Which of the following is a common nosocomial infection?

A common nosocomial infection is one that is acquired in a healthcare setting. Pneumonia fits this definition as it is often associated with hospital stays, particularly in patients who are intubated or have weakened immune systems. This type of pneumonia, known as hospital-acquired or ventilator-associated pneumonia, occurs due to prolonged exposure to invasive procedures and the hospital environment, where certain pathogens may flourish.

In contrast, the common cold, influenza, and chickenpox are primarily viral infections that are typically transmitted through community exposure rather than within hospital settings. While these viruses can be contracted in healthcare settings, they are not classified specifically as nosocomial infections due to their transmission routes more commonly occurring outside the hospital environment. Thus, pneumonia is the most representative example of a nosocomial infection among the options provided.