A nosocomial illness (the word derives from a Latin term for hospital, and, traced further back, to a Greek one for disease) is one that occurs in a hospital or other healthcare facility.

It can be caused by various agents, including infection by other patients or health professionals, as well as poor hygiene, vermin, fungal spores, air droplets, and catheters.

Often, pneumonia-like symptoms are the result of such infections, but they can also lead to vomiting bugs, and necrosis.

The phenomenon was first addressed by the Hungarian physician Ignaz Semmelweis (1813-1865) who played a particular role in addressing hygiene on maternity wards. It has been suggested that, ironically, he died of such an infection himself, but this is open to dispute.

To this day, prevention of such conditions is achieved by following Semmelweis's principles of both personal and environmental hygiene in healthcare facilities.

More Info: en.wikipedia.org