Asymptomatic means absence of symptoms and colonization is the innocuous presence of a microorganism. Thus, asymptomatic colonization is the condition in which Candida spp. can be grown from a body surface without appearing to be causing a disease. Asymptomatic colonization with Candida spp. is common.
However, colonization is also the prelude to development of most candidal infections. This has been particularly well demonstrated for patients at high risk to develop invasive candidiasis [1454, 1808, 2131, 2343]. It has been shown by DNA typing that the colonizing is often identical with the infecting strain [1879, 2343]. Thus, asymptomatic colonization is presumed to be a marker for potential invasive infection in patients at risk for invasive candidiasis.
Asymptomatic colonization with Candida has also been linked with an ill-defined syndrome or group of syndromes referred to under the broad title of chronic candidiasis (also referred to as the Yeast Connection).
Asymptomatic colonization commonly occurs in these parts of the body:
- Oropharynx (mouth region)As discussed in detail under Oropharyngeal Candidiasis, Candida spp. are part of the normal mouth flora in 25-50% of healthy individuals .
- StoolThe primary reservoir of Candida spp. is the digestive tract. Candida spp. appear to thrive in the gastrointestinal (GI) tract of all warm-blooded animals including human beings.
If nosocomial acquisition of GI colonization in the hospital setting is defined as a positive culture (stool) for Candida preceded by a negative one, rates as high as 50% among Surgical Intensive Care Unit (ICU) patients, and 30% in Neonatal ICU patients have been reported . Among neonates, low birth weight infants have been reported to have colonization rates as high as 63% .
- VaginaCandida species are part of lower genital tract flora in 20 to 50% of healthy and asymptomatic women . Carriage rates are higher in:
- Lower Respiratory TractAlthough the mucosa of the lower respiratory tract should normally be sterile, it can become colonized with a variety of organisms, including Candida spp [357, 653, 662]. Such colonization probably reflects spread from the oral mucosa . Such colonization is especially common in hospitalized patients (regardless of underlying diseases), patients with HIV/AIDS, diabetic patients, cancer patients, and mechanically ventilated patients. In ventilated patients, frequencies of asymptomatic colonization as high as 40% have been reported . However, clinically relevant candidal pneumonia is a relatively rare event and isolation of Candida spp. from a specimen obtained from the respiratory tract, including sputum, tracheal aspirates, or even by bronchoalveolar lavage and protected specimen brush is not diagnostic of invasive candidiasis. Rather, such colonization should be placed in the context of the patient’s overall condition and other risk factors for invasive disease.
- Urinary TractCandida spp. are only rarely found in the urine of healthy individuals. If present, colony counts of less than 1000 organisms/ml are found. The incidence of asymptomatic candiduria is higher in girls than boys, which is probably related to vaginal colonization . Even a single course of therapy with an antibiotic increases the chances of finding yeast in the urine . Pregnancy also increases the rate of colonization, but, short of bladder catheterization to obtain a clean specimen, it is hard to decide if small numbers of organisms represent vaginal or urinary colonization [1637, 2301].
The most important cause of candiduria in the hospital setting is the presence of a urinary catheter [859, 2448]. Although candiduria can be a clue to the presence of renal and/or disseminated candidiasis, making a distinction between colonization and disease is difficult. See the discussion of urinary candidiasis for more details.
- Skin and WoundsCandida spp. can also be cultured from both healthy skin and wounds [1033, 1438, 1968, 2327, 2393]. Colonization of healthy skin would appear to have little clinical relevance. Colonization of the large areas of denuded skin that are present in burn patients would appear likely to increase the risk for invasive candidiasis , but there are few data on this topic. Candida spp., in combination with one or more bacteria, are very commonly isolated from wounds [1033, 2393]. As with isolation of Candida spp. from burns, the clinical relevance of this finding is usually uncertain and the presence of colonization is simply one of many factors that might increase a given patient’s risk for invasive candidiasis. However, the mere presence of Candida spp. from a wound is not diagnostic in and of itself.
Rates of skin colonization increase during prolonged hospitalization . Carriage of C. parapsilosis is especially common on the hands of healthcare workers and has been linked to nosocomial spread of this organism . Isolation of Candida spp. from wounds is very common and usually of little significance.