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Policy should be based on evidence not speculation

Posted by plosmedicine on 30 Mar 2009 at 23:44 GMT

Author: Richard Carnevale
Position: Vice-President, Regulatory, Scientific,and International Affairs
Institution: Washington, DC
Submitted Date: July 07, 2005
Published Date: July 8, 2005
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

I was quite surprised to see the authors assertion that contaminated food could have a greater impact on human resistance than hospital use having never heard any medical experts make such an allegation. Rather, the view seems to be that widespread use and misuse of antibiotics in human medicine is the principle cause of resistance in human bacterial infections. Published risk assessments also arrive at the conclusion that the extent of animal contribution is likely minimal at best.1,2,3

The papers basic premise is that there is a high rate of exposure to resistant bacteria in contaminated food. However, USDA reports relatively low rates of contamination of meat and poultry with food-borne bacteria that are readily destroyed by cooking.4 Resistant bacteria are only a small fraction of the bacteria that may remain on raw meats.5

The authors use a model which assumes that all antimicrobials and resistant bacteria from animals are equally likely of causing clinically important resistance in humans. But, the vast majority (85%) of all antimicrobials used in humans is for treatment of respiratory tract pathogens such as Staphyloccoccus, Pseudomonas, Hemophilus, Streptococcus, and Klebsiella.6 There is no known connection between these pathogens and those which could be passed from animals via the food supply.

As even the authors point out, significant genetic differences exist between isolates from hospital infections and those found in food animals. VRE bacteria that circulate in hospitals appear to be from a single clonal lineage possessing specific genes(complex 17) giving them a selective advantage in hospital environments.7 This complex is rare, if found at all, in isolates from animal sources or those from human community stool samples.

Banning growth promoters in Europe has had no demonstrable impact on resistant foodborne bacterial infections in humans, nor would it have been expected because, with the possible exception of macrolides, growth promoters are not effective or even used for enteric disease in humans.8,9 In fact, the only documented effect in human isolates has been a decrease in VRE from fecal carriers. 9 However, there has been an increase in human infections with VRE due to the increased use of vancomycin to treat MRSA in European hospitals.9,10


1. Cox, L.A. & Popken, D.A. 2004. Quantifying human health risks from virginiamycin used in chickens. Risk Analysis 24(1):271-288.
2. Hurd, 2004. Public health consequences of macrolide use in food animals: a deterministic risk assessment. J. Food Prot. 67(5):980-992.
3. Phillips, I. 1999. The use of bacitracin as a growth promoter in animals produces no risk to human health. J. Antimicrob. Chemother. 44:725-728.
4. Progress Report on Salmonella Testing of Raw Meat And Poultry Products, 1998-2003, Food Safety and Inspection Service, USDA.
5. USDA Agricultural Research Bacterial Epidemiology and Antimicrobial Resistance; NARMS reports.
6. Jones, Ronald N. - Presentation ?? Annual Conference on Antimicrobial Resistance - National Foundation for Infectious Diseases, Bethesda, Maryland June 27-29, 2005).\
7. Rob J.L. Willems, 2005. Global Spread of Vancomycin-resistant Enterococcus faecium from Distinct Nosocomial Genetic Complex, Emerging Infectious Diseases. Vol.11, No. 6: 821-828.
8. World Health Organization: Impacts of antimicrobial growth promoter termination in Denmark, Foulum, Denmark, 6-9, November 2002
9. Casewell, 2003. The European ban on growth-promoting antibiotics and emerging consequences for human and animal health, J. Antimicrob. Chemother. 52:159-161.
10. Goosens H, 2003. European survey of vancomycin-resistant enterococci in at-risk hospital wards and in vitro susceptibility testing of ramoplanin against these isolates, Journal of Antimicrobial Chemotherapy 51 (suppl S3):ii5-iii12.

Competing interests declared: I am an employee of the Animal Health Institute, a trade association representing the animal pharmaceutical and vaccine industry.