CDC Flu Update: Influenza A Viruses Continue to Predominate

According to the CDC's FluView report for the week ending Feb. 4, 2017 (week 5), flu activity continues to increase and is widespread in most of the United States. Also, CDC reported five additional flu-associated pediatric deaths for the 2016-2017 season. The proportion of people seeing their healthcare provider for influenza-like-illness (ILI) has been at or above the national baseline for eight consecutive weeks so far this season. Influenza A (H3) viruses continue to predominate. CDC recommends annual flu vaccination for everyone 6 months of age and older. Anyone who has not gotten vaccinated yet this season should get vaccinated now.

Influenza-like Illness Surveillance: For the week ending February 4, the proportion of people seeing their health care provider for influenza-like illness (ILI) increased to 4.8%. This remains above the national baseline of 2.2%. All 10 regions reported ILI at or above their region-specific baseline level. For the last 15 seasons, the average duration of a flu season by this measure has been 13 weeks, with a range from one week to 20 weeks.

Influenza-like Illness State Activity Indicator Map: New York City and 23 states (Alabama, Arkansas, Connecticut, Georgia, Hawaii, Indiana, Kansas, Louisiana, Minnesota, Mississippi, Missouri, New Jersey, New Mexico, New York, North Carolina, Oklahoma, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Virginia, and Wyoming) experienced high ILI activity. 10 states (California, Colorado, Florida, Illinois, Iowa, Michigan, Nebraska, North Dakota, Oregon, and Wisconsin) experienced moderate ILI activity.  Puerto Rico and eight states (Alaska, Arizona, Kentucky, Maryland, Massachusetts, Nevada, Rhode Island, and West Virginia) experienced low ILI activity. Nine states (Delaware, Idaho, Maine, Montana, New Hampshire, Ohio, Utah, Vermont, and Washington) experienced minimal ILI activity. The District of Columbia did not have sufficient data to calculate an activity level. ILI activity data indicate the amount of flu-like illness that is occurring in each state.

Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by Puerto Rico and 43 states (Alabama, Alaska, Arkansas, California, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, 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, Texas, Vermont, Virginia, Washington, Wisconsin, and Wyoming).  Regional influenza activity was reported by Guam and six states (Arizona, Colorado, Indiana, Tennessee, Utah, and West Virginia). Local influenza activity was reported by the District of Columbia and one state (Hawaii). No influenza activity was reported by the U.S. Virgin Islands. Geographic spread data show how many areas within a state or territory are seeing flu activity.

Flu-Associated Hospitalizations: Since October 1, 2016, a total of 6,804 laboratory-confirmed influenza-associated hospitalizations have been reported. This translates to a cumulative overall rate of 24.3 hospitalizations per 100,000 people in the United States. This is lower than the hospitalization rate at this time (50.8 per 100,000) during the 2014-2015 flu season, when influenza A (H3N2) viruses also predominated. Additional data, including hospitalization rates during other influenza seasons, can be found at http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html. ?The hospitalization rate among people 65 years and older is 113.5 per 100,000. This is the highest rate of any age group. The hospitalization rates for people 65 and older for the same week during the 2014-2015 and 2012-2013 flu seasons were 252.6 per 100,000 and 146.3 per 100,000 respectively. The 2014-2015 and 2012-2013 flu seasons were the last influenza A (H3N2)-predominant seasons in the United States.
?The hospitalization rate among adults 50-64 years is 23.5 per 100,000. During 2014-2015 and 2012-2013 flu seasons, the hospitalization rate for that age group for the same week was 39.8 per 100,000 and 30.4 per 100,000 respectively.
?The hospitalization rate among children younger than 5 years is 13.6 per 100,000). During 2014-2015 and 2012-2013 flu seasons, the hospitalization rates for people in that age group for the same week were 43.4 per 100,000 population and 45.8 per 100,000 respectively.
?During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates. ?Hospitalization data are collected from 13 states and represent approximately 9% of the total U.S. population. The number of hospitalizations reported does not reflect the actual total number of influenza-associated hospitalizations in the United States.

Mortality Surveillance: ?The proportion of deaths attributed to pneumonia and influenza (P&I) was 7.9% for the week ending January 21, 2017 (week 3). This percentage is above the epidemic threshold of 7.4% for week 3 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.

Pediatric Deaths: ?Five influenza-associated pediatric deaths are being reported by CDC for the week ending February 4, 2017.
?Three deaths were associated with an influenza A (H3) virus and occurred during weeks 1, 2, and 4 (the weeks ending January 7, 14, and 28, 2017, respectively).
?Three deaths were associated with an influenza A (H3) virus and occurred during weeks 2 and 4 (the weeks ending January 14, and 28, 2017, respectively
?One death was associated with an influenza A (H1N1)pdm09 virus and occurred during week 4 (the week ending January 28, 2017). 
?A total of 20 influenza-associated pediatric deaths have been reported for the 2016-2017 season.
?Additional information on pediatric deaths for the 2016-2017 season is now available on FluView Interactive at: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.

Laboratory Data: ?Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending February 4 was 20.9%.
?Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 12.8% to 24.8%.
?During the week ending February 4, of the 5,722 (20.9%) influenza-positive tests reported to CDC by clinical laboratories, 5,017 (87.7%) were influenza A viruses and 705 (12.3%) were influenza B viruses.
?The most frequently identified influenza virus type reported by public health laboratories during the week ending February 4 was influenza A viruses, with influenza A (H3) viruses predominating. 
?During the week ending February 4, 1,245 (89.1%) of the 1,397 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 152 (10.9%) were influenza B viruses. Of the 1,170 influenza A viruses that were subtyped, 1,142 (97.6%) were H3 viruses and 28 (2.4%) were (H1N1)pdm09 viruses.
?Since October 1, 2016, antigenic and/or genetic characterization shows that the majority of the tested viruses remain similar to the recommended components of the 2016-2017 Northern Hemisphere vaccines.
?Since October 1, 2016, CDC tested 921 specimens (94 influenza A (H1N1)pdm09, 633 influenza A (H3N2), and 194 influenza B viruses) for resistance to the neuraminidase inhibitors antiviral drugs. None of the tested viruses were found to be resistant to oseltamivir, zanamivir, or peramivir.

Source: CDC