Can the microbiology lab give too much information to the clinicians?

Take the following hypothetical example regarding reporting of enteric type organisms:

Patient X presents with acute appendicitis with perforation. They are taken to theatre for appendicectomy and peritoneal washout, and started on IV cefuroxime and metronidazole. The sample of peritoneal fluid is returned from the microbiology lab as being “mixed enteric flora”. the patient recovers well, and they are discharged after 3 days on oral co-amoxiclav to complete a 1 week course of antibiotics.

Patient Y presents with acute appendicitis with perforation. They are taken to theatre for appendicectomy and peritoneal washout, and started on IV cefuroxime and metronidazole. However, in this patient, the microbiology lab decides to work up the individual organisms in the peritoneal fluid sample. The report states that the patient has grown an ESBL E.coli, an Enterococcus faecium, a Pseudomonas aeruginosa and a Candida albicans. Even though the patient is recovering well, the clinician feels obliged to cover the organisms that the micro lab has grown and reported, and changes the antibiotic therapy to meropenem, vancomycin and fluconazole. The patient unfortunately develops a bout of Clostridium difficile diarrhoea (!), extending their hospital stay by a week.

Microbiology labs can get very nervous about reporting “mixed enteric flora” from sterile site samples. They really shouldn’t be.

Here are a few pointers as to when it may be reasonable for the microbiology laboratory to report “mixed enteric flora”

• Non-sterile site samples:- almost always
• When several organism types are present- the number of different microorganism types present in a sample is inversely proportional to the value the lab can provide to the clinician
• When no specific organism is dominant over the others
• When source control has been achieved-this is important as in the hypothetical example above.
• Drain samples- generally of low value unless the drain has just been inserted
• When the clinical microbiologist has liaised with clinical team and clear that patient is doing well on current therapy- Treat the patient, not the result.

Such an approach saves the lab time and money, and may also be beneficial to the patient, as demonstrated above. Sometimes in our efforts to do the right thing, we end up trying just a bit too hard…

Michael