Monday, December 10, 2007

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:

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