Food Safety and Environmental Health Blog : Disease Prevention, Public Health, Sanitation Information & Analysis : Environ Health Associates

Media types looking for a sound bite on Listeria in cantaloupes are pulling their hair out tonight.

You couldn’t ask for a more complicated scenario. Advice like “wash your hands” or “cook your foods” or “don’t cross contaminate” is nearly worthless. Here are some troubling facts

Listeria monocytogenes:

• Psychrophilic, multiplication possible all the way to 29 degrees
• Ubiquitous, found in almost all environments, terrestrial and aquatic
• Found in feces of animals
• Most problematic in ready to eat foods
• Forms bio films on food prep surfaces that resist sanitizers, nearly impossible to remove once adhesion occurs
• Incubation period can be days to months
• Huge dose response curve, from 100 or less cells, to 1,000,000 or more
• High morbidity and mortality up to 50% of cases
• Some strains are pathogenic some are not
• Highly virulent strains may be emerging
• Targets immune-suppressed victims, fetuses, neonates, pregnant, those on immunosuppressive drugs, those with disorders of the liver, gut, blood
• Attaches to nervous tissues, systemic infections 

Cantaloupes:

• Rough netted exterior traps contaminants
• The rind surfaces of these melons likely can support adhesion as well as colonization by many pathogenic bacteria
• Melon meat is highly conducive to bacterial multiplication, rich in nutrients and moisture just below the rind
• Keeps well under refrigeration
• When cut, surface pathogens are transferred into the meat
   

Combine the two and you have a marriage made in hell.
 

Could it be that the Jensen Farms LM outbreak will be traced to contaminated irrigation water?

Looks like the Arkansas river is the irrigation source for this entire farming region through a series of diversion canals and ditches. We also have to remember that pesticides are also applied using surface water sources in some regions.

For some great pictures of water usage in this region see:

cwrri.colostate.edu/publications/cr/205.pdf

I offer this theory because the low flow rates of the river due to the drought conditions in this region, and the access of the water source to all sorts of animal vectors is a very likely exposure pathway for LM.

For a look at  NOAA drought conditions reporting in this region see:

http://www.crh.noaa.gov/product.php?site=pub&product=dgt&issuedby=PUB

The growing region is in Prowers County, in extreme southeastern Colorado.

Given the wide spread of cases over time, this points to pre-harvest contamination, as opposed to post-harvest contamination. Although its been reported that LM was found in the production areas of the packing operation, such may have been introduced through contaminated incoming products.

For the latest from CDC and the report on LM findings from the facility see:

http://www.cdc.gov/listeria/outbreaks/cantaloupes-jensen-farms/092711/index.html

I hope we get the details of this investigation. If drip irrigation is used, and there is little exposure to irrigation water except through the roots, then my theory is less plausible. 

In spite of what some people have said about the Del Monte Salmonella cantaloupe outbreak, knowing the cause of outbreaks does help prevention efforts in the future.

http://www.perishablepundit.com/index.php?date=09/07/11#2
 

We have heard the retail industry insist that more must be done by the growers to prevent these events.

www.barfblog.com/blog/150653/11/09/29/try-harder-retailer-tells-cantaloupe-growers-improve-food-safety

If we are to do more, we need to know what.