Listeria-based illnesses that first spread in early September linked to tainted cantaloupes are already being called  the deadliest outbreak in over ten years will likely rise higher in the next month, health officials said on Wednesday. 

Officials from U.S. Centers for Disease Control and Prevention (CDC) say as more people who have been infected with the bacteria begin to develop symptoms, more may be sickened or even die as result of the dangerous infection.

To date, 13 people have died and 72 people have been infected in the outbreak in 18 states, including two pregnant women, according to the U.S. Centers for Disease Control and Prevention, who have used only laboratory-confirmed evidence.

We will see more cases likely through October, Margaret Hamburg, U.S. Food and Drug Administration Commissioner, told Reuters in a telephone briefing.

Health officials have traced the source of the outbreak to cantaloupes grown by Jensen Farms in Colorado shipped between July 29 and September 10.

We do expect the number of cases will increase and the number of deaths may well increase, Mahon told the briefing.

Such outbreaks are far more common in processed meats and cheeses and it is not yet clear how listeria bacteria got into the fruit.

Listeria is a very common organism, which means it is very easily introduced into food at any point in a food chain - in the field, at home and anywhere in between, said Martin Wiedmann, a professor of food science and a listeria expert at Cornell University in Ithaca, New York.

After consumption, symptoms of E. coli and salmonella usually take one to three days to emerge but listeria's symptoms are not noticed for one to eight weeks.

That also makes it very difficult to trace back the source of outbreaks, particularly if they are small, Wiedmann said.

Most people don't remember what they ate in the last two months.