Leafy vegetables are the second leading source of E. coli infections in the United States, behind ground beef, but the government relies primarily on voluntary safety steps by farmers and packagers to prevent outbreaks.

The cleanliness of fresh produce is drawing new attention amid reports that tainted spinach has been found recently in 21 states, killing at least one person and sickening more than 100 others. A second death was under investigation.

The Associated Press reports that some consumer groups believe the government should do more to regulate farming and packaging, including the quality of water used for irrigation, the application of manure and sanitary facilities used by workers.

In recent years, the FDA has acknowledged problems involving the safety of produce, particularly with lettuce and spinach.

Robert Brackett, director of the agency’s Center for Food Safety and Applied Sciences, sent a letter in November to California firms that grow, pack and ship lettuce. He noted that 19 known outbreaks of E. coli have come from fresh-cut lettuce or spinach since 1995.

In March, the agency issued draft guidance for the safe production of fresh-cut fruits and vegetables. Last month, the agency issued what it called the Lettuce Safety Initiative. It calls for visits to farms and packing operations so staff can monitor potential trouble spots and offer recommendations on reducing food contamination.

But warning letters and guidance are not enough, the consumer groups say. They contend many producers never hear of the recommendations, and that means the level of food safety remains hazardous and deadly.