CDC Flu Update: Activity Continues to Increase

According to the CDC's FluView report for the week ending Jan. 14, 2017 (week 2), 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 five consecutive weeks so far this season and the number of states reporting widespread flu activity increased from 21 states to 29 states. Also, CDC reported two additional flu-associated pediatric deaths for the 2016-2017 season. Influenza A (H3) viruses continue to predominate. Flu activity is expected to continue over 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 January 14, the proportion of people seeing their health care provider for influenza-like illness (ILI) increased to 3.3%. 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 six states (Missouri, New Jersey, New York, Oklahoma, South Carolina, and Tennessee) experienced high ILI activity. Puerto Rico and eight states (Alabama, Alaska, Georgia, Louisiana, Pennsylvania, Utah, Virginia, and Wyoming) experienced moderate ILI activity.  14 states (Arizona, Arkansas, California, Colorado, Hawaii, Idaho, Illinois, Kansas, Kentucky, Michigan, Mississippi, Nebraska, Nevada, and South Dakota). 22 states 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 29 states (Alaska, California, Connecticut, Delaware, Florida, Idaho, Illinois, Kentucky, Maryland, Massachusetts, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New York, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, Texas, Virginia, Washington, Wisconsin, and Wyoming).  Regional influenza activity was reported by Guam and 17 states (Alabama, Arizona, Arkansas, Colorado, Georgia, Hawaii, Iowa, Kansas, Louisiana, Maine, Michigan, Minnesota, Mississippi, New Mexico, North Carolina, South Dakota, and Utah). Local influenza activity was reported by the District of Columbia and four states (Indiana, Tennessee, Vermont, and West Virginia). 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 2,864 laboratory-confirmed influenza-associated hospitalizations have been reported. This translates to a cumulative overall rate of 10.2 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 (47.3 per 100,000), followed by adults 50-64 years (10.1 per 100,000) and children younger than 5 years (6.8 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 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 7.0% for the week ending Dec. 31, 2016 (week 52). This percentage is below the epidemic threshold of 7.3% for week 52 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.

Pediatric Deaths: Two influenza-associated pediatric deaths were reported to CDC during the week ending Jan. 14, 2017.
One death was associated with an influenza A virus for which no subtyping was performed and occurred during week 49 (the week ending Dec. 10, 2016.
One death was associated with an influenza virus for which the type was not determined and occurred during week 1 (the week ending Jan. 7, 2017).
A total of 5 influenza-associated pediatric deaths have been reported during the 2016-2017 season.

Laboratory Data: Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending January 14 was 15.3%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 9.2% to 28.0%.
During the week ending January 14, of the 4,258 (15.3%) influenza-positive tests reported to CDC by clinical laboratories, 3,916 (92.0%) were influenza A viruses and 342 (8.0%) were influenza B viruses.
The most frequently identified influenza virus type reported by public health laboratories during the week ending January 14 was influenza A viruses, with influenza A (H3) viruses predominating.
During the week ending January 14, 824 (94.2%) of the 875 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 51 (5.8%) were influenza B viruses. Of the 777 influenza A viruses that were subtyped, 761 (97.9%) were H3 viruses and 16 (2.1%) were (H1N1)pdm09 viruses.
Since Oct. 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 545 specimens (59 influenza A (H1N1)pdm09, 385 influenza A (H3N2), and 101 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