Weekly US Influenza Surveillance Report: Key Updates for Week 39, ending October 3, 2026

Summary

*The reporting period for each influenza season begins during epidemiologic Week 40 and ends Week 39 of the following year. Epidemiologic weeks refer to the sequential numbering of weeks (Sunday through Saturday) during a calendar year. This means that the exact start of the new influenza surveillance season varies slightly from season to season. The 2025-2026 influenza season began October 5, 2025, and ends on October 3, 2026. The new 2026-2027 influenza season begins October 4, 2026, and ends on October 2, 2027.

U.S. virologic surveillance

Nationally and in HHS regions 1, 2, 3, 4, 7, 8, and 9, the percentage of respiratory specimens testing positive for influenza virus in clinical laboratories increased (change of ≥ 0.5 percentage points) compared to the previous week. In regions 5 and 6, the percentage remained stable but continued to trend upward. Although this proportion decreased in Region 10 compared to last week, this could be a result of a reduction in reporting. Percent positivity varied by region, ranging from 1.7% (Region 2) to 9.5% (Region 9). Influenza A(H1N1)pdm09 viruses were the most frequently reported by public health laboratories this week; however, the distribution of circulating viruses varied by region.

Clinical Laboratories

The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

Public Health Laboratories

The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza virus type/subtype/lineage. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.

_{*These data reflect specimens tested, and the number determined to be positive for influenza viruses at the public health labs (specimens tested are not the same as cases). The data does not reflect specimens tested only at CDC and could include more than one specimen tested per person. For more information on the number of people infected with A(H5) viruses, please visit the "How CDC is monitoring influenza data among people to better understand the current avian influenza A (H5N1) situation"}

_{^†When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a "variant" influenza virus. Most human infections with variant influenza viruses occur following exposure to swine, but person-to-person transmission can occur. It is important to note that in most cases, variant influenza viruses have not shown the ability to spread easily and sustainably from person to person.}

Novel Influenza A Virus Infections

No new confirmed human infections with a novel influenza virus were reported to CDC this week.

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 summary of confirmed novel influenza virus cases is available at https://gis.cdc.gov/grasp/fluview/Novel_Influenza.html.

An up-to-date summary of human cases of avian influenza A(H5) virus 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. A(H5N1) virus interim recommendations for Prevention, Monitoring, and Public Health Investigations are available at https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html.

Outpatient and Emergency Department Illness Surveillance

Outpatient Respiratory Illness Visits

The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and may capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity.

Nationally, during Week 39, 1.8% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This week’s percentage is below the national baseline of 3.1% and remained stable (change of ≤ 0.1 percentage points) compared to Week 38. However, ILI activity has been increasing slowly since late August/early September. HHS regions 4 and 10 increased (change of > 0.1 percentage points) and regions 1, 2, 3, 5, 6, 7, 8, and 9 remained stable (change of ≤ 0.1 percentage points) this week compared to the previous week. All 10 HHS regions are below their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.

_{*Some calendar years do not include an epidemiologic Week 53. In those years, the Week 53 value shown is the average between Week 52 and Week 1.}

_{**Effective October 3, 2021 (Week 40), the respiratory illness definition (fever plus cough or sore throat) no longer includes "without a known cause other than influenza."}

Outpatient Respiratory Illness Visits by Age Group

About 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Based on these data, the percentage of visits for respiratory illness for the 0-4 years and 5-24 years age groups increased (change of > 0.1 percentage points) while the 25-49 years, 50-64 years, and 65 years and older age groups remained stable (change of ≤ 0.1 percentage point) in Week 39 compared to Week 38.

Outpatient Respiratory Illness Activity Map

Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).

National Syndromic Surveillance System (NSSP)

The national percentage of emergency department (ED) visits with a discharge diagnosis (DD) of influenza reported in NSSP was 0.6% during Week 39 and remained stable (change of ≤ 0.1 percentage point) compared to the previous week but has been gradually increasing since early September. Nationally, the percentage of ED visits with a DD of influenza increased (change of > 0.1 percentage point) among the 0-4 years and 5-17 years age groups and remained stable among the 18-64 years and 65 years and older age groups. The percentage of ED visits with a DD of influenza increased this week compared to the previous week in HHS regions 4, 6, 9, and 10, and remained stable in all other regions (1, 2, 3, 5, 7, and 8). The age group trends varied by region.

Hospitalization surveillance

FluSurv-Net

Influenza-Associated Hospitalizations: The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 10% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.

The weekly hospitalization rate observed during Week 39 was 0.6 per 100,000 population and has been increasing since August.

Additional FluSurv-NET data are available on FluView Interactive including hospitalization rates for the current and past seasons by age, sex, and race/ethnicity (http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html) as well as data on patient characteristics at: (http://gis.cdc.gov/grasp/fluview/FluHospChars.html.)

FluSurv-NET data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at Estimated US Flu Disease Burden | Flu Burden | CDC.

National Healthcare Safety Network (NHSN) Hospital Respiratory Data

Hospitals report to NHSN the weekly number of patients with laboratory-confirmed influenza who were admitted to the hospital. Nationally, during Week 39, 3,334 laboratory-confirmed influenza-associated hospitalizations were reported. This week's influenza-associated hospital admission rate (1.0 per 100,000 population) increased (difference of ≥ 0.2) compared to Week 38, and hospital admission rates have been gradually increasing since early September.

Laboratory-confirmed influenza-associated hospital admission rates per 100,000 population increased in HHS regions 1, 4, 6, 7, 9, and 10 and remained stable in all other HHS regions this week compared to the previous week. Regional admission rates during Week 39 ranged from 0.5 (Region 1) to 1.4 (Region 10).

When examining rates by age for Week 39, the 0-4 and 65 years and older age groups increased and all other age groups remained stable compared to the previous week. The highest hospital admission rate per 100,000 population was among those 65 years and older (3.3), followed by the 50-64 years age group (0.9) and the 0-4 years age group (0.8).

National Healthcare Safety Network (NHSN) Long-Term Care Respiratory Pathogens & Vaccination Module

Beginning with the 2026–27 influenza season, NHSN long-term care influenza hospitalization data will no longer be reported in FluView. Previously reported LTC data and related information are available on the NHSN LTC webpage.

Mortality surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on October 8, 2026, 0.1% of the deaths that occurred during the week ending October 3, 2026 (Week 39) were due to influenza. This percentage remained stable (< 0.1 percentage point change) compared to Week 38. The data presented are preliminary and may change as more data are received and processed.

Influenza-Associated Pediatric Mortality

Three influenza-associated pediatric deaths occurring during the 2025-2026 season were reported to CDC during Week 39. The deaths occurred during weeks 51, 53, and 12 (the weeks ending December 20, 2025, January 3, 2026, and March 28, 2026).

A total of 198 influenza-associated pediatric deaths occurring during the 2025-2026 season have been reported to CDC.

All data in this report are preliminary and may change as more reports are received.

A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component, is available on the surveillance methods page.

Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

Additional National and International Influenza Surveillance Information

Additional surveillance information