Tag Archives: diagnostic stewardship

“ASA Antimicrobials 2026 Adelaide”

Confessions of a Microbiologist, , ,

I was privileged to go to the ASA Antimicrobials conference in Adelaide last week. Although I have not been to this particular conference for a few years, it is one of my favourites. It is not too big, it has a good mixture of clinical microbiologists, ID physicians and microbiology scientists attending, and the quality of the talks is generally very high. there were very few talks that I did not take anything away from.

Here are a few of the highlights below:

Angela Huttner gave an excellent talk on UTI, and reminded us that the definitions of uncomplicated v complicated UTI have changed, moving more towards extent of infection within the urinary system, and away from host factors. This makes a lot of sense to me, and simplifies things a lot for the lab in terms of testing and reporting.

Angela also reminded the audience that enterococci and Group B streptococci are uncommon causes of uncomplicated cystitis in young women. Voided midstream urine culture and acute cystitis in premenopausal women – PubMed. I will need to go back to my lab and sort out suitable comments to go on enterococcal and Group B strep urinary isolates on this cohort. We almost certainly overplay their significance…

Hemalatha Varadhan informed us that they were no longer culturing central line tips at their institution in NSW, on the grounds of poor sensitivity, specificity, and the fact that it is not required for the definition of a CLABSI. Good for her I thought. If they can do it, why can’t we at our own lab. I will do some reading and have a chat to our stakeholders…

Chris Blyth presented on “newish vaccines” with a focus on RSV, meningococcal and emerging Gp B strep vaccines. He also reminded us that it is one thing to develop new vaccines, it is quite another to persuade people to get them…

Steven Tong presented an update on the legendary SNAP trial for Staphylococcus aureus bacteraemia. A good refresher, and a reminder that further evidence-based answers on SAB management issues are not far away. 

Tony Korman gave us an irreverent but highly entertaining review of 2025: The Year in Clinical Microbiology” and highlighted the debates on Twitter/X such as “Oral is the new IV”, “Shorter is better” and the CRP/ESR “Zombie tests”. Angela Huttner commented on the lack of nuance that sometimes occurs in such debates when the argument is presented in a black and white fashion. 

John Turnidge and his team gave an excellent EUCAST/AUSCAST session. It was a good reminder of the amount of work that goes into antimicrobial breakpoint setting. Tony Korman made the excellent point that implementation of EUCAST guidelines on a practical level is becoming increasingly problematic for diagnostic laboratories and that this should be taken into consideration by the EUCAST team when issuing their annual updates.

I was fortunate enough to be able to present myself at the conference, kindly invited by BD to present on diagnostic stewardship at the BD sponsored lunchtime symposium. Being an inveterate introvert, I was quite nervous to begin with, but soon settled down and got my diagnostic stewardship messages across to an audience which seemed engaged in my presentation (I think!). 

It was my first visit to Adelaide. It is a very nice place, nice climate, friendly people and quite a lot to do. Unfortunately, I did not get a chance to visit the Barossa Valley vineyards, next time hopefully!

Michael

“Sometimes you just have to admit that you were wrong”

Confessions of a Microbiologist, The Science of Microbiology, , ,

Many microbiology laboratories, including my own, have in place a CSF leucocyte count cut-off of 5 × 10⁶/L as a criterion for performing multiplex PCR in the investigation of meningoencephalitis. This diagnostic stewardship policy has attempted to focus testing on those most likely to have CNS infection, and to reduce unnecessary testing. However, growing evidence indicates that this approach is not appropriate when there is clinical suspicion of encephalitis…

Take this hypothetical case study…

A 58-year-old man, Mr J Bloggs, presents with fever, headache, confusion and a vague history of what could be a focal seizure. MRI was unremarkable. A lumbar puncture is performed within eight hours of presentation. The CSF shows a white cell count of 4 × 10⁶/L, normal glucose, and mildly elevated protein. Under existing laboratory policy, the CSF multiplex PCR panel is not performed because the leucocyte count is below 5 × 10⁶/L. Empirical acyclovir therapy is discontinued on the basis of the normal CSF leucocyte count. However, the diagnosis remained uncertain and persistent symptoms prompted a repeat CSF several days later. HSV-1 DNA is detected by PCR on the second CSF sample.

CSF analysis is excellent for detecting meningeal inflammation, as occurs in meningitis, but it is less reliable for parenchymal infection, which characterises encephalitis. In encephalitic processes, inflammation may be largely confined to the brain parenchyma, without a corresponding CSF pleocytosis, especially early in the disease. Leucocyte thresholds designed for meningitis are therefore poorly suited to encephalitis and potentially risk giving false reassurance.

Recent evidence has demonstrated that a substantial proportion of patients with encephalitis have normal CSF leucocyte counts. The most compelling data to date come from a recent large retrospective study by Habis et al., involving 597 adult patients with encephalitis. They found that 25.3% had no CSF pleocytosis (<5 × 10⁶/L). Among those with infectious encephalitis, 19% lacked pleocytosis, and notably, 23.7% of HSV-1 encephalitis cases had normal CSF cell counts at presentation. Patients without pleocytosis were also less likely to receive empiric acyclovir, showing how laboratory thresholds influence clinical care. These findings strongly challenge the validity of using a fixed leucocyte cut-off to determine whether PCR testing should be performed, as it would exclude roughly one in four encephalitis patients, including many with HSV infection.

In addition, and as also shown by Habis et al., patients without pleocytosis are less likely to receive prompt antiviral therapy. This matters because early treatment, particularly for HSV encephalitis, improves outcomes. Diagnostic stewardship should promote timely, appropriate testing, not create barriers based on outdated assumptions…

Laboratory protocols should always be responsive to new data. When high-quality evidence emerges that challenges existing practice, policies must be reviewed and revised. While a 5 × 10⁶/L CSF leucocyte threshold may remain reasonable in the investigation of suspected meningitis, it is no longer valid in the setting of suspected encephalitis, where pleocytosis may be absent in a substantial proportion of cases. Stewardship frameworks should incorporate these distinctions, and most importantly, allow flexibility in order to optimise patient safety.

Laboratory practice must evolve with emerging data to ensure that diagnostic stewardship supports, rather than hinders, accurate and timely diagnosis. I am a diagnostic stewardship enthusiast, but I am the first to admit that we don’t get it right all the time.

Michael

p.s. Check out this great editorial on this topic!

References

“Less is more in the microbiology laboratory?”

The Art of Microbiology, , ,

I am by nature quite a lazy person. Don’t get me wrong, I am not afraid of working hard at times, but I am always on the lookout for ways in which I can optimise the productivity and the quality of the laboratory, whilst creating time and resource for other opportunities.

Time and effort are terrible performance metrics…

Aside from efficiencies, can doing less work in the microbiology laboratory actually lead to better patient outcomes? We know that our ultimate aim is to improve patient management. Are there circumstances where in our enthusiasm to optimise patient care, we might actually do the opposite?

Here are some examples where doing less work in the microbiology lab might actually be beneficial to patient care:

Minimising work up on probable contaminants – If coagulase negative staphylococci isolated from blood cultures are routinely reported with susceptibility profiles without any supporting clinical information that they might actually be significant, this will lead to unnecessary antibiotic use with the potential for adverse effects, along with the potential for delayed patient discharge.

Avoiding tests with low clinical utility – Sputum cultures in the community setting are rarely useful, and the results may lead to undertreatment, overtreatment or simply the wrong treatment.

Reducing unnecessary microbiology tests– Rejecting urine cultures from patients where there is no evidence of UTI symptoms on the request form prevents unnecessary treatment of these patients with antibiotics.

Not processing duplicate specimens – Rejecting repeat samples (e.g. urine, sputum, stool) submitted on the same day from the one patient means that conflicting results are avoided.

Avoiding overuse of broad-range multiplex PCR panels – Running a full respiratory viral panel for a simple upper respiratory tract infection may end up delaying patient discharge from hospital. More targeted testing is often better.

Following proper sample collection and rejection criteria – Rejecting poorly collected specimens (e.g., saliva instead of sputum for pneumonia testing) avoids misleading results and unnecessary treatments.

Optimised result reporting – For example, reporting Group C/G beta-haemolytic streptococci from throat swabs in patients with acute pharyngitis may lead to unnecessary antibiotic prescribing. Along the same lines, testing and reporting unnecessarily broad antibiotics when performing susceptibility testing can lead to unnecessarily broad antibiotic coverage with concomitant side-effects on the patient and selection of antibiotic resistant bacteria.

As demonstrated above, there are lots of ways in which doing less work in the microbiology lab is not only cost-efficient, but it can also improve the overall management of the patient.

As the range of different assays we are able to offer in the microbiology lab continues to increase, we need to constantly review our current test repertoire and whether it is providing significant value to the clinicians, and ultimately the patient.

Less is often more when it comes to the microbiology laboratory.

Michael