“Weighing up the evidence…”

  • There are some microbiology results which point so strongly towards a particular clinical diagnosis, that even counter-evidence should not put you off the scent without investigating further…

For example:

  • An Enterococcus faecalis growing in 6/6 blood culture bottles in a patient with a prosthetic valve suggests infective endocarditis, even if the trans-thoracic echo is “normal”.
  • A Streptococcus gallolyticus growing from a blood culture is suggestive of a colorectal adenoma or adenocarcinoma, even if the patient has no symptoms or colorectal history. (this bacterium was formerly called Streptococcus bovis)
  • A Bacteroides fragilis isolated from a blood culture is suggestive of an intra-abdominal collection or intestinal micro/macro perforation, even if the abdominal examination is unremarkable.
  • A Fusobacterium necrophorum isolated from the blood cultures of a young adult is suggestive of Lemierre’s syndrome, even if the patient is not complaining of neck pain.
  • 2 or more different enterobacteraciae isolated from a CAPD fluid is suggestive of a bowel perforation, even if the patient is not systemically unwell.
  • An Aspergillus species isolated from 2 or more sputum samples is suggestive of architectural lung disease, even if the patient has no history of such.

Sometimes microbiological evidence is ignored by clinicians. 

What are the reasons for this?

Sometimes the result is thought to represent contamination. Sometimes the result is ignored due to lack of knowledge. And occasionally it is just plain denial.

Part of our job as microbiologists is to make clinicians aware of the strength of the microbiological evidence, so that a prospective diagnosis is not dismissed lightly….


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