Candida colonization index and subsequent infection in critically ill surgical patients: 20 years later

Abstract

Introduction: For decades, clinicians dealing with immunocompromised and critically ill patients have perceived a link between Candida colonization and subsequent infection. However, the pathophysiological progression from colonization to infection was clearly established only through the formal description of the colonization index (CI) in critically ill patients. Unfortunately, the literature reflects intense confusion about the pathophysiology of invasive candidiasis and specific associated risk factors.

Methods: We review the contribution of the CI in the field of Candida infection and its development in the 20 years following its original description in 1994. The development of the CI enabled an improved understanding of the pathogenesis of invasive candidiasis and the use of targeted empirical antifungal therapy in subgroups of patients at increased risk for infection.

Results: The recognition of specific characteristics among underlying conditions, such as neutropenia, solid organ transplantation, and surgical and nonsurgical critical illness, has enabled the description of distinct epidemiological patterns in the development of invasive candidiasis.

Conclusions: Despite its limited bedside practicality and before confirmation of potentially more accurate predictors, such as specific biomarkers, the CI remains an important way to characterize the dynamics of colonization, which increases early in patients who develop invasive candidiasis.

Fig. 1

Pathophysiology of invasive candidiasis in different patient populations. Detailed mechanisms are summarized in the corresponding sections of the text

Fig. 2

Colonization index. This index is defined as the ratio of the number of distinct non-blood body sites with Candida spp. colonization to the total number of distinct body sites tested. It was recorded for each patient from the first day of colonization until discharge from the intensive care unit (uninfected patients) or severe candidiasis development (infected patients). Black circles represent patients who developed severe candidiasis, white circles represent patients who remained colonized. Reproduced with permission from Pittet et al. [24]

Fig. 3

Proposed study designs to select high-risk patients who would truly benefit from early empirical antifungal treatment. First, patients should be stratified according to pathophysiological characteristics specific to invasive candidiasis (i.e., immunocompromised individuals, after digestive surgery, other critically ill patients). The three-step approach: In a first optional step, increased intrinsic risk of invasive candidiasis is identified by specific genetic polymorphisms related to innate immunity. In the second step, patients at low objective risk of invasive candidiasis are ruled out by using the high negative predictive values of current risk-assessment strategies (CI, Candida score, peritonitis score, predictive rule). In the third step, empirical antifungal treatment is started early in high-risk patients identified by increased biomarkers values, such as beta-glucan performed only in patients retained by who met criteria outlined in previous steps. A simplified approach restricted to steps two and three may be also of potential interest