Influenza Surveillance Data

Virginia 2012/2013 Influenza Surveillance Activity Level: No Activity^#

Virginia Weekly Influenza Activity Report (Week Ending September 21, 2013)

Purpose:

The Virginia Department of Health monitors the level of activity of influenza-like illness (ILI) each week from October through May. Those are the months when influenza ("flu") is most likely to occur in Virginia, and that time period is referred to as the "flu season".

Data Sources:
The Virginia Department of Health uses a number of different data sources to determine the level of flu activity that is occurring each week during flu season. The main data sources that are used to make the weekly flu activity level determination are:

• laboratory reports
• outbreak reports, and
• data on visits to hospital emergency departments and urgent care centers for flu-like illness.

Flu Activity Levels:
Flu surveillance is not designed to count every person who has the disease. That would be nearly impossible because not all people with the disease are diagnosed by a physician and even fewer have their illness confirmed by a laboratory test.

Instead, VDH monitors changes in flu activity from week to week in each of the five health planning regions to look for increases compared to a baseline period. Activity is based on illness complaints that lead people to seek care in a hospital emergency department or urgent care center. Flu-like illness is defined as a fever along with a cough and/or a sore throat.

In addition to looking at changes in the number of visits for flu-like illness in each region from week to week, VDH staff also factor in information about outbreaks that have been reported in each region as well as cases of influenza that have been confirmed by specific laboratory methods.

In order for the weekly flu activity level in Virginia to be comparable to those reported by other states, national definitions established by the Centers for Disease Control and Prevention are followed. The national definitions of flu activity levels are:#

No Activity: No laboratory-confirmed cases† of influenza and no reported increase in the number of cases of ILI. Sporadic: Small numbers of laboratory-confirmed influenza cases or a single laboratory-confirmed influenza outbreak has been reported, but there is no increase in cases of ILI. Local: Outbreak of influenza or increases in ILI cases and recent laboratory-confirmed influenza in a single region of the state Regional: Outbreaks of influenza or increases in ILI and recent laboratory-confirmed influenza in at least 2 but less than half the regions of the state. Widespread: Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least half the regions of the state.

† Laboratory-confirmed case = case confirmed by culture, antigen detection by DFA, or PCR.

---

Return to Top of Page