Norovirus in a confined space

I am currently down at Scott Base, Antarctica, heading out into the field tomorrow for two to three weeks' scientific work.

The base is on high alert, but not because of weather or acts of terrorism etc.  The concern this time is the outbreak of norovirus at McMurdo Station, which is only just over the hill from here and is normally visited regularly by both scientists and service personnel.

We are taking extreme precautions; the Thursday night American Night has been cancelled and visitors are strongly discouraged if not completely barred.  There are hand sanitiser pumps throughout the base and it is a requirement to sanitise hands before entering the mess.  Communal food items, such as loaves of bread are not to be handled with bare hands, because the virus can easily be transmitted on surfaces.  The bathrooms and toilets are being regularly sanitised and there too, there are warning signs that hands must be washed with soap and water and hand sanitiser is freely available.

It is to be hoped that the virus doesn't make it over to Scott Base - there are several projects kicking off now, and many more scientific teams will be arriving shortly, to the extent that some teams are being asked to reschedule their time at Scott Base to free up bunk room space.  An outbreak here could be catastrophic for the scientific programme, not to mention the misery for the victims.

Unwanted passenger on cruise liner

Recently, the cruise liner Voyager of the Seas was struck with what appears to have been a Norovirus outbreak.   'Norovirus' is not a unique organism; there are many different strains, so you can become infected several times during your life.   Norovirus causes diarrhoea and vomiting, which in turn result in contamination of surfaces and generation of aerosols.  If you get virus particles in your mouth, you are highly likely to contract the disease, which appears to have a very high hit rate in exposed people.  (Now do you understand why I never get invitations to be an after-dinner speaker?)

 The virus may be present in the intestines before the onset of symptoms, and may remain in faeces for more than two weeks after recovery.  During all of this time, the virus can be spread. The problem is compounded when a population is effectively captive, such as in hostels or on a cruise liner.  The virus lives for quite a long time on surfaces, so door knobs, bathroom surfaces, lift buttons, soiled bed linen and clothes can be sources of virus particles.  If someone throws up in the dining room, other diners are immediately at risk from the aerosol.  Obviously, if the ill person is working in the kitchens, this is even more serious, as all exposed food and utensils may become contaminated.

The cruise line might be criticised for not promptly informing passengers waiting to board in Sydney about the problem, but the necessary disinfection of a whole ship is a major undertaking, and it appears that the line has made strenuous efforts to protect new passengers from infection.

What can you do to protect yourself?  Rigorous hand washing with soap and hot water (sing Happy Birthday to yourself twice while washing, to ensure that you spend enough time working the soap into hands and under nails) particularly after visiting the toilet or changing baby's nappy and before eating or preparing food.  Do not prepare food for others if you have diarrhoea.  Use of alcohol hand sanitisers may be beneficial, but these are not a substitute for washing.

Wash raw fruits and vegetables before eating them and be sure to cook seafoods thoroughly - Norovirus can survive temperatures of around 60 C.

If you are caring for someone who has symptoms of vomiting and diarrhoea,  handle soiled clothing carefully to avoid generating aerosols; wear rubber or disposable plastic gloves.  Use strong bleach solution to disinfect surfaces in bathrooms etc.  

Odd spot:

In the case of chlorine solutions, more is not necessarily better.  If the solution is made from bleaching powder (sodium or potassium hypochlorite), the more powder we add, the more alkaline the solution becomes.  The active component in a solution of bleach is actually hypochlorous acid.  This acid is unstable and breaks down in alkaline solution.  At pH 10, almost no hypochlorous acid is present in the solution.  Thus, a solution of hypochlorite containing 1000 ppm has a pH of 11.0 - 12.00 and has no active hypochlorous acid, while a solution with only 25 ppm has a pH of 8.0 - 9.0 and so is actually more germicidal than the higher concentration.

It’s not quite about food safety…

Recently I was asked by a reporter to test magazines found in doctors’ waiting rooms for presence of pathogens. She wanted to do a story about the risks of going to the GP. I wasn’t sure what to expect, but asked her to collect a range of magazines from various waiting rooms. She brought me ten glossy or super glossy magazines covering popular women’s and men’s titles.

Each magazine was opened randomly and two pieces of the right hand page were cut aseptically, using sterile scissors. Each piece was 100mm x 100mm; one piece was cut from the top right, the other from the bottom right. This was to increase the chance of sampling the area most handled by readers.

The pieces of paper were transferred to a sterile bag with sterile diluent and massaged thoroughly by hand and then for two minutes in a machine called a Stomacher. I transferred samples onto agar plates that would enable me to assess general microbial contamination, faecal bacteria and Staphylococcus.

After incubation, I examined the plates, looking for typical bacterial colonies. The levels of contamination on all media were low. The limit of detection in this analysis was 3.7 colony forming units/10 cm². In the food industry, a count of less than about 100 cfu/cm² is considered acceptable, though the count on food contact surfaces at the start of food processing should be close to zero. Thus, the analysis I used was sufficiently sensitive to indicate whether the magazines were microbiologically hazardous with respect to Staphylococcus and faecal bacteria.

Staphylococcus is typically found on the skin and can be transferred to food and there produce enterotoxin, which causes food poisoning when we eat the contaminated food. It is unlikely that the low levels of S. aureus detected in this work would lead to significant transfer between readers. No typical colonies of faecal coliforms were detected, suggesting that there were no, or very low numbers of faecal bacteria on the magazines and hence that the likelihood of faecal contamination of the pages was also low.

All of the samples were printed on glossy paper, which doesn’t absorb water, a fact I confirmed by measuring the water activity* of the samples. There was thus no opportunity for bacteria to grow on the pages and in fact, they may have died off reasonably quickly.

One thing I should point out is that it is not possible by any simple analysis to detect viruses, so the work done here doesn’t completely rule out contamination by viruses of upper respiratory tract or gastrointestinal tract origin. Some, such as the Norwalk virus that causes gastroenteritis, can survive on surfaces for long periods.

I conclude from this cursory examination that, with the possible exception of viruses, the pages of the magazines were relatively free of pathogens. Handling the magazines is therefore relatively hazard free. However, as always, it would be advisable to wash or sanitise hands before consuming foods, snacks or sweets after visiting the surgery.

Have a happy and safe Christmas, everyone. Make sure your Christmas fare and BBQs are safe.

* For a description of water activity see:

http://foodsafetywithjaybee.blogspot.com/2007/06/free-choice-or-safety-of-population.html

Norovirus spreads fast

We have all read of the mystery illnesses that strike down students in schools and universities and perhaps thought that these outbreaks were caused by overcrowding or poor cleaning in these establishments.

The importance of properly educating food handlers has been emphasized once again. Workers at a Michigan restaurant displayed an almost unbelievable ignorance of simple food handling rules in January last year. (Warning: those with a weak stomach should receive guidance from a food microbiologist before reading further).

Three staff reported for work at the restaurant even though they were suffering intestinal illness. The US Centre for Disease Control and Prevention reports this in a summary of findings of an investigation released two weeks ago. One of the workers vomited into a waste bin before continuing their kitchen duties. They may have believed that using the waste bin was OK, but obviously didn’t think about aerosol generation, transfer of infective particles by their hands and contamination of surfaces in the kitchen and washrooms (or even plain old aesthetics).

The infection turned out to be a Norovirus. These viruses are highly contagious and have an infecting dose as low as 10 particles. The efficiency of infection may be as high as 93% of those people exposed. That’s why we see these outbreaks spread like wildfire through student hostels. The normal transmission pathway is the faecal-oral route, but the particles can survive on surfaces for up to four weeks, so washrooms used by sufferers become very hazardous. The particles can be killed by chlorine (bleach) solutions, but the quaternary ammonium compound used on cleaning cloths in the restaurant was thought to be ineffective.

The CDC recommended that after a vomiting event like this, all exposed food, paper serviettes, takeaway containers and straws should be discarded. All surfaces within an 8-metre radius and all washrooms should be disinfected with a chlorine solution. I would also rewash all crockery and cutlery. It was suggested that restaurant owners should consider briefly closing down for complete cleaning after someone has vomited in the facility. Staff training is critical. Part of the training should be an injunction to stay away from work for at least three days after gastrointestinal illness (and not to handle utensils or ready-to-eat foods for a further three days). Rigorous hand washing and segregation of raw and cooked foods is another obvious precaution.

You can find more information on Norovirus at:
http://www.nzfsa.govt.nz/consumers/food-safety-topics/foodborne-illnesses/
norovirus/factsheetnorovirusv2.htm