Abstract
Background: Clostridium difficile infection (CDI) requires production of toxins A and/or B to manifest clinically but not all strains produce these specific virulence factors. Nontoxigenic C. difficile strains (NT-CD) cause asymptomatic colonization of gastrointestinal tract. Studies using hamster model have demonstrated that colonization with NT-CD decreases risk of subsequent infection with toxigenic strains (T-CD). The aim of this study was to investigate if use of two-step stool toxin assay can determine if colonization with NT-CD protects against CDI.Methods:CDI testing involves a two-step stool assay: Glutamate dehydrogenase (GDH) and toxin ELISA followed by PCR. GDH detects the presence of both T-CD and NT-CD. The ELISA and PCR tests detect presence of toxins A and B. Two groups of patients tested for clinically suspected CDI were identified GDH negative / toxin negative (G-T-) (No CDI or colonization) and GDH positive / toxin negative and PCR negative (G+T) (Colonization with NT-CD). Only patients with high risk for CDI (Age > 50 years, ≥ 2 hospitalizations and recent antibiotic use) were included. Patients with prior history of CDI or current infection (GDH positive and toxin or PCR positive) were excluded. Based on previous studies, CDI rate in patients colonized with NT-CD is about 1% as compared to 15% in those not colonized. Chart review was performed retrospectively from October 2013 to include a total of 100 subjects in each group (80% power and 95% Confidence intervals). Incidence of CDI in one year follow up period after initial negative toxin assay was assessed. Chi-square test for binomial data and 2 tailed t-test for continuous data were used. Results: A total of 200 patients (Age = 68.7 ± 11.8 years, 57.5% women) were included. 9 CDI occurred in G+Tgroup compared to 7 CDI in G-Tgroup (p=0.79). The recurrence rates were 22.2% (2 cases) in G+T-group and 14.2% (1 case) in G-T-group (p=0.69). Hospitalization rates were similar between two groups (3.45 ± 2.1 days in G+T-and 3.65 ± 2 days in G-T-group, p=0.49). The average length of stay was 7.39 ± 4 days in G+Tcompared to 7.73 ± 4.7 days in G-T-group (p=0.58). Discussion: Our study indicates that colonization with NT-CD does not protect against future CDI or reduce recurrence of CDI. This is contradictory to previous animal studies supporting protective effects of NT-CD. The explanation for this discordance could be that protective effect of NT-CD may be related to specific strains of NT-CD. Moreover unlike in animal studies, human microbiome may be impacted by several additional factors like exposure to antibiotics and frequent hospitalizations, leading to acquisition of toxigenic strains. It would be interesting to study in future if fecal microbiota transplantation works by favoring colonization with specific NT-CD strains to prevent recurrent CDI .
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