Guinea pigs do NOT carry salmonella. They can potentially carry another disease and intestinal parasites that might be transmitted to humans, but this is not common. A lot of people have guinea pigs and children, and NEVER have a problem with either. Children are more likely to get sick from being around other children, playing in the sandbox, and eating dirt (all normal child activities). As a young, 5-month old, I highly doubt your child will be doing a lot of GP petting, but this will increase with time, as will other activities that are more likely to make your child ill. As with all activities and pets, wash your child's hand before eating and after petting the GP, and don't let him/her put her fingers in the pig poo and then touch her eyes or mouth. This holds true with any pet.

The issue truly is "Is the guinea pig safe around a child?" And, the answer is "Only when supervised". A child may be the gentlest in the world, but may still injure the pet without realizing it ever did anything wrong. Your child is still young and probably won't be able to crawl to make it to the guinea pig. However, as you grow, it is very important to educate your child about caring for guinea pigs and being gentle toward all animals with which s/he comes in contact. If you are successful in this, you are bound to raise a loving child who enjoys the companionship of animal friends.

Just think off all the germs a guinea pig would have and having a 5 month old baby around may cause it to become sick as the child may have a weak immune system

Too young to be close to guinea pig, you can't be sure if he/she is safe from your guinea pigs' germs...

not the best idea. baby might catch salmonella.