Half of them had no idea where they caught it

Colorado's stay-at-home order took effect on 26 March 2020. To work out
what should be advised after reopening, the state interviewed people
diagnosed during 9–26 March — the window when community transmission was
already happening and nothing had been closed.

600 people were selected at random from the state surveillance system,
across nine counties holding about 80% of Colorado's population. At least
three contact attempts were made on at least two separate days at different
times.

364 (61%) were interviewed. Of the rest: 133 (22%) unreachable, **57
(10%) declined**, 46 (8%) ineligible.

Who they were

Median age 50, 51% male, 57% non-Hispanic white, 21% Hispanic,
95% insured. 35% were hospitalised and 5% died — a severity profile
that reflects who could get a test in March 2020, not who was infected.

Of the 264 (73%) who were working, the workplaces were:

The central finding

**Only 99 (27%) reported known contact with a person with laboratory-confirmed
COVID-19.**

Of the 265 without such contact, **30% (79) had been around someone they
knew had a fever or respiratory symptoms.**

Put together: **roughly half of all participants could not name contact with
either a confirmed case or anyone they knew to be unwell.** They caught it from
someone who, as far as they could tell, was fine.

What they had been doing

In the two weeks before falling ill:

Health care appears twice, from both sides of the counter — which is why the
recommendations address facility managers as well as employers generally.

What follows from "about half"

The advice is the ordinary list, and the reasoning behind each item is what
this study supplies:

• **Anyone with COVID-compatible symptoms should avoid public settings and
  isolate from others, even within their own household** — because the people
  in this study who did know of an exposure knew because somebody was
  visibly ill
• Employers should follow CDC workplace guidance, because workplaces are
  common exposure locations
• **Health care facilities should continue infection prevention and control
  practices**, for employees and visitors alike
• And for the half who could point to nothing: **hand hygiene, distancing and
  face coverings**, which are the measures that do not depend on knowing who is
  infectious

Source: Centers for Disease Control and Prevention, MMWR.