Antimicrobial use (AMU) in animal agriculture contributes to antimicrobial resistance (AMR) in humans, which imposes significant health and economic costs on society. Economists call these costs negative externalities, societal costs that are not properly reflected in market prices. We review the relevant literature and develop a model to quantify the external costs of AMU in animal agriculture on AMR in humans. Parameters required for this estimate include (a) the health and economic burden of AMR in humans,(b) the impact of AMU in animal agriculture on AMR in animals, (c) the fraction of AMR in humans attributable to animal agriculture, and (d) AMU in animals. We use a well-documented historic case to estimate an externality cost of about US$1,500 per kilogram of fluoroquinolones administered in US broiler chicken production. Enhanced data collection, particularly on the third and fourth parameters, is urgently needed to quantify more fully the externalities of AMU in animal agriculture.
Keywords: AMR; animal agriculture; antimicrobial resistance; externality; human health; societal cost.