Stool cultures may be requested when you have had diarrhoea for several days and when you have blood and/or mucous in your loose stools. This is especially true when you have eaten food or drunk fluids that you or your doctor suspect may have been contaminated with a pathogenic bacteria, such as undercooked meat or raw eggs, or the same food that has made others ill. Recent travel outside the United Kingdom may also suggest possible food contamination.
If you have had a previous pathogenic bacterial infection of your gastrointestinal tract and have been treated for it or recovered on your own, your doctor may request one or more stool cultures to verify that the pathogenic bacteria are no longer detectable. This can be important because in some cases people can become carriers of the bacteria. For instance, people with Salmonella typhi may become carriers (like "typhoid Mary") - they are not ill themselves any more but they can infect other people.
Results are frequently reported out as “isolated” – which means the particular pathogen was found in your stool sample, or “not isolated” - which means that bacteria was not found. Negative results usually reflect the fact that the stool culture was checked for pathogens at several intervals and none were found (not isolated). A report may say something like: “no Campylobacter isolated in 24 or 48 hours,” “no Salmonella or Shigella isolated in 24 or 48 hours,” etc. If the culture is negative for the major pathogens, then it is likely that your diarrhoea is due to another cause. It is also possible that the pathogenic bacteria are present in the gastrointestinal tract but were not found in this particular stool sample. If your doctor suspects this is the case and your symptoms continue, he may occasionally request another stool culture.
If your stool culture is positive for pathogenic bacteria, then that is the most likely cause of your prolonged diarrhoea. The stool culture report may say something like, “Salmonella isolated, species to follow” (which means the doctor is still trying to identify the particular type of salmonella), or “Salmonella enteritidis isolated” (which means that you have an infection caused by this particular pathogenic bacterium). Usually it will be a single type of bacteria causing your infection, but it is possible to have more than one present.
Severe pathogenic bacterial infections of the gastrointestinal tract, and those causing complications, may be treated with antibiotics but many uncomplicated cases are left to run their course. Those patients with competent immune systems will usually get better on their own within a week or so. Patients are instructed in how to prevent the spread of the infection and are treated and monitored for symptoms such as dehydration.
Pathogenic bacterial infections are monitored on a community level. Other than travel related cases, health officials want to try to determine where your infection came from so that they can address any potential public health concerns. For instance if your salmonella or shigella is due to eating food from a particular restaurant, the Communicables Diseases section of the local Health Board will want to investigate whether or not other people have also become ill from their food, and visit the restaurant to determine the source of the infection, taking steps to ensure that the spread of the infection is stopped.
This article was last reviewed on 7 March 2007. | This article was last modified on 31 October 2011.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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