Q2.Norovirus is prone to massive outbreaks. What is the mechanism that causes it to spread?

A characteristic of norovirus is that it is very easily spread through oral infection. It is a highly contagious virus and the frequency of infection is also high. The infectivity of intestinal tract infections can be expressed as "infective dose(about how many will it take for an infection if taken orally)", for example, 1 million organisms for Salmonella Entertidis or 1 million viral particles for hepatitis A virus. On the other hand, norovirus infection will occur when 10 to 100 viral particles enter from the mouth. Incidentally, infection with the least amount of germs can occur with O-157 (enterohemorrhagic E. coli) and Shigella with as few as around 10 organisms.

The norovirus is found in the small intestine of infected people and is detected in the stool and regurgitation (vomit). There are 10 million viral particles in the stool. The concentration is not as high in regurgitation (vomit) compared to stool and is about 1 million viral particles. There are 100,000 viral particles even in 0.1 gram meaning that infection will occur even from trace amounts that cannot be seen.
The cause of infection spreading is often when food handlers (such as cooks) touch the food with hands contaminated with stool or vomit and norovirus entering the mouth from consuming the food. In 2017, it was reported that a widespread infection of norovirus occurred from nori(cut dried seaweed) in the school lunch. Genetic analysis revealed that after the dried seaweed manufacturer vomited, the dried seaweed was manufactured without sufficiently washing the hands. The children who ate the dried seaweed about 3 months later, became infected. In this manner, it was confirmed that the norovirus can survive for very long periods of time even in a dry environment.
Additionally, there was also a case where norovirus infection occurred even without touching the vomit at all. This is a pattern where the regurgitated matter (virus) when vomiting is scattered as a mist and attaches to the pharynx and infection occurs when the virus is swallowed along with the saliva. There is also a pattern where dried vomit (virus) becomes airborne and attaches to the pharynx and is swallowed along with the saliva. In that respect, norovirus can also be transmitted by droplet infection or airborne infection.

Q3.In order to prevent the spread of infection, it is necessary to be self-aware. After using the restroom, what precautions are necessary?

It is very important to not get any fecal matter (stool) on your hands in the first place. If it does not get on your hands, the cause of infection will not spread by adhering to door knobs, food or cookware.
In my laboratory in 2017, there was a comparative experiment for the contamination of hands after defecating. First, the condition after defecating was simulated with model buttocks and artificial stool containing germs then a wiping test was conducted to see how much germs adhered to hands was investigated.

Source：Shigeharu Oie, Hiromi Aoshika, Emiko Arita, Akira Kamiya. The Use of Electric Toilet Seats with Water Spray Is Efficacious in Maintaining Hand Hygiene in Experimental Model. Japanese Journal of Infectious Disease 2018 Volume 71 Issue 4 306-308

Four layered sheets of toilet paper were used for wiping. This was based on the result of a survey conducted by the Japan Sanitary Equipment Industry Association that the largest number of people replied that they used "4 layers of sheets to wipe". The results were that germs were attached to the hands after wiping with four layered sheets of toilet paper. Toilet paper is full of infinite holes when viewed under a microscope. Because the size of the holes were about 100 times larger than the size of the germs, it was easy for the germs to pass through even when 4 sheets were layered.

At the same time, tests were conducted by wiping with 4 layered sheets of toilet paper after washing for 30 seconds using a spray seat to cleanse buttocks. The results were that after using a spray seat for 30 seconds, the number of germs attached to the hand was less than 10,000 times lower than when not used.

Next, a test at the actual time of excretion was conducted. The results were that the number of germs attached to the hand was about 10 times less than people who did not use the spray seat. When a spray seat is used, the risk of infection will be reduced to about 90%. Although there are individual differences such as usage, the use of a spray seat can reduce the number of germs attaching on hands and can be said to be extremely effective in preventing intestinal infections.

Q4.What should you do if a family member or person living in your surroundings is infected with norovirus?

It would be better to have everyone in the family be aware that infection is easily spread among family members. Careful hygiene of hands should be taken especially when preparing food.
It is thought that the possibility of norovirus is 60% to 70% when vomiting occurs during winter and so disinfection should be done carefully. Wear disposable gloves when cleaning regurgitated matter (vomit) and also wearing surgical masks is ideal.

Additionally, it is dangerous to leave regurgitated matter (vomit) for prolonged periods. There has also been cases reported that people were infected from dust after vacuuming dried regurgitated matter. When dried, it is easier for it to become airborne and become attached to the pharynx causing infection.
It is also imported to clean the toilet after defecation or vomiting. There are few disinfectants that can be used in homes, however, sodium hypochlorite 0.1% (1,000 ppm) solution or ethanol (sold at pharmacies as a non-prescription drug) for disinfecting carpets and solid wood etc., can be used. It is fundamental to use these two disinfectants properly according to the location.
In addition, it should be noted that the disinfection ability of sodium hypochlorite is easy rendered less effective when exposed to direct sunlight and with the passage of time. When purchasing products, choose products with a specified concentration and expiration date. To be specific, it is recommended that disinfectant solutions for infants, such as Milton^®, Purifan^® P and Milkpon^®, be diluted and used.
Even if you don't have any symptoms, it is also important to wash your hands after defecation. You should know that many cases of the norovirus are also "subclinical infections". For example, eating oysters infected with norovirus does not mean that everyone will show the symptoms and some people do not. In other words, some people will carry the norovirus without developing the disease and outbreaks that occur in hotels, hospitals, etc. may spread as a result of such “subclinical infections”.
Children and the elderly are especially prone to norovirus infection; however, this is related to the gastric liquids showing germicidal effects. In children, this is because the gastric liquids are still insufficient while in the elderly, one reason is that it is difficult for them to produce it sufficiently. Accordingly, special consideration is required for households with children and elderly persons. Additionally, even in adults, if they are taking medication for symptoms of stomach ulcers to suppress stomach acid (H2 blocker gastrointestinal medication, etc.), they will be more susceptible to infection.

Q5.What are some precautions in avoiding infection from O-157, etc.?

Maintaining normal intestinal flora is one important preventive measure in avoiding infection from O-157, etc. In healthy intestines, a wide variety of microorganisms make up the microbiota and these act to control the growth of specific germs and function to prevent infections. For example, even if O-157 should enter the intestines, if large numbers of microorganisms are there, the O-157 will not be able to multiply and the occurrence of infection will be less likely.

In hospitals, serious intestinal infections such as pseudomembranous colitis caused by Clostridioides difficile (formerly called Clostridium) germs are a major problem, however, these only affect people who are administered antibiotics and anticancer drugs. Because some antibiotics and anti-cancer drugs are germicidal, they will "harm intestinal flora".
When we eat, we also provide some nutrients to the intestinal microorganisms and in turn, the internal microorganisms play a role in protecting us from infections. We also know that we acquire vitamin B and vitamin K that the microorganisms produce. We coexist with the various intestinal microorganisms. It is very important to maintain normal intestinal flora to prevent the abnormal increase of problem causing microorganisms.