Effect Measure

Salmonella is an enteric pathogen that causes quite a lot of foodborne illness. I learned there were several species of Salmonella bacteria of which the cause of typhoid fever was called Salmonella typi. Spread via food and water it used to kill a lot of people in the 19th and early 20th centuries. Nowadays all Salmonella bacteria are considered to be different subspecies (serovars) of just one species, Salmonella enterica. There are more than 2500 of them, of which several routinely infect humans. Salmonella enteritidis is the most common form of foodborne bacterial infection (NB: many foodborne infections are of unknown agent and many are probably viral). Since the 19th century we’ve cleaned up the water supplies with disinfection and filtration and improved the food supplies. We can even treat typhoid and some of the other salmonella infections with antibiotics. Typhoid fever responds well but is only a tiny fraction of salmonellosis these days. For non-typhoid salmonella gastroenteritis whether to treat with antibiotics is a matter of clinical judgment. Randomized trials don’t show a clear-cut benefit and even suggest antibiotic treatment may prolong bacterial shedding in the stools, but for serious illness or infants less than 2 months, people with significant co-morbidities like sickle cell disease or immune deficiencies, antibiotics are still used. The main types are fluoroquinolones (e.g., Cipro) or the new generation of cephalosporins (ceftrioxone). Unfortunately both classes of antibiotics are also used in industrial livestock production to increase growth of animals and that has caused worries that these huge operations are incubators for drug resistant organisms. A paper just being published in Foodborne Pathogens and Disease asked whether retail supermarket chickens might be a place where one could contract drug resistant salmonellosis. The answer seems to be, “maybe.” From the abstract:

Methods: We isolated Salmonella from raw chicken purchased from a randomly selected sample of retail outlets in central Pennsylvania during 2006-2007. Salmonella isolates from meat were compared, using pulsed-field gel electrophoresis, to isolates in the PulseNet database of Salmonella recovered from humans.

Results: Of 378 chicken meat samples, 84 (22%) contained Salmonella. Twenty-six (31%) of the Salmonella isolates were resistant to ≥3 antimicrobials and 18 (21%) were resistant to ceftiofur. All ceftiofur-resistant isolates exhibited reduced susceptibility (minimum inhibitory concentration >2μg/mL) to ceftriaxone and carried a blaCMY gene, as detected by polymerase chain reaction. Among the 28 Salmonella serovar Typhimurium isolates, 20 (71.4%) were resistant to ≥3 antimicrobials and 12 (42.9%) were resistant to ceftiofur. One ceftiofur-resistant Salmonella serovar Typhimurium poultry isolate exhibited a rare pulsed-field gel electrophoresis pattern indistinguishable from a human isolate in PulseNet; both isolates carried the blaCMY-2 gene. (M’ikanatha et al., Multidrug-Resistant Salmonella Isolates from Retail Chicken Meat Compared with Human Clinical Isolates, Foodborne Pathogens and Disease [onlinhe ahead of print; doi:10.1089/fpd.2009.0499, sub required]

In essence they determined a molecular fingerprint of salmonella isolated from supermarket chicken and compared it to those in a database of molecular fingerprints from salmonella isolated from people with salmonellosis. There was one exact match, but the sample was pretty small. Was chicken a source of that case? We don’t know. We only know that this rare salmonella serovar was found in both supermarket chicken and a human. It isn’t clear if they were even from the same geographic area. Of interest is that the match was for salmonella resistant to the new generation of cefalosporins. Make of that what you will.

About a fifth of the supermarket chicken samples contained salmonella. That doesn’t mean you would get sick from eating the chicken if it was properly prepared and cooked, since cooking kills salmonella. On the other hand, it would be possible to cross-contaminate foods that are eaten raw, say by cutting salad on a cutting board that was not properly washed after being used to cut up the chicken or by unwashed hands that handled the raw meat and then the salad. Sometimes juice from the raw meat drips onto food eaten raw. Lots of possibilities, so don’t count on cooking alone to protect you.

Of the salmonella that was there, almost a third were resistant to three or more antibiotics and a fifth to the third generation cephalosporins. This included the one that matched the fingerprint of the human isolate in CDC’s Foodnet surveillance system.

If large commercial poultry operations are breeding grounds for drug resistant salmonella, the bugs still have to get out and into the community. This small study shows that they make it all the way to the supermarket refrigerator case as one possible route.

Bon apetit.

Comments

  1. #1 granny sue
    May 11, 2010

    I buy chicken raised without antibiotics from Whole Foods. Does it make any difference?

  2. #2 granny sue
    May 11, 2010

    I buy chicken raised without antibiotics from Whole Foods. Does it make any difference?

  3. #3 A Canuck
    May 11, 2010

    Granny Sue,

    I am guessing that it won’t make a difference if the chicken is killed and cleaned in the same plant as other chicken.

  4. #4 Hand Gel Geek
    May 11, 2010

    Hi Revere
    ‘About a fifth of the supermarket chicken samples contained salmonella.’
    It’s very sad that this level of contamination is now considered acceptable. What other food is sold with a 20% chance of containing salmonella; a percentage of which may be drug resistant.
    On top of that you have the question of whether chlorination of poultry is good practice – http://www.euractiv.com/en/food/outrage-plans-lift-chlorine-chicken-ban/article-172810.
    Food safety, especially in poultry production should not be the paltry matter that it currently is.

  5. #5 Lowlander
    May 11, 2010

    While these studies are interesting, it is important to point out that chicken meat is not the main vehicle for salmonelosis in humans.
    Campylobacter is by far the most significant foodborne pathogens in absolute terms and chicken meat is definatelly involved in the vast majority of cases.

  6. #6 Namnezia
    May 11, 2010

    How does the chicken meat get contaminated with salmonella? Is this from fecal matter during processing? How come salmonella is not as common in other meats? Are cows less susceptible to salmonella infection?

  7. #7 Rogue Epidemiologist
    May 12, 2010

    AFAIK, chickens in the US are endemically colonized with Salmonella. Raw chicken is commonly eaten in Japan because Salmonella is not endemic to their chickens.

    As for cows, they appear to be less susceptible to Salmonella, but plenty problematic with other pathogens (Brucella et al).

    Lowlander made a good point, but didn’t finish the statement. When dealing with salmonellosis, one should also consider unpasteurized dairy, eggs (particularly serovar Enteritidis) and reptiles as sources.

  8. #8 Dr. Ingersol B
    May 14, 2010

    That level of contamination may actually be good for the population. Any consumable with a quarter or less contamination is actually good for the immunity of the population. You cannot make food and other consumables completely sterile in the name of food safety.

  9. #9 Revere
    May 14, 2010

    Dr. Ingersoll: I see this claim often. Do you think there is solid data to back it up?

  10. #10 Cosmoskitten
    May 15, 2010

    Its possible to lower that 20% infection rate a lot:

    “Sweden has achieved an efficient control of Salmonella, despite the industrialisation of animal production. The prevalence of Salmonella in feed, live animals and animal products produced in Sweden is very low. In beef and pork it is less than 0.05% and less than 0.1% in poultry at slaughter. This unique position has been achieved by a national control strategy from feed to food, which was initiated more than 40 years ago. A severe domestic Salmonella epidemic during 1953, involving more than 9000 people of which a few died, demonstrated the need for a more comprehensive control programme.”

    From http://www.fao.org/docrep/meeting/004/ab456e.htm

    This may or may not be economical, but it is certainly feasible.

  11. #11 Jane
    June 20, 2010

    I thought that all meat can’t have antibiotics or hormones in it.

  12. #12 dr. v. p. singh
    May 9, 2011

    Your opinions on the subject are vastly superior to those I have seen written before. It is evident you have done your homework, and spent many hours perfecting this content.

  13. #13 Flavia
    HsyrCJubC
    July 22, 2012

    Having spent 8 out of 12 months in the field last year in Mexico rnnniug tests on seafood, vegetables,etc., we quickly discovered that the majority of cilantro was contaminated with salmonella. We found it in hotel restaurants and cilantro farms. We found it on lettuce as well, however, we had no findings on tomatoes, and other vegetables, including peppers. It is my opinion, that more attention should be paid to cilantro than tomatoes and peppers from Mexico. The Mexicans are very aware that they have problems, and I was pleasantly surprised at how good their food safety programs are run at their restaurants. Every utensil, pot and pan, and cutting boards were color coded so that they don’t cross contaminate when preping their food. Why, are they so careful, because they know they have problems. There was a time when you went to a restaurant, and all the food was from the USA. Now, over 70% is imported from other countries. In my opinion, when you find salmonella at several farms growing the same thing, it is more proof positive than finding one pepper out of millions. There were some reports that salsa could have been the culprit, and Mexican salsa usually has cilantro in it.