Yeast infection

candidiasis

candidiasis (kănˌdĭdīˈəsĭs), infection caused by fungi of the genus Candida; also called moniliasis after a former name of the genus. The most common forms of candidiasis, caused by C. albicans, are infections of the mucous membranes of the mouth (also known as thrush) and of the vagina and often the vulva (also known as yeast infection). The fungus C. albicans is a normal inhabitant of the mouth and vagina, and its growth is usually kept in check by certain bacteria that also live in these areas. When the balance of these organisms is disturbed by antibiotic treatment, by hormonal imbalances, or by a weakening of the body's resistance to disease (as occurs in AIDS), the fungus can begin to proliferate. Candidiasis of the penis (usually traceable to a female with the infection) is called balanitis. Candidal infections are most often treated topically with antifungal drugs such as clotrimazole, nystatin and miconazole, but oral or intravenous antifungal drugs are prescribed when the infection does not respond to topical treatments.

Invasive candidiasis, a more serious infection, occurs most commonly when Candida fungi invade the bloodstream. Hospital and nursing home patients, such as those with a central venous catheter, in an intensive care unit, with weakened immune system, or taking broad-spectrum antibiotics, are most likely to develop invasive candidiasis. Antifungal medications may be prescribed prophylactically to patients who are likely to develop invasive candidiasis. An invasive infection is typically treated by an echinocandin administered intravenously.

C. auris, another species that causes invasive candidiasis, typically infects the bloodstream, wounds, or the ear, and especially affects individuals with weakened immune systems. First identified in Japan in 2009, it is of concern because most forms of the fungus are drug resistant and some are multidrug resistant; additionally, infection can be difficult to identify from its primary symptoms of fever, aches, and fatigue. It has caused outbreaks in health-care facilities, where it can be difficult to eradicate.

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Yeast infection

An infection mainly caused by fungi of the genus Candida. Although members of the genus Candida continue to be the most common agents of yeast infections, numerous nosocomial (related to medical treatment) factors have altered this etiologic pattern over the last 20 years. Reports in professional publications have described over 200 species in 25 yeast genera as being associated with human infections. See Fungal infections, Fungi, Yeast

Etiologic agents

Candida, species particularly C. albicans, cause almost 70% of all yeast infections. However, recent changes in medical practices such as the use of broad-spectrum antibiotics, steroids, and immunosuppressive drugs, along with the recognition of new and highly debilitating diseases [for example, acquired immune deficiency syndrome (AIDS)], have increased the diversity of the agents of these infections. Species that were once rarely encountered in patient specimens (for example, C. parapsilosis, C. krusei, and C. guilliermondii) are being isolated with increased frequency. Equally important is the fact that yeasts that have never been described as the cause of human infections, (for example, Blastoschizomyces capitatus, C. dubliniensis, and Trichosporon cutaneum) are now being associated, albeit rarely, with human disease. See Acquired immune deficiency syndrome (AIDS), Opportunistic infections

Predisposing factors

Since yeasts are not as adept as other microbial pathogens at evading or overwhelming the body's immune defenses, they generally require some disruption in the natural protective mechanisms of humans to initiate an infection. Minor breaks in the skin (such as those caused by a cut or scrape) to more significant disruptions in the integrity of the skin (as created by the delivery of medications or nutrients through intravenous catheters) can provide the means by which the yeasts on human skin may enter the body and potentially initiate an infection. The use of broad-spectrum antibacterial agents eliminates a large portion of the normal bacterial flora, allowing the yeasts in the mouth and intestines to grow rapidly and seed the blood to create a temporary benign infection or a chronic, potentially life-threatening infection. Natural hormonal imbalances as created by pregnancy or diabetes mellitus, as well as those caused by the use of medications such as corticosteroids, depress the immune system and predispose the individual to possible yeast infections. The common use of immunosuppressive drugs, and the depressed immunity associated with newer human diseases such as AIDS cause a decrease in the immune system's ability to prevent and eliminate yeast infections. Finally, the longer human life expectancy created by modern medical practices has contributed to an ever-increasing population of senior citizens with naturally lowered resistance to all forms of microbial infections. See Immunosuppression

Clinical symptomology

Although yeast infections usually affect the skin and mucous membranes, the illness can take several different forms, each with different symptoms. For example, in newborns and infants, candidiasis can appear as reddening and blisterlike lesions of skin infections (diaper rash), or it can present as white-gray lesions on the mucosal tissue lining the oral cavity (thrush). The symptoms observed in the vast majority of yeast infections mimic those of other microbial pathogens and thus are generally of little value in establishing their etiology. The diagnosis of most yeast infections involves obtaining detailed medical histories from patients, conducting extensive physical examinations, analyzing clinical laboratory data, and utilizing the education, training, and experience of the attending physicians and infectious disease specialists. See Clinical microbiology

Treatment

The introduction of the first clinically effective antifungal antibiotic (nystatin) closely followed the use of antibacterial drugs (penicillin). However, nystatin was found to be effective only when brought into direct contact with the infectious agent. The broad-spectrum and fungicidal (killing fungi) activity of amphotericin B, another member of the same chemical family, maintains its use as the drug of choice for several yeast infections and as the antifungal of last resort when all other antibiotics have failed. Two closely related families of drugs, the azoles and triazoles, were introduced in the early 1970s and quickly established themselves as the first-line antibiotics for yeast infections. However, the newer triazoles are fungistatic (limiting growth) rather than fungicidal. As a result, recurrences of infection happen frequently once therapy is discontinued. Although new antifungal antibiotics continue to be introduced, the perfect drug with broad-spectrum and fungicidal activity, easy delivery, and limited side effects has yet to be found. See Antibiotic, Antimicrobial agents

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