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Agricultural Antibiotics and Human Health

  • David L Smith mail,

    To whom correspondence should be addressed. E-mail: smitdave@helix.nih.gov

    X
  • Jonathan Dushoff,
  • J. Glenn Morris Jr
  • Published: July 05, 2005
  • DOI: 10.1371/journal.pmed.0020232

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Precaution and Consequences

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

Author: Louis Anthony Cox, Jr.
Position: Clinical Professor
Institution: University of Colorado and Cox Associates
E-mail: tcoxdenver@aol.com
Submitted Date: July 06, 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.

Drs. Smith et al. offer the intriguing suggestion that, for resistance in human pathogenic bacteria caused by agricultural antibiotic use, "the intrinsic problem of knowability, posed by the biological complexity of the problem, makes the use of precautionary decision making particularly suitable in this arena. The assumption that plausible dangers are negligible, even when it is known that such dangers are constitutively very difficult to measure, may be more unscientific than the use of precaution." But is precautionary decision-making really suitable when complexity obscures causal relations? A potentially severe limitation of "precautionary" decision-making in complex settings where cause and effect are not well understood is that the resulting decisions may turn out not to be precautionary after all. Well-intended actions taken without first adequately assessing and understanding the effects that they will probably cause can not only fail to produce desired and intended consequences, but may (and often do) produce undesired and unintended ones instead. (This is an aspect of what is sometimes referred to as Merton's "Law of Unintended Consequences.")

For animal antibiotic use, well-intended efforts to minimize risk to humans by restricting antibiotic use in animals may backfire if they increase the prevalence of relatively rare, high microbial loads of susceptible bacteria and resulting human illnesses, leading to a greater need to treat humans with antibiotics, thus accelerating resistance in human pathogens. For example, in Europe, banning several animal antibiotics used as growth promoters was followed by reductions in some resistant bacteria in healthy animals and in healthy members of the community, as hoped. But it s far from clear that the one group that public health risk managers should care most about -- human patients -- received any health benefit. In fact, some important human foodborne illness rates and resistance rates of isolates from humans appeared to increase sharply following the ban, at rates that would not necessarily have been expected prior to the ban (Hayes and Jensen, 2003, Figure 2.)

In summary, what constitutes genuinely "precautionary" (health-protective, risk-reducing) decisions may simply remain unknown in the absence of a useful risk assessment of probable health consequences caused by interventions. As Smith et al. have said "The assumption that plausible dangers are negligible, even when it is known that such dangers are constitutively very difficult to measure, may be more unscientific than the use of precaution." This warning should apply to actions that are intended to be precautionary but that implicitly assume that the dangers that they themselves create are negligible. Restricting animal antibiotic uses without first carefully assessing the likely responses of susceptible as well as resistant bacterial populations may be a prime example of decision-making that is not likely to be effective in producing its intended human health consequences.

Cox LA Jr., Potential human health benefits of antibiotics used in food animals: a case study of virginiamycin. Environ Int. 2005 May;31(4):549-63.

REFERENCES

Hayes DJ, Jensen HH, Lessons from the Danish ban on feed-grade antibiotics. http://www.choicesmagazin....)

Competing interests declared: Cox is author of Quantitative Health Risk Analysis Methods:
Modeling the Human Health Impacts of Antibiotics Used in Food Animals (Springer 2005). Since 2000, he has been retained by the US Food and Drug Administration (FDA) and by the Animal Health Institute (AHI) and some of its members for research on human health risk assessments for animal antibiotics.