- Patients going to the medical centers are often sicker and so they are not able to fight off disease-producing microorganisms.
- The types of germs present in hospitals are often more dangerous than those encountered in the general community.
Infirmary-acquired pneumonia occurs more often in invalids who are using a respirator or ventilator machine to help them breathe. When pneumonia occurs in a person who is ill and on a ventilator, it is known as "ventilator-associated pneumonia".
Nosocomial pneumonia may be introduced into the lungs of sufferers with contaminated respiratory therapy equipment or simply by breathing the air filled with droplets of infections from other patients or coughing medical personnel; especially, when those who are sick are close together in intensive care units.
The increased use of drugs that reduce the body's rejection of implants, but at the same time, suppress the body's immune system, leaves the invalid vulnerable to infections that can kill; for example, nosocomial pneumonia.