CDC Flu Update: Activity Increasing for Second Consecutive Week

According to the CDC's FluView report for the week ending Dec. 24, 2016 (week 51), flu activity increased in the United States. The proportion of people seeing their health care provider for influenza-like-illness (ILI) is above the national baseline for the second consecutive week this season. Influenza A (H3) viruses were most commonly reported during week 51 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 Dec. 24, the proportion of people seeing their health care provider for influenza-like illness (ILI) increased to 2.9% (ILI was 2.3% during the week ending Dec. 17, 2016). This is above the national baseline of 2.2%. Nine regions (regions 2, 3, 4, 5, 6, 7, 8, 9 and 10) reported ILI at or above their region-specific baseline level.

Four states (Alabama, Arizona, Georgia and Oklahoma), New York City, and Puerto Rico experienced high ILI activity. Five states (Louisiana, Mississippi, New Jersey, North Carolina, and Utah) experienced moderate ILI activity. Seven states (California, Colorado, Illinois, Michigan, Nevada, Virginia, and Washington) experienced low ILI activity. 34 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 Guam and eight states (California, New Hampshire, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, and Virginia). Regional influenza activity was reported by the U.S. Virgin Islands and 17 states (Alabama, Alaska, Colorado, Connecticut, Idaho, Indiana, Louisiana, Maryland, Massachusetts, Mississippi, Nebraska, New Jersey, North Dakota, Ohio, South Carolina, Utah, and Washington). Local flu activity was reported by the District of Columbia and 19 states (Arizona, Arkansas, Delaware, Florida, Hawaii, Illinois, Kentucky, Michigan, Minnesota, Missouri, Montana, Nevada, New Mexico, South Dakota, Tennessee, Texas, West Virginia, Wisconsin, and Wyoming). Sporadic flu activity was reported by five states (Iowa, Kansas, Maine, Rhode Island, and Vermont). Puerto Rico and one state (Georgia) did not report. Geographic spread data show how many areas within a state or territory are seeing flu activity.

Since Oct. 1, 2016, a total of 863 laboratory-confirmed influenza-associated hospitalizations have been reported. This translates to a cumulative overall rate of 3.1 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 (12.7 per 100,000), followed by adults 50-64 years (3.3 per 100,000) and children younger than 5 years (2.5 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 6.1% for the week ending December 10, 2016 (week 49). This percentages is below the epidemic threshold of 7.0% for week 49 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 24 was 10.4%. Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 3.7% to 18.5%. During the week ending Dec. 24, of the 1,813 influenza-positive tests reported to CDC by clinical laboratories, 1,575 (86.8%) were influenza A viruses and 239 (13.2%) were influenza B viruses. The most frequently identified influenza virus type reported by public health laboratories during the week ending December 24 was influenza A viruses, with influenza A (H3) viruses predominating. During the week ending Dec. 24, 235 (91.8%) of the 256 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 21 (8.2%) were influenza B viruses. Of the 186 influenza A viruses that were subtyped, 182 (97.8%) were H3 viruses and 4 (2.2%) were (H1N1)pdm09 viruses.

One human infection with a novel influenza A virus was reported to CDC during the week ending December 24, 2016. The patient was infected with an avian lineage influenza A (H7N2) virus. The patient reported close, prolonged unprotected exposure to the respiratory secretions of infected, sick cats at an affected New York City animal shelter. The patient was mildly ill, was not hospitalized, and has completely recovered. No ongoing human-to-human transmission has been identified. This is the first influenza A (H7N2) virus infection in humans identified in the United States since 2003 and the first known human infection with an influenza A virus likely acquired though exposure to an ill cat.

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 274 specimens (40 influenza A (H1N1)pdm09, 176 influenza A (H3N2), and 58 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