CDC Flu Update: Activity is Increasing, Influenza A Viruses Predominate


According to the CDC's FluView report for the week ending December 10, 2016 (week 49), flu activity increased slightly in the continental United States. Influenza A (H3) viruses were most commonly reported during week 49 and have been the predominant virus so far this season. While the timing of influenza activity varies and is unpredictable, 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.

For the week ending December 10, the proportion of people seeing their health care provider for influenza-like illness (ILI) was 1.9%. This is below the national baseline of 2.2%. Two regions (Regions 2 and 4) reported ILI at or above their region-specific baseline level.

Puerto Rico experienced high ILI activity. One state (Georgia) experienced moderate ILI activity. New York City and four states (Arizona, Louisiana, Nevada, and Oklahoma) experienced low ILI activity. 45 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.

Widespread influenza activity was reported by Puerto Rico. Regional influenza activity was reported by Guam, the U.S. Virgin Islands and seven states (Indiana, Massachusetts, New Hampshire, New York, North Carolina, Oklahoma, and Washington).Local flu activity was reported by the District of Columbia and 22 states (Alabama, Arizona, Colorado, Connecticut, Delaware, Hawaii, Kentucky, Louisiana, Michigan, Minnesota, Mississippi, Nebraska, Nevada, Ohio, Oregon, Pennsylvania, South Carolina, Tennessee, Texas, Utah, Virginia, and Wyoming). Sporadic flu activity was reported by 20 states (Alaska, Arkansas, California, Florida, Georgia, Idaho, Illinois, Iowa, Kansas, Maine, Maryland, Missouri, Montana, New Jersey, New Mexico, North Dakota, South Dakota, Vermont, West Virginia, and Wisconsin). No flu activity was reported by one state (Rhode Island). Geographic spread data show how many areas within a state or territory are seeing flu activity.

Data regarding influenza-associated hospitalizations for the 2016-2017 influenza season is now available. 487 laboratory-confirmed influenza-associated hospitalizations have been reported since October 1, 2016. This translates to a cumulative overall rate of 1.7 hospitalizations per 100,000 people in the United States. Additional data , including hospitalization rates during other influenza seasons, can be found at and The highest hospitalization rates are among people 65 years and older (7.2 per 100,000), followed by adults 50-64 years (1.8 per 100,000) and children younger than 5 years (1.4 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.

The proportion of deaths attributed to pneumonia and influenza (P&I) was 5.6% for the week ending November 26, 2016 (week 47). This percentages is below the epidemic threshold of 6.8% for week 47 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.

No influenza-associated pediatric deaths for the 2016-2017 season have been reported to CDC.

Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending December 10 was 4.8%.

Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 1.4% to 8.6%.

During the week ending December 10, of the 728 influenza-positive tests reported to CDC by clinical laboratories, 575 (79.0 %) were influenza A viruses and 153 (21.0%) were influenza B viruses.

The most frequently identified influenza virus type reported by public health laboratories during the week ending December 10 was influenza A viruses, with influenza A (H3) viruses predominating. During the week ending December 10, 198 (96.1%) of the 206 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 8 (3.9%) were influenza B viruses. Of the 164 influenza A viruses that were subtyped, 158 (96.3%) were H3 viruses and 6 (3.7%) 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 178 specimens (28 influenza A (H1N1)pdm09, 119 influenza A (H3N2), and 31 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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