Rats can transmit disease to humans, but with a clean home and good hygiene the risk is very low.
The occasional rodent visitor is no reason to call in the exterminators. Nor is it a reason to get out the poison, glue traps and snap-traps: these are inhumane and/or toxic options that cause painful deaths and may also harm wildlife and children.
Instead, use preventative measure to make your home unappealing to rats (many of these tips will help deter insect pests too). For example, remove clutter, food and water sources, and seal gaps that act as entry points. Peppermint, garlic and cayenne pepper are reputed non-toxic deterrents.For more info and tips:
See Rats alive!