Informe semanal de vigilancia de la influenza en los EE. UU.: actualizaciones clave para la semana 51 que finalizó el 21 de diciembre del 2024

Resumen

Virus

Enfermedad

Todos los datos son preliminares y pueden variar a medida que se reciban más informes.

Las flechas direccionales indican los cambios entre la semana actual y la semana previa. Hay información adicional sobre las flechas en la parte inferior de esta página.

A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.¹

Hay más información sobre la temporada de influenza actual y la temporada anterior para cada componente de vigilancia disponible en  FluView Interactive.

U.S. virologic surveillance

Nationally, 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. Influenza A(H1N1)pdm09 and A(H3N2) were the predominant viruses reported this week. Para obtener datos a nivel estatal y regional y la distribución de grupos de edad, visite FluView Interactive. Los virus que se sabe que están asociados a la vacunación reciente con la vacuna de virus vivo atenuado (LAIV) o hallados después de pruebas más exhaustivas como virus de vacunas no están incluidos, o no son virus de la influenza en circulación.

Laboratorios clínicos

A continuación se resumen los resultados de las pruebas realizadas por los laboratorios clínicos a nivel nacional. Los datos de laboratorios clínicos (el porcentaje de muestras positivas para virus de la influenza) se utilizan para monitorear si la actividad de la influenza está aumentando o disminuyendo.

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Laboratorios de Salud Pública

A continuación se resumen los resultados de las pruebas realizadas por laboratorios de salud pública a nivel nacional. Los datos de los laboratorios de salud pública se utilizan para monitorear la proporción de virus de influenza en circulación que pertenecen a cada subtipo/linaje de influenza.

_{*These data reflect specimens tested, and the number determined to be positive for influenza viruses at the public health labs (specimens tested is not the same as cases). The data do not reflect specimens tested only at CDC and could include more than one specimen tested per person. The guidance for influenza A(H5) virus testing recommends testing both a conjunctival and respiratory swab for people with conjunctivitis which has resulted in more specimens testing positive for influenza A(H5) virus than the number of human A(H5) cases. For more information on the number of people infected with A(H5) viruses, please visit the "¿Cómo los CDC están monitoreando los datos de la influenza entre las personas para comprender mejor la situación actual de la influenza aviar A (H5N1)?"}

_{^†When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a "variant" influenza virus. La mayoría de las infecciones en seres humanos por variantes del virus de la influenza ocurren después de una exposición a cerdos, pero puede haber contagio entre personas. It is important to note that in most cases, variant influenza viruses have not shown the ability to spread easily and sustainably from human-to-human.}

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_{*En este gráfico se muestra la cantidad de muestras analizadas y la cantidad que se determinó que fueron positivas para los virus de la influenza en el laboratorio de salud pública (las muestras analizadas no son lo mismo que los casos). No refleja muestras analizadas únicamente en los CDC y podría incluir más de una muestra analizada por persona. Se incluyen las muestras analizadas como parte de la vigilancia de rutina de la influenza, así como las analizadas como parte de pruebas específicas para personas expuestas a la influenza A(H5).}

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Nuevo virus de influenza A

Five confirmed cases of influenza A(H5) were reported to CDC this week. Hasta la fecha, no se ha identificado transmisión entre personas del virus de la influenza A(H5) en Estados Unidos.

Three of these cases were reported by the California Department of Public Health. The cases occurred in workers aged ≥18 years at commercial dairy cattle farms 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 37 total confirmed cases and one probable case in California during the 2024-2025 influenza season.

One case was reported by the Wisconsin Department of Health. This case occurred in an individual aged ≥18 years who worked at a poultry facility where HPAI A(H5N1) virus had been identified in birds. This individual developed respiratory symptoms during Week 50. Specimens were collected from the individual and initially tested at the state public health laboratories using the CDC influenza A(H5) assay before being sent to CDC for further testing. Influenza A(H5) virus was confirmed at CDC. This is the first influenza A(H5) case in Wisconsin.

One case was reported by the Iowa Department of Health and Human Services. This case occurred in an individual aged ≥18 years who worked at a poultry facility where HPAI A(H5N1) virus had been identified in birds. This individual developed conjunctivitis and respiratory symptoms during Week 50. Specimens were collected from the individual and initially tested at the State Hygienic Laboratory at the University of Iowa using the CDC influenza A(H5) assay before being sent to CDC for further testing. Influenza A(H5) virus was confirmed at CDC. This is the first influenza A(H5) case in Iowa.

Notification to WHO of the cases reported by the Wisconsin and Iowa departments of health 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 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.

Caracterización de virus de la influenza 

Los CDC hacen la caracterización genética y antigénica de los virus que circulan en los Estados Unidos enviados por laboratorios de salud pública estatales y locales, de conformidad con las normas de Right Size Roadmap. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing the current influenza vaccines. Los datos también se utilizan para monitorear los cambios en la evolución que se producen constantemente en los virus de la influenza que circulan en seres humanos. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the polymerase acidic protein (PA) endonuclease inhibitor baloxavir. The HA clade and subclades were assigned using Nextclade (https://clades.nextstrain.org).

CDC has genetically characterized 577 influenza viruses collected since September 29, 2024.

CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, H3N2, and B/Victoria viruses) or neutralization-based HINT (virus H3N2) usando antisuero producido por hurones infectados por los virus de referencia que representaban los virus de referencia de las vacunas de cultivo celular o recombinantes recomendados para el hemisferio norte en el 2024-2025. Las diferencias antigénicas en los virus se determinan al comparar la capacidad de los anticuerpos generados contra los virus de referencia de la vacuna de reconocer los virus en circulación generados en cultivo celular. Los antisueros de hurones son útiles porque los anticuerpos que se generan contra un virus en particular por lo general pueden reconocer pequeños cambios en las proteínas de la superficie de otros virus. En pruebas de HI, los virus con propiedades antigénicas similares tienen diferencias en la titulación de anticuerpos de menos o igual a 4 veces con respecto al virus de referencia (candidato para la vacuna). Con la HINT, los virus con propiedades antigénicas similares tienen diferencias de titulación de neutralización de anticuerpos menor o igual a 8 veces. Viruses selected for antigenic characterization are a subset of the recent genetically characterized viruses and are chosen based on the genetic changes in their surface proteins and may not be proportional to the number of such viruses circulating in the United States.

Virus de la influenza A

• A(H1N1)pdm09: 40 A(H1N1)pdm09 viruses were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/67/2022-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines.
• A(H3N2): 34 A(H3N2) viruses were antigenically characterized by HI or HINT, and 19 (55,9 %) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer in HI or reacting at titers that were less than or equal to 8-fold of the homologous virus in HINT) by ferret antisera to cell-grown A/Massachusetts/18/2022-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

Virus de la influenza B

• B/Victoria: 7 influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
• B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

Evaluación de la susceptibilidad del virus a los medicamentos antivirales

Los CDC evalúan la susceptibilidad de los virus de la influenza a los medicamentos antivirales, incluidos los inhibidores de la neuraminidasa (oseltamivir, zanamivir y peramivir) y el inhibidor de la endonucleasa de la subunidad PA (baloxavir), mediante el análisis de secuencias de última generación que se complementa con ensayos de laboratorio. Puede encontrar información sobre los métodos de análisis de susceptibilidad a los antivirales en Vigilancia de la influenza en los EE. UU.: propósito y métodos.

Viruses collected in the U.S. since September 29, 2024, were tested for antiviral susceptibility as follows:

One A(H1N1)pdm09 virus had NA-I223V and NA-S247N amino acid substitutions and showed reduced inhibition by oseltamivir.

Altos niveles de resistencia a los adamantanos (amantadina y rimantadina) persisten entre los virus de influenza A (H1N1)pdm09 e influenza A (H3N2) (los adamantanos no son efectivos contra los virus de influenza B). Por consiguiente, no se recomienda el uso de estos antivirales para el tratamiento y la prevención de las infecciones por el virus de la influenza A y no se presentan datos de análisis de resistencia a la adamantina.

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 will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza virus, SARS-CoV-2, and RSV. 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 51, 4,9 % 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 increased (change of > 0.1 percentage points) compared to Week 50 and is above the national baseline of 3 % for the fourth consecutive week. The percentage of visits for ILI increased (change of > 0.1 percentage points) in all HHS regions compared to Week 50. All HHS regions are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infections to ILI varies by location.

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Outpatient respiratory illness visits by age group

Aproximadamente un 70 % de los participantes de ILINet informan tanto la cantidad de pacientes que consultaron por enfermedades respiratorias como la cantidad total de pacientes de una semana, clasificadas por grupo de edad. Based on these data, the percentage of visits for respiratory illness increased (change of > 0.1 percentage point) in all age groups in Week 51 compared to Week 50.

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Outpatient respiratory illness activity map

Los datos recopilados en ILINet se usan para medir la actividad de ILI* por estado/jurisdicción y áreas estadísticas básicas (CBSA).

National Syndromic Surveillance System (NSSP)

The overall percentage of emergency department (ED) visits with a discharge diagnosis of influenza reported in NSSP was 3,1 % during Week 51, an increase (change of > 0.1 percentage points) from 1,8 % the previous week. In all 10 HHS regions and among all age groups, the percentage of ED visits for influenza increased (change of > 0.1 percentage points) in Week 51 compared to the previous week.

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Vigilancia de hospitalización

FluSurv-Net

La Red de Vigilancia de Hospitalizaciones por Influenza (FluSurv-NET) lleva adelante tareas de vigilancia basadas en la población para detectar hospitalizaciones relacionadas con la influenza, y confirmadas por laboratorio, en determinados condados en 14 estados y representa aproximadamente el 9 % de la población estadounidense. Los datos de hospitalizaciones en FluSurv-NET son preliminares. A medida que se reciben datos todas las semanas, se actualizan las cantidades y tasas de casos anteriores.

Entre el 1 de octubre del 2024 y el 21 de diciembre del 2024, los sitios de FluSurv-NET reportaron un total de 2 345 hospitalizaciones asociadas a la influenza confirmadas por laboratorio. La tasa de hospitalizaciones observada en la semana 51 fue de 2.4 por cada 100 000 habitantes. The cumulative hospitalization rate observed in Week 51 was 7.7 per 100 000 population.

When examining rates by age, the highest cumulative hospitalization rate per 100 000 population was among adults aged 65 years and older (22), followed by adults aged 50-64 years (8.7), children aged 0-4 years (7.3), adults aged 18-49 (3.6), and children aged 5-17 (3.1).

When examining age-adjusted rates by race and ethnicity, the highest cumulative hospitalization rate per 100 000 population was among American Indian/Alaska Native persons (11.4), followed by non-Hispanic Black persons (10.8), Hispanic persons (8.6), non-Hispanic White persons (6.4), and Asian/Pacific Islander persons (4.8).

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_{**En esta imagen, las tasas semanales para todas las temporadas anteriores a la 2024-2025 reflejan tasas de final de temporada. Para la temporada 2024-2025, las tasas de hospitalizaciones recientes están sujetas a demoras en la notificación y se muestran con una línea discontinua para la temporada actual. A medida que se reciben datos de hospitalizaciones todas las semanas, se actualizan las cantidades y tasas de casos anteriores.}

National healthcare safety network (NHSN) hospitalization surveillance

Hospitals report to NHSN the weekly number of patients with laboratory-confirmed influenza who were admitted to the hospital. Nationally, during Week 51, 12 543 laboratory confirmed influenza-associated hospitalizations were reported. This is an increase (change of >5 %) compared to Week 50 when 9 087 hospitalizations were reported.

The weekly hospital admission rate observed in Week 51 was 3.8 per 100,000. The weekly rate of hospital admissions in the 10 HHS regions ranged from 1.5 (Region 1) to 5.8 (Region 10) and increased in regions 2, 3, 4, 5, 6, 7, 8, 9, and 10. Region 1 remained stable.

When examining rates by age for Week 51, all age groups increased this week (change of >5 %) compared to the previous week. The highest hospital admission rate per 100 000 population was among those 75+ years (14.4), followed by 65-to-74-year age group (6.8), and 50-to-64-year age group (4).

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Vigilancia de mortalidad

Vigilancia de mortalidad del Centro Nacional de Estadísticas de Salud (NCHS, en inglés)

Based on NCHS mortality surveillance data available on December 26, 2024, 0,3 % of the deaths that occurred during the week ending December 21, 2024 (Week 51), were due to influenza. This percentage remained stable (≤ 0.1 percentage point change) compared to Week 50. Los datos presentados son preliminares y pueden cambiar a medida que se reciba y se procese más información.

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Mortalidad infantil asociada a la influenza

Five influenza-associated pediatric deaths occurring during the 2024-2025 season were reported to CDC during Week 51. The deaths occurred during weeks 49, 50 and 51 (the weeks ending December 7, December 14, and December 21 of 2024). All the deaths were associated with influenza A viruses. Se analizó el subtipo de cuatro de los virus de influenza A; uno resultó ser un virus A(H1N1) y tres fueron virus A(H3).

A total of nine influenza-associated pediatric deaths occurring during the 2024-2025 season have been reported to CDC.

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Información de vigilancia adicional sobre la influenza a nivel nacional e internacional

Estado de los indicadores por sistema

Additional surveillance information