動物飼料中抗生素或可導致人類感染， Antibiotics in Animals Tied to Risk of Human Infection

動物飼料濫用抗生素或導致超級病菌泛濫

健康SABRINA TAVERNISE2014年02月20日

馬里蘭州波科莫克城一家農場的雞。本來為了保護農場動物的抗生素已成為消費者維權的焦點。

Chickens on a Pocomoke City, Md., farm. Antibiotics meant to protect farm animals have been a concern to consumer advocates.

Marty Katz

美國一家健康倡導團體在周一發佈文件稱，科學家們對可用於動物飼料的30種抗生素進行了一項全國性分析，結果表明，這些藥物中有絕大部分都可造成人體內的細菌感染對治療產生耐受性，且這一問題正日趨嚴峻。

該分析由美國食品和藥品監督管理局(Food and Drug Administration, FDA)進行，調查範圍涵蓋了2001年至2010年，詳情記載於非營利組織自然資源保護委員會(Natural Resources Defense Council)根據《信息自由法》(Freedom of Information Act)和後續訴訟獲得的內部記錄中。

《紐約時報》查閱了其中的部分資料。這些文件描述了FDA的科學家們就動物飼料使用的30種青霉素和四環素添加劑進行的有關研究。他們發現，其中18種為高風險藥物，它們有可能通過食物渠道將人體暴露於抗生素耐受性細菌。

耐葯菌導致人們難以甚至不可能通過常規抗生素來治療感染。至於其他的12種藥物，現有數據尚不足以使科學家們作出評判。

據美國疾病控制和預防中心(Centers for Disease Control and Prevention)估計，美國每年至少有200萬人罹患各種疾病，其中約有2.3萬人死於抗生素耐受性感染。食品工業的代表們往往將造成致命性超級病 菌泛濫的主要責任歸咎於醫院和對患者採取的治療。但許多科學家認為，在動物飼料中濫用抗生素才是罪魁禍首。

在動物的飼養周期中，農民和農場主們一直向其投喂少量的藥物，以在擁擠的飼養條件下確保動物健康。但這種方法可導致細菌產生耐藥性，且這種耐藥性可通過環境、食用上述動物的肉製品等方式傳播至人體。

FDA在聲明中表示，該研究審查的藥物均為「獲批已久的青霉素和四 環素產品」，且該機構已致函這些藥物的生產商，要求他們提供更多的安全性數據。並補充道，這些工作是針對食用動物用抗生素（又稱抗菌素）進行的一項更全面 評估的一部分。目前它們已經促成了若干重大的政策改變，期望能解決相關的問題。

FDA曾多次嘗試對此類藥物在動物中的使用嚴加管制。1973年，該機構通過了一項法規，要求有關公司提交研究報告，證明在動物飼料中使用某種藥物不會促進人體內的病菌產生耐藥性。

1977年，FDA撤銷了此前的批准令，不再允許常規使用含有青霉 素和大多數四環素的動物飼料添加劑。不過自然資源保護委員會的律師阿維納什·卡爾(Avinash Kar)說，該法令始終未得到徹底的貫徹，該保護組織於2012年起訴了FDA，試圖迫使它執行1977年的議案。

「FDA自20世紀70年代起就不斷發現這些藥物會對人體健康構成風險，但迄今為止，該機構卻未對此採取過任何有意義的措施，」卡爾先生指出。

然而近年來，FDA已經在有步驟地展開行動。2012年，該機構限制了頭孢菌素在動物中的使用——這些藥物也可處方用於治療人類的肺炎和鏈球菌性喉炎。

去年，FDA更進一步，逐步廢止了奶牛、豬和雞飼養業中的抗生素濫用，但仍允許這些藥物繼續用於治療疾病。有消費者健康倡導人士認為，後一條政策削弱了新法規的效力。

「2013年12月，FDA正式開始實施一項策略，逐步停止使用所有重要的醫用抗菌劑，」該機構表示。「FDA確信，現有策略足以保持重要醫用抗菌劑（包括青霉素類和四環素類）的有效性，它是改變畜牧業中上述產品使用情況的最有效、也是最高效的方式。」

卡爾先生指出，在研究所涉及的30種藥物中，只有一種藥物曾經達到政府的安全性標準。但它也只是符合了1973年的法規，即要求公司提交研究報告，證明在動物飼料中使用該藥物不會導致細菌產生足以影響人體健康的耐藥性。

2003年，FDA發佈了一系列指南，根據其對人體健康的風險將各種藥物分為三類。指南要求，高風險藥物的單次用藥期不得超過21天，且僅可用於單只動物，不得用於整個牛群或羊群。

自然資源保護委員會的微生物學家卡門·科爾多瓦(Carmen Cordova)說，過去，高風險藥物的使用往往較為寬鬆，2003年的一系列指南只適用於在該年後批准的藥物，而FDA分析中的30種藥物無一屬於這個 範疇，不過卡爾認為，FDA的這項分析在當下仍然具有其重要意義。  

本文最初發表於2014年1月28日。
翻譯：任扶搖

Antibiotics in Animals Tied to Risk of Human Infection

By SABRINA TAVERNISEFebruary 20, 2014

A federal analysis of 30 antibiotics used in animal feed found that the majority of them were likely to be contributing to the growing problem of bacterial infections that are resistant to treatment in people, according to documents released Monday by a health advocacy group.

The analysis, conducted by the Food and Drug Administration and covering the years 2001 to 2010, was detailed in internal records that the nonprofit group, the Natural Resources Defense Council, obtained through a Freedom of Information Act request and subsequent litigation.

In the documents, some of which were reviewed by The New York Times, scientists from the F.D.A. studied 30 penicillin and tetracycline additives in animal feed. They found that 18 of them posed a high risk of exposing humans to antibiotic-resistant bacteria through food.

Resistant bacteria make it difficult and sometimes impossible to treat infections with ordinary antibiotics. The scientists did not have enough data to judge the other 12 drugs.

At least two million Americans fall sick every year and about 23,000 die from antibiotic-resistant infections, the Centers for Disease Control and Prevention estimates. Representatives of the food industry largely blame hospitals and treatments given to people for the rise of deadly superbugs. But many scientists believe that indiscriminate use of antibiotics in animal feed is a major contributor.

Farmers and ranchers feed small amounts of the drugs to animals over their lifetimes to keep them healthy in crowded conditions, causing bacteria to develop a resistance passed on to people through the environment and eating meat from the animals.

In a statement, the F.D.A. said the drugs under review had been “older, approved penicillin and tetracycline products,” and that the agency had issued letters to their producers asking for additional safety data. It said those efforts had been part of a broader assessment of antibiotics, also called antimicrobials, given to animals raised for food, and that it has since made major policy changes to address them.

The F.D.A. has tried repeatedly to rein in the use of the drugs in animals. It adopted regulations in 1973 that required companies to submit studies showing that a drug’s use in animal feed did not promote resistance in people.

In 1977, the agency proposed withdrawing approvals for animal feed additives containing penicillin and most tetracyclines, but it never followed through, said Avinash Kar, a lawyer for the Natural Resources Defense Council. The group sued the agency in 2012 to try to force it to carry out the 1977 proposal.

“This is an agency that has repeatedly found, since the 1970s, that these drugs pose a risk to human health, but it has not done anything meaningful with those conclusions,” Mr. Kar said.

But the agency has taken some steps in recent years. In 2012, it restricted the use of cephalosporins in animals. They are drugs that are also prescribed to treat pneumonia and strep throat in people.

Last year, the F.D.A. moved to phase out the indiscriminate use of antibiotics in cows, pigs and chickens, though it continued to allow them for the treatment of illness, a policy decision that consumer health advocates said weakened the new rule.

“In December 2013, the F.D.A. began formal implementation of a strategy to phase out the use of all medically important antimicrobials,” the agency said. “The F.D.A. is confident that its current strategy to protect the effectiveness of medically important antimicrobials, including penicillins and tetracyclines, is the most efficient and effective way to change the use of these products in animal agriculture.”

Mr. Kar said that only one of the 30 drugs studied ever met the government’s safety criteria. And it only satisfied the 1973 regulations that required companies to submit studies showing that a drug’s use in animal feed did not lead to drug resistance in bacteria that can affect human health.

In 2003, the agency issued guidelines that divided drugs into three categories according to how risky they were for human health. Under the guidelines, a high-risk drug should be used for no longer than 21 days at a time, and only for individual animals, not entire herds or flocks.

High-risk drugs are often allowed to be used much more broadly, said Carmen Cordova, a microbiologist for the Natural Resources Defense Council. The 2003 guidelines apply only to drugs that were approved after 2003, and the consumer group said none of the 30 drugs fell into that category. Mr. Kar said the F.D.A. analysis was still relevant.