So now there are other causes of invasive diarrhea such that we call acute dysentery and
these patients usually have fever to 38.5 or more and they have stools that are frequent but
this is the difference. They are small volume stools with mucus. They are generally unformed
and many of these patients have bloody diarrhea. I want to stop here and talk about the small
volume diarrhea. So invasive colitis is characterized by maybe frequent stools but small in
volume so part of the history that you want to take is "Tell me something about your diarrhea sir"
and you want to find out not only how often but the volume of the stool and this is where you
also want to ask about tenesmus because if they have the frequent urgency to defecate but
without much productivity, that is a big point in favor of a large bowel invasive problem.
So abdominal cramps and these cramps are going to be localized below the umbilicus, they're
going to be in the area of the colon with tenesmus and fecal urgency. Now the causes in the US
that are common are <i>Salmonella enteritidis</i>, <i>Campylobacter</i>, <i>Shigella</i> and the uncommon causes
would be <i>Aeromonas hydrophila</i>. So when would you think of that organism? Well, the history
would tell you that they have had some recent exposure to swimming in fresh water, lake
water or maybe brackish water and <i>Yersinia enterocolitica</i> and just a small point about this
organism. A lot of these patients will present like they have appendicitis and then the
non-cholera <i>Vibrios</i> like for example <i>Vibrio vulnificus</i> or <i>Vibrio parahaemolyticus</i>. In the
non-cholera <i>Vibrios</i>, the way to remember those is we're talking about saltwater and these
organisms are part of the normal flora of the sea and so if someone has had exposure to food
that comes from the sea, a fish, crustaceans and so forth they could get this non-cholera
<i>Vibrios</i> invading the colon. Now, dysentery is not that frequent a problem, the outbreaks are
pretty infrequent in the United States and a lot of them are caused by enteroinvasive <i>E. coli</i>.
Let's talk about <i>Salmonella</i>, an important cause of invasive colon disease. There really are 2
species of <i>Salmonella</i>. The first is <i>Salmonella enterica</i> which you usually get from lower animals,
it's a zoonosis and in this classification are subspecies numbering 6. Subspecies I <i>(enteritica</i>)
contains almost all pathogenic serotypes and here we're talking about <i>Salmonella typhi</i>, the
cause of typhoid fever; <i>Salmonella typhimurium</i> and <i>Salmonella choleraesuis</i> and each of these
can present in one of 3 clinical patterns, either acute dysentery, septicemia, or enteric fever.
Now <i>Salmonella typhi</i> is the one that causes most of the enteric fever, the so-called typhoid
fever. The other organism is <i>Salmonella bongori</i> which was formally classified among subspecies
V. Next, we need to consider <i>Shigella</i>. The <i>Shigella</i> species are <i>Shigella dysenteriae</i>, <i>flexneri</i>,
<i>sonnei</i> and <i>boydii</i>. <i>Sonnei</i> is the most common. These are highly contagious organisms. If you
ingest as few as 180 organisms and that isn't much if you think about the organisms being
maybe 3 microns long and a micron wide. So these are tiny bugs and just ingesting of that few
could give you dysentery. Then another cause is enteroinvasive <i>E. coli</i> which causes acute
dysentery. This one contains a plasmid which encodes a protein that allows the organism to
invade and multiply epithelial cells and also affects actin. It hijacks the actin filament and
enables it to spread cell to cell. Another important cause of acute dysentery is <i>Campylobacter</i>
<i>jejuni</i>. This probably is the leading bacterial cause of foodborne dysentery and it attaches to
intestinal cells and subverts the microtubules in the cell to gain entry and causes rest of the
cell cycle, cell swelling and death. So when someone has a history of acute dysentery, they
obviously need to see a physician and they need a work-up and the first thing we'll do is do a
stool culture and most of these pathogens grow quite well on typical selective agar like
MacConkey's agar. That's the most important test in somebody with acute dysentery. Another
extremely important test is to examine the stool to see if there are white cells present and
I think you can see a number of neutrophils in this particular stool sample and the other thing
I hope you've noticed is the red cells so this patient probably did have bloody diarrhea. So
we're looking for fecal leukocytes and seeing those tells you we've got an invasive problem.
There is a more automated test called the fecal lactoferrin and lactoferrin is a glycoprotein
that you find in the granules of neutrophils and we can test simply for fecal lactoferrin where
it's more difficult to do microscopy on stool and it's more sensitive than doing stool microscopy.
When we have other diagnostic uncertainties, we may have to employ imaging like a CT scan of
the abdomen and occasionally colonoscopy but we wouldn't do colonoscopy on somebody
who's got an active inflammation of their colon unless they had persistent or recurrent disease.