Click here to view next page of this article

 

Acute Infectious Diarrhea

Causative agents of acute diarrhea in children in the U.S. resulting in hospitalization. You can see that the majority of cases are due to viral agents. Really Rotavirus, Norwalk agent and others. So you would think that when studying for the Boards that gee youíd better really pay attention to three-quarters of this pie. Itís true that these are important things to pay attention to, but notice that Salmonella and Shigella and Campylobacter and these others do have real specific presentations, specific complications and specific therapies associated with them. So you have to pay attention to them out of proportion to the epidemiology.

So first of all, we are going to look at watery diarea and with watery diarrhea the site of predominant involvement is the small bowel. These are the causative agents, just as an overview, and weíll go through each of these individually. But enterotoxicogenic E. coli and vibrio cholera, and viruses such as Rotavirus, Norwalk agent, certain strains of adenovirus, astrovirus.

Now the features of watery diarrhea are obviously the symptom of watery diarrhea and this is usually accompanied by either a low grade fever or no fever at all, and vomiting is a prominent manifestation in the presentation of watery diarrhea.

A brief overview of dysentery; in dysentery the predominant site of involvement is the colon, the large bowel. The causative agents of dysentery are shown here. Bacteria such as Shigella, Salmonella typhi, non-typhoid Salmonella - which presents differently so we separate that out - Campylobacter jejuni, Yersinia enterocalitica, enterohemorrhagic E. coli, Clostridium difficile.

Now the features of dysentery include, obviously, dysentery which is the stool containing mucus, blood and tenesmus. Fever is usual.

Okay, now we are going to go through the specific causative agents and the first thing we are going to look at is the causative agents of watery diarrhea. The significance of enterotoxicogenic E. coli is that this is the most common cause of travelers diarrhea. Vibrio cholera causes a voluminous diarrhea, and this is called a "rice water" diarrhea because the stool does look almost clear but does have a bit of a white tinge to it. Vibrio cholera is not acquired in this country. Almost all cases that are seen in this country are imported.

Norwalk agent is another viral cause of watery diarrhea. Itís similar to Rotavirus but it occurs in older age groups. So when epidemics occur they occur in schools, institutions, cruise ships, and restaurants. Itís known as "winter vomiting disease" because it also occurs in the winter.

Giardia usually presents with a watery diarrhea as well. Itís transmitted by water in wilderness areas. Many animals in the wild may carry Giardia and then contaminate the streams, and thatís why you need to purify water in the wild. It can also be transmitted in daycare centers.

Cryptosporidium also causes watery diarrhea. Itís also transmitted in water. Farm animals carry Cryptosporidium and many of you may be aware of the recent outbreak in Milwaukee where, due to runoff from areas where there were farm animals.

Weíll move on to food poisoning as a cause of watery diarrhea. These agents are all relatively similar and Iíll point out some differences. These are all acquired by ingestion of pre-formed toxin and the toxin is in the food. Staph aureus and Bacillus cereus are similar in that they have very short incubation periods, 1-6 hours. The illness is brief and vomiting is the predominant part of food poisoning. The diarrhea is more secondary. The way you can differentiate them really is the foods that they would normally contaminate. For staph aureus the foods, the typical ones, are mayonnaise-containing salads, egg salad, potato salad, pastries, poultry and ham. Bacillus cereus typically will contaminate cooked rice - the typical one is fried rice at a banquet - meat or vegetables. Then Clostridium perfringens differs from the above two in that the incubation period is a little bit longer, 8-12 hours, and it does cause a severe diarrhea with prominent cramps. Thatís different from the others where the vomiting is more common. With Clostridium perfringens the vomiting is less common and is typically not associated with a fever. The foods that Clostridium perfringens typically contaminates are meat and poultry, gravies as well as Mexican-style foods. Obviously with any food poisoning you should look to see if there was an outbreak situation because anybody who shared that food probably also ingested pre-formed toxin and may have symptoms.

Now we are going to switch gears and go through the causative agents of dysentery and the first one we are going to look at is Shigella. Shigella sonnei is the most common species that causes infection in the U.S. but there are three other species. Incubation period is relatively short, and itís most common in the 1-5 year old age group. The clinical features of Shigella include typically dysentery.

Next weíll look at Salmonella typhi and this has a longer incubation period, 1-2 weeks. And this is more of a prolonged illness. Salmonella typhi causes typhoid fever, which is also known as enteric fever. This has a gradual onset associated with fever, headache, malaise, abdominal pain, enlarged liver, enlarged spleen and occasionally rose spots are typical but donít occur in the majority of cases.

Non-typhoid Salmonella has a different presentation. Itís caused by several different serotypes, the most common of which is Salmonella enteritidis. This has a 6-72 hour incubation. Youíll notice that I put up there that itís the most common cause of diarrhea in the U.S. but I also said that Rotavirus was the most common cause of gastroenteritis in the U.S. That is a difference that non-typhoid Salmonella typically will cause diarrhea. Rotavirus may cause a gastroenteritis, which is a vomiting in association with the diarrhea.