What is an opportunistic infection?

An opportunistic infection is defined as an infection that occurs when a pathogen takes advantage of a weakened immune system. This typically happens in individuals whose immune defenses are impaired, such as those with HIV/AIDS, cancer patients undergoing chemotherapy, or individuals who have undergone organ transplants and are on immunosuppressive therapy. In these cases, normally non-pathogenic microorganisms can cause disease due to the compromised state of the host.

The key aspect of opportunistic infections is that they rely on the host's vulnerability. In healthy individuals, these pathogens typically do not cause disease because the immune system can effectively eliminate them. However, when the immune response is diminished, these opportunistic pathogens can enter the body or proliferate unchecked, leading to infections that would otherwise be prevented.

Understanding this concept is crucial in microbiology, particularly in health professions, as it highlights the importance of immune system integrity in preventing infections and managing conditions that predispose individuals to such infections.