Marin County Department of Health and Human Services tracks influenza activity by analyzing laboratory testing data, visits to local emergency departments for influenza-like illness, and measuring virus levels in wastewater. In 2022, Public Health began tracking levels of Respiratory Syncytial Virus (RSV), another common seasonal virus, in Marin County wastewater. The result of this surveillance is below and is updated weekly. You can find additional information about respiratory illness and COVID-19 in Marin County here.
Influenza and Respiratory Syncytial Virus (RSV) in Wastewater
Figure 1. The amount of virus in wastewater (sewage) reflects the level of transmission in the community. These interactive charts show the amount of Influenza A RSV virus in five Marin County wastewater collection sites, and a composite measure of all sites combined. For most sites, samples are obtained twice per week and results are updated weekly. Find more information about Bay Area wastewater surveillance here and National wastewater surveillance here.
Figure 2. Influenza Tests in Marin County, 2022-2023 and 2023-24 Influenza Seasons
Influenza-like Illness Activity
ILI refers to the familiar symptoms shared by several seasonal viral respiratory illness, including cough, muscle aches, and fever. Tracking ILI is a helpful way to measure potential rises in flu, RSV, COVID or other illness before diagnostic test results are complete, or when lab testing is not performed on all cases. Flu season typically begins around the 40th week of any calendar year, approximately the first week in October, and epidemiologists track cases by week.
Figure 3. Proportion of Visits due to ILI: at Local County Emergency Departments, 2021-22, 2022-23, and 2023-24 Influenza Seasons
Influenza Related Deaths
There were no reportable influenza-related deaths in Marin County during the 2021-22 flu season.
Note: Per Title 17 California Code of Regulations, influenza-related deaths among laboratory-confirmed cases less than 18 years old must be reported to the California Department of Public Health.
Visit the California Department of Public Health's influenza website here for more information.
For national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website here.