It's a tough one - a friend of mine had it recently, she had no idea until her cough just wouldn't go away even though Drs kept saying it was just asthma or a chest infection - wasn't until one cluey doc made her get a nasal swab that it was diagnosed.

I'd suggest have a chat with your GP and get your DS tested to be on the safe side, as once antibiotics are started they need to be quarantined for 5 days. Fingers crossed it's just a cold but better to know for sure