Wiktionary
n. (context medicine English) Any infection that causes disease and occurs only when the host's immune system is impaired.
WordNet
n. any infection caused by a microorganism that does not normally cause disease in humans; occurs in persons with abnormally functioning immune systems (as AIDS patients or transplant patients receiving immunosuppressive drugs)
Wikipedia
An opportunistic infection is an infection caused by pathogens ( bacteria, viruses, fungi, or protozoa) that take advantage of an opportunity not normally available, such as a host with a weakened immune system, an altered microbiota (such as a disrupted gut flora), or breached integumentary barriers. Many of these pathogens do not cause disease in a healthy host that has a normal immune system. However, a compromised immune system, a penetrating injury, or a lack of competition from normal commensals presents an opportunity for the pathogen to infect.
Usage examples of "opportunistic infection".
HIV itself was an opportunistic infection that made itself known in the final stages of immune-system deterioration brought about in other ways.
A damaged immune system is susceptible to theaids virus, which then destroys that system, so inviting opportunistic infection.
I did not go on to say that it was PCP pneumonia and that this AIDS-related opportunistic infection would kill me if my doctor didn't find a way to kill it first.
She could go on for quite some time, awaiting the opportunistic infection that eventually claimed most ventilated patients, living beyond the time when even the remotest voluntary impulses could stir her body.
Then he went over to herb-and-marijuana panatelas, anxious to maintain his image as a Golden Age wheeler-dealer, but not so anxious for a long convalescence or opportunistic infection following a double pulmonary.
The AIDS epidemic arose about this time also, and tuberculosis became an opportunistic infection among many homosexuals.
Less time for an opportunistic infection to get a killing foothold.