Diagnostic Value of Candida Colonization Index in The Early Diagnosis of Invasive Candidal Infection İnvaziv Kandida İnfeksiyonlarının Erken Tanısında Kandida Kolonizasyon İndeksinin Tanı Değeri

Objective: To investigate the diagnostic value of Candida colonization index (CCI) in the early diagnosis of invasive candidal infection in medical mix (medical and surgical intensive care units (ICU). Methods: Mouth, axillae, nasogastric catheter, rectum, and urine culture samples taken from the patients admitted to the reanimation and neurological ICU for 19 months were retrospectively evaluated and CCI were calculated. Results: CCI reached ≥0,5 in the cultures of 29 patients. 29 patients developed candidal infection; 27 (27/29) of them had CCI ≥0,5. 18 patients developed urinary infections, 10 patients developed candidemia, and 1 patient developed wound infection. CCI ≥0,5 was found as the only independent predictor for invasive candidal infection (p<0,001, OR: 701,553, %95 CI; 28,310-17385,22). The positive predictive value, sensitivity, and specifity of CCI for the candidal infection were found to be 93.1% and 96.2%, respectively. Conclusions: We concluded that monitoring for CCI in patients with unknown fever, severe sepsis or septic shock in the medical ICU offers an early diagnosis and intervention to prevent invasive candidal infection. Independently from the other risk factors, CCI may be considered as an effective test for early diagnosis of invasive candidal infection in medical and surgical ICU patients.


INTRODUCTION
There has been an overall increase in fungal health care-associated infections (HAIs), including patients in intensive care units (ICU), in the last few decades (1). This increase in invasive fungal infections is multifactorial which is likely a consequence of the advances in medical and surgical therapies. In spite of the the new development of diagnosis and treatment of candidiasis, fungal infection still causes high mortality rates (2).
Candida infections occur five to ten times more often (2-6.7 in 1000 admitted patients) in ICUs than on medical or surgical wards. According to National Nosocomial Infections Surveillance (NNIS) data, Candida spp. (%70-90) and Aspergillus spp. (%10-20) are the most common causes of invasive fungal infections in critically ill patients (3,4). Unfortunately, the diagnosis of invasive candidiasis carries on a challenge because rapid microbiological markers are not available. Although serological tests are promising, the lack of sufficient studies among the patients in ICU, and extensive cost limit widely usage of these serological markers. Physicians often make the diagnosis of invasive Candida infection on the basis of symptoms and signs of an infection and the presence of risk factors (5,6). Many ICU patients represents risk factors for invasive candidiasis, and a large proportion of them become colonized with Candida spp. during the ICU stay (7)(8)(9)(10). The patients were reported 50-80% to have Candida colonization during their stay in ICU (11). As assessed by the colonization index proposed by Pittet et al in 1994, increasing growth of Candida spp. from multiple body sites is predictive for subsequent invasive candidiasis (7). Prior colonization could allow recognition of these patients. On the other hand Candida colonization increase the risk of invasive candidiasis (12).
Candida scoring has been shown to be effective in surgical intensive care units but there is a few data on medical intensive care units. The aim of the study is to investigate the diagnostic value of Candida colonization index (CCI) in the early diagnosis of invasive candidal infection in the medical and mix (medical and surgical) ICU setting.

MATERIALS and METHODS
The study was designed in a 12-bed Anesthesiology and Reanimation ICU (ARICU), and in a 7-bed Neurological ICU (NICU) for the 19 months. All patients admitted to ICU were included in the study. The following data of the patients were collected and analyzed: age, gender, cause of ICU admission, previous hospital stay, previosus antibiotic use, duration of ICU stay, hemodialysis or hemofiltration, APACHE (Acute Physiologic and Chronic Health Evaluation) II score, the number and duration of invasive procedures such as mechanical ventilation, endotracheal tube, arterial line, peripheral and central venous catheters, urine catheter, and parenteral nutrition.
Culture samples were obtained from the urine, mouth, axillae, nasogastric aspiration, and rectum on admission to ICU, and then repeated three times in a week until death or discharge from ICU. Blood samples were obtained on admission and then repeated each time when two or more systemic inflammatory response syndrome (SIRS) criteria were present. Specimens were inoculated onto Sabouraud Dextrose and Cornmeal agar. Yeast identification was made based on combination of microscopic examination and biochemical characteristics in the API-32C® system (bioMerieux, France).
Blood cultures are obtained from both peripheral blood and, if exist, central venous catheter (CVC). In case of growth in CVC cultures, the catheter was removed. One or more positive blood culture yielding Candida spp., was accepted as an episode of candidemia. Severe non-bloodstream invasive candidal infections were defined as isolation of Candida spp. from sterile body sites, and the presence of at least one of the following conditions: body temperature ≥38 0 C or <36 0 C; unexplained prolonged arterial hypotension (systolic blood pressure <90 mmHg for at least 2 h, unresponded to volume challenge; absence of response to adequate antibiotic treatment for suspected bacterial infection (13). The diagnosis of candiduria required the recovery of at least 100 cfu/ml of the same Candida spp. in two distinct urine samples obtained within 1 week (14). Candida colonization was defined as the isolation of fungi in various body sites or fluid samples (urine, mouth, axillae, nasogastric aspiration, rectal swap samples) (15). A Candida colonization index (CCI) was determined as the ratio of the number of distinct body sites colonized with identical strains over the total number of distinct body sites tested (15).
The statistical analysis of the data was performed using the SPSS version 15.0 software package. Categorical variables were analyzed using chisquare or Fisher's exact tests where appropriate. Student's t-test was used for comparison of continuous variables. To test the independence of the risk factors for invasive candidiasis, a multivariate analysis was performed by logistic regression. Statistical significance was set at a p value of < 0.05.
The mean time of onset of candidal infection was 22,41±3,39 days after ICU admission. The mean time until colonization was 9,90±10,16 days for the 29 patients who became colonized after admission to the ICU.
Previously established risk factors for invasive candidiasis were present in most of patients. 56,1% of them were hospitalized within prior 6 month, 90,3% had prior bacterial infection, 71,9% were exposed to broad spectrum antibiotics, 98,8% had peripheral venous catheter, 48,8% had central venous catheter, 82,9% were intubated, 81,7% required a mechanical ventilation, and 97,6% had urinary catheterization. The risk for the development of Candida infections was increased by the lengthened duration of hospitalization. The risk of Candida infection were 2.5 times higher in patients who stayed ≥16 days than those of patients who stayed <16 days in ICU (p <0.001, OR 2.54, 95% CI 0.45 to 0.373). The most common species isolated from the samples was Candida albicans (62,1 %).
Increased age (≥ 65), lengthened duration of hospitalization prior to ICU admission, stay in reanimation ICU, use of broad spectrum cephalosporins, presence of renal failure, loss of consciousness, invasive procedures such as central venous catheter, peripheral arterial catheter and intubation were determined as predictors of Candida colonization.
Evaluation of the risk factors revealed that age (≥65 year), stay in ARICU, lengthened duration of hospitalization, prior urinary infection, use of broad spectrum antibiotics, recent antibiotic use (0-15 days), renal failure, peripheral arterial catheter, central venous catheter, and intubation were found to be associated with Candida infection (Table 2).

DISCUSSION
Invasive candidiasis (IC) in patients admitted to the medical ICU is a serious problem and, of particular concern, associated with high mortality and morbidity (16). The adequate antifungal treatment is a major factor associated with a good prognosis in fungal infection (1). Intravascular catheters, endotracheal tubes, naso-and oro-gastric tubes, and foley catheters etc., conduce biofim formation by Candida spp. (15). Substantially these may explain progressive colonization of many patients after prolonged stay in the ICU (12,15). Among the different risk factors Candida colonization is an important one. In our study we observed only immunocompetent patients in ARICU and in NICU and complications and many of them were already colonized by Candida spp. During the observation period ten patients developed Candida bloodstream infection, who presented with CI ≥ 0.5.
Multiple site colonization and its degree has a crucial role in the development of invasive Candida infection (17)(18)(19). Pittet et al (7) proposed a clinically relevant colonization index in an attempt to assess fungal colonization density with time in high risk surgical ICU patients. Positive predictive value of CCI was determined as 66-100%. This was confirmed by several subsequent studies. It has been shown that the incidence of Candida colonization and candidiasis infection is increased due to translocation in the gastrointestinal tract during surgery and multiple trauma or damage to the skin and mucous membranes (12). In a study performed in the surgical ICU, Öhman-Agvald et al (20), showed that high colonization index in the presence of large gastroabdominal surgery may be predicting factor for invasive candidiasis (20). Similarly, Solomkin et al., reported that 31 of 63 surgical ICU patients were colonized with Candida spp. in at least two body sites before detected fungemia (21). Charles et al (22) showed that prior colonization with Candida spp. reaches to a higher density in patients admitted to medical ICU than those in the surgical ICU. The Candida Score (CS) combined in a predictive clinical the results of a prospective cohort study, where surgery, multifocal colonization, total parenteral nutrition and severe sepsis predicted invasive candidiasis, with 81% of sensitivity and 74% of specificity and a had negative predictive value (NPV) of 98% (23). We did not find these parameters as meaningful because of the low number of traumatized patients who underwent surgery in our study. In addition, no significant difference was found between hospitalization diagnoses and IC (p>0,05). CCI could be of predictive value for the diagnosis of systemic candidiasis in high-risk surgical patients, but a few studies have performed Candida score, and colonization index for identifying patients at risk of development of IC in medical ICU setting. Lahmer et al showed that fungal colonization is independently associated to mortality in cirrhotic ICU-patients (24). In a retrospective study of 29 critically ill patients, Chronic Health Evaluation II (APACHE II) score and duration of antibiotic exposure before colonization were higher among the 11 patients who ultimately developed invasive candidiasis (25). Smilar to this study, in our study APACHE II scores were >25 among the patients who developed multiple site Candida colonisation.
Massou et al (26) determined that the most common risk factors were broad-spectrum antibiotics and foreign material. The CI was greater than or equal to 0.5 at 53% of the patients, and less than 0.5 in 47% of the cases. Among the patients, 15% developed an invasive candidiasis. In multivariate analysis, the corticosteroid therapy was associated with a high colonisation (IC ≥ 0.5) and neutropenia with a high risk of systemic candidiasis. In contrast our study the positive predictive value of CI was 26%, the negative predictive value was 98%, the sensitivity and specificity was 93% and 48% respectively. Although they thought that it wasn't helpful with patients having an invasive candidiasis in medical intensive care unit, the positive predictive value, sensitivity and specifity of CCI were 93.1 %, 93.1%, and 96,2% for the candidal infection, and 52,6%, 100%, 74,6% for candidemia, respectively, in our study. Charles PE et al (27) found that broad-spectrum antibiotic therapy promote fungal growth in patients with prior colonization. They suggest that reducing antibiotic use could be useful in preventing fungal infections. In our study prior antibotic usage was found to be associated with Candida colonisation and infection.
Unfortunately, to date prospective surveillance studies of fungal colonization in the medical ICU are still limited. We determined that CCI was the only independent predictor for candidal infection by the logistic regression analysis (p<0,001, OR: 701,553, %95 CI; 28,310-17385,22). Several other risk factors found to be associated with candidemia in other studies were not independently associated with candidaemia in our study. The timely recognition of IC is essential to driving clinical decision processes and specific therapeutic strategies. Independently from the other risk factors, CCI may be considered as an effective test for early diagnosis of invasive candida infections in medical and surgical ICU patients. Therefore it may be a useful tool to prevent mortality.
It is obvious that Candida score could be of predictive value for the diagnosis of systemic candidiasis in high-risk surgical and trauma patients but the datas are limited in medical ICU. Although further studies are needed to compare, standardize and eventually confirm these data, our experience suggests that monitoring for CCI is a good predictor for candidasis in medical ICU patients with unknown fever, severe sepsis or septic shock and APACHEE scores are high.
Prospective trials with a large patient population in medical ICU based on CCI and other risc factors such as APACHEE score, prior antibiotic usage, lenght of hospital stay etc. would be useful.