Ever since the beginning of the Covid-19 pandemic, we have known that it is a highly contagious disease. It first came to the attention of the world when hundreds of people on the Diamond Princess cruise ship became ill and nine passengers died. The ship had taken on an infected passenger who had recently been in Wuhan, China. Even though that passenger left the ship at its next port of call, the damage had been done. Restricting passengers to their cabins did not halt the spread of the virus.
Cruise companies are very well acquainted with viral diseases at sea, and have developed effective procedures against them. Noroviruses have traditionally been the bane of cruise ships, but the disease caused by the SARS-Cov-2 coronavirus, which later came to be called Covid-19, was more serious than anything that the cruise industry had confronted before. In fact it was more serious than any disease that the world had faced in a hundred years.
At first, there was a lot of speculation about how the disease was being transmitted from one person to another. One idea was that droplets containing virus particles were expelled from people’s mouths when they spoke, shouted, sang, or otherwise expelled air from their mouths, while in close proximity to another person.
Another idea was that the virus was spread by fomites. These are viral particles expelled by an infected person that land on surfaces which are then touched by an uninfected person. If that person then touches her eyes, nose, or mouth, the virus can cause an infection. We all make those kinds of touches several times a day without even thinking about it.
As a defense against virus-laden droplets in the air, we have all been advised to wear a mask, preferably an N95 mask, to protect our mouth and nose from a viral invasion. This still leaves our eyes as possible entry points for a virus. For that reason, goggles are part of the personal protective equipment (PPE) that medical workers wear when dealing with people who might be infected.
We have learned a lot about the SARS-Cov-2 virus since it first came to the world’s notice on the Diamond Princess. Some of the modes of disease transmission that at first seemed to be plausible culprits, have since come to be recognized as less important. And some of the practices that we were advised to follow to mitigate the chance of infection have proven to be ineffective in some cases and unnecessary in others.
Initial suspects in disease transmission were:
- Droplets greater than 100 micrometers in diameter
- Fomites (viral particles that land on surfaces and persist there for a period of time)
- Aerosols smaller than 100 micrometers in diameter
Based on these possible transmission paths we have been advised to engage in several practices:
- Practice social distancing by staying at least two meters (6 feet) away from any possibly infected person. A person could be infected and not know it, showing no symptoms.
- Wear a mask, preferably an N95, whenever near people who are not included in your household bubble.
- Wipe off any deliveries that come into the house with a disinfectant such as Lysol to inactivate any fomites that might be present
- Don’t touch anyone outside of your household bubble. That includes handshakes and fist bumps.
Do these practices contribute to slowing the spread of Covid-19? Are there other things that perhaps we should be doing in addition, or perhaps instead?
An article appearing in the August 27, 2021 issue of Science, the flagship scientific journal of the American Association for the Advancement of Science (AAAS), titled Airborne transmission of respiratory viruses, describes the evidence for each of the purported modes of transmission of the SARS-Cov-2 virus, as well as for other viruses, such as SARS-Cov and MERS-Cov.
The article is highly detailed and backed up by references to numerous peer-reviewed papers on the topic. I will summarize the major takeaways.
- Droplets greater than 100 micrometers in diameter, expelled by talking, shouting, singing, or coughing will generally fall within two meters (6 feet) of an infected person.
- Fomites on objects (such as delivered grocery items or UPS deliveries) are probably not a significant source of infection.
- ATTENTION!!: Aerosols smaller than 100 micrometers are likely the primary agents of infection
The US Centers for Disease Control (CDC) officially acknowledged that inhalation of virus-laden aerosols is a main mode of spreading the SARS-Cov-2 virus at both short and long ranges. Virus-laden aerosols dominate all other modes of transmission in indoor environments that are poorly ventilated.
This finding by the CDC validates the updates that Princess Cruise Line has made to their entire fleet of ships, by changing the circulation of air in the ships to send fresh rather than recirculated air into cabins and other indoor spaces. Other cruise lines have followed Princess’ lead in this. All cruise lines are hyper-aware of the importance of keeping passengers and crew safe, and of conveying to those constituencies the actions that they are taking to assure that safety. As a result, the first tentative steps to returning cruise ships to the world’s oceans have been taken. Although cruise lines cannot absolutely guarantee that the SARS-Cov-2 virus will never make it onto a cruise ship, they are ready to deal with it if it occurs. Passengers can feel confident that cruising on a modern cruise ship is now safer than it has ever been.
BIO:
Allen G. Taylor is a 40-year veteran of the computer industry and the author of over 40 books, including Develop Microsoft HoloLens Apps Now, Get Fit with Apple Watch, Cruise for Free, SQL For Dummies, 9th Edition, Crystal Reports 2008 For Dummies, Database Development For Dummies, Access Power Programming with VBA, and SQL All-In-One For Dummies, Third Edition. He lectures internationally on astronomy, databases, innovation, and entrepreneurship. He also teaches database development and Crystal Reports through a leading online education provider. For the latest news on Allen’s activities, check out his blog at wwwallengtaylor.com or contact him at allen.taylor@ieee.org.