CDC Flu Update: Increasing Number of Influenza B Viruses Detected

According to the CDC's FluView report for the week ending Feb. 25, 2017 (week 8), flu activity remained elevated. Also, CDC reported six 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 11 consecutive weeks so far this season. Influenza A (H3N2) viruses continue to predominate, but there has been an increasing proportion of influenza B viruses detected in recent weeks.  Based on early estimates, flu vaccines this season have reduced a vaccinated person’s risk of getting sick and having to go to the doctor because of flu by about half (48%). 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 18, the proportion of people seeing their health care provider for influenza-like illness (ILI) for influenza-like illness (ILI) was 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: 27 states (Alabama, Arkansas, Connecticut, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, and Virginia)) experienced high ILI activity. Four states (Arizona, Massachusetts, New Hampshire, and Wisconsin) experienced moderate ILI activity.  New York City, Puerto Rico and six states (California, Florida, Iowa, North Dakota, West Virginia, and Wyoming) experienced low ILI activity. 13 states (Alaska, Colorado, Delaware, Hawaii, Idaho, Maine, Montana, Nebraska, Nevada, Oregon, 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, Arizona, Arkansas, California, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Texas, Vermont, Virginia, West Virginia, Wisconsin, and Wyoming).  Regional influenza activity was reported by Guam and five states (Colorado, Montana, Tennessee, Utah, and Washington). Local influenza activity was reported by the District of Columbia and two states (Hawaii and Oregon). Sporadic 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 11,018 laboratory-confirmed influenza-associated hospitalizations have been reported. This translates to a cumulative overall rate of 33.7 hospitalizations per 100,000 people in the United States. This translates to a cumulative overall rate of 39.4 hospitalizations per 100,000 people in the United States. This is higher than the hospitalization rate at this time (38.2 per 100,000) during the 2012-2013 flu season, when influenza A H3N2 viruses also predominated. The 2012-2013 flu season was a recent influenza A H3N2-predominant season in the United States. Influenza A (H3N2) viruses also predominated during the 2014- 2015 flu season, but more than 70% of the H3N2 viruses circulating that season were different or "drifted" from the H3N2 vaccine virus.
The hospitalization rate among people 65 years and older is 180.2 per 100,000. This is the highest rate of any age group. The hospitalization rate for people 65 and older for the same week during the 2012-2013 flu season was 165.6 per 100,000.
The hospitalization rate among adults 50-64 years is 38.4 per 100,000. During 2012-2013 flu season, the hospitalization rate for that age group for the same week was 35.2 per 100,000 respectively.
The hospitalization rate among children younger than 5 years is 25.7 per 100,000. During 2012-2013 flu season, the hospitalization rate for people in that age group for the same week was 54.6 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. 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.

Mortality Surveillance:  The proportion of deaths attributed to pneumonia and influenza (P&I) was 7.8% for the week ending February 11, 2017 (week 6). This percentage is above the epidemic threshold of 7.5% for week 6 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.  The weekly percentage of deaths attributed to P&I has exceeded the epidemic threshold for six consecutive weeks this season.

Pediatric Deaths:
Six influenza-associated pediatric deaths are being reported by CDC for the week ending February 25, 2017.

Two deaths were associated with an influenza A (H3) virus and occurred during weeks 7 and 8 (the weeks ending February 18, and February 25, 2017, respectively).
One death was associated with an influenza A (H1N1)pdm09 virus and occurred during week 6 (the week ending February 11, 2017). 
Two deaths were associated with an influenza A virus for which no subtyping was performed and occurred during weeks 6 and 8. 
One death was associated with an influenza B virus and occurred during week 7.
A total of 40 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 25 was 24.2%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 11.7% to 30.9%.
During the week ending February 25, of the 8,515 (24.2%) influenza-positive tests reported to CDC by clinical laboratories, 6,300 (74.0%) were influenza A viruses and 2,215 (26.0%) were influenza B viruses.
The most frequently identified influenza virus type reported by public health laboratories during the week ending February 25  was influenza A viruses, with influenza A (H3N2) viruses predominating. 
During the week ending February 25, 884 (82.6%) of the 1,070 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 186 (17.4%) were influenza B viruses. Of the 830 influenza A viruses that were subtyped, 804 (96.9%) were H3N2 viruses and 26 (3.1%) 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 1,417 specimens (152 influenza A (H1N1)pdm09, 954 influenza A (H3N2), and 311 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



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