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Volume 11, Number 11—November 2005

Fluoroquinolone Use in Food Animals

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To the Editor: Two recent articles (1,2) show that fluoroquinolone use in food animals is associated with infections by antimicrobial drug–resistant strains of Campylobacter in humans. These infections cause problems in treating illnesses as well as increased rates of illness and death (3). Despite a large body of scientific evidence and a judicial review (13) that show harmful results in many persons, some members of the poultry and pharmaceutical industries argue that fluoroquinolone use in food animals has no adverse effects in humans (4) and continue to supply these drugs for use in poultry (2,5). The use of these drugs has caused rapidly increasing resistance rates in most countries. In the United States, 19% of Campylobacter isolates from humans are now ciprofloxacin resistant (2), and resistance rates >80% are seen in Spain (5). By contrast, in Australia, where fluoroquinolones were never approved for use in food animals, domestically acquired infections with fluoroquinolone-resistant Campylobacter spp. are rarely found in humans (6). Drug-resistant Escherichia coli is also of concern. In Spain, humans frequently acquire fluoroquinolone-resistant E. coli associated with fluoroquinolone use in poultry (7).

In the United States, better controls in meat and poultry slaughter and processing, as well as improved food-safety education campaigns, have resulted in 28% fewer Campylobacter infections annually since 1996 (8). However, ≈1.8 million persons (600 per 100,000) are likely to contract symptomatic Campylobacter infections per year (3,8), and fluoroquinolone resistance is now 19% (2). Thus, the risk of a person's contracting fluoroquinolone-resistant Campylobacter infection is 114 per 100,000 per year. If 80% of Campylobacter infections are foodborne (3), and 90% of these infections are acquired from poultry (9), then ≈82 of 100,000 persons per will contract ciprofloxacin-resistant Campylobacter infections from poultry each year. Most persons with Campylobacter infections would not benefit from antimicrobial drug therapy. However, if only 10% of infected persons would benefit from antimicrobial drug therapy, fluoroquinolone use in poultry could cause ≈82 persons per million to have a compromised response to therapy. In the United States (population 300 million), this number translates to >24,000 persons annually.

Data on the number of animals that receive fluoroquinolones are difficult to find. Bayer (manufacturer of the only fluoroquinolone used in poultry in the United States) states that Baytril (enrofloxacin) is used in <1% of US broiler flocks (4). This statistic allows us to estimate how many persons will potentially have an adverse outcome compared to the number of animals receiving fluoroquinolones. If 24,000 persons in the United States have an adverse outcome annually after <84 million chickens (1% of 8.4 billion) are treated with enrofloxacin, then ≈285 persons are at risk of having an adverse outcome for every 1 million chickens treated.

This risk seems needless. In Australia, consequences from not using these agents in food animals (i.e., neither therapeutic nor prophylactic use is approved) have not been seen. Thus, I do not agree with Iovine and Blaser (1), who would allow fluoroquinolones to be used to treat sick food production animals. Bayer claims that "Baytril is used for therapeutic purposes only..." (4). Thus, continuation of fluoroquinolone use for these therapeutic purposes will allow the consequent development of resistant bacteria in humans, which will include resistant strains of Campylobacter, E. coli, and Salmonella. Discontinuing fluoroquinolone use by mass dosing (the current practice for poultry [10]) would decrease the amount of the drug used. However, why use fluoroquinolones at all? Narrower spectrum antimicrobial drugs (e.g., sulfonamides, amoxicillin) could be used to adequately treat sick animals. Surely E. coli drug resistance in food animals in the United States cannot be at a level that makes fluoroquinolones indispensable. If resistance levels to narrower spectrum antimicrobial drugs are at high levels, does this finding not imply that major changes concerning antimicrobial drug use in food animals are needed?

Better methods are needed to accurately estimate how many persons are negatively affected annually because of the misuse of antimicrobial drugs in food animals. Compromised therapeutic outcomes occur in many persons throughout the world because of fluoroquinolone-resistant Campylobacter infections (10). Fluoroquinolone use is not essential for food animal production or the welfare of animals. Many ways to keep animals healthy and productive exist other than treating or trying to prevent infections with the mass use of antimicrobial drugs such as fluoroquinolones.


Peter Collignon*

Author affiliation: *Canberra Hospital, Garran, Australian Capital Territory, Australia



  1. Iovine  NM, Blaser  MJ. Antibiotics in animal feed and spread of resistant Campylobacter from poultry to humans. Emerg Infect Dis. 2004;10:11589.PubMed
  2. Gupta  A, Nelson  JM, Barrett  TJ, Tauxe  RV, Rossiter  SP, Friedman  CR, Antimicrobial resistance among Campylobacter strains, United States, 1997–2001. Emerg Infect Dis. 2004;10:11029.PubMed
  3. Mead  PS, Slutsker  L, Dietz  V, McCaig  LF, Bresee  JS, Shapiro  C, Food-related illness and death in the United States. Emerg Infect Dis. 1999;5:60725. DOIPubMed
  4. Bayer Animal Health Care. Baytril for poultry poses no public health threat. [cited 2004 Jun 28]. Available from Accessed June 28, 2004.
  5. Prats  G, Mirelis  B, Llovet  T, Munoz  C, Miro  E, Navarro  F. Antibiotic resistance trends in enteropathogenic bacteria isolated in 1985–1987 and 1995–1998 in Barcelona. Antimicrob Agents Chemother. 2000;44:11405. DOIPubMed
  6. Unicomb  L, Ferguson  JTV, Riley  TV, Collignon  P. Fluoroquinolone resistance in Campylobacter absent from isolates, Australia. Emerg Infect Dis. 2003;9:14823.PubMed
  7. Garau  J, Xercavins  M, Rodriguez-Carballeira  M, Gomez-Vera  JR, Coll  I, Vidal  D, Emergence and dissemination of quinolone-resistant Escherichia coli in the community. Antimicrob Agents Chemother. 1999;43:273641.PubMed
  8. Centers for Disease Control and Prevention. Preliminary FoodNet data on the incidence of infection with pathogens transmitted commonly through food—selected sites, United States, 2003. MMWR Morb Mortal Wkly Rep. 2004;53:33843.PubMed
  9. Hurd  H, Doores  S, Hayes  D, Mathew  A, Maurer  J, Silley  P, Public health consequences of macrolide use in food animals: a deterministic risk assessment. J Food Prot. 2004;67:98092.PubMed
  10. Nelson  JM, Smith  KE, Vugia  DJ, Rabatsky-Ehr  T, Segler  SD, Kassenborg  HD, Prolonged diarrhea due to ciprofloxacin-resistant campylobacter infection. J Infect Dis. 2004;190:11507. DOIPubMed


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DOI: 10.3201/eid1111.040630

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Table of Contents – Volume 11, Number 11—November 2005

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