Two syndromic surveillance systems are being used to monitor trends in outpatient and emergency department visits that may be associated with COVID-19 illness. 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 increased use of telemedicine, compliance with recommendations to limit emergency department (ED) visits to severe illnesses, and increased practice of social distancing. These changes affect the numbers of people seeking care in the outpatient and ED settings and their reasons for doing so.
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 26, 1.1% of patient visits reported through ILINet were due to ILI. This percentage is well below the national baseline of 2.4% but is increasing, which is atypical for this time of year. The pattern of increasing percentage of visits for ILI was reported for all age groups. Nationally, laboratory-confirmed influenza activity as reported by clinical laboratories is at levels usually seen during summer months which, along with changes in healthcare seeking behavior and the impact of social distancing, is likely contributing to the low level of 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 0.5% to 1.9% during week 26. All ten regions are below their region-specific baselines; however, Region 4 (South East) increased from 1.3% during week 25 to 1.7% during week 26, Region 6 (South Central) increased from 1.4% to 1.9% and Region 7 (Central) increased from 0.6% to 0.8%; Regions 2 (NY/NY/PR), 5 (Midwest), 8 (Mountain), 9 (South West/Coast) and 10 (Pacific Northwest) also reported slight increases.
Note: In response to the COVID-19 pandemic, new data sources will be incorporated into ILINet as we move into summer weeks when lower levels of influenza and other respiratory virus circulation are typical. Starting in week 21, increases in the number of patient visits will be seen as new sites are enrolled and the percentage of visits for ILI may change in comparison to previous weeks. While all regions remain below baseline levels for ILI, these system changes should be kept in mind when drawing conclusions from these data. Any changes in ILI due to changes in respiratory virus circulation will be highlighted here.
Overall Percentage of Visits for ILI | Age Group ILI Data
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 26 and the change compared to the previous week are summarized in the table below and shown in the following maps.
*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.