Influenza Activity in the U.S. Key Points: • Nationally, percent positivity for influenza, the percentage of emergency department visits for influenza, percentage of outpatient visits for respiratory illness, and influenza-associated hospitalizations increased this week compared to last week. • During Week 50, of the 871 viruses reported by public health laboratories, 842 were influenza A and 29 were influenza B. Of the 593 influenza A viruses subtyped during Week 50, 274 (46.2%) were influenza A(H1N1)pdm09, 317 (53.5%) were A(H3N2), and 2 (0.3%) were A(H5). • Three confirmed cases and one probable case of influenza A(H5) virus were reported to CDC this week. To date, human-to-human transmission of influenza A(H5) virus has not been identified in the United States. • CDC estimates that there have been at least 1.9 million illnesses, 23,000 hospitalizations, and 970 deaths from flu so far this season. • CDC recommends that everyone ages 6 months and older get an annual influenza (flu) vaccine. •There are prescription flu antiviral drugs that can treat flu illness; those should be started as early as possible and are especially important for higher risk patients. • Influenza viruses are among several viruses contributing to respiratory disease activity. CDC is providing updated, integrated information about COVID-19, flu, and respiratory syncytial virus (RSV) activity on a weekly basis.
Below is a summary of the key influenza indicators for the week ending December 14, 2024: Viral Surveillance - Clinical Lab: The percentage of respiratory specimens testing positive for influenza at clinical laboratories is 9% this week.
Viral Surveillance - Public Health Lab: Influenza A(H1N1)pdm09 and A(H3N2) were the predominant viruses reported this week.
Virus Characterization: Influenza virus characterization information can be found here: U.S. Influenza Surveillance: Purpose and Methods | CDC Outpatient Illness: The percentage of patient visits to a health care provider for respiratory illness in week 50 was 3.8% which is above baseline.
Outpatient Respiratory Illness: ILINet Activity Map: Eleven jurisdictions experienced moderate ILI activity and 15 jurisdictions experienced high or very high ILI activity in week 50.
Laboratory-Confirmed influenza Hospitalizations can be found here: Laboratory-Confirmed Influenza Hospitalizations (cdc.gov) The weekly hospitalization rate observed in Week 50 was 1.5 per 100,000 population. The cumulative hospitalization rate was 4.8 per 100,000 population.
NCHS Mortality: 0.2% of deaths were due to influenza. This percentage remained stable (< 0.1 percentage point change) compared to week 49. (NCHS:National Center for Health Statistics)
Influenza-Associated Pediatric Deaths: Two influenza-associated deaths were reported this week. Four pediatric deaths have been reported so far this season. For more information: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html
CDC FluView Site https://www.cdc.gov/fluview/ Influenza Activity in Massachusetts For more information about flu, please go to our Viral Respiratory Disease Dashboard which includes information not only on influenza but also other acute respiratory diseases, COVID-19, and respiratory syncytial virus (RSV), wastewater data and immunizations for respiratory diseases.
The figure below shows that for MMWR week 50, the percent of ILI visits in the current week is above the regional baseline of 1.9%. (The CDC uses trends from past years to determine a region-specific baseline rate of ILI visits, which for Massachusetts is 1.9%. A rate above this regional baseline indicates higher than normal levels of ILI in the state.) For more information on how regional baselines are calculated see CDC’s influenza surveillance website at U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC) For more information on weekly flu activity, see CDC’s influenza surveillance website at https://www.cdc.gov/fluview/surveillance/index.html. |