Tag Archives: antimicrobial susceptibilities

“Reporting susceptibilities on UTIs, not urinary isolates…”

Antimicrobial Resistance, Antimicrobial Stewardship, , , ,

Urines arrive at diagnostic microbiology laboratories in considerable numbers. My own lab in New Zealand processes a couple of thousand urines a week. A significant proportion of these will have positive cultures. Therefore, the potential for the laboratory to promote good antimicrobial stewardship with respect to urinary tract infection is considerable.

My mantra on this is as follows: “The microbiology lab should never release antibiotic susceptibilities on a positive culture from a urine sample unless there is reasonable evidence accompanying the request that the patient has a UTI.”

The fact that the urine sample has turned up at the microbiology lab is insufficient evidence per se that the patient has a UTI. Urines get sent to microbiology laboratories for all sorts of spurious reasons, see below for a few examples:

  • Urines often get sent “automatically” from acute receiving wards as part of a blanket laboratory screen, where the patient may have a diverse spectrum of symptoms such as chest pain, shortness of breath, collapse, etc.
  • Urines can get sent from Long Term Care Facilities when someone decides to dipstick all their patients and send the urine samples with positive dipsticks to the lab for culture. Yes, it happens, and a lot more often than you might think!
  • Urine from indwelling catheters can get sent when the patient has a blocked catheter, or the catheter bag is cloudy.
  • Urines from patients attending outpatient clinics should also raise a flag. With the exception of urology clinics, patients who attend a pre-planned elective clinic appointment generally do not have an acute UTI. The same principle can apply for patients who are in hospital wards for other reasons.
  • Urines where the clinicians are looking for other tests, i.e. albumin/creatinine ratio, and due to laboratory processes the urine ends up getting cultured as well…

So, my argument is that if a urine sample turns up at the laboratory without any clinical details or with inappropriate clinical details, the lab is under no obligation whatsoever to release antibiotic susceptibilities on any organisms grown. 

The best approach of course is not to process the sample at all unless relevant clinical details are received. I would regard all of the following clinical details as being unacceptable to justify proceeding to urine culture:

  • No clinical details
  • Cloudy urine
  • Concentrated urine
  • Dark urine
  • Smelly urine
  • Urine dipstick urinalysis results only
  • Routine/monitoring/screening urine
  • Fatigue
  • Increased CRP
  • Lots of other non-specific symptoms!

The easy option for the lab of course is just to accept the sample, report the organisms, and the accompanying susceptibilities. However, this is almost certainly not the best way…

Michael

“A Question of Significance”

Confessions of a Microbiologist, , ,

We may not always realise it, but reading and reporting bacterial cultures often involves several decisions, which are often performed sub-consciously. What do we work up on the agar plates? What do we report? How do we report it?  Do we perform and report susceptibilities? Should we add a comment to the report? All these decisions influence how the result is perceived and acted upon by clinicians. Don’t underestimate the influence that the microbiology report can have on how the patient is subsequently managed.

For example, let’s say we receive 5 theatre samples from a patient undergoing a routine prosthetic joint revision, and 1 of the 5 samples has a light growth of Staphylococcus epidermidis. If we report this out with antibiotic susceptibilities, and without a qualifying comment, there is a decent chance that the orthopaedic surgeon will act on this result and the patient may well end up on several weeks of antibiotics. On the other hand, if we suppress the susceptibilities, and add a comment stating. “This result is of doubtful significance. Clinical correlation is required. Antibiotic susceptibilities are available on request.”, then it is very likely that the surgeon will simply note the result and observe the patient.

On the other hand, if we isolated a Cutibacterium acnes from a shoulder aspirate in a patient with a history of rotator cuff repair, then it is likely that this isolate is significant and we should convey the result as such, along with antimicrobial susceptibilities.

Best of all in these cases of course is to liaise directly with the requestor/clinician/surgeon, so that further clinical details can be obtained, the likely significance can be better ascertained, and a subsequent management plan developed. However, this is not always possible, nor practical for every single patient.

Whilst I always encourage pragmatic reporting, one needs to be aware of the potential consequences of reporting something as a likely contaminant. I.e. What if this organism is genuinely causing infection? What are the likely consequences for the patient if it has not been reported as such? Can we obtain further samples for culture to confirm or negate the initial result? With sterile site samples & blood cultures, obviously the stakes are higher than with a simple wound swab, but the same principles apply for both scenarios.

Over-reporting of organisms on agar plates is often driven by inexperience or fear. I have seen it many times in my career. Scientists and clinical microbiologists alike are responsible for ensuring that over-reporting of results is minimised. This is very much a team game. In particular, colonies thought to represent plate contamination should hardly ever make it on to the laboratory report. Along the same lines, when an obvious pathogen, e.g. Staphylococcus aureus is found on a mixed plate, to what extent should the other organisms be worked up and reported. If a plate is clearly growing a mixture of enteric organisms, you need a very good reason not to report it as mixed enteric flora, and leave it at that.

The “easy way out” for the microbiology scientist and the clinical microbiologist is to report everything that is found on the plate along with antimicrobial susceptibilities, and then let the clinician make head or tail of it. However, this is dumbed down microbiology and often leads to sub-optimal management of the patient.

Michael