Current Weekly Influenza Update



2024 - 2025 Weekly Influenza Update: 09/29/2024 - 11/23/2024 (Week 40 - 47)
Fresno County Department of Public Health

The 2024 - 2025 influenza season began on 09/29/2024 (week 40). This surveillance report monitors influenza activity and is updated weekly through the end of the 2024 - 2025 season. Providers must report laboratory-confirmed influenza-associated fatal pediatric cases in those 0-17 years old.1 Fresno County Public Health obtains the number of influenza-associated fatal cases between 0 and 17 years of age from investigations. The number of influenza-associated deaths in those 18 years and older are obtained from vital statistics records. National death and viral surveillance data is from the CDC’s FluView2 applications. California death data is from the California Respiratory Virus Weekly Report.3

INFLUENZA ASSOCIATED DEATHS LOCAL, STATE AND NATIONAL

Table 1: Cumulative Influenza Associated Deaths for the 2024 - 2025 Influenza Season by Location and Age Range

Location 0-17 Years Old 18-64 Years Old 65 Years or Older All Ages
Fresno County4 09/29/2024-11/23/2024 0 0 0 0
California3 06/30/2024-11/23/2024 1 11 37 49
Nationwide2 09/29/2024-11/16/2024 3 39 121 163

INFLUENZA TYPING AT NATIONAL, REGIONAL, STATE AND LOCAL LEVELS

Figure 1 shows the cumulative distribution of influenza types from national, CDC Region 9 and California from 09/29/2024 to 11/16/2024 (week 46). CDC Region 9 includes California, Arizona, Hawaii and Nevada.2

NationalRegion 9California01020304050
A (H3)A (H1N1)pmd09A (subtyping not performed)H3N2vB VictoriaB YamagataB (lineage unspecified)Figure 1: Influenza Types from National, CDC Region 9 and CaliforniaPercent (%)

Figure 2 shows the weekly distribution of influenza types in CDC Region 9 from 09/29/2024 to 11/16/2024 (week 46). CDC Region 9 includes California, Arizona, Hawaii and Nevada.2

09/29/202410/06/202410/13/202410/20/202410/27/202411/03/202411/10/2024020406080100120140
A (H3)A (H1N1)pmd09A (subtyping not performed)H3N2vB VictoriaB YamagataB (lineage unspecified)Figure 2: Influenza Types by Disease Week from CDC Region 9Week StartNumber of Cases

Figure 3 shows the number of influenza positive tests by disease week and influenza type in Fresno County from 09/29/2024 to 11/16/2024 (week 46). The number of weekly tests changes throughout the season (figure 4). The data for figure 3 comes from both public health and clinical laboratories.5

09/29/202410/06/202410/13/202410/20/202410/27/202411/03/202411/10/20240246810121416
A (H3)A (H1N1)pmd09A (subtyping not performed)B VictoriaB YamagataB (lineage unspecified)Figure 3: Influenza Types by Disease Week in Fresno CountyWeek StartNumber of Cases

Figure 4 shows the number of weekly influenza tests, and the percentage of those test that are positive for influenza in Fresno County from 09/29/2024 to 11/16/2024 (week 46). The data for figure 4 comes from both public health and clinical laboratories.5

010020030009/29/202410/06/202410/13/202410/20/202410/27/202411/03/202411/10/20240123
Figure 4: Influenza Tests and Percent Positivity by Disease Week in Fresno CountyWeek StartNumber of Influenza TestsPositive Influenza Tests (%)​*​​*​Maybe Unstable Due to a Small Sample Size​*​Maybe Unstable Due to a Small Sample Size

INFLUENZA-LIKE-ILLNESS (ILI) AT EMERGENCY DEPARMENTS

Figure 5 shows the percent of ED visits attributed to influenza-like illness (ILI) in previous seasons and the current season as of 11/30/2024 (week 48). The baseline and alert curves provide reference points to monitor ILI activity in the current season. The baseline curve and alert thresholds are estimated using prior seasons’ data from 2018 to 2023. The baseline curve is the average expected percent of ED visits due to ILI. The alert curve is the upper 95% confidence limit based off percent ED visits due to ILI. Because COVID-19 and influenza have similar symptoms, ILI from the 2019-2020 season onward may be skewed. Data on previous seasons and current seasons is collected through EpiCenter,6 a syndromic surveillance system.

404142434445464748495051525312345678910111213141516171819202122230123456
2019-202020-212021-222022-232023-242024-25AverageAlertFigure 5: Emergency Department Visits Due to ILI in Fresno CountyDisease WeekPercent (%)

INFLUENZA A CONCENTRATIONS IN WASTEWATER

Figure 6 shows the concentration of influenza A in wastewater samples from Fresno County as of 10/12/2024 (week 41).7 The blue dots represent the average concentration of influenza A for all wastewater samples collected on that date. The black line is the 10-day rolling average of influenza A concentrations and helps to view data trends. Samples are collected from the Fresno-Clovis Regional Wastewater Treatment Facility. More information detailing wastewater surveillance can be found here.

Jan 2023Apr 2023Jul 2023Oct 2023Jan 2024Apr 2024Jul 2024Oct 20240.0e+02.0e−54.0e−56.0e−58.0e−51.0e−41.2e−41.4e−4
Figure 6: Influenza A Concentrations in Fresno County WastewaterSample DateConcentration (Influenza A/PMMoV)
REFERENCES/TECHNICAL NOTES

  1. CDPH Reportable Diseases and Conditions.

  2. CDC FluView.

  3. California Respiratory Virus Weekly Report.

  4. Counts include all influenza deaths that occurred within Fresno County among Fresno County residents.

  5. Data from clinical sentinel and public health laboratories in the Respiratory Laboratory Network (RLN) reporting for Fresno County. These laboratories report the number of laboratory-confirmed influenza positive and negative tests on a weekly basis. When possible, influenza subtype information is also reported. For more information on the RLN, see the California Respiratory Virus Weekly Report. (reference 3).

  6. EpiCenter.

  7. CDPH-Wastewater Surveillance Data, California.

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