Sunny side up with a side of Salmonella, please

by Georgina Lee, PharmD 2011 | lee@myhousecallmd.com

If you’re the type of person that absolutely adores breakfast burritos, scrambled eggs, Egg McMuffins and anything else you can get your hands on made with eggs (think puff pastries), then the recent Salmonella scare is like a real life Steven King novel for you.  More than 500 million eggs have been recalled by the FDA nationwide including brands such as Ralph’s, Albertson and Farm Fresh (that’s a lot of potential omelets).  The question is: How serious are these bugs that have managed to make national headlines?  Do you need to swear off eggs for good?

What is Salmonella?

Salmonella are bacteria, specifically facultative anaerobic gram-negative bacilli (the medical world’s fancy way of specifying a type of microorganism) that tend to infect and colonize mammalian hosts causing the following unfortunate problems:

  • Gastroenteritis (inflammation of the gastrointestinal tract)
  • Enteric fever (systemic illness with fever and abdominal symptoms)
  • Bacteremia (infection of the blood stream)
  • Osteomyelitis (infection of the bone)
  • Abscess (localized collection of pus)
  • Asymptomatic chronic carrier state

These bugs usually enter the body via the gastrointestinal (GI) tract where they can survive for long periods of time.  They can also be found in the GI tracts of domestic and wild animals including insects, reptiles, birds, and mammals (don’t share a cracker with Polly).  There are many strains of Salmonella.  We simply their classification by separating them into two categories: 1) those that cause typhoid and enteric fever and 2) those that primarily induce gastroenteritis.  Given the current media frenzy, we’ll focus on the latter group, also known as non-typhoidal Salmonella.

When does Salmonella become a problem?

Non-typhoidal Salmonella is most commonly spread via improperly handled food that has been contaminated by animal or human fecal material (which we call fecal-oral transmission…totally disgusting, we know).  The two main strains of non-typhoidal Salmonella are S. enteritidis and S. typhimurium, which typically colonize (and subsequently cause gastroenteritis) in humans, mice, and fowl.  According to National Public Radio (NPR), mice were determined to be one of the main sources of S. enteritidis in the recent outbreak of contaminated eggs.

Fun Fact: It is estimated that 1 in 10,000 egg yolks is infected with Salmonella enteritidis.


Does that mean anyone who comes into contact with an animal that hosts Salmonella will get sick?  Not necessarily.  People with clinical conditions associated with a reduction in gastric acidity such as newborns, those who underwent gastric surgery, and those who take antacids (i.e. Tums, Mylanta) and H2-blockers (ie. Pepcid) may be at higher risk of becoming infected by Salmonella.  In addition, those who are taking antibiotics may also be at higher risk of becoming infected because antibiotics alter your intestinal tract’s natural flora (the bacteria in your gut that protect you from infection).

Fun Fact: The incidence of Salmonellosis (infection with the Salmonella bacteria) is highest during the summer in the Northern hemisphere and during the rainy season in tropical climates.

How exactly does Salmonella infect us?

In a normal healthy individual, our bodies are primed with a series of intricately connected defense systems that prevent us from becoming hosts to the world of infectious diseases.  After someone eats a bad egg, the ingested microorganism has to pass through the acidic barrier of the stomach in order to establish an enteric infection.  Most Salmonella never make it through that acidic gauntlet alive; however, a few strains have developed an increased tolerance to acid and can survive in the low pH (talk about survival of the fittest!).  After they survive the acidic gauntlet, they have to compete with your normal GI flora for nutrients and withstand all the other defenses in your gut including bile salts, pancreatic enzymes, and antimicrobial peptides such as secretory IgA (an antibody that helps fight off infections).   In the end, the ones that survive are extremely agile and well-adapted….and are the ones that typically wreak painful havoc on your bowels.

Fun fact: The acid in your stomach is so concentrated that if you were to place a drop on a piece of wood, it would burn right through it!

Salmonella infects our GI tract via two main mechanisms:

1.  Adherence

First, Salmonella attaches to specialized epithelial cells (cells that line the surface of an organ) in the colon and serve as the point of entry for these bugs.  Salmonella then trigger the development of enterocytes (cells that transport substances from the intestine to the circulatory system) to transport them into the body (also known as endocytosis).  Studies show that this form of Salmonella absorption is one of the critical factors in their ability to cause an infection.

2. Invasion (sounds like a Sci-Fi movie)

Invasion can occur both through enterocytes and other cells known as dendritic cells (immune cells), which are also located between epithelial cells.  Once Salmonella has invaded a cell, they remain within a protective phagosome (membrane-bound vesicle) called the Salmonella-containing vacuole (SCV) where they can survive and replicate.  Studies have identified specific Salmonella genes that allow certain strains of the bug to secrete proteins into the cells and facilitate their own uptake (very Trojan Horse-esk).  In addition, virulent strains of Salmonella can trigger a type of white blood cell that responds to infection and trauma, called a neutrophil, to infiltrate the intestine and cause inflammation (diarrhea anyone?).  Another substance, called Lipid A, which is found on the cell wall of Salmonella is toxic to mammalian cells.  Lipid A increases inflammation, decreases your defense responses and increases the virulence (i.e. the severity of illness) of certain strains so much so that it has caused death in mice.

Okay, I think I ate a bad egg.  Do I need to call the paramedics right away?

The initial symptoms of Salmonella gastroenteritis are abdominal cramps, fever and diarrhea starting 12-72 hours after eating the contaminated food.  The good news is that this type of infection is typically self-limiting (meaning that it goes away all by itself) and lasts anywhere from 1 to 7 days in a normal, healthy individual without antibiotics (thanks to our rock star immune system).  However, it’s important to note that in immunocompromised patients (such as those with HIV/AIDs, cancer, or organ transplant recipients as well as in the neonates and elderly populations), Salmonella can lead to more serious infections and should be closely monitored.  In addition, severe persistent diarrhea (i.e. a horrible case of the runs lasting 7+ days) is a big red flag indicating that you may have a more serious infection.  Diarrhea for an extended period of time can also cause dehydration so be sure to drink plenty of fluids (we recommend a mixture of ½ water, ½ electrolyte drink of your choice).  The bottom line is if you’re not sure whether or not your symptoms are normal, it’s better to play it safe and seek medical attention.

Thank my lucky stars, I haven’t eaten a bad egg yet but what can I do to prevent myself from becoming infected?

Here are some tips from the Centers for Disease Control and Prevention (CDC):

  1. Keep eggs refrigerated at ≤ 45°F (≤ 7°C) at all times
  2. Discard cracked or dirty eggs
  3. Wash your hands, cooking utensils and food preparation surfaces with soap and water after contact with raw eggs
  4. Eggs should be cooked until both the white and the yolk are firm and eaten promptly after cooking
  5. Do not keep eggs at room temperature for more than 2 hours
  6. Refrigerate unused or leftover egg-containing foods promptly
  7. Avoid eating raw eggs
  8. Avoid restaurant dishes made with raw or undercooked, unpasteurized eggs (i.e. Hollandaise sauce or Caesar salad dressing)
  9. Consumption of raw or undercooked eggs should be avoided, especially by young children, elderly persons, and persons with weakened immune systems or debilitating illness

As a wise individual once said, not all eggs are bad…there are still some good eggs out there.  We here to tell you that it’s safe to continue ordering your egg McMuffins as long as it’s fully cooked and hasn’t been sitting in your car for 8 hours.  Check the Food and Drug Administration (FDA) and the CDC websites to stay “egg-ducated” on the latest updates and egg recalls (we couldn’t help ourselves!).

Questions? E-mail the Author: lee@myhousecallmd.com

Resources

  1. Hohmann EL. Microbiology and Epidemiology of Salmonellosis. UpToDate. 9 June 2010.
  2. Kotton CN, Hohmann, EL. Pathogenesis of Salmonella gastroenteritis. UpToDate. 27 May 2010.
  3. CDC Features – Tips to Reduce Your Risk of Salmonella from Eggs. Centers for Disease Control and Prevention. 19 Aug 2010. <http://www.cdc.gov/Features/SalmonellaEggs/>.
  4. Recall of Shell Eggs. U S Food and Drug Administration Home Page. 3 Sept. 2010. <http://www.fda.gov/Safety/Recalls/MajorProductRecalls/ucm223522.htm>.

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09 2010

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