We monitor the percentage of emergency department visits that are diagnosed with a respiratory virus to understand the level of respiratory virus activity and whether it is increasing or decreasing.
Transmission alert threshold
The chart below shows a point that is the transmission alert threshold for each virus based on emergency department visits. When the percent of emergency department visits for a virus is above that point, it’s a sign that there is substantial spread of that virus.
Emergency department visits
The data dashboards below show what percent of emergency department visits in King County hospitals were diagnosed with COVID-19, influenza, or RSV.
Hospitals send data on emergency department visits to the Washington State Department of Health's Rapid Health Information NetwOrk (RHINO). Visits related to respiratory viruses are identified by diagnosis codes. The data are stored on the National Syndromic Surveillance Program (NSSP) Biosense ESSENCE platform.
We monitor the percent of tests that are positive for a respiratory virus to understand if activity is increasing or decreasing. Laboratories send respiratory virus testing data to CDC's National Respiratory and Enteric Virus Surveillance System (NREVSS) and the National Syndromic Surveillance Program's ESSENCE platform.
We identify influenza deaths based on reports from medical providers, the Medical Examiner's Office, and review of death certificates. These numbers reflect deaths resulting directly or indirectly from an influenza illness, confirmed by an appropriate laboratory test.
Influenza outbreaks at long-term care facilities
We define long-term care facility (LTCF) influenza outbreaks as when:
- one or more facility residents tests positive for influenza, or
- two or more new cases of respiratory illness occur within 72 hours of each other.
- All data are preliminary and may change as we update data.
- We report data up to the last complete week.
- HMPV: Human metapneumovirus
- RSV: Respiratory syncytial virus
- Seasonal coronavirus refers to HCoV-NL63, HCoV-229E, HCoV-OC43 and HCoV-HKU1. This count does not include SARS-CoV2.
Emergency department visits
- Data on respiratory virus emergency department visits are reported to the Washington State Department of Health’s Rapid Health Information NetwOrk (RHINO) and are stored on the National Syndromic Surveillance Program (NSSP) Biosense ESSENCE platform. All non-federal hospitals and their associated inpatient units report healthcare encounter data in near real-time to RHINO.
- COVID-19, influenza, and RSV emergency department visits include hospital records that contain one or more of the COVID-19, influenza, and RSV-specific ICD 10-CM discharge diagnosis codes. The discharge diagnosis codes for each of these respiratory illnesses can be found in the CDC’s companion guide for NSSP data. Discharge diagnoses do not necessarily reflect a confirmatory laboratory test. For COVID-19 data based on confirmatory laboratory tests, visit COVID-19 data.
- We report emergency department visits at King County hospitals, which includes both King County and non-King County residents seen at King County hospitals.
- If someone visits the emergency department more than once, each emergency department visit is counted. Counts do not reflect unique persons.
- To create geographic regions, we use the location of the hospital (the patient’s area of residence is not used).
- The number of hospitals reporting to RHINO has changed over the past several years as new facilities have begun reporting to the system. Because of this addition of new facilities, the count of emergency department visits has increased over the years. To partially adjust for this effect across seasons, we report the percent of healthcare encounter data per disease condition, rather than the count. However, trends across seasons may still be impacted by the addition of new facilities as different facilities treat different patient populations.
- To protect privacy, we do not report numbers and percentages less than 10 in a category. When there are fewer than 10 emergency department visits for a specific virus, we report the percentage and count as “< 10”.
Transmission alert thresholds
- If the percent of emergency department visits diagnosed with a virus is above the transmission alert threshold, it is a sign that there is substantial transmission of that virus.
- Transmission alert thresholds for COVID-19, influenza, and RSV are calculated using the Moving Epidemic Method.
- The transmission alert threshold is calculated at the start of the respiratory season using data from the previous 5 seasons.
- Because COVID-19 is a new disease that started transmission in King County in 2020 and does not yet have a clear seasonal pattern, the multiple wave algorithm within the Moving Epidemic Method was used to classify the waves. To calculate the transmission alert threshold for COVID-19 for the 2023-24 season, we used data from February 2020 to September 2023.
- To calculate the transmission alert threshold for influenza for the 2023-24 season, we used data from the following seasons: 2017-18, 2018-19, 2019-20, and 2022-23. We excluded the 2020-21 and 2021-22 seasons because of the COVID-19 pandemic.
- To calculate the transmission alert threshold for RSV for the 2023-24 season, we used data from the following seasons: 2017-18, 2018-19, 2019-20, 2021-22, and 2022-23. We excluded the 2020-21 season were because of the COVID-19 pandemic. We defined the RSV seasons as starting on week 30 and ending on week 29 of the following year due to the earlier RSV cases in 2021.
- As our understanding of respiratory viruses continues to grow, we will re-evaluate and update our methods when new science is available.
Respiratory virus seasons
- Respiratory virus activity typically begins to increase in the fall and continues through the following winter. Therefore, we define respiratory virus seasons as starting in early October and ending a year later.
- The 2022-23 respiratory disease season begins on October 2, 2022 and ends on September 30, 2023.
- The 2023-24 respiratory illness season begins on October 1, 2023 and ends on September 28, 2024.
- Laboratories send respiratory virus testing data to the CDC's National Respiratory and Enteric Virus Surveillance System (NREVSS) and the National Syndromic Surveillance Program's ESSENCE platform.
- Participating King County laboratories include Evergreen Hospital Medical Center, Kaiser Permanente Washington, LabCorp, Overlake Hospital Medical Center, Seattle Children's Hospital, Seattle-King County Public Health Laboratory, St. Francis Hospital, University of Washington, Valley Medical Center, Virginia Mason Medical Center, and the Washington State Department of Health.
- NREVSS data are reported in aggregate and cannot be broken down by demographic groups.
- The deaths shown on this page are likely an undercount of the true number of influenza-related deaths given not all patients are tested for influenza and the influenza virus is detectable for a limited number of days after infection.
Influenza Outbreaks at Long-term Care Facilities
- Long-term care facilities report suspected outbreaks of influenza to Public Health, and we investigate them. Only confirmed outbreaks are included in the chart.
- We define outbreaks of influenza at long-term care facilities as one or more facility residents testing positive for influenza, or two or more new cases of respiratory illness that occur within 72 hours of each other.
- We consider long-term care facilities healthcare settings and include nursing homes and skilled nursing facilities, adult family homes, assisted living facilities, enhanced services facilities, and intermediate care facilities.