Hospital-acquired pneumonia (HAP), also known as nosocomial pneumonia, is a lower respiratory infection that occurs at least 48-72 hours after a patient is admitted to a hospital. It is different from community-acquired pneumonia, which is contracted outside of a hospital setting. HAP is usually caused by bacterial infections, rather than viruses. It is the second most common nosocomial infection (after urinary tract infections) and accounts for 15-20% of the total. It is also the most common cause of death among nosocomial infections and is the primary cause of death in intensive care units. Hospital-acquired pneumonia typically lengthens a hospital stay by 1-2 weeks.

Symptoms of HAP include a new or progressive infiltrate on the chest X-ray, fever, purulent sputum, leukocytosis, cough with greenish or pus-like phlegm, fever, chills, and mental changes or confusion in older adults. The first sign of HAP in elderly patients may be mental changes or confusion.

HAP is usually caused by bacterial infections, with the most common pathogens being gram-negative bacilli and Staphylococcus aureus. The development of HAP represents an imbalance between normal host defenses and the ability of microorganisms to colonize and then invade the lower respiratory tract. The types of germs present in a hospital are often more dangerous and more resistant to treatment than those outside in the community.

Prevention of HAP includes taking steps to prevent the spread of germs, such as hand-washing, wearing gowns, and using other safety measures in the hospital. People can be more likely to get pneumonia while in the hospital if they abuse alcohol, have had chest surgery or other major surgery, have a weak immune system from cancer treatment, certain medicines, or severe wounds, have long-term (chronic) lung disease, breathe saliva or food into their lungs as a result of not being fully alert or having swallowing problems, are not mentally alert due to medicines or illness, are older, or are on a breathing machine (ventilator) .

Treatment of HAP involves antibiotics, oxygen therapy, and respiratory therapy. The choice of antibiotics depends on the suspected pathogen and the patients individual risk factors[[6]](https://www.merckmanuals.com/professional/pul...