Sunday, July 05, 2009

More on Salmonella and mycotic aneurysms

If my recent post on this subject seems a little dry go read the case report by Lisa Sanders in a recent issue of the New York Times magazine. Because Salmonella mycotic aneurysm is a very uncommon presentation of a not so common disease and presents with nonspecific symptoms it's likely to unfold as a mysterious case.

Dr. Sanders commented:

I published a similar case in a very different forum, the New York Times Magazine. I think the case gives a sense of how this might unfold in real time...

The patient presented with fever, back pain and confusion. The resolution of the case:

The radiologist called as soon as the scan was done. There was no abscess on the spinal cord, but the patient's aorta had weakened and the pressure of the blood flow had caused the tube to bulge like a worn garden hose. He was also concerned that this weak spot had sprung a leak....

...the patient was rushed to the operating room.

The left side of his abdominal cavity was filled with blood, and parts of the normally thick tube of the aorta were in tatters. The surgeon quickly replaced the shredded portion of the aorta and sent the dissected bits to the lab. Under the microscope, it became clear what had caused all of this man's symptoms. The tissue had been invaded by a bacterium -- an unusual type of salmonella, one usually found in uncooked pork. This bug -- salmonella choleraesuis...

So what is Salmonella choleraesuis? I have always been confused by the taxonomy of Salmonella. In my post I mistakenly said:

Species associations, according to the brief review, tend to be enteritidis and typhimurium.

Well, after a little digging it turns out that those aren't species. They're serotypes, also known as serovars. (I plan to make the correction). Salmonella choleraesuis is indeed a species. One popular classification denotes this species, which contains many serotypes and is also called Salmonella enterica, as the one which accounts for virtually all human Salmonella infections. The patient in the New York Times report apparently had an unusual organism acquired from uncooked pork, so maybe the name choleraesuis, referring to pigs, denotes something more specific in another classification. I've consulted Cecil, Robbins pathology and a micro textbook and am still more than a little confused.

That's all beside the point of Dr. Sanders's article but one distinction does bear emphasis. This situation, bacteremia causing vascular infection complicated by mycotic aneurysm, is not the same thing as enteric fever, aka typhoid fever.

Image: Salmonella invading cultured human cells. Public domain. Source Wikipedia.

No comments: