I agree with troisgarcons, we all need to build a healthy immune system through exposure to germs, immunisations and the old-fashioned 'peck of dirt' theory - BUT having had a child recovering from a bone marrow transplant, necessitating a year of immuno-suppression, and an enforced year of germ avoidance (aka imprisonment with toddler twins & poorly boy), I share your pain ... every time we dared to venture out, someone would be proudly showing off their chicken pox spots (meaning a trip to GOSH for immunoglobulin shot for DS), coughing and sneezing disgustingly or laughing about their tummy bug ... I just think people don't realise that it's not funny or clever to spread things around, almost deliberately. DS luckily made a good recovery and had a normal childhood, but to this day (he's 25, the twins are 23), we all jump at clear evidence of germ-sharing. This has done us no harm at all, although they laughed at my 'paranoia' as they were growing up, they are ultra-clean themselves now, and in my job as secondary school teacher, and the twins' jobs as social workers, we all strive to avoid catching every germ going, I would have thought this attitude is perfectly understandable ! I attended a residential course in Germany in the summer at which two teachers from Brazil had a really awful cough/cold/flu-type virus, and somehow managed to be one of the few not to catch it in the group of 16. I was probably OCD about not touching things they'd coughed on, tried to avoid sitting next to them, and stuffed back a daily 1000mg Vitamin C. It was probably mind over matter, but I was determined not to catch it !
Speaking as a teacher, I also agree with ZZZenAgain re. DC being sent to school when obviously ill, but given the woeful state of 'childcare' in the UK, I suppose this situation is sadly not surprising :(