California Influenza-like Illness (ILI) Watch *

The following California State Flu Watch graphs are derived from information provided by CEP (California Emergency Physicians) emergency departments within the State of California. These emergency departments see in excess of 144,000 patients/month, and the information is updated on a weekly basis. Click here to see graphs by State Region or County.

A week-by-week trend of influenza-like illnesses activity. The percentage of ED visits for ILI is calculated by dividing the number of ILI visits by the total number of ED visits per week.

 


A month-to-month trend of influenza-like illness admissions. Influenza-like illness admission rates are calculated by dividing the number of patients admitted with ILI by the total number of patients presenting to the ED with ILI.


A season-to-season comparison of influenza-like illnesses across age groups. The data is season-to-date for all three periods, sharing a cut-off point through the most complete week for the current flu season. Percentages are calculated by dividing the number of ILI visits by the total ED visits for each the respective age groups.


A season-to-season comparison of influenza-like illness admission rates across age groups. The data is season-to-date for all three periods, sharing a cut-off point through the most complete week (indicated in the chart title) of the current flu season. Percentages are calculated by dividing the number of ILI admissions by the total ILI visits for each the respective age groups.

* NOTE: data within the most recent weeks' activity is subject to change as there may be delays in the receipt of encounter data. A minimum of 30% of total expected visits must be available before the week is included in the graphs.

Terms and Definitions
Influenza-Like Illnesses

Influenza like illnesses, as defined by the Centers for Disease Control, include the following symptoms:
  • Fever
  • Headache
  • Tiredness (can be extreme)
  • Dry cough
  • Sore throat
  • Nasal congestion
  • Body aches
These symptoms are referred to as "influenza-like illnesses". A variety of illnesses, including the common cold, can result in similar symptoms. For purposes of this study, patients were considered to have an influenza-like illness when fever was present along with one or more of the following: upper respiratory infection, cough, sore throat, or nasal congestion.

The Flu Season

Flu activity is most commonly tracked during a 33-week span of time between October and May (weeks 40 - 20), with peak activity varying from year to year but typically experienced between December and March.