Current Weekly Influenza Update



2023 - 2024 Weekly Influenza Update: 10/01/2023 - 03/23/2024 (Week 40 - 12)
Fresno County Department of Public Health

The 2023 - 2024 influenza season began on 10/01/2023 (week 40). This surveillance report monitors influenza activity and is updated weekly through the end of the 2023 - 2024 season. Providers must report laboratory-confirmed influenza-associated fatal pediatric cases in those 0-17 years old. Laboratory-confirmed influenza-associated deaths in those 18 years of age and older are voluntarily reported by providers in California.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 and viral surveillance data is from the California Weekly Report: Influenza (Flu), RSV, and Other Respiratory Viruses.3

INFLUENZA ASSOCIATED DEATHS LOCAL, STATE AND NATIONAL

Table 1: Cumulative Influenza Associated Deaths for the 2023 - 2024 Influenza Season by Location and Age Range

Location 0-17 Years Old 18-64 Years Old 65 Years or Older All Ages
Fresno County4 10/01/2023-03/23/2024 1 4 18 23
California3 10/01/2023-03/16/2024 14 170 386 570
Nationwide2 10/01/2023-03/16/2024 159 1981 5474 7614

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 10/01/2023 to 03/16/2024 (week 11). CDC Region 9 includes California, Arizona, Hawaii and Nevada.2

Figure 2 shows the weekly distribution of influenza types in CDC Region 9 from 10/01/2023 to 03/16/2024 (week 11). CDC Region 9 includes California, Arizona, Hawaii and Nevada.2

Figure 3 shows the weekly distribution of influenza types in California from 10/01/2023 to 03/16/2024 (week 11).3

Figure 4 shows the number of influenza positive tests by disease week and influenza type in Fresno County from 10/01/2023 to 03/16/2024 (week 11). The number of weekly tests changes throughout the season (figure 5). The data for figure 4 comes from both public health and clinical laboratories.5

Figure 5 shows the number of weekly influenza tests, and the percentage of those test that are positive for influenza in Fresno County from 10/01/2023 to 03/16/2024 (week 11). The data for figure 5 comes from both public health and clinical laboratories.5

INFLUENZA-LIKE-ILLNESS (ILI) AT EMERGENCY DEPARMENTS

Figure 6 shows the percent of ED visits attributed to influenza-like illness (ILI) in previous seasons and the current season as of 03/23/2024 (week 12). 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 form 2019-2020 season onward may be skewed. Data on previous seasons and current seasons is collected through EpiCenter,6 a syndromic surveillance system.


REFERENCES/TECHNICAL NOTES
  1. CDPH Recommendations for Influenza and Other Respiratory Virus Testing and Reporting - 2023-2024.

  2. CDC FluView.

  3. California Weekly Report: Influenza (Flu), RSV, and Other Respiratory Viruses.

  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 weekly influenza report (reference 3).

  6. EpiCenter.