Two syndromic surveillance systems are being used to monitor trends in outpatient and emergency department visits that may be associated with COVID-19. Each system monitors a slightly different syndrome, and together these systems provide a more comprehensive picture of mild to moderate COVID-19 illness than either would individually. Both systems are currently being affected by recent changes in healthcare seeking behavior, including increasing use of telemedicine, recommendations to limit emergency department (ED) visits to severe illnesses, and increased practice of social distancing. These changes affect the numbers of people and their reasons for seeking care in the outpatient and ED settings.
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) provides data on visits for influenza-like illness (ILI) (fever [≥100○F] and cough and/or sore throat) to approximately 2,600 primary care providers, emergency departments and urgent care centers in all 50 states, Puerto Rico, the District of Columbia and the U.S. Virgin Islands. Mild COVID-19 illness presents with symptoms similar to ILI, so ILINet is being used to track trends of mild to moderate COVID-19 illness and allows for comparison with prior influenza seasons.
Nationwide during week 17, 1.8% of patient visits reported through ILINet were due to ILI. This percentage is below the national baseline of 2.4% and represents the fifth week of a decline after three weeks of increase beginning in early March. The percentage of visits for ILI decreased in all age groups. Nationally, laboratory-confirmed influenza activity as reported by clinical laboratories has decreased to levels usually seen in summer months which, along with changes in healthcare seeking behavior and the impact of social distancing, is likely contributing to the decrease in ILI activity.
* Age-group specific percentages should not be compared to the national baseline.
On a regional levelexternal icon, the percentage of outpatient visits for ILI ranged from 0.9% to 3.7% during week 17. Compared to week 16, the percent of outpatient visits for ILI increased slightly in region 5, but decreased in all other regions, and six regions are below their region-specific baselines.
ILI Activity Levels
Data collected in ILINet are used to produce a measure of ILI activity for all 50 states, Puerto Rico, the District of Columbia and New York City. The mean reported percentage of visits due to ILI for the current week is compared to the mean reported during non-influenza weeks, and the activity levels correspond to the number of standard deviations below, at or above the mean.
The number of jurisdictions at each activity level during week 17 and the change compared to the previous week are summarized in the table below and shown in the following maps. The decreasing percentage of visits for ILI described above are reflected in this week’s ILI activity levels.
|Activity Level||Number of Jurisdictions|
(Week ending April 25, 2020)
|Compared to Previous Week|
|Insufficient Data*||1||No change|
*Data collected in ILINet may disproportionally represent certain populations within a state, and may not accurately depict the full picture of influenza activity for the whole state. Differences in the data presented here by CDC and independently by some state health departments likely represent differing levels of data completeness with data presented by the state likely being the more complete.