Infection: The invasion and multiplication of microorganisms such as bacteria, viruses, and parasites that are not normally present within the body.
An infection may cause no symptoms and be subclinical, or it may cause symptoms and be clinically apparent.
You may call them simply doctors. But most doctors have extra expertise in one type of medicine or another. In fact, there are several hundred medical specialties and subspecialties. Here are the most common types of doctors you'll likely see.