An organism that ordinarily does not cause disease but can do so when the host’s defenses are impaired constitutes an opportunistic pathogen. These microorganisms exploit vulnerabilities in the immune system or breached physical barriers, leading to infections that typically would not occur in healthy individuals. For example, Pneumocystis jirovecii, a fungus, rarely causes illness in individuals with intact immune systems but can induce severe pneumonia in immunocompromised patients, such as those with HIV/AIDS.
The significance of understanding these types of pathogens lies in their increasing prevalence in healthcare settings and among populations with weakened immunity. The rise of antibiotic resistance further complicates the treatment of infections caused by such pathogens. Historically, these infections were less common, but advancements in medical treatments like chemotherapy and organ transplantation, which often suppress the immune system, have expanded the population susceptible to opportunistic infections. This underscores the need for robust infection control measures and proactive management of underlying conditions that predispose individuals to these infections.
