Monona, once again, just as we thought we had seen it all, you bring us news of someone who has managed to create a new low in health and safety in the workplace.  And I thought that was the exclusive purview of us academics... wrong again!

While this all sounds like a nightmare, here is a suggestion just in case your clients decide to go ahead with their experiment in measuring human infection rates.

How about bromine?  Like most, I use chlorine in our pool, but pool shops also carry "bromine" i.e tablets that release bromine; it is used when people are allergic or react to chlorine, and is apparently effective as a sterilizer.  I would reason that bromine is a less powerful oxidant than chlorine, and so the red dyes might be more stable and oxidized less, or less fast.  No idea if this will work, just a suggestion.

Best,
Paul