What do bedbugs and norovirus have in common? Well recent research has found that like norovirus, it may take only from one to 10 bugs to cause a full-blown infestation.
It is indeed that low infectious dose that also makes norovirus such a difficult bug to stop in its tracks and brought us recent headlines of 700 sick on one cruise ship alone.
Unlike many viruses that need to gang up on a cell by way of a virus cloud, this extremely low infectious dose is paired with how much virus is shed in vomit or diarrhea. It is the perfect infectious storm able to overcome common everyday hand hygiene measures with ease and causing some 20 million cases of norovirus in the US annually and around 600 to 800 deaths.
Consider this, virus particle counts of up to 10 billion per gram of feces have been detected and it has been reported that the same levels can be shed in vomitus during projectile vomiting. Based on the quantity of fecal material and vomitus shed by an infected person, it is easy to see that there is enough virus shed from one person if spread super-efficiently, to infect practically everyone on the planet. Some gastrointestinal infections play nice by only being transmitted by hand contact, but with norovirus aerosol transmission is all too common with reports of up to 10 million particles aerosolized in a single forceful up-chuck shot.
Not only are public restroom facilities turned into hot spots worthy of avoidance, but during these events ventilation systems become contaminated as well. We have some vivid records of norovirus attacks on food workers where in a 6-hour period, a cake decorator had five episodes of diarrhea and two of vomiting and this is not uncommon. Needless to say the cakes she decorated were highly infectious.
With several hundred people sick at one time it is the microbial equivalent of achieving critical mass and initiation nuclear fission chain reaction. This virus exhibits near ideal microbial characteristics of opportunistic spread, survival in the environment (8 hours to a week, freezing and heat 140 ° F) and a mutation rate that stays at least one step ahead of our protective immune system. These viruses are a model of economy, as a single stranded RNA virus once it gets into a cell it is primed for action and able to take over the cellular machinery, set up “replication complexes” and churn-out hundreds of copies of itself. Without fore warning these cruise ships were sitting ducks for a situation that reaches a tipping point in terms of shipboard health. In the weeks to come, you can be sure that the cruise ship industry will arm themselves to the teeth with everything needed to minimize these outbreaks and eventually turn the corner and get ahead of the curve.
All of this sets the stage for the science around the best methods to remove or kill norovirus on hands. Soils as described above have a major effect in reducing efficacy of any hand hygiene intervention and thus the first focus of public health authorities. Hand washing and effective surface disinfection should be the primary response to norovirus exposure. Because of the real concern for the presence of physical soil when ever norovirus is encountered the CDC and FDA have been opposed of allowing antiviral claims on hand sanitizer products despite accumulating data on some level of effectiveness once soil has been eliminated.
For removal of norovirus (previously termed Norwalk virus or small-round-structured-viruses - SRSV) friction seems to play more of a role than surfactant activity. We need the surfactants in hand soap to get rid of the soil or in technical terms “filth”. There are half dozen scientific articles that show friction during the rinsing phase can be particularly effective against similar small viruses including human norovirus surrogates. The most effective hand sanitizers have been shown to repeatedly do a good job at reducing norovirus counts delivering up to 2 log reduction on hands. It has been credited as an effective tool in outbreak control, but cannot be relied upon as the primary means of preventing infections.
This was seen in the studies published in the last few years looking at infection rates in long-term care facilities where too heavy a reliance on hand sanitizers, operating under conditions dependent on part-time staff and low staff to patient ratios combined contributed to outbreaks. Systematic reviews of interventions also do not identify silver bullets that stop outbreaks in their tracks, but instead show that it is a labor-intensive effort. When all is said and done, frequency that the intervention is carried out is the most commonly identified characteristic of any of the programs described as working. A study by Greig and Lee published in 2012 showed that in healthcare facilities restricting the movements of patients and staff, enhanced environmental cleaning and hand hygiene was key. Shared toilet facilities can literally be a killer, not just for norovirus but for C. difficile as well, another microbial agent even more refractory to hand sanitizer treatment.
The medical, humanitarian and economic impact of norovirus and other virus diseases cannot be underestimated. If there is one constant in the fog of war against virus disease, it is frequency and with norovirus in the cruise ship industry, it will be no different. Like the cruise ship casino, fighting norovirus is a numbers game and the deck is stacked in favor of the virus's superior numbers, therefore frequency rules.
There will be constant roving gangs of sanitation workers, copious amounts of hand sanitizer and rapid response of cleaning crews that will smother human soils with surface disinfectant. With aggressive hand washing and use of strong disinfectants it is easy to damage skin and frequency cannot be sustained without appropriate glove use and hand sanitizers that will provide some kill while at the same time re-nourishing the skin with moisturizers and humectants. Keep safe my friends, wash hands often and use sanitizer for skin protection and back up to good old fashion hand washing.
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