Monday, December 31, 2012

Vomiting Larry And His Aerosolized Norovirus


Credit UK’s Health & Safety Laboratory


# 6812


Sounding vaguely like an invention lifted from one the Tom Swift books of my youth (e.g. Tom Swift and His Atomic Earth Blaster, Tom Swift and His Electric Rifle), Vomiting Larry is a dummy that . . . well, vomits.

All in the name of science, of course.


In order to test how well (and how far) Norovirus (aka `The Winter Vomiting Bug’) can spread through the air, scientists have created a dummy that spews. A move, I suspect, prompted primarily by a lack of willing  human volunteers for this study.


By adding a florescent dye marker to Larry’s `vomitus’, researchers at the UK’s Health & Safety Laboratory have determined that droplets – too small to be readily seen – can end up as far as 3 meters away from the source.


Vomiting Larry featured on the BBC website


Winter Vomiting bug has been very much in the news of late due to the recent major outbreaks of norovirus, which causes this illness. A recent article on the BBC news website has highlighted the work that the Health and Safety Laboratory has done to establish the extent with which the surrounding environment becomes contaminated when an individual vomits.


This is an important consideration for infection control during outbreaks of norovirus where the key symptom is projectile (forced) vomiting. Catherine Makison of HSL's Occupational Hygiene Unit has developed a humanoid simulated vomiting system affectionately known as "Vomiting Larry".


"Larry" was primed with a vomitus substitute (to which a fluorescent marker was added so as to identify even small splashes post vomiting), and simulated vomiting was carried out. As the BBC video shows graphically, these tests demonstrated the full extent of room contamination post vomiting and that small droplets can spread over three metres from the "Larry" system, which are not easily visible under standard white hospital lighting.


HSL studies have shown that Norovirus can be isolated from these small droplets at concentrations capable of causing an infection. This information might highlight why this robust and highly infectious virus is transmitted between people so readily.


The outcomes of these studies have contributed to reviews of healthcare guidance in hospitals and are due to be published in relevant journals in the near future.


The role of direct aerosolized human-to-human transmission of norovirus remains less than clear, although there are numerous anecdotal reports that suggest that it happens.


The CDC – in a an MMWR report from 2011 called Updated Norovirus Outbreak Management and Disease Prevention Guidelines describes transmission thusly:



Norovirus is extremely contagious, with an estimated infectious dose as low as 18 viral particles (41), suggesting that approximately 5 billion infectious doses might be contained in each gram of feces during peak shedding. Humans are the only known reservoir for human norovirus infections, and transmission occurs by three general routes: person-to-person, foodborne, and waterborne.


Person-to-person transmission might occur directly through the fecal-oral route, by ingestion of aerosolized vomitus, or by indirect exposure via fomites or contaminated environmental surfaces.



And last May, in Norovirus: The Gift That Keeps On Giving, we looked at an incident involving a girl’s soccer team where 17 girls were exposed via a reusable grocery bag, likely contaminated from an airborne route.




While one of the keys to prevention is good hand hygiene, unlike with many other bacteria and viruses, alcohol gel doesn’t do a particularly good job of killing the virus (see CMAJ: Hand Sanitizers May Be `Suboptimal’ For Preventing Norovirus).


Which makes a good old fashion hand scrubbing with soap and water the best preventative.


As new studies that show the aerosolized spread of noroviruses are published, hospital infection control policies may need to revisit the use of facemasks for HCWs caring for infected patients.