It’s interesting that the presence or lack of “the sniffles” has become important. The “sniffles" are a gauge for the efficacy of COVID19 screening procedures, and the commitment of the work force to follow the procedures. The sniffles don’t indicate COVID19, but they are the canary in the coal mine.
If a company develops effective screening rules for preventing COVID19 from getting on a vessel, and mariners follow the rules, not so much as a sniffle should be found in the crew (absent nasal allergies). Rules to avoid COVID19 infection will rule out catching the common cold.
So if someone comes down with a common cold aboard ship it means either the rules aren’t being followed or the rules aren’t tight enough.
Most companies take the temps of mariners before they board a vessel now. Overkill, perhaps, because a person with a fever is going to feel unwell, and will likely simply tell the screener this. Perhaps just as important, the screener should ask if the mariner has runny nose, and if so, why? No history of allergies? Then it could be a cold. And a cold indicates that the protection of the screening rules has been broken.