Reflections from HIS 2014, Part I: Updates on C. difficile, norovirus and other HCAI pathogens

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The 2014 Healthcare Infection Society (HIS) Conference was in Lyon, France, and combined with SFH2 (The French Society for Hospital Hygiene). Congratulations to all involved (especially Martin Kiernan and Prof Hilary Humphreys) for such a stimulating programme, and enjoyable conference. The abstracts from the oral presentations can be downloaded here, and the posters here. I plan to share some of my reflections on key conference themes over the next few days:

Prof Wing-Hong Seto – Airborne transmission and precautions – facts and myths

Prof Seto’s energy and enthusiasm lit up the stage, just like a few years ago in Geneva for ICPIC. Prof Seto spent his lecture convincingly debunking the idea that airborne transmission of respiratory viruses is common, notwithstanding some data that, prima facie, suggests this. Only very few pathogens require obligate airborne transmission (e.g. TB); some have preferential airborne transmission (e.g. measles); and some have potential airborne transmission (respiratory viruses). There is some evidence that respiratory viruses such as influenza can be transmitted via the airborne route, but the most important route of transmission will depend on context. One important point is that studies demonstrating airborne “transmission” using PCR rather than viral culture as an endpoint, or using artificial aerosol generation should not be taken as definitive evidence of airborne transmission. Prof Seto’s view is that medical masks are sufficient to prevent the transmission of respiratory viruses, as demonstrated by his own work during SARS. Finally, we can forget the requirement for negative pressure isolation rooms: open doors and windows yields a whopping 45 air changes per hour!

Prof Mark Wilcox – Is Clostridium difficile infection (CDI) underestimated due to inappropriate testing algorithms?

Prof Wilcox began by reporting an unusual epidemic: “PCRitis”, which can cloud rather than clarify accurate diagnosis of CDI. Perhaps the most important point made by Prof Wilcox is that the ultimate “gold standard” for CDI should be clinical, and not laboratory based. Prof Wilcox spent most of his time reflecting on the recent multicentre European study of CDI underdiagnosis in Europe. There are some real shockers in here: the reported rate of CDI in Romania was 4 cases per 1000 patient days vs. closer to 100 per 1000 patient days when samples from the same patients were tested in the reference lab. This is no surprise in a sense because only 2/5 local laboratories were using optimal methods. However, even in the UK where around 80% of local labs are using optimal methods, around 2-fold more cases were identified in the reference vs. the local laboratory. Clearly, if we’re going to have a hope of controlling the spread of C. difficile in Europe, laboratory diagnosis needs to improve.

Norovirus

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Norovirus is especially topical in the UK given the recent PHE announcement about unusually high rates of norovirus in the NHS. The prolific Dr Ben Lopman (CDC) began by explaining the ‘image problem’ that norovirus has in US hospitals, where it is considered an uncommon cause of gastroenteritis. In fact, a systematic review found that norovirus cases around 20% of acute gastroenteritis. However, I would say it’s just not possible to get an accurate assessment of how common norovirus is on a population level due to chronic under-reporting. When we had an outbreak of ”norovirus” in the Otter household, the last thing we felt like doing was submitting a specimen, and I suspect we are not alone in this! Although norovirus is usually mild and self-limiting, it is by no means benign: one Lopman study suggested that it is responsible for 20% of deaths due to gastroenteritis not caused by C. difficile in those ages >65. And then there’s the infection control challenges. Due to the exquisitely low infectious dose, 2g of stool from an infected individual is enough to infect the entire human population! Plus, it is shed in high titre, stable in the environment, and resistant to many disinfectants. Rather depressingly, it seems that effective interventions to control norovirus teeter around the cost-effectiveness threshold. More optimistically though, prospects for vaccines look promising.

Prof Marion Koopmans then described the huge diversity within the “norovirus” family, spanning more phylogenic space than many single species occupy. For chapter and verse on nomenclature, see Norovirus Net. It’s difficult to know what works to control norovirus due to dynamic outbreak settings combined with multiple interventions. One key aspect for control is understanding shedding profiles of infected, recovered and asymptomatic individuals. Whilst all can shed norovirus, much like Ebola, those who are symptomatic are by far the highest risk for transmission. Finally, our inability to culture norovirus in the lab has been an important barrier to understanding the virus; a recent study (in Science no less) suggests that a working lab model for culturing norovirus may be just around the corner.

Dr Lennie Derde – Rapid diagnostics to control spread of MDR bacteria at ICU

Given the turnaround times of conventional culture (24 hours to preliminary results – at best), rapid PCR-based diagnostics make sense in principle. But do they work in practice? There is some evidence that rapid diagnostics may work to reduce MRSA transmission, although other studies suggest that they don’t make a difference. In order to put rapid diagnostics to the test Dr Derde et al. ran the impressive MOSAR study. This study suggest that screening and isolation by conventional or rapid methods does not help to prevent the transmission of MDROs in the ICU, but I don’t think we should take that away from this study, not least due to the fact that many units were already doing screening and isolation during the baseline period!

New insights from whole geneome sequencing (WGS)

WGS is trendy and trending in the infection prevention and control sphere. Prof Derrick Crook gave an engaging overview of the impact that WGS has made. It’s analogous to the manual compilation and drawing of maps to GPS; you wouldn’t dream of drawing a map by hand now that GPS is available! Desktop 15 minute WGS technology will be a reality in a few years, and it will turn our little world upside down. The major limiting step, however, is that mathematics, computer science and computational biology are foreign to most of us. And we are foreign to most of them! But, these issues are worth solving because the WGS carrot is huge, offering to add new insight into our understanding of the epidemiology of pathogens associated with HCAI. For example, Prof Crook WGS study on C. difficile suggests that transmission from symptomatic cases is much less common than you’d expect. So if the C. difficile is not coming from symptomatic cases, where is it coming from? Contact with animals and neonates in the community are plausible sources However, I was surprised that Prof Crook didn’t mention the large burden of asymptomatic carriage of toxigenic C. difficile, which must be a substantial source for cross-transmission in hospitals.

WGS has yielded similar insight into the epidemiology of TB and MRSA, outlined by Drs Timothy Walker and Ewan Harrison, respectively. One challenging idea from Dr Harrison is how much of the “diversity cloud” that exists within an individual is transferred during a transmission event? Finally, WGS can turn a ‘plate of spaghetti’ of epidemiological links to a clear transmission map, as was the case during a CRE outbreak at NIH in the USA.

Look out for some more reflections from HIS posted over the next few days…

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