Objectives: To determine the proportion of patients who received a treatment for Clostridioides difficile infection (CDI) among those presenting a discordant Clostridioides difficile diagnostic assay and to identify patient characteristics associated with the decision to treat CDI.

Design: Cross-sectional study.

Setting: Monocentric study in a tertiary care hospital, Geneva, Switzerland

Participants: Among 4562 adult patients tested for C. difficile between March 2017 and March 2019, 208 patients with discordant tests’ results (positive nucleic acid amplification test [NAAT+]/negative enzyme immunoassay [EIA-]) were included.

Main outcome measures: Treatment for CDI.

Results: CDI treatment was administered in 147 (71%) cases. In multivariate analysis, an abdominal computed tomography scan with signs of colitis (OR 14.7; 95% CI 1.96-110.8) was the only factor associated with CDI treatment.

Conclusions: The proportion of NAAT+/EIA- patients who received treatment questions the contribution of the EIA for the detection of toxin A/B after NAAT to limit overtreatment. Additional studies are needed to investigate if other factors are associated with the decision to treat.

We conducted a cross-sectional study at Geneva University Hospitals, a 2000-bed Swiss tertiary care centre. Clinical and biological data (results of NAAT/EIA assays performed on stool samples) were collected from electronic medical records (EMR) and the hospital bacteriology laboratory, respectively. Inclusion criteria were all adult patients (≥18 years) hospitalised or not, with C. difficile toxin assays performed on stool samples between 1 March 2017 and 1 March 2019 that yielded discordant results (NAAT+/EIA-). Exclusion criteria were asymptomatic patients (without diarrhoea, ileus or toxic megacolon), paediatric patients, patients with a treatment against C. difficile introduced ≥ 48 h before the results of tests, or without clinical data available in EMR form. In patients presenting several tests with discordant results over the study period, only the first test was considered for analysis. The study was approved by the Geneva cantonal ethics commission and a waiver of informed consent was granted due to its retrospective nature

The decision was made to include all eligible patients and no formal sample size calculation was performed. Instead, we restricted the number of investigated parameters before any confirmatory analysis. Based on the “10 events per variable” rule of thumb, we limited the number of parameters investigated to eight factors selected among known risk factors and clinical characteristics compatible with CDI. Patient characteristics and CDI risk factors were described overall and by treatment for CDI and reported as frequencies and percentages. A multivariate logistic regression model using a backward stepwise method was performed to determine which parameters were independently associated with CDI treatment. At each step, starting from all eight parameters, the variable with the highest p-value on the likelihood ratio test was removed from the model until all remaining factors were statistically significantly associated with CDI treatment at a two-sided level of 5%. Sensitivity analyses were performed to assess the robustness of the results when deceased patients were a) excluded from the analysis and b) considered as not treated. Missing data were systematically removed from analyses. Statistical significance was assessed at a two-sided 0.05 level for all analyses. All statistical analyses were performed using Stata software, version 15 (StataCorp, College Station, TX).