Joannek, I have to 100% diagree. I would take the "risk" because there is no risk. Babies who are BF have fewer gastrointestinal illnesses than babies who are bottle feed, and it is all because of the antiodies. Even if a mom is sick,t he child is much less likely to get that illness if BF, compared to bottle feeding. If they do get an illness, they will have it less severly and recover quicler because of the passive immunity they recieve.
If the baby did get the illness, a gastro illness is passed via oral route, those types of bacteria are not going to be passed via breastmillk, but baby will still get antibodies, for all virus', bacteria mom comes into contact with, even ones that mom isn't aware of. You are exposed to bacteria and virus all day long, but only a small percentage will make you sick.
In fact your baby will also recieve antibodies via prenancy and Bf from some illnesses in the past. This is why youdo not develop long term immunity from live vaccines such as chickenpox and measles when give under 1 year of age, hence they are given after 1 year. By then the antibodies recieved via pregnancy have worn off. Prior to this the antibody will kill of the vaccine virus and you won't get the long term immunity. I do wonder what role BF has in this though, I wonder if it makes it less effetive. I wonder if there are studies on this? Where I live (Canada), still the majority of people do not BF up to a year, so my guess is that there is not a lot of research.
Here is link on illness and BF
http://www.llli.org/FAQ/sick.html