Federal officials predict that the outbreak, linked to romaine lettuce, will continue for several weeks. It is the largest American E. coli flare-up since 2006, when tainted spinach sickened 199 people across 26 states.

The current outbreak, and particularly obstacles to tracing it, underscore vulnerabilities in the monitoring of fresh produce. Complicating the investigation is the fact that the romaine can come from a variety of farms and be commingled at points along the supply chain.

A federal law enacted seven years ago was intended to prevent such outbreaks — or at least to shut them down swiftly. But rollout has been slowed by wrangling over compliance costs and details, and the challenge of training tens of thousands of farmers and facility operators. Standards may not take full effect for years.

When virulent strains of E. coli emerge in ground beef, they can be neutralized by cooking. And beef products, identified by bar codes and lot numbers, are easier to trace than produce.

But leafy greens are usually eaten raw, heightening the likelihood that a dangerous strain like the latest one will infect the consumer. Lettuce’s shelf life is also short: Opportunities to test the offending crop range from limited to nil. And because detailed reporting requirements to track produce from field to supermarket have not yet been hammered out, fine-tracing the source of contamination is exceedingly difficult.

Source: New York Times, FDA.gov