The methodological soundness of literature reviews addressing three potential zoonotic public health issues

Literature reviews are important information sources for multiple stakeholders in zoonotic public health with limited time to keep up with the rapid increase in primary research in this field. However, their validity depends on their methodological soundness. The study purpose was to evaluate the methodological soundness of literature reviews in zoonotic public health. Relevant reviews (n = 132) published between January 2000 and August 2006 were identified on three issues: Mycobacterium avium ssp paratuberculosis as a potential cause of Crohn's disease in humans (30 reviews); antimicrobial use in animals as a risk factor for antimicrobial resistance in human pathogens (36); and the zoonotic potential of transmissible spongiform encephalopathies (66). The zoonotic aspect of the issue was the focus of 59 reviews and a subsection of 73 reviews. Two independent reviewers evaluated reviews using 13 criteria: 10 previously validated in the medical field, and three applicable to aetiology research. No review met more than eight of 13 criteria for methodological soundness; two articles met only one criterion. Two reviews described methods for identifying relevant primary research. In only two and four reviews respectively, authors conducted quantitative syntheses of research evidence or reported summarized measures of effect for the zoonotic risk to humans. Recommendations for future research and economic impact were provided in 64 and 10 reviews respectively. In 14 reviews, conclusions exceeded evidence presented. The various review authors' position on the evidence for the zoonotic association and the zoonotic risk to public health were inconsistent for all three issues. Reviews addressing potential zoonotic public health issues lack structured and transparent methodology preventing the end user from assessing the review's validity. These reviews should adhere to structured scientific principles similar to what is used for primary research articles.