WASHINGTON — Federal health officials said Friday they were never told of repeated findings of listeria at a Blue Bell Creameries facility before an outbreak linked to the ice cream turned deadly.

Results of a Food and Drug Administration investigation released this week showed the company had found 17 positive samples of listeria on surfaces and floors in its Oklahoma plant dating back to 2013. The FDA said Friday that it “was not aware of these findings” before doing its own inspection this year.

The outbreak – and the FDA’s lack of knowledge of the bacteria found in the plant – is a stark illustration of gaps in the nation’s food safety system. Food contamination often isn’t discovered until people get sick or die.

In the outbreak linked to Blue Bell, three people died in a Kansas hospital and seven others were sickened in Kansas, Texas, Oklahoma and Arizona.

The FDA said it isn’t uncommon for companies not to report findings of listeria or other pathogens. Companies are only required to report to the FDA if they find a “reasonable probability” that a food could make people sick. Blue Bell’s listeria samples were found on surfaces and not in the ice cream, and the company hadn’t tested to see if the listeria strains found were among those that are the most dangerous.

The FDA said it is common for a company to take corrective action – sanitizing and cleaning – without doing further testing if the pathogen isn’t found in the food itself.

“Although Blue Bell’s testing did identify listeria, the company did not further identify the strain to determine if it was pathogenic,” FDA spokeswoman Lauren Sucher said.

A law passed by Congress in 2010 sought to prevent such ongoing contamination by requiring companies to do more testing, put detailed food safety plans in place and take more preventive measures to keep pathogens, especially deadly bacteria like listeria, from getting into food.

But that law has been plagued by delays within the Obama administration. The FDA has struggled to get the rules right and appease many of the farmers and companies that will have to abide by it. After lawsuits over the delays, the final version of those rules must come out later this year.

“It certainly has taken far too long to get this done and these outbreaks are the result,” said Christopher Waldrop, director of the Food Policy Institute at the Consumer Federation of America.

Since President Obama signed the food safety bill into law, there have been dozens of outbreaks, including one of listeria in cantaloupe in 2011 that killed 30.