CDC Flu Update: Activity Has Likely Peaked

According to the CDC's FluView report for the week ending March 4, 2017 (week 9), while flu activity remained elevated for the 12th consecutive week, the season has likely peaked. 39 states are reporting widespread flu activity compared to 43 last week and the southern and southeastern parts of the U.S. continues to have high activity. 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 March 4, the proportion of people seeing their health care provider for influenza-like illness (ILI) for influenza-like illness (ILI) was 3.6%. This remains above the national baseline of 2.2%. Eight regions (Regions 1, 2, 3, 4, 5, 6, 7 and 8) 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: 14 states (Alabama, Arkansas, Georgia, Kansas, Kentucky, Louisiana, Mississippi, North Carolina, Oklahoma, Rhode Island, South Carolina, Tennessee, Texas, and Virginia) experienced high ILI activity. 12 states (Alaska, Arizona, Illinois, Maryland, Michigan, Minnesota, Missouri, North Dakota, New Jersey, New Mexico, Pennsylvania, and South Dakota) experienced moderate ILI activity. Eight states (Colorado, Connecticut, Florida, Hawaii, Indiana, Ohio, West Virginia, and Wyoming) experienced low ILI activity. New York City, Puerto Rico and 16 states (California, Delaware, Iowa, Idaho, Massachusetts, Maine, Montana, Nebraska, New Hampshire, Nevada, New York, Oregon, Utah, Vermont, Washington, and Wisconsin) 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 39 states (Alabama, Alaska, Arizona, Arkansas, California, Connecticut, Delaware, Florida, Idaho, 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, Vermont, Virginia, West Virginia, and Wisconsin).  Regional influenza activity was reported by Guam and eight states (Georgia, Hawaii, Illinois, Montana, Tennessee, Texas, Washington, and Wyoming). Local influenza activity was reported by the District of Columbia and two states (Colorado and Utah).  Sporadic influenza activity was reported by one state (Oregon). 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 12,173 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 43.5 hospitalizations per 100,000 people in the United States. This is higher than the hospitalization rate at this time (39.4 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 198.8 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 170.2 per 100,000.
The hospitalization rate among adults 50-64 years is 42.2 per 100,000. During 2012-2013 flu season, the hospitalization rate for that age group for the same week was 36.3 per 100,000 respectively.
The hospitalization rate among children younger than 5 years is 28.8 per 100,000. During 2012-2013 flu season, the hospitalization rate for people in that age group for the same week was 56.9 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 8.0% for the week ending February 18, 2017 (week 7). This percentage is above the epidemic threshold of 7.5% for week 7 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 seven consecutive weeks this season.

Pediatric Deaths: Eight influenza-associated pediatric deaths are being reported by CDC for the week ending March 4, 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 virus for which no subtyping was performed and occurred during week 8.
Five deaths were associated with an influenza B virus and occurred during weeks 6, 7, and 8 (the weeks ending February 11, February 18, and February 25, 2017).
A total of 48 influenza-associated pediatric deaths have been reported for the 2016-2017 season.
Additional information on pediatric deaths for the 2016-2017 season is 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 March 4 was 18.6%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 9.7% to 29.0%.
During the week ending March 4, of the 5,245 (18.6%) influenza-positive tests reported to CDC by clinical laboratories, 3,599 (68.6%) were influenza A viruses and 1,646 (31.4%) were influenza B viruses.
The most frequently identified influenza virus type reported by public health laboratories during the week ending March 4  was influenza A viruses, with influenza A (H3N2) viruses predominating. 
During the week ending March 4, 625 (74.7%) of the 837 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 212 (25.2%) were influenza B viruses. Of the 602 influenza A viruses that were subtyped, 586 (97.3%) were H3N2 viruses and 16 (2.7%) 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 1,581 specimens (179 influenza A (H1N1)pdm09, 1,025 influenza A (H3N2), and 377 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