Luckily, these biologically iced sugar cookies were not cookies of death. I baked these for my preliminary examinations in the Ecology, Evolution, and Behavior PhD program at the University of Texas. Of course, had I not passed...they might have been. I kid, I kid!

Like all cookies, these cookies underwent a baking metamorphosis. These cookies were once a much more delicious product: dough. Eating raw dough is my favorite part of cookie consumption! However, raw dough also poses one of the greatest risks to one's health when it comes to the entire process of cookie production/gourmandization besides exploded stomachs. Raw dough has raw eggs and these raw eggs sometimes have parasites that can kill you.

I'm a bit of a germaphobe but I like to tell myself that probabilistically there isn't that great of a chance of me contracting a horrible disease from dough because a) there is a low prevalence of germy eggs and b) my immune system could eradicate the pathogens. This post aims to investigate the first of these two justifications.

If you’re like me, you’ve no doubt been warned to not eat raw dough but then ignored the advice. There are several different salmonella species and they infect various animals such as cattle, chickens, amphibians and occasionally people. The species, subspecies and serotype we are interested in is Salmonella enterica enterica enteritidis or S. enteritidis (a discussion of the complication and controversies surrounding taxonomic classification of pathogens will undoubtedly ensue at a later date).  Before the 1970s most cases came from feces on the egg shell surface but now egg shells are sanitized. In the 1980s a new strain appeared that actually infects the ovaries of the hens and is passed down vertically within the egg itself. This is the strain we are worried about.

Most of the publications I found on the topic of S. enteritidis prevalence were from the 1990s. In the northeastern region of the United States, 45% of hen houses were contaminated with S. enteritidis while central and southeastern regions were lower, 17% and 3% contamination respectively.  This information made me feel a little better about my raw egg eating ways since the south has a lower prevalence rate but I was still concerned. The sampling was done on the ceca and not the ovaries. Would this detection method be sensitive enough to detect infection inside the eggs? I also found out that salmonella of some type was detected in 80% of egg-laying houses.  So then of course, I wondered if competitive exclusion took place between the different salmonella species and if infection with “good” salmonella prevented infection with “bad” types. (Ebel et al. 1992)

Hogue et al. also found the northern region of the US to have the highest prevalence of S. enteritidis in unpasteurized egg product and slaughtered hens, 40%. Other regions ranged between 10-12% (Hogue et al. 1997).  Another paper, however, only detected S. enteritidis in 1 out of 42 flocks from the southeast and Pennsylvania when sampling directly from ovaries, a 2.4% prevalence rate (Barnhart et al. 1991).  Aha, I thought, here is my vindication finally!   

And because this is a blog post and not a research paper, I’m going to wrap up the post now. Basically, it seems like if you live in the northern region of the United States, don’t eat raw eggs.  Nearly half the flocks/hen houses are contaminated with pathogenic salmonella. Other areas face a risk but depending on the sampling method, the prevalence will vary.  The real question is what prevalence rate are YOU willing to risk eating cookie dough for? Is 17% too high? Is 2.4% too high? And remember, these studies are dated, what is the actual prevalence now? I would also say that if you are immunocompromised or a young child you should definitely not eat raw dough. I don’t have an answer yet as to whether this information will change my behavior, most likely it will not. Maybe if I move to the east coast it will.

So as the holiday season reaches its apex, remember that not only must you beware of cookie dough but also beware of homemade egg nog, sunny side up eggs, bean sprouts, and frogs. Nothing says Christmas like a holiday tree frog. And apparently, even if your eggs are pasteurized and you buy dough from the store, you may still get sick…from E. coli contaminated flour! (http://well.blogs.nytimes.com/2011/12/12/beware-of-raw-cookie-dough/) 

Here is a great link from the CDC on how to reduce your exposure to salmonella: http://www.cdc.gov/Features/VitalSigns/FoodSafety/ 

Barnhart, H.M., Dreesen, D.W., Bastien, R. & Pancorbo, O.C. (1991). Prevalence of Salmonella enteritidis and other serovars in ovaries of layer hens at time of slaughter. Journal of food protection, 54, 488-491.

Ebel, E.D., David, M.J. & Mason, J. (1992). Occurrence of Salmonella enteritidis in the U.S. Commercial Egg Industry: Report on a National Spent Hen Survey. Avian Diseases, 36, 646-654.

Hogue, A.T., Ebel, E.D., Thomas, L.A., Schlosser, W., Bufano, N. & Ferris, K. (1997). Surveys of Salmonella enteritidis in unpasteurized liquid egg and spent hens at slaughter. Journal of food protection, 60, 1194-1200.
   

Author

Stavana Strutz is a doctoral candidate studying disease ecology in the Parmesan lab at UT Austin.