CDC Cites Cantaloupe Outbreak as Having Several Unusual Features

As this issue went to press, federal officials were warning that there may be more illnesses and deaths linked to the cantaloupe listeriosis outbreak of September 2011. In addition to warning consumers to not eat any cantaloupe that they may have from Jensen Farms in Colorado, and to consult the retailer about or discard any cantaloupe of uncertain origin, CDC has cited the outbreak as having several unusual features:

• It is the first listeriosis outbreak associated with melon.
• Four widely differing PFGE pattern combinations and two serotypes (1/2a and 1/2b) have been associated with the outbreak.
• This outbreak is unusually large. Only two U.S. listeriosis outbreaks, one associated with frankfurters (108 cases) and one with Mexican-style cheese (142), have had more cases. Additional cases likely will be reported because of the long incubation period (usually 1 to 3 weeks, range: 3 to 70 days) and the time needed for diagnosis and confirmation.
• The outbreak has the highest number of deaths of any U.S. foodborne outbreak since a listeriosis outbreak in 1998.

A brief overview of the recall to date (Sept. 30, 2011):

• On September 2, 2011, the Colorado Department of Public Health and Environment (CDPHE) notified CDC of seven cases of listeriosis reported since August 28. On average, Colorado reports two cases of listeriosis annually in August.
• By September 6, all seven Colorado patients interviewed with the Listeria Initiative questionnaire reported eating cantaloupe in the month before illness began, and three reported eating cantaloupe marketed as "Rocky Ford." Initial tracebacks of cantaloupe purchased by patients converged on Jensen Farms in Colorado.
• After cantaloupe was implicated, PulseNet, the national molecular subtyping network for foodborne bacterial disease surveillance, detected a multistate cluster with a fourth PFGE pattern combination; a sample of cantaloupe collected from the implicated farm yielded L. monocytogenes with this pattern, and interviews with patients revealed that most had consumed cantaloupe. Isolates with this pattern were then also considered to be among the outbreak strains.
• By September 29, 84 cases with one of the four outbreak PFGE pattern combinations had been reported from 19 states, including 83 with information on the date of illness onset. Fifteen deaths were reported. On September 14, the farm issued a voluntary recall of its cantaloupe.

The most recent information on the outbreak is available at www.cdc.gov/listeria/outbreaks.