Being someone who travels a lot between Korea and China, friends ask various questions about the MERS outbreak. Chief among these concerns are: “isn’t it dangerous to fly on planes that have been contaminated?” and “what can we do to protect ourselves?” Allow me to calm the waters with some proper science.
By this point, it is common knowledge a number of MERS patients have used public transportation. International flights, domestic trains, and buses have no doubt been coughed on and touched by several infected individuals. But the question is: do these vessels pose a threat to the next set of passengers?
As noted in the media, the MERS virus is very similar to cold viruses. When we catch a cold and sneeze or cough, the virus particles are ejected into the air on small droplets of liquid from our mouth, nose, and lungs. These droplets can drift several meters before landing.
Most viruses, including colds and MERS, are not very stable outside of our bodies. Cold viruses, for example, usually become completely inviable (incapable of infecting) within 24 hours after landing on an exposed surface. This is one of the reasons why you can live in the same house as an infected relative without getting sick.
One of the key factors promoting loss of virus viability is dehydration. In order to function, viruses require water. Not surprisingly, viruses stay viable much longer if they land on wet surfaces and lose viability faster if they land on dry or absorbent surfaces. Most research I have seen suggests cold viruses tend to last only about 4-7 hours on dry surfaces. This time can be shortened even more if exposed to sunlight.
What about MERS? Work from Dr. Vincent Munster's lab at the NIH has demonstrated MERS viability is nearly identical to cold viruses: on dry surfaces, viability lasts only about 5-6 hours. It is for this reason buses, trains, and airplanes known to have transported infected individuals are not removed from circulation. It is also for this reason people rarely get sick even when making contact with objects or surfaces patients have coughed on several hours ago.
Now let's talk about prevention. In many ways, sanitary masks have become the symbol of the Korean fight against MERS but are they really helpful? A common misconception is that virus must enter our nose or mouth through the air. The truth is viruses enter our nose and mouth more frequently through objects we touch. A napkin we use to clean our nose, the food we eat, a pen we chew on during class, our computer mouse or keyboard, all of these objects can function as reservoirs of virus that infect our hands, resulting in subsequent infection through our nose or mouth. Another very common route, particularly in children, is rubbing eyes with infected hands.
Sanitary masks, therefore, are not particularly effective preventatives because they only guard against virus dispersed in the air. If someone coughs on your food and you eat it, the mask will not help you. The mask does, however, function well in containing virus. For example, if you are an infected individual, the mask will usually hold back about 60% of the particles you cough or sneeze, offering protection for those around you.
What about hand sanitizers? Most sanitizers marketed for public consumption contain alcohol (ethanol or isopropanol). These alcohols disinfect by disrupting cell membranes, which are made up of oil molecules. Not all viruses have these membranes but, luckily for us, coronaviruses like MERS and most colds do, making alcohol sanitizers particularly effective.
Experiments from Dr. Mark Sobsey’s lab at the Center for Disease Control have demonstrated a 60-second exposure of coronavirus to sanitizers containing 60% or more alcohol can result in a reduction of virus by over 99%. And although the length of this exposure is much longer than what you get by rubbing sanitizer on your hands, it is still compelling evidence they should be effective.
When buying alcohol sanitizers, look for two things. The first is alcohol concentration. The lower concentrations are likely less effective so choose products with 60% or more. A second consideration is age. Alcohols are prone to evaporation. If the container is left open or the product is old, chances are the alcohol concentration has decreased.
Safe travels, everybody.
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