All data are preliminary and may change as more reports are received.
During week 41 (October 11-17, 2015), influenza activity was low in the United States.
|HHS Surveillance Regions*||Data for current week||Data cumulative since October 4, 2015 (week 41)|
|Out-patient ILI†||Number of jurisdictions experiencing high or moderate ILI activity§||% respiratory specimens positive for flu in clinical laboratories‡||A(H1N1)pdm09||A (H3)||A (Subtyping not Performed
||B Victoria lineage||B Yamagata lineage||B lineage not performed||Pediatric Deaths|
|Influenza test results from public health laboratories only|
|Nation||Normal||0 of 53||1.7%||4||45||4||1||1||1||0|
|Region 1||Normal||0 of 6||1.4%||0||6||0||0||0||0||0|
|Region 2||Normal||0 of 4||0.4%||0||2||0||0||0||0||0|
|Region 3||Normal||0 of 6||0.5%||1||2||1||0||0||0||0|
|Region 4||Normal||0 of 8||2.2%||0||4||0||0||1||1||0|
|Region 5||Normal||0 of 6||1.0%||3||8||1||0||0||0||0|
|Region 6||Normal||0 of 5||1.0%||0||5||0||1||0||0||0|
|Region 7||Normal||0 of 4||0.7%||0||3||1||0||0||0||0|
|Region 8||Normal||0 of 6||0.6%||0||4||1||0||0||0||0|
|Region 9||Normal||0 of 4||3.8%||0||6||0||0||0||0||0|
|Region 10||Normal||0 of 4||1.0%||0||5||0||0||0||0||0|
*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
WHO and NREVSS collaborating laboratories, which include both public health and clinical laboratories located in all 50 states, Puerto Rico, and the District of Columbia, report to CDC the total number of respiratory specimens tested for influenza and the number positive for influenza virus type. In addition, public health laboratories also report the influenza A subtype (H1 or H3) and influenza B lineage information of the viruses they test and the age or age group of the persons from whom the specimens were collected.
Additional data are available at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html..
The results of tests performed by clinical laboratories during the current week are summarized below.
|Week 41||Data Cumulative since
October 4, 2015 (Week 40)
|No. of specimens tested||7,998||17,482|
|No. of positive specimens (%)||138 (1.7%)||249 (1.4%)|
|Positive specimens by type|
|Influenza A||101 (73.2%)||180 (72.3%)|
|Influenza B||37 (26.8%)||69 (27.7%)|
The results of tests performed by public health laboratories, as well as the age group distribution of influenza positive tests, during the current week are summarized below.
|Week 41||Data Cumulative since
October 4, 2015 (Week 41)
|No. of specimens tested||444||1,067|
|No. of positive specimens||19||56|
|Positive specimens by type/subtype|
|Influenza A||18 (94.7%)||53 (94.6%)|
|A(H1N1)pmd09||1 (5.6%)||4 (7.5%)|
|H3||14 (77.8%)||45 (84.9%)|
|Subtyping not performed||3 (16.7%)||4 (7.5%)|
|Influenza B||1 (5.3%)||3 (5.4%)|
|Yamagata lineage||0 (0%)||1 (33.3%)|
|Victoria lineage||1 (100%)||1 (33.3%)|
|Lineage not performed||0 (0%)||1 (33.3%)|
CDC characterizes influenza viruses through one or more tests including genome sequencing, hemagglutination inhibition (HI) and/or neutralization assays. This data is used to compare how similar currently circulating influenza viruses are to the reference viruses used for developing influenza vaccines, and to monitor for changes in circulating influenza viruses. Historically HI data has been used most commonly to assess the similarity between reference viruses and circulating viruses as a proxy for vaccine effectiveness. Beginning in the 2014–2015 season and to date, however, a portion of influenza A (H3N2) viruses do not yield sufficient hemagglutination titers for antigenic characterization by HI. For many of these viruses, CDC performs genetic characterization to determine the genetic group identity of circulating viruses. In this way, antigenic properties of these viruses can be inferred from viruses within the same genetic group that have been characterized antigenically.
No characterization data is currently available for specimens collected after October 1, 2015.
During May 24-Septemer 30, 2015, CDC has characterized 225 influenza viruses [8 A (H1N1)pdm09, 155 A (H3N2), and 62 influenza B viruses] collected by U.S. laboratories.
Influenza A Virus 
Influenza B Virus : Thirty-eight (61%) of the influenza B viruses characterized belonged to B/Yamagata/16/88 lineage and the remaining 24 (39%) influenza B viruses characterized belonged to B/Victoria/02/87 lineage.
Yamagata Lineage : All 38 (100%) B/Yamagata-lineage viruses were antigenically characterized as B/Phuket/3073/2013-like, which is included as an influenza B component of the 2015-2016 Northern Hemisphere trivalent and quadrivalent influenza vaccines.
Victoria Lineage : All 24 (100%) B/Victoria-lineage viruses were antigenically characterized as B/Brisbane/60/2008-like, the virus that is included as an influenza B component of the 2015-2016 Northern Hemisphere quadrivalent influenza vaccine.
No antiviral resistance data is available for specimens collected after October 1, 2015. During May 24-Septemer 30, 2015, 192 specimens (8 influenza A (H1N1)pdm09, 118 influenza A (H3N2), and 66 influenza B viruses) collected in the United States were tested for susceptibility to the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir). None of the tested viruses were found to be resistant to either oseltamivir, zanamivir, or peramivir.
The majority of recently circulating influenza viruses are susceptible to the neuraminidase inhibitor antiviral medications, oseltamivir, zanamivir, and peramivir; however, rare sporadic instances of oseltamivir-resistant and peramivir-resistant influenza A (H1N1)pdm09 and oseltamivir-resistant influenza A (H3N2) viruses have been detected worldwide. Antiviral treatment 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 at http://www.cdc.gov/flu/antivirals/index.htm.
Rapid tracking of pneumonia and influenza-associated deaths is done through two systems, the National Center for Health Statistics (NCHS) Mortality Surveillance System and the 122 Cities Mortality Reporting System. NCHS mortality surveillance data are presented by the week the death occurred and P&I percentages are released two weeks after the week of death to allow for collection of enough data to produce a stable P&I percentage. Users of the data should not expect the two systems to produce the same percentages, and the percent P&I deaths from each system should be compared to the corresponding system-specific baselines and thresholds.
NCHS Mortality Surveillance Data:
Based on NCHS mortality surveillance data available on October 22, 2015, 5.6% of the deaths occurring during the week ending October 3, 2015 (week 39) were due to P&I. This percentage is below the epidemic threshold of 6.3% for week 39.
Region and state-specific data are available at http://www.cdc.gov/flu/weekly/nchs.htm.
122 Cities Mortality Reporting System:
During week 41, 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 6.0% for week 41.
No influenza-associated pediatric deaths were reported to CDC during week 41.Additional data can be found at: http://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.
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 and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.
Nationwide during week 41, 1.4% 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 below the national baseline of 2.1%.
(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 0.5% to 2.9% during week 41. All 10 regions reported a proportion of outpatient visits for ILI below their region-specific baseline levels.
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 41, the following ILI activity levels were calculated:
*This map uses the proportion of outpatient visits to health care providers for ILI 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 are 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.
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 41, the following influenza activity was reported:
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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, visit http://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.
World Health Organization: Additional influenza surveillance information from participating WHO member nations is available through FluNet and the Global 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 at http://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 at https://www.gov.uk/government/statistics/weekly-national-flu-reports
An overview of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component, is available at: http://www.cdc.gov/flu/weekly/overview.htm.--------------------------------------------------------------------------------