An unusual and interesting outbreak of CPE was published recently in Clinical Infectious Diseases. Several key points: don’t rely solely on a PCR detecting the “Big 5” carbapenemases (NDM, KPC, OXA-48, IMP, VIM) – at some point you need to test for phenotypic carbapenemase activity; WGS can really help us in unravelling complex transmission routes; and covert plasmid propagation within and between species is a reality.
A fascinating study from a European research group has unravelled the molecular epidemiology of a large European collection of carbapenem-resistant Klebsiella pneumoniae clinical isolates. Most carbapenem resistance was due to an acquired carbapenemases, transmission clusters were common within and between hospitals, carbapenemase-producing isolates are more likely to spread in hospitals, and 21 SNPs is the magic number for defining CPE person-to-person transmission using WGS.
In a remarkable quirk of academic publishing, two virtually identical studies by separate research groups in the UK (one in London, and one in Cambridge) published a week apart have come to the same conclusion: that we are missing a sizable portion of MRSA transmission by focussing solely on wards in a single hospital. A referral-network level view is required for an accurate picture of MRSA transmission. (You may have seen some press about the Cambridge article, e.g. on the BBC here.)
I posted a blog a couple of years ago (was it really that long!) on a fascinating study suggesting that only 1/5 of S. aureus in hospital patients is hospital-acquired. My key conclusion from that study was that the number of potential sources for S. aureus that the team investigated was inadequate to draw any firm conclusions (they didn’t include staff, surfaces, or visitors). I concluded that ‘the next frontier of transmission mapping must be a more comprehensive evaluation of other potential sources…’. The authors must have been reading, because this study from the same group was published recently in Lancet ID, which is a more comprehensive evaluation of other potential sources.
A PNAS paper on the genomic diversity of carbapenemase producing bacteria in the US reports strong evidence of carbapenamase (an enzyme produced by bacteria that breaks down carabapenem antibiotics) activity but no sign of a carbapenemase gene. This provides a timely reminder that we are only really scratching the surface in our understanding of carbapenemases and how they work.
A groundbreaking study just published in PLOS Genetics provides new insight into the transmission dynamics of bacteria in the ICU setting using WGS. The ambitious authors performed WGS on virtually all bacterial isolates from ICUs in a US hospital for a year. The first surprise was that 12% of the bacteria considered clinically relevant were previously undescribed.
The next – and perhaps biggest – surprise was that whilst transmission of the usual suspect pathogens (MRSA, VRE etc) was rare, 9% of the other bacteria were shared by multiple patients, often with overlapping admissions (see the figure below). This suggests that there is a fair bit of transmission going on under the radar in the ICU setting.
Figure: Clonal lineages extending across multiple patients.
This study reminds me of one published in CID a few years ago showing that outbreaks of resistance probably occur regularly and usually undetected across multiple species.
So, is it time to start using WGS for all bacteria identified in the clinical laboratory? Not quite yet I don’t think: the analytical methods have not yet caught up with the sequencing technology. But this study is a glimpse of the future, no doubt about it.
Now that you have digested your Christmas turkey, I thought that it would be a good time to send out an update. These articles have been posted since the last update:
- Who’s harbouring CRE? (Published 22nd December 2014)
- ECDC data shows progressive, depressing increase in antibiotic resistance in Europe (Published 16th December 2014)
- Is deliberately seeding hospital rooms with Bacillus spores a good idea? No, I don’t think so either! (Published 8th December 2014)
- Filling the gaps in the guidelines to control resistant Gram-negative bacteria (Published 2nd December 2014)
- Journal Roundup November 2014: Journal Roundup: Ebola (again), The rise (and rise) and fall of MRDOs & Infection Prevention 2014 (Published 28th November 2014)
- The inanimate environment doesn’t contribute to pathogen transmission in the operating room…OR does it? (Published 27th November 2014)
- Being bitten by antibiotic resistant CRAB hurts! (Acinetobacter that is.) (Published 25th November 2014)
- Reflections from HIS 2014, Part III: Education, communication, and antibiotic resistance (Published 21st November 2014)
- Reflections from HIS 2014, Part II: Dealing with the contaminated environment (Published 20th November 2014)
- Reflections from HIS 2014, Part I: Updates on C. difficile, norovirus and other HCAI pathogens (Published 19th November 2014)
- What’s trending in the infection prevention and control literature? (Published 16th November 2014)
- HIS Poster Round: Dealing with contaminated hands, surfaces, water and medical devices (Published 15th November 2014)
- Carbapenem-resistant Enterobacteriaceae (CRE): so what should an infection prevention and control team do now? (Published 11th November 2014)
- A postcard from Portugal: “Some days we don’t have any needles on the ICU” (Published 5th November 2014)
- Ebola: infection prevention and control considerations (Published 30th October 2014)
- ID Week 2014 as seen by an Infection Preventionist (Published 28th October 2014)
- Selective Digestive Decontamination (SDD) is dead; long live faecal microbiota transplantation (FMT) (Published 27th October 2014)
I’m in a rather reflective mood, so time to remind you of some of the key themes from 2014: Ebola, MERS-CoV, universal vs. targeted interventions, faecal microbiota transplantation (FMT), whole genome sequencing (WGS), carbapenem-resistant Enterobacteriaceae (CRE), and some interesting developments in environmental science. And what will we be still talking about come Christmas 2015? Let’s hope it won’t be Ebola, and I think that WGS will be a lab technique akin to a Vitek machine rather than subject matter for NEJM. But I think we still have ground to cover on whether to go for universal or targeted interventions, FMT, and improving our study designs in infection prevention and control. I can also foresee important studies on the comparative and cost-effectiveness of the various tools at our disposal.
And finally, before I sign off for 2014, a classic BMJ study on why Rudolf’s nose is red (it’s to do with the richly vascularised nasal microcirculation of the reindeer nose, apparently).
Image: Christmas #27.