Public Health - Seattle & King County conducts influenza surveillance in order to provide information on local influenza activity to health care providers and the public. Because influenza is not a reportable disease, Public Health monitors data from several sources in order to understand when influenza has arrived, is most active, and subsides in our community. The main sources of influenza surveillance data are:

King County Sentinel Influenza Providers

Volunteer physicians obtain specimens of respiratory secretions from a subset of patients who present with influenza-like illness ( ILI ) and submit them for viral culture at the Public Health Laboratory. This system helps us confirm when influenza has arrived in our area. The Public Health Laboratory, a National Respiratory and Enteric Viral Surveillance System Collaborating Laboratory, determines the type and subtype of influenza (A or B) and submits a sample of influenza viruses to the Centers for Disease Control and Prevention for further antigenic characterization. Specimens submitted to the Public Health laboratory are also tested for other common respiratory viruses, including parainfluenza virus, respiratory syncytial virus (RSV) and enterovirus.

Rapid Antigen Test Submissions and Results

Several local microbiology laboratories report influenza rapid antigen test results each week. When influenza is circulating, the number of rapid antigen tests ordered, and proportion positive can reflect the level of influenza in the community. Rapid tests are generally reliable when positive, but when influenza activity is low, the rate of false positive results is increased.

Hospital Emergency Department Visits for Influenza-Like Illness ( ILI )

Emergency department chief complaint data from 17 of the county’s 18 hospitals are monitored for visits due to influenza-like illness (fever, sore throat, cough, headache, myalgias, etc). This surveillance may act as an early alert system for possible outbreaks, as well as provide information about specific areas of the county, or age groups that are being particularly affected.

School Absenteeism

During the school year, King County schools are asked to report to Public Health when 10 percent or more of students are absent during a given week. An increase in the number of schools reporting high levels of absenteeism, especially during the winter months, generally correlates with the level of influenza in the community.

Respiratory Disease Outbreaks at Long Term Care Facilities

Long Term Care Facilities (LTCFs), such as nursing homes and assisted living facilities, are required to report outbreaks of respiratory disease to Public Health.

Deaths Due to Pneumonia and Influenza (P&I Deaths)