Risk of secondary cases of Clostridium difficile infection among household contacts of index cases

Objectives: We aimed to estimate the risk of secondary cases of Clostridium difficile infection (CDI) among household contacts of index cases. Methods: We reviewed all 2222 patients with confirmed CDI in a region of Quebec, Canada, during 1998-2009. Our laboratory serves a well-defined population for which it is the sole centre providing CDI testing, enabling us to calculate accurate population annual incidence rates of CDI. Cases with the same phone number were verified individually to determine whether they were indeed related. We considered as related two cases occurring in the same household within one year of each other. Results: We estimated that 1061 spouses and 501 children (<25 years-old) lived in the same household as the index cases, of which respectively 5 and 3 developed CDI. Among spouses and children, the attack rate was 4.71/1000 and 5.99/1000 respectively, and the relative risk was 7.61 (95% CI: 5.77-9.78) and 90.6 (95% CI: 33.89-487.64) for the three months after the diagnosis in the index case. Conclusions: Although the relative risk of CDI among household contacts is somewhat increased for a few months, the absolute risk is too low to justify interventions, apart from avoiding unnecessary courses of antimicrobials. (C) 2011 The British Infection Association. Published by Elsevier Ltd. All rights reserved.