Opportunistic infection

An opportunistic infection is an infection that occurs most commonly in individuals with an immunodeficiency disorder and acts more severe on those with a weakened immune system. These types of infections are considered serious and can be caused by a variety of pathogens including viruses, bacteria, fungi, and parasites.^[1] Under normal conditions, such as in humans with uncompromised immune systems, an opportunistic infection would be less likely to cause significant harm and would typically result in a mild infection or no effect at all. These opportunistic infections can stem from a variety of sources, such as a weakened immune system (caused by human immunodeficiency virus and acquired immunodeficiency syndrome), when being treated with immunosuppressive drugs (as in cancer treatment),^[2] when a microbiome is altered (such as a disruption in gut microbiota), or when integumentary barriers are breached (as in penetrating trauma). Opportunistic infections can contribute to antimicrobial resistance in an individual making these infections more severe. Some pathogens that cause these infections possess intrinsic resistance (natural resistance) to many antibiotics while others acquire resistance over time through mutations or horizontal gene transfer.^[3] Many of these pathogens, such as the bacterium Clostridioides difficile (C. diff), can be present in hosts with uncompromised immune systems without generating any symptoms, and can, in some cases, act as commensals until the balance of the immune system is disrupted.^[4][5][6][7] With C. diff and many other pathogens, the overuse or misuse of antibiotics can cause the disruption of normal microbiota and lead to an opportunistic infection caused by antibiotic resistant pathogens.^[8] In some cases, opportunistic infections can be labeled as a hospital-acquired infection due to individuals contracting them within a healthcare/hospital setting.^[9] In terms of history, there is not one individual that can be attributed for discovering opportunistic infections. Over time and through medical advancement, there have been many scientists that have contributed to the study and treatment options for patients affected by these infections.^[10][11]