Outpatient/Emergency Department Illness

Two syndromic surveillance systems are being used to monitor trends in outpatient and emergency department (ED) 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 changes in health care seeking behavior, including increased use of telemedicine, compliance with recommendations to limit ED visits to severe illnesses, and increased social distancing. These changes affect the numbers of people seeking care in the outpatient and ED settings and their reasons for doing so.

ILINet

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 37, 1.0% of patient visits reported through ILINet were due to ILI. This percentage is well below the national baseline of 2.4% and is typical for this time of year compared to previous influenza seasons. Compared with week 36, the percentage of visits for ILI during week 37 slightly increased overall and among the pediatric age groups (0-4 years and 5-24 years) and the 50-64 year olds.

* Age-group specific percentages should not be compared with the national baseline.

On a regional levelexternal icon, the percentage of outpatient visits for ILI ranged from 0.6% to 1.6% during week 37 and was below the region-specific baseline in all regions. Compared with week 36, the percentage increased in three of the ten regions: Regions 2 (New Jersey/New York/Puerto Rico), 5 (Midwest), and 6 (South Central).

Note: In response to the COVID-19 pandemic, new data sources are being incorporated into ILINet through the summer weeks, when lower levels of influenza and other respiratory virus circulation are typical. Starting in week 21, enrollment of new sites began, leading to increases in the number of patient visits. While all regions remain below baseline levels for ILI, these system changes should be considered when drawing conclusions from these data. Any changes in ILI due to changes in respiratory virus circulation will be highlighted here.

ILI Activity Levels

Data collected in ILINet are used to produce a measure of ILI activity for all 50 states, Puerto Rico, the U.S. Virgin Islands, the District of Columbia, and New York City. The mean reported percentage of visits due to ILI for the current week is compared with 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 37 and changes compared with the previous week are summarized in the table below and shown in the following maps. The “high” level of activity in Iowa is due to visits for ILI associated with COVID-19 activity.

ILI Activity Levels Activity Level Number of Jurisdictions Week 37

(Week ending

September 12, 2020) Compared with Previous Week Very High 0 -1 High 1 +1 Moderate 1 +1 Low 0 -1 Minimal 49 -1 Insufficient Data 3 +1

*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.