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From: Infectious Disease: Congenital and Perinatal Infections: A Concise Guide to Diagnosis Edited by: C. Hutto © Humana Press Inc., Totowa, NJ
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Candida
Patricia Whitley-Williams
THE ORGANISM
Candida spp are ubiquitous dimorphic yeasts that can exist as 2- to 5-μm round-oval cells called blastospores, which reproduce by budding. They have the ability to pro- duce pseudohyphae, which are filamentous processes elongating from the cells. Fifty years ago, these round vegetative cells were considered nonpathogens. Some Candida spp, especially Candida albicans, exist as normal flora on skin and in the lower gas- trointestinal (GI) tract and female genital tract. However, therapeutic and technologi- cal advances in medicine have enabled these yeasts to become true pathogens, especially in the immunocompromised hosts. In addition to causing insignificant and mild mucocutaneous infections in the normal host, these yeasts cause invasive and life- threatening disease affecting almost any organ.
Of the 200 Candida spp, C. albicans has been the most common, accounting for about 60–80% of neonatal infections. Other Candida spp that act as human pathogens include Candida tropicalis, Candida pseudotropicalis, Candida lipolytica, Candida krusei, Candida guilliermondii, Candida parapsilosis, Candida lusitaniae, Candida globrata, and Candida stellatoidea.
There are reports that infections in low birth weight infants caused by other Candida spp, such as C. parapsilosis, have increased. C. parapsilosis accounted for 29–60% of blood isolates in neonatal intensive care units, including one large multicenter study that demonstrated 60% prevalence between 1991 and 1995 (1–3). C. parapsilosis and C. albicans account for 90% of Candida blood isolates in low birth weight infants. C.
parapsilosis appears to be less virulent than C. albicans because of its inability to pro- duce phagocytosis-resistant pseudohyphae and its poor adherence and penetration of human endothelium. The mortality rate in one study from C. albicans was 26% com- pared to 4% from C. parapsilosis (1,2).
TRANSMISSION
The majority of neonatal Candida infections are acquired either through vertical
transmission or by nosocomial spread. Electrophoretic karyotyping and pulsed field
gel electrophoresis have been used to demonstrate the mode of transmission of some
Candida spp. There is some evidence to suggest that most C. albicans infections in
preterm infants are transmitted vertically (1,3–5). The timing of vertical transmission may occur prenatally or at the time of delivery.
Intrauterine infection or true congenital infection occurs as a result of an ascending maternal infection and may lead to placentitis or chorioamnionitis. Fewer than 100 cases of congenital candidiasis have been reported in the literature (6). Histopathologi- cal evidence of fungi within umbilical or chorionic vessels supports the diagnosis of fetal candidemia in congenital candidiasis. Hematogenous spread of the infection to the fetus via the umbilical vein is extremely rare and has been reported in only three cases of congenital candidiasis (6). The rare occurrence of fetal candidemia supports the fact that the placenta is a highly effective barrier against these fungi. Congenital infection results more often in cutaneous than in disseminated candidiasis; however, the latter occurs more often in premature infants.
Perinatal or neonatal candidiasis, which is acquired as a result of passage through an infected birth canal, can result in infection in the newborn period. The most common presentation is mucocutaneous candidiasis in the form of oral thrush or perineal derma- titis. Disease occurs for the most part in infants who were colonized at the time of birth or within the first several weeks after birth. Disseminated disease, which is far less common than mucocutaneous candidiasis, occurs in the first 30–90 days of life and is more likely to occur in preterm colonized infants. Rarely does neonatal candidiasis produce an invasive fungal dermatitis, as is seen in congenital cutaneous candidiasis.
Severe pulmonary disease as a result of aspiration of infected vaginal secretions is rare (6).
Intimate contact such as breast-feeding with an infected mother as well as nosoco- mial spread may lead to postnatal candidiasis. In an earlier study, environmental con- tamination with Candida on chest tubes, ventilators, water reservoirs, breast milk, umbilical or central line catheters, or isolette walls could not be documented, although it does occur (5). Hospital personnel carry C. parapsilosis as the most common Can- dida species on their hands. Inadequate hand washing has allowed horizontal transmis- sion of this organism, especially among the very low birth weight infants, and has been the cause of several nursery outbreaks (4,7).
COLONIZATION
The fungal colonization rate for low birth weight infants (<1500 g) ranges from 19 to 47% in the first 24 hours of life (3,5,8). In one study, the most common site of early colonization (i.e., at birth or first 24 hours of life) was the GI tract, as demonstrated by positive rectal fungal cultures. At birth, 86% had rectal colonization, followed by 60%
with tracheal colonization and 57% with oropharyngeal colonization (5). The endotra- cheal acquisition at birth represents aspiration of the yeast during labor and delivery.
Oropharyngeal acquisition at birth was not as frequent as rectal acquisition. At 1–2 weeks of age, the detection of yeast in the rectum and oropharynx was less likely. Late colonization was more often detected in the groin cultures. By 2 weeks of age, 64–85%
of low birth weight neonates were colonized with Candida in the groin sites.
Colonization rates were higher for C. parapsilosis (56%) than C. albicans (44%) in one study in which surface cultures were obtained between the first and second weeks, third and fourth weeks, and fifth and sixth weeks of age (9). In several studies, C.
parapsilosis colonization occurred after the first or second week of life and could not
be accounted for by a maternal reservoir (3,4,9). However, this was not true in one
study in which C. parapsilosis colonization occurred early in the first day or week of life
(5). C. tropicalis, however, tends to appear as a colonizer later, after the first 2 weeks of life, and therefore tends to appear as a pathogen in late-onset disease (>7 days of age).
PREDISPOSING FACTORS IN MATERNAL INFECTION
Candida vulvovaginitis occurs in about 25% of pregnant women; however, this is usually not associated with obstetrical complications (10,11). Although infrequent, as- cending infections from the vagina and cervix can occur, leading to infection of the placenta. Because of the presence of chorioamnionitis or funisitis, candidemia and sep- sis may occur in the pregnant woman, but this is rare. Invasive disease would be un- likely unless the mother was immunosuppressed. Such conditions would include human immunodeficiency virus, immunosuppressive therapy, prolonged corticosteroid or broad-spectrum antibiotic use, burns, trauma, and indwelling vascular and urinary catheters.
PREDISPOSING FACTORS IN FETAL AND NEONATAL INFECTION Despite its presence in 25% of all pregnant women, isolation of Candida from the placenta is rare (12,13). Baley reported an incidence of less than 1% (14). In the pres- ence of chorioamnionitis, fetal infection can occur and presents as congenital cutane- ous candidiasis (CCC). Risk factors for congenital infection include early preterm birth, the presence of a foreign body such as an intrauterine device or cervical sutures, and possibly diagnostic amniocentesis (6,12). Factors that do not appear to play a role in congenital candidiasis are maternal age, prolonged rupture of membranes, diabetes, urinary tract infection, parity, and antibiotic, tocolytic, or corticosteroid therapy (15).
The role of congenital candidiasis in precipitating preterm labor or premature rupture of membranes remains unknown and warrants further investigation (16,17).
There are many factors that may make the neonate more susceptible to fungal infec- tions. These include an immature immune system, low birth weight, prematurity, con- genital immunodeficiency, indwelling vascular and urinary catheters, prolonged broad-spectrum antibiotic use, intralipid and parenteral nutrition, and early fungal colo- nization of the GI tract. At the end of the 20th century, the incidence of candidemia and its relationship to colonization has been studied.
The overall incidence of neonatal candidemia is 7.7% in low birth weight colonized infants (5). The incidence of candidemia in the low birth weight infants has increased over the last 20 years. In one study, the rate of candidemia in 1407 infants weighing less than 1000 g increased from 10.4 cases per 1000 admissions in 1981–1985 to 98.9 per 1000 in 1991–1995 (1). The mean age of onset of candidemia ranged from 15 to 173 days of age, with mean ages of 43–47 days in some studies (1,2). The incidence of candidemia was 0.2% (7/3033) in infants with birth weights above 2500 g admitted to the neonatal intensive care nursery (18). This risk is much lower than that for low birth weight infants. The most frequent underlying condition in these term infants was a major congenital malformation, which occurred in half of the infants with fungal sepsis.
Colonization has been shown to be a significant risk factor for mucocutaneous and
invasive candidiasis. In one study, one third of the colonized infants developed muco-
cutaneous candidiasis, and 7.7% developed systemic fungal disease (5). In another
study of 383 low birth weight infants, the overall incidence of invasive disease was
4.5%, and for mucocutaneous candidiasis, it was 7.8%. Invasive disease developed in
32% of the infants with mucocutaneous candidiasis compared to 2% without (19).
The largest prospective multicenter cohort study was conducted in six level-III neo- natal intensive care nurseries in diverse geographical areas from 1993 to 1995 to deter- mine the incidence and associated risk factors for candidemia in 2847 infants (20). The overall risk for candidemia was lower than previous reports (1.2%). The significant risk factors identified included preterm, low 5-minute Apgar score, disseminated intra- vascular coagulation, prior use of intralipid, parenteral nutrition, central venous cath- eters, H
2blockers, intubation, or length of stay for more than 7 days. Although GI tract colonization was not identified as an independent risk factor, almost half of the patients who developed candidemia had preceding colonization. In fact, enteral feeds may be protective and prevent or decrease GI colonization.
Some studies have looked at other factors, such as the nursery environment (5).
There was no evidence of environmental contamination found in chest tubes, ventila- tors, water reservoirs, breast milk, umbilical or central line catheters, or isolette walls documented, but it probably does occur. Vaginal delivery (compared to cesarean sec- tion) did not seem to be a risk factor. The only statistically significant factor was a grade 3 or 4 intraventricular hemorrhage (for infants delivered vaginally) (5). These infants tended to be sicker.
A univariate analysis of factors associated with colonization in a study of 116 low birth weight infants showed no significant difference between colonized and noncolonized infants. These factors included birth weight, gestational age, duration of nursery stay, vaginal delivery, steroid administration, or duration of intubation. Infants with colonization had a significantly longer duration of antimicrobial therapy, parenteral nutrition, and intralipid infusions. The duration of use of intravascular cath- eters approached significance (3).
Because of the increasing occurrence of C. parapsilosis, the risk of invasive disease associated with colonization of the GI tract in newborns was investigated (9). Of 82 colonized, low birth weight infants, 6% developed C. parapsilosis septicemia. There was an association with umbilical artery catheters and absence of enteral feeds. In that particular nursery, enteral feeds were not given if an umbilical artery catheter was in place.
Colonization of the urinary tract and respiratory tract may be risk factors for inva- sive candidiasis in the newborn. In one study, almost 15% of the infants with urinary tract colonization developed invasive disease (5). There is evidence to suggest that endotracheal colonization, especially in the first week of life, is a marker for invasive disease in low birth weight infants. These infants were 10 times more likely to develop invasive disease. It is unclear whether the trachea is a portal of entry or is a marker of high fungal burden (8).
PRENATAL EVALUATION
Any pregnant woman with a vaginal discharge or inflamed vulvovaginal area should
be evaluated for Candida. Candida vulvovaginitis is the second most common cause of
vaginitis after bacterial vaginosis. Many women are asymptomatic, but the classic signs
are a profuse, pruritic, thick, white, curdlike discharge associated with dysuria, dys-
pareunia, and pruritus ani. The diagnosis of Candida vulvovaginitis is a clinical diag-
nosis that is confirmed by culture and microscopic detection of the yeast. A drop of the
cervicovaginal fluid should be immersed in a 10% potassium hydroxide (KOH) prepa-
ration on a glass slide with a coverslip for microscopic examination. Sometimes, this
slide is heated before examining it under the microscope. The presence of ovoid bud- ding yeast cells 3–7 μm in diameter, seen sometimes with pseudohyphae, can make a presumptive diagnosis. The diagnosis is confirmed by isolating Candida from the cervicovaginal secretions cultured on Sabouraud’s dextrose agar, which is commer- cially available. If bacterial contamination of the specimen is expected, then chloram- phenicol should be used in the culture medium. Cycloheximide, which prevents fungal overgrowth, should not be used because it may inhibit some strains of Candida.
Candida is an unlikely pathogen in the immunocompetent pregnant woman. If the mother is immunosuppressed or has other risk factors for systemic candidiasis and is symptomatic, a workup should be initiated. If a pregnant woman who is immunocom- petent has signs of systemic infection, such as fever, shock, or respiratory distress, or focal signs, a full sepsis work should be done. This would include multiple blood cul- tures, midstream clean catch or catheterized urine sample for urinalysis and culture, complete blood cell count and differential, liver function tests, and chest x-ray. At- tempts to isolate Candida from blood and any other affected areas, such as cerebrospi- nal fluid, joint fluid abscess formation, bone marrow, bronchial alveolar lavage washings, skin lesions, tissue biopsy specimens, urine, and placenta should be made.
The isolation of Candida from urine, sputum, or bronchial washings does not al- ways confirm the diagnosis. Candida isolated from respiratory and urinary cultures, especially in the presence of bacteria, may reflect contamination from oral or vaginal flora. Quantitative urine cultures are not helpful.
The lysis-centrifugation blood culture method (Isolator system), which is the most sensitive method for detection of bacteria in blood cultures, can detect almost all clini- cally significant yeast isolates. Therefore, Candida can be easily detected and isolated from routine blood cultures. Blood isolation may take from 24 to 72 hours. On the agar plate, Candida colonies are white or cream-colored colonies, with filamentous exten- sions coming from the edges of the colonies indicating the formation of pseudohyphae.
C. albicans may undergo a transformation when placed in human serum for several hours. These new forms, chlamydospores, have cylindrical extensions called germ tubes. Because this is unique to C. albicans, a positive germ tube test confirms the diagnosis of C. albicans infection. Determining which Candida species has been iso- lated is important in invasive disease because of possible resistance. For example, C.
krusei is known to be resistant to fluconazole. Routine susceptibility testing is not rec- ommended. These tests are not always done in hospital laboratories, may not be reli- able, and may be difficult to interpret.
Because the yield from cultures may be low in patients who are immunocompromised,
tissue diagnosis may be required to confirm the diagnosis. The presence of yeast cells or
pseudohyphae on histologic sections helps to confirm the diagnosis. The presence of
pseudohyphae suggests tissue invasion rather than colonization; however, blastospores
or yeast cells can be virulent as well. Diagnosis should be made in conjunction with the
clinical picture and other diagnostic tests, such as urinalysis, radiographic imaging of
the lungs or kidneys, or endoscopy, to rule out esophagitis or tissue biopsy. The isola-
tion of Candida from cultures and histological detection of Candida in tissue speci-
mens confirms the diagnosis. The pregnant woman should be treated for vaginal or
invasive candidiasis. Preliminary studies do not justify the use of antifungal chemopro-
phylaxis to prevent invasive candidiasis in the newborn. Whether chemoprophylaxis is
beneficial needs further study.
FETAL EVALUATION
Although sampling of amniotic fluid obtained by transabdominal amniocentesis for prenatal detection of Candida may allow earlier diagnosis and intervention for inva- sive neonatal candidiasis as well as obstetrical intervention, this is not routinely recom- mended. Further investigation regarding obstetrical and perinatal management of mother and fetus is needed for the detection of Candida in amniotic fluid. The use of antifungal agents for chemoprophylaxis in the mother for preventing CCC or neonatal candidiasis and the use of oxytocin vs the continuation of tocolytic administration need further study.
PERINATAL EVALUATION
Although intrauterine infection is rare, chorioamnionitis may lead to preterm labor, congenital and neonatal infections, Candida sepsis, and endometritis. In intrauterine infection, gross examination of the placenta and umbilical cord will reveal a yellow exudate on the placental surface and areas of necrosis and discrete, yellow macular lesions along the cord near the funicular vessels. Histological examination of the cord and placenta may reveal spores and pseudohyphae on periodic acid-Schiff stain, Gomori methenamine silver stains, toluidine blue, or Gram stain. There is an inflam- matory infiltrate of neutrophils, lymphocytes, and histiocytes as well as microabscess formation.
NEONATAL EVALUATION
Maternal Candida vulvovaginitis may result in colonization of the newborn or mu- cocutaneous, invasive candidiasis or congenital candidiasis. Congenital candidiasis can present in infants as CCC or invasive disease (6,12,17,21). CCC is a severe cutaneous candidiasis that is far less common.
Mucocutaneous candidiasis consists of oral thrush or diaper dermatitis or both. Oral thrush typically presents on the days 7–10 of life as whitish patches (resembling milk curds) anywhere on the oral mucosa. The lesions can extend to the posterior pharynx but most often are located on the buccal mucosa, tongue, and palate. Scraping of these lesions results in a denuded erythematous base. Microscopic examination of these scrapings placed in 10% KOH suspension on a glass slide reveals blastospores or oval- round yeast cells and pseudohyphae. The diagnosis of oral thrush is based on clinical findings. Even though this is a presumptive diagnosis, routine culturing or microscopic examination of the scrapings is not necessary unless the thrush is persistent or atypical.
Candida dermatitis appears as 1- to 3-mm vesicular or pustular lesions on an erythematous base in the perineum, axillae, and neck folds. These discrete lesions can coalesce to form large patches of inflamed, denuded skin, especially in the perineal area. Again, the diagnosis is a clinical one unless the lesions are atypical or persistent or there is evidence of systemic disease.
Invasive candidiasis in the newborn infant presents as acute respiratory distress usu-
ally after the first 2 weeks of life. This may be accompanied by apnea, bradycardia,
temperature instability, metabolic acidosis, coagulopathy, and other focal signs. It may
lead to meningitis, endocarditis, brain abscesses, pneumonia, endophthalmitis, renal
and hepatic abscesses, and other organ involvement. Infants with C. albicans fungemia
(compared to C. parapsilosis) are more likely to present early with hypoxemia, respira-
tory distress requiring intubation, shock, and bradycardia and thrombocytopenia. They were also more likely (46 vs 2%) to have positive cultures from sites other than the bloodstream, including abscess fluid, cerebrospinal fluid, ascitic fluid, and sputum (2).
Therefore, in any low birth weight infant with respiratory distress and history of pro- longed antibiotic therapy, parenteral nutrition, intralipid infusions, or with indwelling intravascular catheters, fungal sepsis should be suspected.
Infants with CCC typically present on the first day of life with a generalized rash consisting of erythematous macules, papules, or pustules on a 5- to 10-mm erythema- tous base. Generalized erythema can be seen initially, which then can evolve into a severe skin eruption with discrete papules or vesicles and sometimes bullae. The erup- tion occurs predominantly on the back, extensor surfaces, skin folds, palms, and soles, but the perineum area is spared. The rash in very low birth weight infants can rapidly progress to bullae, erosion, and desquamation resembling burns or scalded skin. This is associated with an extreme leukemoid reaction. The nails may also be involved and appear opaque, raised, and rough. With the loss of the skin barrier, the preterm infant is at risk for dehydration and secondary bacterial infections. The differential includes staphylococcal pustulosis, bullous impetigo, syphilis, neonatal pustular melanosis, toxic epidermolysis bullosa, incontinentia pigmenti, neonatal listeriosis, herpes sim- plex, or varicella-zoster. CCC may also involve multiple organ systems, leading to hemorrhage and necrosis of the heart, lungs, kidneys, spleen, and other organs.
A definitive diagnosis of Candida infection in the newborn is made by isolation of the organism from culture of a sterile site or demonstration of the organism in tissue specimens. A sepsis workup should be performed in any infant suspected of having congenital candidiasis or Candida sepsis. This includes a blood culture, urinalysis, urine culture, complete blood count, lumbar puncture, and chest x-ray. A buffy coat culture can also be done to isolate Candida. Urine samples should be obtained for culture by suprapubic aspiration if possible. Straight bladder catheterization is an alter- native method for obtaining the urine but may be contaminated with normal or coloniz- ing flora. The cerebrospinal fluid evaluation should include cell count, Gram stain, culture, protein, glucose, and KOH preparation. Demonstration of spores and pseudohyphae in tissue, urine, and skin scrapings should be attempted.
It is recommended that daily blood cultures be done until sterilization of the blood
has been achieved, which may take several days. In one study, as many as 60% of
infants with neonatal candidemia had persistently positive cultures (>72 hours after
initiation of antifungal therapy) (22). These infants were more likely to have focal
complications. Therefore, if Candida cannot be eliminated from the blood stream after
48–72 hours or if clinically indicated, an evaluation for focal sites of infection is rec-
ommended. An electrocardiogram and echocardiogram should be done to rule out fun-
gal endocarditis. Magnetic resonance imaging or computeed axial tomography scan of
the brain should be obtained to rule out brain abscesses. An abdominal or renal ultra-
sound should be performed to look for abscesses in the kidney, spleen, and liver. A
computed tomographic scan of the abdomen and pelvis may provide further delinea-
tion of intra-abdominal or renal involvement or may be indicated for the purpose of
localization for biopsy or drainage of an abscess. An ophthalmological examination
should be performed to rule out retinitis or endophthalmitis. Diagnostic procedures
such as bronchoscopy; biopsies of liver, lung, or bone; aspiration or incision and drain-
age of abscesses; and bone marrow aspiration should be performed if clinically indi- cated to obtain specimens for culture, Gram stain, KOH prep, and histological exami- nation with special stains (periodic acid-Schiff, Gomori methenamine silver, toluidine blue). Indwelling vascular devices should be removed.
DIRECT DIAGNOSTIC ASSAYS FOR EVALUATING THE MOTHER AND INFANT
A number of immunological and serologic diagnostic tests have been investigated because of the difficulty with interpreting the isolation of Candida from the urinary and respiratory tracts as well as confirming the diagnosis of invasive candidiasis, espe- cially in immunocompromised hosts. Some of these tests look promising; however, most are not commercially available for routine use. Several rapid antigen detection assays are available, including latex particle agglutination (LPA), enzyme immunoas- say, and radioimunoassay. Most assays detect mannan as the main Candida antigen.
Some of these tests have a high rate of false negatives. The LPA is the easiest to per- form and has been shown to be useful in quantitation of Candida. Using a titer of 1:4 or above as a positive result, it has an excellent specificity of more than 90% but at best a sensitivity of only 70%. The LPA is more useful for monitoring response to therapy than diagnosis because there is some correlation with decreasing titers and successful antifungal treatment. The enzyme immunoassay is a rapid and quantitative test for Candida antigen that has excellent specificity but has poor sensitivity and cannot pro- vide species information and therefore is not very useful.
Antibody tests are not routinely recommended because there is a high rate of false negatives, especially in the immunocompromised patients. Complement fixation and indirect immunofluorescent antibody tests are not very helpful in the diagnosis of dis- seminated disease. Deoxyribonucleic acid probes are used as a rapid diagnostic test for vulvovaginal candidiasis with excellent specificity (99%) and good sensitivity (75%).
Candida skin tests are not useful and should not be used because they cannot distin- guish between colonization and invasive disease. Assays to measure levels of
D- arabinitol, a metabolite of pathogenic Candida species in the urine and serum, have been developed but are expensive and difficult to perform. The measurement of the
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