Hospital Acquired Infections (also called Nosocomial infections) are infections which are a result of treatment in a hospital or a healthcare service unit, but secondary to the patient's original condition. Infections are considered nosocomial if they first appear 48 hours or more after hospital admission or within 30 days after discharge. Nosocomial comes from the Greek word nosokomeion (νοσοκομείον) meaning hospital (nosos = disease, komeo = to take care of). This type of infection is also known as a hospital-acquired infection (or more generically healthcare-associated infection).

Nosocomial infections are even more alarming in the 21st century. The main reasons are as follows:

  • Hospitals house large numbers of people who are sick and whose immune systems are often in a weakened state;
  • Increased use of outpatient treatment means that people who are in the hospital are sicker on average;
  • Medical staff move from patient to patient, providing a way for pathogens to spread;
  • Many medical procedures bypass the body's natural protective barriers;
  • Sanitation protocol regarding uniforms, equipment sterilization, washing, and other preventative measures may be either unheeded by hospital staff or too lax to sufficiently isolate patients from infectious agents.
  • Patients are often prescribed antibiotics and other anti-microbial drugs to help treat illness; this may increase the selection pressure for the emergence of resistant strains.

Thorough hand washing and/or use of alcohol rubs by all medical personnel before and after each patient contact is one of the most effective ways to combat nosocomial infections. More careful use of anti-microbial agents, such as antibiotics, is also considered vital.