Okay, so you have TM 0. The human race lucked out, the virus is transmitted by droplets rather than by aerosol, so it stays in the air only a few seconds before splattering on all nearby surfaces and contact with surfaces are how most people get infected. (Read up on measles if you want to know more about aerosol transmission. Nasty.) TM 0 drops stuff in locker, clocks in and grabs equipment. That's 3-5 days. TM 0 goes to the bathroom, touches the exterior door handle. Possibly TM 0 touched their face at some point during the time they were washing their hands, to fix the fit of the mask after looking down, so possibly touching the interior door handle. 3-5 days. Breaktime, TM 0 grabs stuff out of locker, removes mask and eats. Any surface within 6 feet of TM 0's mouth is going to end up covered in viral laden droplets, since the water vapor you breathe out carries the virus. So fun time in the breakroom. Possibly washing hands again, possible fixing of mask. Touching the locker again. While bending all around in the course of duties, air going out of any gaps in the sides of the mask have droplets. Turning in equipment, grabbing items out of locker, and leaving.
Even wiping on the hour every hour, there's still time for someone else to touch the exterior and interior bathroom door handle, touch items in the breakroom that were within 6 feet of TM 0's mouth, working in the same area that TM 0 worked that resulted in exertion and body contortion and possibly allowing droplets to escape, interior of the locker, and lots of other surfaces inbetween.
So that's where TM 1 and 2 come in. They touched something shortly after TM 0. They get infected while TM 0 is presymptomatic. A couple of days later you get TM 3. The next day TM 0 isn't feeling so hot and wisely stays home, but whoops. During the time that TM 0 is waiting for a test, TM 1 and 2 are now contagious and spreading the love. When TM 0 finally gets a positive diagnosis, TM 1 and 2 have spread their droplets and snared TM 4, 5 and 6. TM 3 is also hitting contagious time.
All because someone touched the inside bathroom door handle or got a cup of water from the breakroom sink or chose a locker before cleaning, or because someone cleaned half assed.
When someone is identified as having COVID-19, it's a safe bet that not only has that person infected others, but those others have hit the contagious period and have infected a third set of people. Only partial containment of the raging fire. Better than none at all, but don't pretend it's 100% containment.
