Dr John P Wright
Updated: 5 November 2006
Eating out is often presumed to be a dangerous activity. Patients who present with a recent history of diarrhoea are often presumed to have been infected by some pathogen in the food. This is not necessarily true. Two questions need to be assessed when faced by a patient with a recent history of diarrhoea:
It is a common human response to presume that others are the source of infection but this may not be as simple as is often presumed. An underlying irritable bowel may well be at the centre of the patient’s symptomatology rather than a food contaminant. We will now look closer at each question.
Where have you travelled recently?
This concern is realistic as 40 to 60 percent of travelers to developing countries may develop diarrhea. These attacks of diarrhea are usually benign and self-limited. In some patients however dehydration may pose a threat (1).
More than 90 percent of cases of travelers diarrhoea are caused by bacteria; the most common organism is enterotoxigenic E. coli(2). Simple variations in water, spices and changes in climate do not of themselves cause travelers' diarrhea but do alter how a patient perceives symptoms. Diarrhoea at 25°C is very much more manageable than at 35°C.
While non-specific parasites may be a common diagnosis of the alternative practitioner, in traveler’s diarrhea Giardia Lamblia may be a real threat. In St. Petersburg this organism is found in the water while in Nepal, as in some areas of South Africa and the USA, heavy contamination of the environment may be found(3).
Other parasites such as cyclospora, cryptosporidia and microsporidia may also cause problems while the larger parasites such as Helminthes are not usually associated with diarrhoeal symptoms.
Some parts of the world carry a higher risk than others. Most of Asia, Africa, South and Central America carry a high risk while Europe, USA, Australia and New Zealand are considered safe destinations. South Africa and countries around the Mediterranean are ranked as moderate risk. These divisions in to first, second and third world may be oversimplifications(1).
Most attacks of diarrhea occur between 5 and 15 days after arrival. The delay in presenting with symptoms is related to the dose of pathogenic bacteria ingested. Patients on acid reducing drugs such as proton pump inhibitors are at increased risk as the gastric acid barrier is removed allowing rapid colonization by bacterial pathogens(4).
Most patients experience malaise, anorexia, nausea and abdominal cramps followed by the sudden onset of watery diarrhea. In more severe cases there may be a pyrexial element but in the vast majority of cases the infection is self-limited and lasts a few days.
One can reduce the chances of infection by avoiding certain foods(5). Salads especially when cold meat such as chicken is added are particularly dangerous. As freezing does not kill organisms ice cream and ice cubes are to be avoided.
Any prepared food, particularly if cooked and then cooled, is probably best avoided. Drinks straight from the bottle are generally safe. In most parts of the world beer and bread, if not handled, are often a sound dietary choice. Hot beverages made with boiling water are usually safe.
The use of prophylactic antibiotics is not recommended. They are not without their own risks and may simply ensure an antibiotic resistant infection or a dose of unpleasant thrush. In some situations doxycyline may be useful particularly when also taken for malaria prophylaxis. Probiotics such as lactobacillus may prevent some attacks of traveler’s diarrhoea(6).
Treatment of traveler’s diarrhea has three components. Rehydration is particularly important in the young and elderly(7). Electrolyte solutions with glucose to enhance absorption may be life saving. Antidiarrhoeals with or without antispasmodics may make the symptoms more manageable but in the end most infections are swiftly dealt with by the human gastrointestinal tract. Antibiotics are generally not needed. However when the vacation is to last only a few days the use of an antibiotic is often called for. More severe infections when blood is found in the stool probably warrant antibiotics although most of these will also settle in 2 to 3 days. A stool examination will also be useful to identify the pathogens present. If antibiotics are to be used quinolones such as ciprofloxacin 500mg BD will bring most infections under control in a few hours(8). In patients unable to take quinolones, trimethoprim/ sulfamethoxazole preparations are the next choice. If Giardasis is suspected metronidazole will bring about a dramatic improvement but may interfere with alcohol metabolism and ruin the last few days in paradise.
It must be remembered that the use of antidiarrhoeals has been shown to delay clearance of an infective agent and in cases of missed inflammatory bowel disease have been associated with the development of a toxic megacolon.
Patients who develop diarrhea on their return home after a prolonged stay in the Far East or Central America may have “tropical sprue”. This is a fascinating condition in which the main histological features are blunting of the small bowel villi with infiltration of chronic inflammatory cells. The resulting steatorrhoea and lactose intolerance may cause the symptoms of diarrhea but the vitamin B12 and folic acid malabsorption are almost diagnostic of the condition. The etiology is unclear but normally attributed to bacterial overgrowth in the small intestine. Antibiotics such as tetracyclines may be useful but many will respond to simple folate replacement with or without vitamin B12(9).
Where have you eaten recently?
Abdominal symptoms of cramps and/or diarrhea occurring during or on arriving home after a meal in a restaurant are frequently attributed to “food poisoning”(10).
The time between the meal and onset of the symptoms is a critical diagnostic feature. Poisoning with a food toxin such as Staphylococcus aureus will present within 6 to 12 hours and symptoms will be predominantly upper gastrointestinal. Pathogens such as Enterotoxigenic Escherichia coli which secrete a toxin may present as a diarrhoeal illness 24 hours after ingestion. If a pathogen is to actually invade the intestinal cells such as Salmonella the onset may be further delayed.
Patients, however, who develop cramps and diarrhea while eating or on arriving home, are either suffering a serious toxin load or more likely an attack of irritable bowel syndrome. In the latter condition fat reaching the terminal ileum due to intestinal hurry precipitates giant colonic contractions in addition to causing gastric stasis. These effects are designed to reduce fat malabsorption. Fat is a food constituent that our gastrointestinal tract is designed to absorb if at all possible. We are indeed designed for tough times. This is a gentle reminder that while we may have moved out of the gutter, our genes have not. This mismatch is manifested in the irritable bowel syndrome.