There are a lot of virus' and bacteria that can cause vomitting and diahorrea and the viruses alter there make up often which is why you can "re-catch it" Rotavirus is a very potent virus that can make young children very ill, more than your average tummy bug.

To prevent getting tummy bugs
1. make sure you are safe from food poisoning - keep cold food cold and hot food hot, be wary of undercooked chicken and eggs (salmonella) and also cream in bakery and deli products as well.

2. good personal hygine after using the toilet

3. make sure you have a good intestinal flora. If you have been on antibiotics, medications or have had a tummy virus try a probiotic to build up the good bacteria which prevents bad bacteria and viruses from being able to get a hold on you.

4. To lessen the severity of tummy bugs. Reintroduce foods slowly starting with very basic foods like clear broth and potatoes.

Also have heard that the more tummy bugs kids get the better they will resist them as adults. I obviously didn't get sick much as a kid as I get every stupid tummy bug that does the rounds. I have been using a probiotic lately and found myself to be much more resistant.