to estimate influenza activity in the United States. For more information and activity estimates from the United States and worldwide, see http://www.google.org/flutrends/
World Health Organization: Additional influenza surveillance information from participating WHO member nations is available through FluNet and theGlobal Epidemiology Reports.
WHO Collaborating Centers for Influenza located in Australia, China, Japan, the United Kingdom, and the United States (CDC in Atlanta, Georgia).
Europe: for the most recent influenza surveillance information from Europe, please see WHO/Europe at http://www.flunewseurope.org/ and visit the European Centre for Disease Prevention and Control athttp://ecdc.europa.eu/en/publications/surveillance_reports/influenza/Pages/weekly_influenza_surveillance_overview.aspx
Public Health Agency of Canada: The most up-to-date influenza information from Canada is available at http://www.phac-aspc.gc.ca/fluwatch/
Public Health England: The most up-to-date influenza information from the United Kingdom is available athttps://www.gov.uk/government/statistics/weekly-national-flu-reports
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
In addition to the eight data components of CDC influenza surveillance for the 2014-2015 influenza season, the use of National Center for Health Statistics (NCHS) pneumonia and influenza mortality surveillance data for the rapid assessment of influenza-associated mortality will be piloted. An overview of influenza surveillance, including a description of the NCHS mortality surveillance data, is available here.--------------------------------------------------------------------------------
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