The CDC reports today 123 ill with 25 deaths in what has become the second most deadly foodborne illness outbreak in United States history. According to the FDA, tracing of the cantaloupes that ill persons ate show that they came from Jensen Farms and Frontera. These cantaloupes were shipped from July 29 through September 10 to at least 24 states, with possible further distribution.

How long will the illness and death count go on? Setting aside those who become ill with listeria and are never tested, and those elderly or fetuses that die and are never counted, the official count (blood or spinal fluid culture positive for listeria) will certainly go higher. Here is why.

Among persons for whom information is available, illnesses began on or after July 31, 2011 (2 days after first shipment). Illnesses that occurred after September 23, 2011, might not be reported yet due to the time it takes between when a person becomes ill and when the illness is reported.

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The incubation period for listeriosis is variable and ranges from 3 to 70 days, with the median incubation period being three weeks. According to the FDA, given that the Jensen Farms Frontera recall has been in effect for more than three weeks, and that the shelf life of a cantaloupe is approximately two weeks, it is expected that all of the recalled whole Jensen Farms Frontera cantaloupes have been removed from the marketplace.

So, if you assume that someone consumed cantaloupe purchased on the last day product was shipped, and given the two week shelf life, tainted cantaloupe could have been consumed as late as September 24th. And, with an incubation period of up to 70 days, we may well not see the end of illnesses until early December.

Scope of Outbreak thus far: A total of 123 persons infected with any of the four outbreak-associated strains of Listeria monocytogenes have been reported to CDC from 26 states. All illnesses started on or after July 31, 2011. The number of infected persons identified in each state is as follows: Alabama (1), Arkansas (1), California (2), Colorado (36), Idaho (1), Illinois (2), Indiana (3), Iowa (1), Kansas (7), Louisiana (2), Maryland (1), Missouri (4), Montana (1), Nebraska (6), New Mexico (13), New York (2), North Dakota (1), Oklahoma (11), Oregon (1), Pennsylvania (1), South Dakota (1), Texas (18), Virginia (1), West Virginia (1), Wisconsin (2), and Wyoming (3). Pennsylvania has reported their first case since the last CDC update. Twenty-five deaths have been reported: 6 in Colorado, 1 in Indiana, 2 in Kansas, 2 in Louisiana, 1 in Maryland, 1 in Missouri, 1 in Nebraska, 5 in New Mexico, 2 in New York, 1 in Oklahoma, 2 in Texas, and 1 in Wyoming. Among persons who died, ages range from 48 to 96 years, with a median age of 87 years. In addition, one woman pregnant at the time of illness had a miscarriage. State and local health departments in these and other states are investigating other listeriosis illnesses to determine if they are part of this outbreak.