Last spring, the World Health Organization stated that there are “major gaps” in surveillance and data sharing related to the emergence of antibiotic-resistant foodborne pathogens and their impact on both animals and humans. One gap to fill is the amount of antibiotics consumed by food-producing animals worldwide each year. Estimates so far have been simply based on expert opinions, but now an international team has combined maps of livestock densities, economic projections of demands for meat, and current estimates of antimicrobial consumption in certain countries to objectively model antimicrobial use in food animals for 2010 and 2030. “Without reliable evidence to estimate global antimicrobial consumption in livestock, the links between antimicrobial consumption and resistance patterns are poorly quantified, and efforts and policies to optimize antibiotic use in animals are poorly targeted,” wrote the authors of the new study published in the Proceedings of the National Academy of Sciences. “Mapping the antimicrobial consumption in livestock provides a baseline estimate of its global importance.” The scientists — including two Princeton University researchers who also recently published an analysis of the economics of antibiotic use in U.S. swine and poultry production — estimated that livestock consumed about 63,151 tons of antimicrobials in 2010. They expect the number to increase by 67 percent by 2030. The scientists believe that this will stem from an increasing consumer demand for meat products and will lead to the need for farms to shift toward large-scale production systems where antibiotics are routinely used in subtherapeutic doses for disease prevention and growth promotion rather than disease treatment. “There are always assumptions in models, but it’s probably a conservative estimate,” said Gail Hansen, senior officer of the antibiotic resistance project at The Pew Charitable Trusts. For both the 2010 and 2030 estimates, China and the United States are at the top of the list for their shares of worldwide animal antibiotic consumption. But the countries with the greatest projected percentage increases are Myanmar, Indonesia, Nigeria, Peru and Vietnam. The authors also wrote that if trends continue, India will be one country contributing to a large portion of the growth because it is already facing antibiotic overuse in human medicine and a high prevalence of antibiotic resistance. “Widespread resistance may be more consequential for India than for other countries because India’s bacterial disease burden is among the highest in the world, and therefore antimicrobials play a critical role in limiting morbidity and mortality,” the study noted. Looking at the distribution of their data, the researchers identified consumption hotspots as the southeast coast of China, Guangdong and Sichuan provinces, the Red River delta in Vietnam, the northern suburbs of Bangkok, the south coast of India, the south of Brazil, the suburbs of Mexico City, the midwestern and southern U.S., the Nile delta, and the city of Johannesburg, South Africa, and its surrounding townships. Going forward, the model can be used to track the progress of antimicrobial stewardship efforts and can be updated with new data to provide updated projections. Data on animal antibiotic use are currently limited due to a lack of publicly funded surveillance systems and the reluctance of food animal producers, animal feed producers, and veterinary pharmaceutical companies to provide reports of consumption or sales. For this study, the scientists could only get consumption data for 32 countries — all of which were high-income. They then had to extrapolate from this to develop estimates for low- and middle-income countries. Another limit of the research is that the figures don’t account for choices of drugs, potential differences in drug potencies, resistance selection pressures, or use for treatment in human medicine. In addition, aquaculture was not included in this study even though some aspects of it have been associated with very high rates of antimicrobial consumption. The study calls for the implementation of a publicly funded international surveillance network of antimicrobial consumption in food animals in countries undergoing rapid intensification in the livestock sector, collaboration with veterinary drug manufacturers and animal feed producers to cross-validate estimates of consumption with sales data, implementation of an international agenda to harmonize regulatory frameworks among countries, and the ultimate phasing out of antimicrobial use for growth promotion. Hansen said that this study is a reminder that the issue of antibiotic resistance is a global one. “This really brings it home that we can’t just pretend the rest of the world doesn’t exist,” she said. “The bacteria don’t respect boundaries at all.” The decision many American businesses have been making to stop feeding antibiotics to their food-producing animals can be useful in tackling resistance, she said, but regulations may still be required in certain places because antibiotic-free announcements such as McDonald’s only apply to U.S. products. “We’re not the only country in the world,” Hansen said.