Does antibiotic use in farmed animals pose a risk to human health? — No

There is ample independent evidence supporting the long history of appropriate use of antibiotics in Australian livestock. For example, the past six annual reports of the National Residue Survey contain the results of tests for the presence of up to 38 antibacterial agents in the edible tissues of cattle, pigs, poultry and sheep.1 Almost 400 000 assays were performed and compliance with Australian standards was at or above 99.99% for each of the four species tested.

Given the high morbidity and mortality associated with many of the diseases of livestock (eg, necrotic enteritis and coccidiosis in poultry, bovine respiratory disease and mastitis in cattle, and post-weaning diarrhoea and porcine respiratory disease in pigs), prevention of infectious diseases is of fundamental importance. Judicious use of antibiotics in integrated animal health plans has an important role to play in protecting the health and welfare of animals and in contributing to the safety and quality of the food that is produced. Only 39 antibacterial agents are approved and available for use in Australian livestock, six of which are from classes with no human medical use counterpart. As an example of contemporary patterns of use, a recent survey of the use of antimicrobial agents in the Australian pig industry found most use was for control of infections with Lawsonia intracellularis, Mycoplasma hyopneumoniae and Escherichia coli and relied on sulfonamides, tetracyclines and penicillins2 — all drugs considered by the Expert Advisory Group on Antimicrobial Resistance to be of low importance to public health.3

What led the Australian Department of Health and Ageing to conclude that “Australia’s food supply is one of the safest and cleanest in the world”4? In 2008, Food Science Australia was commissioned to survey the presence of bacteria with antimicrobial resistance in samples of raw whole poultry, beef mince and pork chops collected from shops in Melbourne, Sydney, Brisbane and Perth. Among the isolates of Campylobacter jejuni, Salmonella and E. coli that were collected, no fluoroquinolone or ceftiofur resistance was identified. No Enterococcus faecium was isolated and all Enterococcus faecalis isolates were susceptible to ampicillin, penicillin and vancomycin; only one of 300 E. faecalis isolates was resistant to gentamicin. In contrast, Denmark, despite being recognised as having one of the most regulated and conservative approaches to the use of antibiotics in livestock, noted significant antibiotic resistance in their most recent antimicrobial resistance monitoring report: fluoroquinolone-resistant C. jejuni in 17% of broiler meat samples; high-level gentamicin resistance in E. faecalis from pork samples; vancomycin-resistant E. faecium in 47% of isolates from broiler chickens; extended-spectrum β-lactamase producing E. coli (ceftriaxone resistant) in 27% of broiler cloacal swabs and 9% of broiler meat samples; fluoroquinolone-resistant Salmonella enterica subspecies enterica serovar Enteritidis in 8% of sporadic cases of human salmonellosis; multiresistant Salmonella enterica subspecies enterica serovar Typhimurium definitive type 104 (DT104) in 7% of isolates from pigs; and ceftiofur-resistant E. coli in 1% of domestic pork and broiler meat samples.5

OzFoodNet (http://www.ozfoodnet.gov.au) was established by the Australian Government in 2000 to enhance surveillance of foodborne disease. It has published eight annual reports, which do not identify any cases of domestically acquired foodborne illness caused by infections with Salmonella, Campylobacter or Shiga toxin-producing E. coli complicated by antibiotic resistance of livestock origin. By contrast, a number of human cases of fluoroquinolone-resistant Campylobacter infection and S. Typhimurium DT104 infection have been described, but each originated from overseas (especially South-East Asia) or from imported food.

Since 2001, the Australian Salmonella Reference Centre has tested more than 18 000 Salmonella isolates from cattle, pigs, sheep, chickens (broilers and layers), raw meat and eggs. No fluoroquinolone-resistant isolates were found and only nine isolates (most of which were submitted before 2004) were phenotypically resistant to cefotaxime at 1 g/mL.

Australians should be reassured that food safety is the highest priority in livestock production. The Australian Veterinary Association is currently updating a series of guidelines for responsible use of antibiotics, the poultry industry is supporting leading edge research to develop a vaccine to prevent necrotic enteritis, and the pig industry has spent over $7 million on projects to refine and replace the use antibiotics and has committed to halving antibiotic use by 2018.

Antibiotics used prudently and selectively can clearly benefit animal health and welfare, leading to overall human health benefits, not risks.