Lawmakers in the House of Representatives plan to investigate what caused a deadly food poisoning outbreak in cantaloupes from a Colorado farm.

The bipartisan group of lawmakers on the House Energy and Commerce committee wrote to Ryan and Eric Jensen, who own Jensen Farms, asking them to brief committee staff and preserve documents related to the outbreak of listeria, which has killed 25 people and made 123 ill.

Unsanitary conditions at the farm's packing plant probably contributed to the outbreak, the U.S. Food and Drug Administration has said.

The committee also wants to hear from the FDA and the Centers for Disease Control and Prevention about what could be done to prevent future outbreaks, the lawmakers said in a letter on Friday.

Listeria monocytogenes is a frequent cause of U.S. food recalls in processed meats and cheeses, but contamination in fresh produce is a new development.

The elderly, pregnant women and people with weakened immune systems are most at risk. Symptoms include fever and muscle aches, sometimes preceded by diarrhea and other gastric problems.

The illness has a long incubation period, with symptoms sometimes not showing up until two months after people consume listeria-contaminated foods.