「没有生菜检出阳性」之争：CDC与FDA书面解释为何食品样本阴性不能推翻疫情关联
华盛顿10月4日——据食品安全法律媒体LexBlog报道，Taylor Farms在其环孢子虫专题页面中强调，没有任何生菜样本检出环孢子虫阳性，以此回应FDA将其墨西哥工厂与美国史上最大环孢子虫疫情（12,883人感染）关联的结论；公司同时表示支持召回决定。FDA 10月2日的结案文件称，两份环境样本——工厂外排废水水箱与一名供货种植户的排水沟——检出该寄生虫，与流行病学数据及追溯交汇共同支持关联结论。
LexBlog逐一查阅公开文件后指出，CDC、FDA、农业部、各州流行病学家团队与农产品行业协会都曾以书面形式解释过同一方法论：暴发关联由三类证据构成——流行病学（患者共同进食史）、追溯（供应链交汇点）与食品或环境检测；食品检出病原体可以「同样」确认来源，但从来不是唯一标准。反之，仅在食品中检出病原体、而患者访谈不支持进食史，也不能单独确认来源。
换言之，监管机构在证据标准上采取的是多线汇合原则，样本阴性既可能源于批次间分布不均，也可能源于采样时涉事批次早已售完。消费者层面的实际影响不变：被召回批次的冰山生菜不应再食用，可按召回公告办理退款。
信息来源：LexBlog 10月4日分析报道，查阅CDC公开调查步骤与FDA结案文件后写成。
图片来源：The Nation's Salad Bowl — Malcolm Carlaw / CC BY 2.0 (via Openverse)
Taylor Farms Says No Lettuce Tested Positive; CDC and FDA Explain in Writing Why That Has Never Been the Test
WASHINGTON, Oct. 4 — Taylor Farms is stressing on its Cyclospora information hub that no lettuce tested positive for the parasite, even as it says it stands behind the decision to recall, according to LexBlog. The FDA's Oct. 2 closing document said two environmental samples — outgoing wastewater at the Taylor Farms de Mexico plant and a drainage ditch at a supplying grower — tested positive, adding to epidemiological data and traceback convergence linking the recalled iceberg lettuce to the largest Cyclospora outbreak on record in the U.S., with 12,883 illnesses.
Reviewing the public record, LexBlog found that the CDC, FDA, USDA, the nation's state epidemiologists and the produce industry's own trade groups have each explained, in writing, the same methodology: an outbreak link is built from epidemiology, traceback, and food or environmental testing. Finding the strain in a food can 'also' confirm the source — also, not only. Conversely, a positive food sample alone, without interviews showing patients ate the product, cannot by itself confirm a source.
In practice, negative product samples may reflect uneven distribution between lots or the simple fact that the implicated lot had already sold through before sampling. For consumers, the practical guidance is unchanged: recalled iceberg lettuce should not be eaten and can be returned under the recall notice.
Source: LexBlog, Oct. 4, reviewing the CDC's published investigation steps and the FDA closing file.
Photo: The Nation's Salad Bowl — Malcolm Carlaw / CC BY 2.0 (via Openverse)
图片来源：The Nation's Salad Bowl — Malcolm Carlaw / CC BY 2.0 (via Openverse)
