Hugh Maguire, PhD, a senior microbiologist with the Colorado Department of Public Health & Environment (CDPHE), said, “People in this area look forward to the end of summer when local cantaloupe becomes available.”

Late last summer, Maguire learned that cantaloupe can also be a vehicle for one of the nastier foodborne bacteria: Listeria monocytogenes. In fact, cantaloupe and L. monocytogenes are a particularly bad combination, as the bacteria thrive in the refrigerator, where the melon is likely to be stored, and the simple act of slicing the fruit is sufficient to spread the bugs from rind to flesh.

In a typical year, the DPHE laboratory receives two patient specimens per month that test positive for L. monocytogenes.  So when the laboratory confirmed nine cases of L. monocytogenes infection between August 28 and September 2, red flags went up.

Using two DNA ‘fingerprinting’ techniques–PFGE and MLVA–Colorado scientists quickly determined that the patients could be assigned to one of three unique clusters, each with a Listeria bug with a different and distinct genetic ‘fingerprint.’ This information was crucial, as each cluster represented a potential outbreak source.

State epidemiologists interviewed cluster patients to look for common food exposures.  On September 7, they contacted the laboratory and, said Maguire, “asked if we could purchase cantaloupe from retail sites and test it for the presence of L. monocytogenes. Would we be able to find it if it were there? And the answer was, ‘Yes, we’ll get on it.'”

​​Would we be able to find it if it were there? And the answer was, ‘Yes, we’ll get on it.’

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Senior Microbiologist, Colorado Department of Public Health & Environment (CDPHE)

At the same time, investigators had a fortuitous break: one of the patients had purchased two cantaloupes, one stored as cut chunks in the refrigerator and the other still uncut. The scientists prepared to test these immediately, while two staff members went grocery shopping. The pair went to three stores–one outlet of store A and two outlets of store B–returning with 15 Colorado-grown cantaloupes.

In the meantime, the patient count continued to rise. Speed was all important.

“We fast-tracked everything to the limits of the protocol,” said Maguire. “If the protocol said incubate for four to 16 hours, we incubated for four hours on the dot.”

The scientists performed PFGE analysis in parallel with MLVA, both running at max speed.

They bagged each cantaloupe with an enrichment broth and let it incubate. Then they plated the broth on agar growth media and waited for dark blue dots to appear, a tell-tale sign of Listeria.

Working over the weekend, food microbiologist Skip Gossack recovered and confirmed those Listeria colonies, while molecular biologist Justin Nucci, MPH, initiated MLVA.

The results? All five melons from store A tested negative for L. monocytogenes. All ten from store B tested positive. This information alone, said Maguire, exonerated some cantaloupe farms on the list of suspected sources.

Even more importantly, all of the distinct Listeria fingerprints associated with patient isolates were represented in the isolates from store B cantaloupes. Maguire said, “This eliminated concerns that there might be an alternate source of Listeria. Everything we were seeing in the patients, we were seeing in the cantaloupe.”

The PFGE data, coming a day or so later, was “100% concordant” with MLVA data.

As the link to cantaloupe developed, regulators were already busy with traceback investigations. Ultimately, they identified one farm as the sole source. On September 14, the farm issued a voluntary cantaloupe recall.

However, since L. monocytogenes can incubate for up to 70 days before onset of illness, cases continued to mount.  By September 29, 84 cases from 19 states were reported to the CDC, among them, 15 deaths.

The good news is that the contamination did not occur three years earlier, before the CDPHE laboratory had the benefit of cooperative agreement funding from the US Food and Drug Administration and Food Emergency Response Network. Maguire said, “Without this support, the instrumentation, training and collaborative relationships [critical to breaking the investigation] would not have existed, because we wouldn’t have had the money to put them in place.”

Instead, with the infrastructure up and running, the laboratory moved quickly. Maguire said it met its major challenge:  “how to identify a dangerous product but not impact the entire Colorado cantaloupe industry.”

Colorado Department of Public Health & Environment, Laboratory Division Scientific Team Responsibl​e for Testing During the Listeria Outbreak, October 2011. (Left to right) Garth Summers (temporary​-Molecular lab), Kristin Mayo (lab technician​-Molecular lab), Skip Gossack (scientist​-Environme​ntal Microbiolo​gy lab), Margot Stuchin (APHL fellow-Mol​ecular lab) and Justin Nucci (scientist​-Molecular lab). — APHL photo

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“Success Stories: A Colorado Cantaloupe Saga” is reposted, with permission, from the Association of Public Health Laboratories website.

Around Thanksgiving we talked about safely handling raw meat. Quick! Do we rinse our turkeys or not?  I hope you said NOT. This time of year I think we need to talk about eggs and Salmonella. That unexciting ingredient that goes into cookies, cakes and other sweet treats, and let’s not forget about latkes, a Chanukah staple, and of course eggnog. I don’t know about you, but I often quickly add them and move on to the more exciting ingredients like chocolate chips!  Let’s take a step back and think about those eggs.

Shell eggs (ie, eggs in their shells as opposed to the egg product in a carton – more on this below) are not pasteurized. That means they can contain Salmonella. There are regulations in place that mandate certain procedures to clean the outside of eggs sold commercially so you’re good there. The issue is that Salmonella can live inside the shell. That means we have to be careful.

Here are a few suggestions to make sure you aren’t contaminating your kitchen:

1. When handling raw egg, you should think of it like raw meat. Would you rub your raw chicken all over your countertops? Would you get raw chicken on your hand, wipe it on your dishtowel and just move on without washing with soap and water?  I hope not. And if you do, please don’t invite me over for dinner. After you crack your eggs into the bowl, wash your hands and anything else you touched. Wash with water AND soap. Come on. Will these soaps that look like bacterial cultures help make hand washing more fun?

2. Now don’t forget that whatever you just mixed your egg into has raw egg in it. Did that sound like the most obvious statement ever?  hen why would you roll cookie dough out on your counter, cut out your adorable Rudolph cookies, line them up like a reindeer army marching across your baking sheet, and then NOT wash your hands again and anything else you touched including the counter? I mean, really people! If your eggs are contaminated, you just shmeared Salmonella all over the place and *bing bong* your guests are here and not interested in eating your Salmonella cookies while gathered around your Salmonella countertops. Do everything you possibly can to NOT cross contaminate.

3. OK. Now we need to have a difficult talk. This won’t be easy for either of us to discuss but it is necessary. Eating raw cookie dough. I know, I know … it is delicious. I’m right there with you!  So I’m not going to tell you not to eat raw cookie dough. I know you’ll stop reading right now and brush me off as the mean lady who ruined your favorite indulgence. What I am going to tell you is that you have to lick those delicious spoons at your own risk. Just like with raw meat or fish, it could make you sick. Any egg could contain Salmonella. Just because you got it at Fancy Pants Grocery doesn’t mean it is exempt from contamination. Officially we don’t recommend eating raw cookie dough. Unofficially? You decide if you feel it is worth the risk. I would strongly discourage you from letting your kids, an elderly friend or relative or anyone with a compromised immune system have it. In that case, it probably is not worth the risk. Salmonella is potentially very dangerous. And to those of you tough guys who are like, “Oh, I eat raw cookie dough all the time and I’m still alive!” You may get sick – you may not get sick. But ask any person who has ever contracted Salmonella and they will likely tell you about the time when they wish they weren’t alive as the slept on the bathroom floor cuddled up to the toilet.

4. As I already mentioned, shell eggs are not pasteurized but egg product is. Egg product is the stuff that comes in cartons. Many restaurants use egg product for that reason – Pasteurized! No lawsuit! Hooray! If you’re making sauces that call for raw egg (Caesar dressing, Hollandaise, béarnaise, etc), using egg product is safer. Some egg product won’t work well for baking so check the side of the carton first. It will tell you.

5. Make sure things are cooked all the way through. You’re not going to stick a meat thermometer in every cookie and latke, but you can still check to make sure they aren’t raw in the center. You want the chocolate chips to be gooey, not the cookie part. And when frying latkes, be sure your pan isn’t too hot so they cook through before the outside burns. In both cases, break one in half to check the center. Oh, and you know those delicious runny sunny side up eggs you love to dip your toast in? Yeah, those aren’t cooked all the way through.  Just like with the cookie dough, eat at your own risk.

6. Don’t drink unpasteurized eggnog. You can get pasteurized eggnog, so why risk it?  Friends don’t let friends drink unpasteurized eggnog and hold their own hair back … if you know what I mean.

As GI Joe said, “Now you know, and knowing is half the battle.”  He was obviously referring to safe food handling when he said that.

Why do we go to so much trouble to entertain and be entertained this time of year? Because it is nice. Because seeing people enjoy cookies and latkes that you made makes you feel good. You know what won’t make you feel good? Seeing people snacking on thumbprint cookies with a dollop of Salmonella in the center where a Hershey kiss should be. That won’t end well for anyone.

Related articles:

DO NOT RINSE YOUR TURKEY! And other Thanksgiving food rules for every day (aphl.org)

Saving the Food Emergency Response Network (FERN) (aphl.org)

Food Testing in Public Health Laboratories: Revolutionized by the Food Emergency Response Network (FERN) (aphl.org)

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By Michelle Forman, Senior Media Specialist, the Association of Public Health Laboratories. First published on the APHL Public Health LabLog. Reposted with permission.