Monthly Archives: December 2016

“Trending…”

Antimicrobial Resistance, Confessions of a Microbiologist, Data Interpretation,

I get the occasional anxious phone call from clinicians concerned about the “rising rates ” of trimethoprim resistance to E. coli…

Not being entirely convinced, I did a (20 year) search for E. coli resistance to trimethoprim at my lab, analysing over 2 million isolates, and came up with the following graph.

capture

 

I couldn’t work out how to insert a trendline into the graph (I am so useless…), but I think you will agree that it is going to be fairly flat.

The antibiotic apocalypse is not arriving in New Zealand anytime soon. In fact the whole concept of “antibiotic resistance” as perceived by the public is horribly generic and oversimplified…

This example above of course is just one microbe/antimicrobial combination out of many hundreds that could have been analysed, but the observation did highlight a couple of things to me:

  • If antibiotic usage is relatively constant in a population over a prolonged period of time, then antimicrobial resistance does not necessarily rise inexorably. (q.e.d.)
  • Always back your claims up with objective data wherever possible. It is the trends which are critical in the surveillance of antibiotic resistance. We are lucky that at my lab we can now search back through 20 years of electronic data. Before 1996 the data was paper based (and likely lost in a basement or incinerated by now!)

If you did a similar exercise for all the possible microbe/anti-microbial combinations (I just might if the Christmas holidays are quiet!), you will find some trends that are upwards, some that are static, and some where the resistance rate is trending downwards.

A bit like Twitter really….

So when someone says to you. “Antibiotic resistance is increasing all the time. In 10 years time, all infections will essentially be untreatable” (I really detest this type of generic, off the cuff, unsubstantiated statement…)

…you should respond with something along the lines of “Exactly which microbe and antimicrobial combination are you talking about?” and “Show me your data…”.

Some infections will be, and already are, untreatable (mostly due to extreme and focused selection pressure), but the chances of a whole bacterial species becoming pan-resistant are remote. There are two main reasons for this. i) Bacteria survive in open systems, and ii) Bacteria need to expend energy to become resistant.

But these are other stories altogether…

Michael

“Creating a rod for your own back”

Antimicrobial Resistance, The Science of Microbiology,

la34808Treatment of sexually transmitted diseases in most places in the world is empiric in nature, based on the presenting clinical syndrome of the patient. A generation ago, the laboratory diagnosis of STDs was fairly rudimentary. No NAAT testing, viral culture and serology only for HSV, etc. Add this to the fact that getting some of the patients back for a second visit isn’t always easy and it is easy to understand why the Sexual Health community have traditionally gone for this model of care.

However things are changing, and changing fast… 

Our ability to accurately diagnose STDs has increased markedly over the past decade. C. trachomatis, N. gonorrhoeae, HSV are now all routinely diagnosed by NAAT testing in most laboratories. “Emerging” organisms such as Mycoplasma genitalium are now coming onto the radar of STD clinicians, primarily because we can now diagnose it…

Whilst empiric treatment works (most of the time anyway), it does have its downsides. Empiric therapy on a population basis usually leads to overtreatment. Resistance to N. gonorrhoeae has reached worrying levels for both fluoroquinolones and ceftriaxone. Resistance of M. genitalium to macrolides has been increasing, most probably in areas where azithromycin is used empirically for urethritis.

We need to be careful we don’t create a rod for our own back…

It may be that Sexual Health needs to start exploiting the progress in laboratory diagnostics that has been made over the past few years and start moving away from empiric based management of STIs. Some NAAT tests are now available (e.g. Cepheid CT/NG) that can give a result in around 90 minutes. Thus it could theoretically be possible to see the patient, take the samples, send the patient away for a coffee, test the samples in the clinic with an automated benchtop PCR analyser, and see the patients back in an hour or two with the results and directed management.

This might well be the future of STD clinics…

Michael