Two stylists worked with COVID, and none of their 139 clients caught it

In May 2020, **two hair stylists in Springfield, Missouri worked while
symptomatic with what turned out to be COVID-19.** Between them they served
139 clients.

Both the stylists and the clients wore face masks, under a policy the
city and the company both required.

Why this is a good natural experiment

It is not a trial — nobody assigned anyone to anything — but the circumstances
are close to ideal for the question being asked:

• Prolonged, close, indoor, face-to-face contact. A haircut is fifteen to
  forty-five minutes at arm's length in an enclosed room. If masks failed
  anywhere, this is where
• A known infectious source, symptomatic at the time
• A defined, countable, contactable exposed group — a salon has an
  appointment book, which is exactly what the unlicensed spa in the New Mexico
  HIV investigation did not
• Universal compliance, because two independent policies required it

67 of the 139 were tested, and none was positive; none of the remainder
reported symptoms.

What it does and does not show

**Adherence to the community's and company's face-covering policy likely
mitigated spread.**

Zero out of 139 is a striking result, and the report's language is appropriately
careful — one salon, one fortnight, and an unmeasured number of other factors.
What it establishes is that a setting everyone assumed was high-risk produced
no transmission when everyone was masked, which is a hard result to explain
any other way.

The conclusion drawn from it is about timing, and reads differently now than it
did:

**As stay-at-home orders are lifted, professional and social interactions in
the community will present more opportunities for spread of SARS-CoV-2.
Broader implementation of face covering policies could mitigate the spread of
infection in the general population.**

Published July 2020 — when the question of whether reopening was compatible
with control was entirely open, and a salon in Missouri was one of the few
places an answer could be observed.

Source: Centers for Disease Control and Prevention, MMWR.