Antibiotic-resistant bacteria have been in the news a lot lately.
Sunday's San Francisco Chronicle had a front page story about the growing problem of antibiotic-resistant bacteria. One of the causes is the routine addition of antibiotics to animal feed as "growth promoters" — including some antibiotics used for treatment of humans.
In a New York Times Sunday Magazine article last month, Michael Pollan wrote about MRSA (an antibiotic-resistant strain of the Staphylococcus bacteria that killed almost 20,000 people in 2005) and its potential connection to CAFOs.
Meanwhile, Newsday recently covered a study showing how workers in the poultry industry can be infected by drug-resistant E. coli while on the job and then spread the pathogens into the community. The study authors claim that it is the first of its type ever performed in the U.S., and because it shows yet another way that overuse of antibiotics in animal agriculture poses risks to the general public's health, I thought it would be worthwhile to present the study's findings in a separate post.
Oh my gOSHA
The animal industry can be a risky place for its workers, exposing them to a multitude of air pollutants (biological agents like bacteria and chemicals like ammonia), various liquids, and other dangers. Animal agriculture can also be hazardous to local communities through transmission of pathogens into the groundwater, waste lagoon failures that damage rivers, and air pollution.
I'll start by going back to two papers published in Environmental Health Perspectives (a peer-reviewed journal published by the U.S. National Institute of Environmental Health Sciences, with all content available online for free). One is about the role of CAFOs in epidemics and antibiotic resistance, the other about animal feeding practices in the United States. My comments below are drawn from these papers unless otherwise indicated.
In the United States, antibiotics are frequently given to animals as part of their regular diet, euphemistically called "growth promoters" or "growth enhancers." Some of these antibiotics are tetracyclines, macrolides, streptogramins, and fluoroquinolones; others are such nasty things as arsenic (!), which is fed to chickens to reduce parasites (and creates a disposal problem for the chicken manure).
No one is exactly sure what quantity of antibiotics are given to food animals — the FDA and USDA refuse to require mandatory reporting and sales figures are considered confidential business information by the drug companies. An analysis from the Union of Concerned Scientists estimates that 60%-80% of antibiotics produced in the U.S. are used as growth promoters on healthy livestock (i.e., not for treating sick animals). Other estimates put the number closer to 50%. Whatever the number, there is evidence that the U.S. uses a lot more than other countries. Citing a report from the World Health Organization, the authors of the CAFO paper write that Sweden and Denmark — two nations that forbid routine use of antibiotics as growth promoters — use less than 3 grams of antimicrobial agent per pig, while producers in the U.S. use 47 grams per pig.
Fortunately, public awareness of the issue and activism by public interest groups and health care providers have started to turn the tide on routine antibiotic use in animal production. The pressure has even reached some big producers and resellers: McDonald's and Tyson Foods have pledged to reduce their use of antibiotics.
Bringing your work home
The study by researchers at Johns Hopkins looked at workers in the "broiler" industry (meat chickens as opposed to laying hens), which employs over 200,000 people in the U.S. Job types in this industry include "growers" (those who operate the chicken houses), "catchers" (those who catch chickens and put them in cages for their trip to the slaugherhouse) and "live hangers" (those who attach live chickens to the disassembly line). Workers with each of these jobs can come in contact with thousands of live chickens each day.
The researchers collected stool samples and health questionnaires from 16 poultry workers and 33 rural residents of the Delmarva region of Maryland and Virginia (an area that produces 600 million broiler chickens annually). The samples were cultured to grow Enterobacteriaceae on agar supports that were supplemented by one of six different antimicrobial agents used in treatment of humans (ampicillin, ciprofloxacin, ceftriaxone, gentamicin, nitrofurantoin, and tetracycline). Two of these (gentamicin and tetracycline) are approved for use in broiler operations (see Appendix 1 of the article for a full list of approved antibiotics).
After analyzing the results, the researchers found that the poultry workers were 32 times more likely to be carrying gentamicin-resistant E. coli than the rural residents, and almost five times more likely to carry multidrug-resistant E. coli. The other drugs were roughly as effective on bacteria in both sample groups. The authors propose that gentamicin-resistant bacteria are so prevalent in poultry workers because the drug is the most commonly used antimicrobial in broiler production (it is given to day-old chicks as a preventative measure). Thus, it is possible that poultry workers will come in contact with gentamicin-resistant bacteria while working around poultry and somehow absorb it into their bodies.
A big question is, Will the drug-resistant E. coli make you sick? The researchers do not provide an answer. They write that the multiple-drug-resistant strains of E. coli can be the cause of urinary tract infections and sepsis, and that these resistant bacteria act as a source of genetic material that can be transferred to pathogenic bacteria. In other words, the relatively benign E. coli can be accomplices for dangerous E. coli.
One surprising detail in the study is that the vast majority (88%) of poultry workers in the survey wash their contaminated work clothes at home, thus creating a way to expose their household to the dangers of the poultry house. We can only hope that this study stimulates the poultry industry to install some laundry facilities or set up a central laundry service for the workers of the regions.
For those interested in scholarly research of this sort, the entire archive of Envirionmental Health Perspectives (EHP) is available for download. There have been quite a few food-related articles, like the articles mentioned above, as well as a mini-monograph on various CAFO-related topics, and how the use of arsenic in chicken feed creates a waste management problem. In addition, the Union of Concerned Scientists has lengthy report and a resource page of links to websites run by non-profits, the government, and the animal industry on the subject of antibiotic resistance.
Photo of E. coli bacteria for the USDA's Agricultural Research Service by Photographer Eric Erbe, with digital colorization by Christopher Pooley. Photo of chickens for the USDA's Agricultural Research Service by Photographer Stephen Ausmus