The death toll from 2011’s cantaloupe-related listeria outbreak stands at 33 with confirmation from Montana officials that a 75-year-old man who died in January was infected.

“We finished the investigation July 18 and the CDC is adding him to the death toll,” said Job Ebelt, public information officer for the Montana Department of Public Health and Human Services.

Some health officials said there is potential for additional victims to be identified now that a fifth listeria isolate is linked to the outbreak. A spokeswoman for the Centers for Disease Control and Prevention confirmed July 24 that the death toll is now 33.

Montana officials knew the man from Bozeman had eaten fresh cantaloupe in September 2011, so he was tested for listeria. They sent the results to the PulseNet database Sept. 17.

“CDC reviewed the patterns and compared them to the outbreak strains, and we received notice on Oct. 24 that the pattern did not match,” Ebelt said, adding that until recently only four isolates were linked to the 28-state outbreak.

Meanwhile, in September 2011 Colorado officials were investigating dozens of cases linked to what turned out to be the contamination source — cantaloupe from Jensen Farms, Holly, Colo.

At one Colorado victim’s house, investigators collected samples of whole and cut cantaloupe. However, the results from the cut cantaloupe were not uploaded to PulseNet, said Hugh Maguire, program manager for microbiology at Colorado’s Department of Public Health and Environment.

“It wasn’t uploaded because we couldn’t guarantee the integrity of the sample,” Maguire said. “We are changing our practice. Now we will provide all data, regardless of the source.”

Maguire said there was no way to know where the listeria in the cut cantaloupe had oroginated. It was not among the four known isolates present in outbreak victims in Colorado. The whole cantaloupe in the home tested positive for three of the four known isolates, but not for the isolate in the cut cantaloupe.

Colorado investigators bought whole cantaloupes from stores near the victim’s home to see if they could find any with listeria that matched the isolate found in the cut cantaloupe. They found none.

State and federal officials finally realized the isolate from the Montana man was the same one in the cut cantaloupe in the Colorado victim’s home after Colorado officials uploaded the fifth isolate to the national database June 18.

An attorney working for victims and their families pursuing legal action against Jensen Farms requested “any and all” test results as part of the federal court case. Review of those results revealed the link between the Montana case and the fifth isolate found in the Colorado victim’s home.