How this calculator works
This implements the independent-attendee model used by Chande and colleagues. You supply contemporaneous active infectious cases and the multiplier for undetected infections; no location data are fetched. Attendees are assumed to reflect the population prevalence independently. Household clustering, selective attendance and immunity can violate that assumption. Presence of an infectious person is different from transmission at the event. The result is an estimate for information only and is not medical advice.
Formula
p = detected active cases × multiplier / population. P(at least one infectious attendee) = 1 - (1 - p)^n. Expected infectious attendees = n p.
Worked example
If p is 1% and there are 10 attendees, risk is 1 - 0.99^10 = 9.5618%. At p = 10% with two attendees, risk is 19% and the expected count is 0.2.
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Frequently asked questions
Does this estimate my chance of catching COVID-19?
No. It estimates infectious presence under a sampling model. Ventilation, exposure duration and other factors determine transmission.
What should the multiplier represent?
It is total infectious cases divided by detected infectious cases for the same time and population. It is an assumption, not a fixed universal constant.
Are these current local figures?
No. The examples are hypothetical. Enter reliable local estimates for the date of interest.