Can animals in your home lOwer a humas emmue system?

My brother just got two hamsters about 3 weeks agao we have NEVER gotten sick with ANYTHING in the 4 years we havent had pets even through the winter when everyone gets hit hard with viruses about the second week in having the hamsters he got strep and no one in his class had it and then our whole family got strep then on the third week we were all sick with a bad cold and I am a germaphobe but this is a questioning factor is having an animal or maby mOre in your home cause to lower your immune system answeres fast and ASAP