Clinical predictors of enzyme immunoassay accuracy in Clostridioides difficile infection: the impact of immune status and infection predisposing factors

Clostridioides difficile infection (CDI) is a major cause of healthcare-associated diarrhea, with increasing prevalence in China and the Asia-Pacific region. Despite its limited sensitivity, the enzyme immunoassay (EIA) is widely used for CDI diagnosis in clinical practice due to its cost-effectiveness and rapid results. However, false-negative results can lead to underdiagnosis and poor patient outcomes. Limited research has examined the clinical characteristics of EIA false negative (FN) cases in the Chinese healthcare setting. In this retrospective cohort study, we analyzed 673 stool samples from suspected patients with CDI. Patients were classified as false-negative (FN; GDH-positive/EIA-negative, cytotoxicity culture-positive) or true positive (P; GDH-positive/EIA-positive, cytotoxicity culture-positive). Multivariable logistic regression was used to identify independent predictors of FN results and their association with clinical outcomes. In the multivariable analysis, immunocompromised status was the strongest factor associated with a lower likelihood of a false-negative result (adjusted odds ratio aOR for FN: 0.12, 95% CI: 0.06–0.24). Patients in the FN group presented with a significantly milder degree of clinical severity at diagnosis, as measured by the Zar CDI severity score. Critically, after adjusting for baseline disease severity, an FN result was independently associated with a 2.83-fold increased risk of developing shock (aOR = 2.83, 95% CI: 1.23–6.52). Host immune status is a key factor associated with EIA accuracy, while the influence of other traditional risk factors like PPI use appears to be confounded. False-negative EIA results are not benign; they are independently associated with a substantially higher risk of shock, suggesting that reliance on EIA alone in high-risk patients may carry significant prognostic implications. These findings highlight the limitations of EIA in immunocompetent patients with milder symptoms and underscore the critical need for adjunctive testing to improve patient outcomes.