CDC Flu Update: More People Seeing Their Healthcare Provider for Influenza-Like Illness

According to the CDC's FluView report for the week ending Dec. 31, 2016 (week 52), flu activity continues to increase in the United States. The proportion of people seeing their healthcare provider for influenza-like-illness (ILI) has been at or above the national baseline for three consecutive weeks so far this season. Influenza A (H3) viruses continue to predominate. Flu activity is expected to increase further in the coming weeks. 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 December 31, the proportion of people seeing their health care provider for influenza-like illness (ILI) increased to 3.4% (ILI was 2.9% during the week ending December 24, 2016). This is above the national baseline of 2.2%. Nine regions (regions 1, 2, 3, 4, 5, 6, 7, 8, and 10) 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, Puerto Rico, and 10 states (Alabama, Georgia, Louisiana, Missouri, New Jersey, New York, Oklahoma, Oregon, South Carolina, and Utah) experienced high ILI activity. Ten states (Arizona, Illinois, Indiana, Kentucky, Minnesota, Mississippi, Nevada, North Carolina, Pennsylvania, and Virginia) experienced moderate ILI activity. Five states (Arkansas, California, Michigan, Tennessee, and Washington) experienced low ILI activity and 25 states (Alaska, Colorado, Connecticut, Delaware, Florida, Hawaii, Idaho, Iowa, Kansas, Maine, Maryland, Massachusetts, Montana, Nebraska, New Hampshire, New Mexico, North Dakota, Ohio, Rhode Island, South Dakota, Texas, Vermont, West Virginia, Wisconsin, and Wyoming) experienced minimal ILI activity. (The District of Columbia did not have sufficient data to calculate an activity level.)

Geographic Spread of Influenza Viruses: Widespread geographic influenza activity was reported by 12 states (California, Connecticut, Idaho, Massachusetts, New Hampshire, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Virginia, and Washington). Regional influenza activity was reported by Guam and 28 states (Alabama, Alaska, Arizona, Arkansas, Colorado, Florida, Georgia, Hawaii, Indiana, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, Mississippi, Montana, Nebraska, Nevada, New Jersey, North Dakota, Ohio, Rhode Island, South Carolina, Texas, Utah, Wisconsin, and Wyoming). Local influenza activity was reported by the District of Columbia and 10 states (Delaware, Illinois, Iowa, Kansas, Missouri, New Mexico, South Dakota, Tennessee, Vermont, and West Virginia). Sporadic influenza activity was reported by the U.S. Virgin Islands. Puerto Rico did not report.

Flu-Associated Hospitalizations: Since October 1, 2016, a total of 1,376 laboratory-confirmed influenza-associated hospitalizations have been reported. This translates to a cumulative overall rate of 4.9 hospitalizations per 100,000 people 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.  The highest hospitalization rates are among people 65 years and older (21.1 per 100,000), followed by adults 50 years to 64 years (5.0 per 100,000) and children younger than 5 years (4.2 per 100,000). 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 representing 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 6.3% for the week ending Dec. 17, 2016 (week 50). This percentages is below the epidemic threshold of 7.1% for week 50 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.

Laboratory Data:
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending December 31 was 13.7%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 5.5% to 27.4%.
During the week ending Dec. 31, of the 2,995 influenza-positive tests reported to CDC by clinical laboratories, 2,702 (91.4%) were influenza A viruses and 253 (8.6%) were influenza B viruses.
During the week ending Dec. 31 influenza A viruses were most frequently reported by public health laboratories, with influenza A (H3) viruses predominating.
During the week ending Dec. 31, 405 (93.5%) of the 433 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 28 (6.5%) were influenza B viruses. Of the 337 influenza A viruses that were subtyped, 333 (98.8%) were H3 viruses and 4 (1.2%) 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 Oct. 1, 2016, CDC tested 285 specimens (43 influenza A (H1N1)pdm09, 176 influenza A (H3N2), and 66 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