Cantaloupes contaminated with listeria have now killed 15 people and sickened 84 in an outbreak that has lasted for more than two months, the Centers for Disease Control said on Friday.

The toll is expected to rise throughout October because, although the contaminated cantaloupes were recalled last month, some people may have had them in their refrigerators for a while after the recall, and symptoms can appear more than a month after exposure.

Listeria is usually spread through processed meats and unpasteurized dairy products. It is less common, but not unheard of, for it to be found in produce. Most healthy people will experience only mild symptoms, but listeriosis can be deadly in the elderly and people with compromised immune systems.

Listeriosis outbreaks are less common and affect fewer people than outbreaks of salmonella and E. coli, but listeria is more deadly when it does strike. As a result, four out of the five worst outbreaks in terms of number of deaths were from listeria, but four out of the five worst outbreaks in terms of number of illnesses were from salmonella.

The CDC is calling this the worst outbreak of a food-borne illness in more than a decade. Here are the worst outbreaks in U.S. history in terms of infections and deaths.

Most deaths

1.      1985, listeria: 52 deaths from Mexican-style soft cheese.

2.      1998, listeria: 14-22 deaths from hot dogs and cold cuts.

3.      2011, listeria: 15 deaths and counting from cantaloupes.

4.      2009, salmonella: 9 deaths from peanut butter.

5.      2002, listeria: 8 deaths from turkey and other cold cuts.

Most infections

1.      2009, salmonella: 22,500 illnesses from peanut butter.

2.      1985, salmonella: 16,284 illnesses from milk.

3.      2010, salmonella: 1,600 illnesses from eggs.

4.      2008, salmonella: 1,442 illnesses from peppers and tomatoes.

5.      1993, E. coli: 700 illnesses from meat served at Jack in the Box restaurants.