#18,500
The post-Thanksgiving bounce in seasonal flu is readily apparent from the above graphic, with the CDC estimating nearly 2 million illnesses, and 1,000 deaths, already this fall. Key points from this week's FluView include:
Key Points
• Seasonal influenza activity continues to increase across the country.
• 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.
• Two pediatric deaths associated with seasonal influenza virus infection were reported this week, bringing the 2024-2025 season total to four pediatric deaths.
• 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.1
• 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.2
• 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.
Details on this week's HPAI H5 human infections follow. Not mentioned in today's report (possibly because of pending test results) is the case reported by Wisconsin a couple of days ago.
Novel Influenza A Virus
Three confirmed cases and one probable influenza A(H5) case 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.
Two of these confirmed cases were reported by the California Department of Public Health. The cases occurred in a workers aged ≥18 years at a commercial dairy cattle farm in an area where highly pathogenic avian influenza (HPAI) A(H5N1) viruses had been detected in cows. The individuals had mild symptoms, which they reported to local health department officials. There have now been 34 total confirmed cases and one probable case in California.
The other confirmed case was reported by the Louisiana Department of Health. This case occurred in an individual aged ≥18 years. This individual developed respiratory symptoms during week 48 and was hospitalized with their illness. A respiratory specimen was collected at the healthcare facility and tested positive for influenza A, but negative for seasonal virus subtypes. The specimen was sent to the Louisiana Public Health Laboratory for further testing, where it tested presumptive positive for influenza A(H5) virus using the CDC influenza A(H5) assay. Influenza A(H5) virus was confirmed at CDC. The investigation by public health officials identified exposure to backyard poultry prior to the patient's illness onset. The patient remains hospitalized. This is the first influenza A(H5) case in Louisiana and the first instance of severe illness from influenza A(H5) virus infection in the United States.
The probable case was reported by the Delaware Division of Public Health. The case occurred in an individual aged ≥18 years. This individual developed respiratory symptoms during week 48 and sought healthcare for their illness. A respiratory specimen was collected at the healthcare facility and tested positive for influenza A. The specimen was sent to the Delaware Public Health Laboratory for routine surveillance, where it tested presumptive positive for influenza A(H5) virus using the CDC influenza A(H5) assay. The specimen was negative for influenza A(H5) virus using diagnostic RT-PCR at CDC. The investigation by public health officials did not find any exposure to poultry or cows or consumption of raw dairy products prior to the patient's illness onset. The patient has since recovered. This is the first probable case in Delaware.
Notification of the case reported by the Louisiana Department of Health to WHO was initiated per International Health Regulations (IHR). More information regarding IHR can be found at http://www.who.int/topics/international_health_regulations/en/. No additional notification to WHO of the probable case or confirmed cases exposed to dairy cows in California is required per International Health Regulations (IHR).
The CSTE position statement, which includes updated case definitions for confirmed, probable, and suspected cases is available at http://www.cste.org/resource/resmgr/position_statements_files_2023/24-ID-09_Novel_Influenza_A.pdf
An up-to-date human case summary during the 2024 outbreak by state and exposure source is available at www.cdc.gov/bird-flu/situation-summary/index.html
Information about avian influenza is available at https://www.cdc.gov/flu/avianflu/index.htm.
Interim recommendations for Prevention, Monitoring, and Public Health Investigations are available at https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html.
The latest case reports on avian influenza outbreaks in wild birds, commercial poultry, backyard or hobbyist flocks, and mammals in the United States are available from the USDA at https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/avian/avian-influenza/2022-hpai.
Given that we've seen late Friday HPAI announcements nearly every Friday this fall, these numbers are absolutely subject to change.
