Even though foodborne illnesses peak in the summer, the recent salmonella outbreak — and the farm that produced it — shows that they can occur year-round.

The subject of a food safety investigation since July, Foster Farms caused two other outbreaks in March and July of this year, and could be forced to shutdown three of their plants, according to a letter sent from the U.S. Department of Agriculture obtained by the Los Angeles Times.

The letter, sent on Monday, threatened to shut down Foster Farms unless they provided an adequate plan to ensure the safety of their customers.

Foster Farms chicken has sickened at least 278 people. Many of these patients contracted an antibiotic-resistant salmonella strain, according to a recent report from the U.S. Centers for Disease Control and Prevention.

CDC officials believe these antibiotic-resistant strains have contributed to the high number of hospitalizations caused by the outbreak — approximately 42 percent of victims have been hospitalized.

Ron Foster, the president of Foster Farms, posted a note on the company’s website in response to the outbreak.

“The alert that regulators issued based on illnesses over the past seven months emphasizes the need to fully cook and properly handle raw poultry,” explained Foster in the note. “Our facilities have always met and exceeded USDA standards. USDA continues to inspect and approve our chicken products as safe to consume.”

The outbreak spread across 18 states, and forced some CDC workers to return to work after being furloughed.

“We have about 30 people working on this outbreak investigation and others,” Barbara Reynolds, Ph.D., director of the division of public affairs at the CDC, told Weather.com.“We brought back about 10 people who had been furloughed. We also reassigned some to this work who were not furloughed; for example, our Public Health Service commissioned officers.”

MORE FROM WEATHER.COM: Ten Killer Foodborne Illness Outbreaks

The CDC has records of the deadliest foodborne illness outbreaks since the early 1970s, and five of the top ten outbreaks have occurred since 2000. Click through to see history's deadliest outbreaks. (Thinkstock/Jupiterimages)