Reply #12: Not necessarily that simple with Salmonella [View All]

[du_grad]

I am a clinical microbiologist in a hospital microbiology laboratory. Some people can ingest the same food and have mild symptoms; others have symptoms bad enough to hospitalize them. Probably only about 10% of these cases ever get cultured, which is the only way to tell if it's Salmonella that's causing the diarrhea. Many people get the runs for a couple of days and it isn't bad enough to call the doctor. Many doctors don't order cultures on mild diarrheal cases, so the actual pool of infection in this latest outbreak is probably ten times what has been reported so far.

The problem with Salmonella is that it is an organism that can go systemic in people with lousy immune systems, very old or very young people. I have seen Salmonella grow in a shoulder aspirate, a couple of sputum cultures, and quite a few blood cultures (causing septicemia) as well as many stool cultures. Many times the people with septicemia never had a baseline stool culture so it is unknown if the organism traveled from the intestine to the extra-intestinal site. You can end up being a carrier of Salmonella. If it is mild diarrhea and "self contained" many times it is not treated with antibiotics because this can induce a long-term carrier state (remember typhoid Mary's story). Obviously if it is in the blood or other extra-intestinal site it is treated with antibiotics.

On the lab end, if we isolate Salmonella this is a "reportable." We call the results to the floor/doctor and put a notation in the report that this is being reported to the state lab. This means the patient's name and his isolate are reported to the state department of health for follow-up by epidemiologists. We send the actual isolate to the state lab for further serogrouping. There are many many serotypes of Salmonella. This is how the CDC can track the causative strains in outbreaks. Our lab only reports the grouping. We have antisera to group Salmonella A, B, C1, C2, D, and E only. Epidemiological study of these outbreaks takes time and lots and lots of detective work. In large outbreaks, people have to be interviewed as to what they ate and when they ate it, when they came down with symptoms, etc. All of this has to be studied and possible routes of infection tracked down. This is why it is not quickly known where these strains come from. Salmonella are spread via ingestion, not the respiratory route, so they know it is in the food chain somewhere. The fact that it is present equals fecal contamination from some source. Salmonella are normal flora in some animals. They can be inside the chicken before the egg is laid, so just washing eggs on the outside will NOT necessarily rid the egg of infection. If you like your eggs soft-boiled or over easy, you are throwing the dice. Only a small percentage of eggs are infected but there is no way of knowing ahead of time which ones they are. It is virtually impossible to culture each and every chicken and egg, so the consumer has to beware. Temperatures above 140 degrees will kill Salmonella but that doesn't necessarily mean the meat is done and edible. It depends on what you're eating.

Always cook chicken to at least 165 degrees F. Use a meat thermometer. Do not microwave chicken as it will not cook evenly and you can have raw pockets of meat that can be below temperature and harbor live organisms. Treat ALL chicken (and meat products in general) as a possible source of infection. Chicken also can carry Campylobacter sp. Some studies have determined that nearly 70% of the chicken in supermarkets (doesn't matter where, or whether it's organic or not) harbors Campylobacter, which also can cause diarrhea, and is also a reportable organism. Don't cut raw vegetables on the same cutting board that you just used for raw meat. Don't put cooked meat on the plate you had it on when it was raw. Be aware of dishrags that you use to wipe up meat blood and throw them in the wash before you use them on anything else. Disinfect your counters after prepping raw meat. Above all, WASH YOUR HANDS after dealing with raw meat before you touch anything else. This includes the telephone, the sink handles, and the refrigerator handle. Alton Brown on the Food Network recommends separately labelled cutting boards for poultry, hamburger, vegetables. I think this is a good idea. I use plastic cutting boards that I can put in my dishwasher. If you don't have one, use extremely hot water and lots of soap and scrub down on the cut marks on the board. A quick wipe just doesn't do it.

There is no way each and every piece of food can be inspected before it reaches your mouth. Use common sense in food prep and storage (don't keep opened or cooked meat too long) and you will do a lot to prevent intestinal illness. Obviously, some of the previous causes of Salmonella outbreaks had really nothing to do with the consumer's behavior and the fault is with the food processor.

Remember, food is the perfect culture medium for microorganisms. Our microbiological media uses things found in food to grow the bugs: cooked meat broth (made from pelletized mystery meat and autoclaved with distilled water to make a broth - bacteria love it), potato dextrose agar (used for molds), tomato juice agar (used for molds), trypticase soy agar with 5% sheep blood (the main medium used for nearly every culture). The list goes on and on.

Now, wash those hands!