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Asymptomatic Colonization


Overview

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:
  1. 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 [1672].

  2. Stool

    The 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 [1871]. Among neonates, low birth weight infants have been reported to have colonization rates as high as 63% [1720].

  3. Vagina

    Candida species are part of lower genital tract flora in 20 to 50% of healthy and asymptomatic women [855]. Carriage rates are higher in:
    • Women treated with antibiotics [1693].
    • Pregnant women [256, 771, 1637, 2301].
    • Diabetic women [2300].
    • Women with diagnosis of AIDS based on the criteria of CD4+ counts (<200 cells/mL) [629].
  4. Lower Respiratory Tract

    Although 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 [1126]. 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 [653]. 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.

  5. Urinary Tract

    Candida 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 [859]. Even a single course of therapy with an antibiotic increases the chances of finding yeast in the urine [859]. 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.

  6. Skin and Wounds

    Candida 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 [2327], 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 [1438]. Carriage of C. parapsilosis is especially common on the hands of healthcare workers and has been linked to nosocomial spread of this organism [2019]. Isolation of Candida spp. from wounds is very common and usually of little significance.





References

256. Bland, P. B. 1937. Experimental vaginal and cutanous moniliasis: Clinical and laboratory studies of certain monilias associated with vaginal, oral and cutaneous thrush. Arch Dermatol Syphil. 36:760.

357. Cabello, H., A. Torres, R. Celis, M. El-Ebiary, J. Puig de la Bellacasa, A. Xaubet, J. Gonzalez, C. Agusti, and N. Soler. 1997. Bacterial colonization of distal airways in healthy subjects and chronic lung disease: a bronchoscopic study. Eur Respir J. 10:1137-44.

629. Duerr, A., M. F. Sierra, J. Feldman, L. M. Clarke, I. Ehrlich, and J. DeHovitz. 1997. Immune compromise and prevalence of Candida vulvovaginitis in human immunodeficiency virus-infected women. Obstet Gynecol. 90:252-6.

653. El-Ebiary, M., A. Torres, N. Fabrega, J. Puig de la Bellacasa, J. Gonzalez, J. Ramirez, D. del Bano, C. Hernandez, and M. T. Jimenez de Anta. 1997. Significance of the isolation of Candida species from respiratory samples in critically ill, non-neutropenic patients. Am. J. Respir. Crit. Care Med. 156:583-590.

662. Eller, J., J. Ede, and W. Rossdeutscher. 1997. Sputum bacteriology of acute infective exacerbation: Chronic obstructive pulmonary disease versus bronchiectasis. Eur Respir J. 9:107.

771. Frerich, W., and A. Gad. 1977. The frequency of Candida infections in pregnancy and their treatment with clotrimazole. Curr Med Res Opin. 4:640-4.

855. Goldacre, M. J., B. Watt, N. Loudon, L. J. Milne, J. D. Loudon, and M. P. Vessey. 1979. Vaginal microbial flora in normal young women. Br Med J. 1:1450-5.

859. Goldberg, P. K., P. J. Kozinn, G. J. Wise, N. Nouri, and R. B. Brooks. 1979. Incidence and significance of candiduria. J. Infect. Dis. 241:582-584.

1033. Hermann, C., J. Hermann, U. Munzel, and R. Ruchel. 1999. Bacterial flora accompanying Candida yeasts in clinical specimens. Mycoses. 42:619-27.

1126. Johanson, W. G., A. K. Pierce, and J. P. Sandford. 1969. Changing pharyngeal bacterial flora of hospitalized patients: Emergence of gram-negative bacilli. N. Engl. J. Med. 281:1137-1140.

1438. Marks, M. I., S. Marks, and M. Brazeau. 1975. Yeast colonization in hospitalized and nonhospitalized children. J Pediatr. 87:524-7.

1454. Martino, P., C. Girmenia, M. Venditti, A. Micozzi, S. Santili, V. L. Burgio, and F. Mandelli. 1989. Candida colonization and systemic infection in neutropenic patients. A retrospective study. Cancer. 64:2030-2034.

1637. Newmann, G., and U. Kaben. 1975. [Blastomycoid flora of the urogenital tract in nonpregnant and pregnant patients]. Zentralbl Gynakol. 97:372-8.

1672. Odds, F. C. 1988. Candida and Candidosis, 2nd ed. Bailliere Tindall, London.

1693. Oriel, J. D., and P. M. Waterworth. 1975. Effects of minocycline and tetracycline on the vaginal yeast flora. J Clin Pathol. 28:403-6.

1720. Pappu-Katikaneni, L. D., K. P. Rao, and E. Banister. 1990. Gastrointestinal colonization with yeast species and Candida septicemia in very low birth weight infants. Mycoses. 33:20-3.

1808. Pittet, D., M. Monod, P. M. Suter, E. Frenk, and R. Auckenthaler. 1994. Candida colonization and subsequent infections in critically ill surgical patients. Ann. Surg. 220:751-758.

1871. Rangel-Frausto, M. S., T. Wiblin, H. M. Blumberg, L. Saiman, J. Patterson, M. Rinaldi, M. Pfaller, J. E. Edwards, Jr., W. Jarvis, J. Dawson, and R. P. Wenzel. 1999. National Epidemiology of Mycoses Survey (NEMIS): Variations in rates of bloodstream infections due to Candida species in seven surgical intensive care units and six neonatal intensive care units. Clin Infect Dis. 29:253-258.

1879. Reagan, D. R., M. A. Pfaller, R. J. Hollis, and R. P. Wenzel. 1990. Characterization of the sequence of colonization and nosocomial candidemia using DNA fingerprinting and a DNA probe. J. Clin. Microbiol. 28:2733-2738.

1968. Rose, H. D., and V. P. Kurup. 1977. Colonization of hospitalized patients with yeast-like organisms. Sabouraudia. 15:251-6.

2019. Sanchez, V., J. A. Vazquez, D. Barth-Jones, L. Dembry, J. D. Sobel, and M. J. Zervos. 1993. Nosocomial acquisition of Candida parapsilosis: an epidemiologic study. Am J Med. 94:577-82.

2131. Solomkin, J. S., and R. L. Simmons. 1980. Candida infection in surgical patients. World J. Surgery. 4:381-394.

2300. Vazquez, J. A., and J. D. Sobel. 1995. Fungal infections in diabetes. Infectious Diseases Clinics of Nort America. 9:97-116.

2301. Vejlsgaard, R., J. Bodenhoff, H. Friis, and W. Fischer-Rasmussen. 1982. Occurrence of yeasts in urine from pregnant women. Dan Med Bull. 29:209-10.

2327. Vindenes, H., and R. Bjerknes. 1995. Microbial colonization of large wounds. Burns. 21:575-9.

2343. Voss, A., R. J. Hollis, M. A. Pfaller, R. P. Wenzel, and B. N. Doebbeling. 1994. Investigation of the sequence of colonization and candidemia in nonneutropenic patients. J. Clin. Microbiol. 32:975-980.

2393. Weiss, C. A., III, C. L. Statz, R. A. Dahms, M. J. Remucal, D. L. Dunn, and G. J. Beilman. 1999. Six years of surgical wound infection surveillance at a tertiary care center - Review of the microbiologic and epidemiological aspects of 20 007 wounds. Arch Surg. 134:1041-1048.

2448. Wise, G. J., P. Goldberg, and P. J. Kozinn. 1976. Genitourinary candidiasis: Diagnosis and treatment. J. Urol. 116:778-780.



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