Epidemiology
Event Risk Estimator (Coronavirus)
Combine reported case counts, an ascertainment multiplier, and planned mitigations to approximate the likelihood that someone at your gathering is infectious. Results are illustrative and depend on accurate, timely surveillance data.
Number of new cases reported in your community during the past 7 days.
Use the population of the county, city, or campus associated with the event.
Multiplier to account for under-reporting (e.g., 3× actual infections vs reported).
Estimated relative reduction from mitigation layers (e.g., rapid testing, high-quality masks, outdoor venue). 0% = no mitigation.
Community prevalence
- Infection probability: 0.45%
- Ascertainment: 3×
Probability ≥1 infectious attendee
6.4%
Base risk (no mitigation): 10.7%
Expected infectious attendees
0.07
Lower probabilityRisk is lower but not zero. Maintain hand hygiene, stay home when ill, and improve ventilation whenever possible.
How to Use This Calculator
Start with reliable surveillance data
Use recent case counts or wastewater trends for the specific community hosting the gathering.
Adjust for under-detection
Estimate an ascertainment multiplier (2–5×) to account for asymptomatic infections and limited testing.
Layer mitigations
Reduce risk by shrinking the event, moving outdoors, requiring masks/testing, and improving ventilation.
Formula
Infection probability (p) = min(1, (Reported cases × Ascertainment) ÷ Population at risk)
Event risk = 1 − (1 − p)n, where n is event size.
Mitigated risk = Event risk × (1 − Mitigation reduction).
Expected infectious attendees = n × p × (1 − Mitigation reduction).
Mitigation reduction is a user-estimated relative risk reduction (0–0.9).
Full Description
This calculator adapts probability theory to estimate the chance that at least one attendee is currently infectious with SARS-CoV-2. It combines local incidence, an ascertainment multiplier to reflect undiagnosed cases, and optional mitigation benefits. Because all inputs are estimates, the result should be interpreted as a range rather than a precise forecast.
Public health recommendations change as variants, vaccination coverage, and therapeutics evolve. Use this tool alongside official guidance, especially for events involving high-risk individuals or critical infrastructure sectors.
Frequently Asked Questions
What if case reporting is delayed?
Use the most recent reliable data (e.g., wastewater, health department dashboards) and adjust the ascertainment multiplier accordingly.
How do I estimate mitigation reduction?
Combine expected benefits: high-quality masks (~30–40%), rapid testing (~20–30%), outdoor setting (~20%). Additively estimate total reduction but stay conservative.
Does this account for superspreading?
No. The model assumes infections are uniformly distributed. Use additional caution in poorly ventilated indoor venues where superspreading is more likely.
Should I cancel the event if risk is high?
Consider postponement, shifting outdoors, reducing attendance, or requiring pre-event testing and masks. Always follow local health regulations.