Toxin Enzyme Immunoassay Identifies Severe Clostridioides difficile Infections

Toxin enzyme immunoassay more accurately identifies severe Clostridioides difficile infections from strains more likely to cause recurrence, but otherwise had similar results for complications and mortality compared with the standard nucleic acid amplification test (NAAT), according to a results of a study published in Clinical Infectious Diseases.

The incidence of C difficile infections increased by 15.7% from 2010 to 2014; this has been attributed to epidemics caused by the ribotypes 027 and 078 strains, both of which have been associated with severe infections. However, there has been conflicting data on the efficacy of toxin assays vs NAATs in identifying infection and colonization with these strains of C difficile.

Therefore, the aim of this large, multisite study was to compare results and outcomes from toxin enzyme immunoassays and NAATs for patients with C difficile infections. Data was obtained from 10 medical sites participating in the United States Centers for Disease Control and Prevention’s Emerging Infections Program. Specimens were tested using an enzyme immunoassay to test for glutamate dehydrogenase and C difficile toxin. Results that were positive for both variables were considered positive for C difficile. If positive results returned for 1 variable, the specimen was tested again, using a NAAT in order to make a final determination for a positive or negative C difficile infection. Positive specimen results were then considered either toxin positive or NAAT positive, based on the method used to determine the infection.

Of the 4878 cases positive for C difficile infection, 61% were women, 42.5% were ≥65 years old, 44.3% were toxin positive, and 55.7% were NAAT positive. Individuals with toxin-positive cases were more frequently white, ≥65 years old, had prior hospitalization, had long-term care facility stay, and had used antibiotics in the previous 12 weeks compared with NAAT–positive cases (P <.0001, for all). Also, toxin-positive cases were more likely to have a history of ≥3 unformed stools for ≥1 day, to have a white blood cell count ≥15,000 cells/μL, and to have endoscopic or histologic evidence of pseudomembranous colitis (P <.0001, P <.0001, and P <.008, respectively).

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C difficile infection treatment occurred in 96.6% of the toxin-positive cases and 95.3% of the NAAT–positive cases (P =.03). Infection reoccurrence was present in 20.6% of the toxin–positive cases compared with 11.4% of NAAT–positive cases (P =.0008). Multivariable analysis indicated reoccurrence was significantly associated with toxin positivity (adjusted odds ratio 1.89; 95% CI, 1.61-2.23). Where data were available (n=679), results showed that 71.4% of toxin-positive cases and 33.0% of NAAT–positive cases had a toxin-positive recurrence (P <.0001). When isolates were available (n=605), results demonstrated 20.6% of toxin-positive cases compared with 4.6% of NAAT–positive cases were associated with ribotype 027 and 078 strains (P <.0001). Further analysis indicated there were no differences in complications, 30-day mortality rates, and time to death between the 2 groups.

Limitations of this study included not being able to control outcomes based on C difficile infection treatment, insufficient information regarding cause of death, and potential variables in testing practices among medical sites.

The researchers concluded “toxin [enzyme immunoassay] appears to capture more severe disease that is more likely to recur, at least as presently diagnosed, there were no differences in adjusted rates of [C difficile infection]-related complications and mortality between toxin-positive and [nucleic acid amplification tests]-positive only [C difficile infection].”

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Guh AY, Hatfield KM, Winston LG, et al. Toxin enzyme immunoassays detect Clostridioides difficile infection with greater severity and higher recurrence rates. Clin Infect Dis. 2019;69(10):1667-1674