Performance of four different diagnostic tests for C. difficile infection in piglets

Abstract

Clostridium difficile is emerging as pathogen in man as well as in animals. In 2000 it was described as a cause of neonatal enteritis in piglets and it is now the most common cause of neonatal diarrhoea in the USA. In Europe, C. difficile infection (CDI) in neonatal piglets has also been reported. Diagnosis of this infection is based on detection of the bacterium or its toxins A and B. Most detection methods, however, are only validated for diagnosing human infections. In this study three commercially available Enzyme Immuno Assays and a commercial RT-PCR were evaluated by testing 172 pig faecal specimens. The results of each test were compared with cytotoxicity assays (CTA) and toxigenic culture as gold standards. Compared with CTA, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were for RT-PCR respectively 91.6%, 37.1%, 57.6%, and 82.5%, and for Premier Toxin A+B (Meridian): 83.1%, 31.5%, 53.1% and 66.7%, and for Immunocard tox A/B (Meridian) 86.6%, 56.8%, 66.9%, and 80.7%, and for VIDAS (BioMerieux): 54.8%, 92.6%, 85.0%, and 72.8%. Compared with toxigenic culture sensitivity, specificity, PPV and NPV were; for RT-PCR 93.0%, 34.7%, 50.0%, and 87.5%, and for Premier Toxin A+B: 80.3%, 27.7%, 43.8%, and 66.7%, and for Immunocard tox A/B: 80.0%, 46.2%, 52.8% and 75.4%, and for VIDAS: 56.4%, 89.8%, 77.5%, and 76.7%. We conclude that all tests had an unacceptable low performance as a single test for detection of C. difficile in pig herds and that a two step algorithm is necessary. Of all assays, the RT-PCR had the highest NPV compared to both reference methods and is therefore the most appropriate test to screen for absence of C. difficile in pigs as a first step in the algorithm. The second step would be a confirmation of the positive results by toxigenic culture.