Antimicrobial resistance surveillance systems: Are potential biases taken into account?

BACKGROUND: The validity of surveillance systems has rarely been a topic of investigation. OBJECTIVE: To assess potential biases that may influence the validity of contemporary antimicrobial-resistant (AMR) pathogen surveillance systems. METHODS: In 2008, reports of laboratory-based AMR surveillance systems were identified by searching Medline. Surveillance systems were appraised for six different types of bias. Scores were assigned as '2' (good), '1' (fair) and '0' (poor) for each bias. RESULTS: A total of 22 surveillance systems were included. All studies used appropriate denominator data and case definitions (score of 2). Most (n = 18) studies adequately protected against case ascertainment bias (score = 2), with three studies and one study scoring 1 and 0, respectively. Only four studies were deemed to be free of significant sampling bias (score = 2), with 17 studies classified as fair, and one as poor. Eight studies had explicitly removed duplicates (score = 2). Seven studies removed duplicates, but lacked adequate definitions (score = 1). Seven studies did not report duplicate removal (score = 0). Eighteen of the studies were considered to have good laboratory methodology, three had some concerns (score = 1), and one was considered to be poor (score = 0). CONCLUSION: Contemporary AMR surveillance systems commonly have methodological limitations with respect to sampling and multiple counting and, to a lesser degree, case ascertainment and laboratory practices. The potential for bias should be considered in the interpretation of surveillance data.