What is the risk for infection right after a major surgery? how many antibiotics are patients usually put on after major surgery to reduce the risk of infection? does the chance for infection increase with age?

That : That depends... The standard of care for antibiotic administration for surgeries not related to infectious process (ie. Abscess, peritonitis, diverticulitis, etc) is preoperative antibiotics administered within one hour of incision and for those antibiotics not to be carried over more than 24hrs post operatively. Usually one dose is given shortly before the operation is started and no additional antibiotics are given. This would be for operations such as hernias, gastric bypass, most uncomplicated intestinal surgery, orthopedics, neurosurgery, etc. For surgeries where a patient is known to have an infectious process that nessecitated the operation, a full course of antibiotics could be given. The range could be for 7-14 days for most scenarios. It could involve giving one or a combination of antibiotics depending on the circumstances.

The : The rate of infection will depend on many factors such as, obesity, diabetes, presence of established infection, the type of surgery as well as if appropriate antibiotics were given as indicated. Completely sterile surgery where there is no entry into the intestinal tract should have a wound infection rate of 1-2%. When the intestinal tract is opened, the patient is obese and open surgery is performed rather than laparoscopy the infection rate can be as high as 15-20%. In the case of established infection such as ruptured appendicitis the infection rate can be 30% or more.