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Prevention of common viral infections

A review by English workers (Journal of Applied Microbiology 91 2001 7) examines the dispersal, persistence and control of some common viruses in the home and in community facilities.

The review covers a range of virus types but these comments will be restricted to its conclusions with regard to gastrointestinal viruses and hepatitis A virus. These conclusions basically are that the importance of hygiene and particularly hand washing cannot be over emphasised as a means of reducing viral infection. Hand hygiene education must be integrated with education about the importance of surface and air hygiene in prevention of infection transmission.

The authors note that close personal contact within home and community settings such as day care centres and schools make them ideal places for the spread of infection. Infants are particularly vulnerable to such infections because they frequently place objects such as toys into their mouths.

Gastrointestinal infections

These authors repeat the view that since cases and outbreaks related to viral agents are often unreported, the impact of viral intestinal infections may be much greater than national surveillance systems suggest. In the UK, the rate of reported NLV infections reaches a peak in children under five years and again in the elderly.

Foodborne outbreaks can arise from contaminated raw foods such as shellfish and through secondary contamination by food handlers carrying the virus. Other foods implicated in outbreaks are those also eaten raw such as salads and fruit or foods not cooked after handling e.g. cold meats.

Worldwide, rotavirus is probably the most important viral pathogen causing diarrhoeal illness in infants. A large proportion of hospital admissions due to gastroenteritis in children under five years in the UK is caused by rotavirus.

Globally, hepatitis A virus is the most common cause of hepatitis in man. Contaminated water or food, particularly filter-feeding fish, frequently transmit hepatitis A virus but other foods have also been implicated. The virus is excreted in high numbers in faeces and is spread from person to person by the faecal oral route. When personal hygiene is not observed, food handlers including asymptomatic persons may transfer the virus to food during the incubation period for the disease. Viral shedding may begin several days before the onset of symptoms and continue after symptoms have ceased.

Persistence and spread of viruses

Virus particles can be shed in large numbers in various body fluids from an infected person or carrier. Although few studies have been carried out in domestic homes, studies in children's day care centres and in hospitals show that viruses can survive on surfaces and that virus transfer and survival on hands plays a part in the transmission of infections.

The reviewers cite a number of studies to support the importance of contact surfaces as a possible vehicle of infection.

Several studies in child day care centres have shown that rotavirus can be widely disseminated when outbreaks occur. One such study showed that 16-30 per cent of surfaces can be contaminated with rotavirus. In particular, hand contact surfaces, e.g. refrigerator handles, toilet handles, telephone receivers and toys, and moist surfaces such as sinks, water fountains and play tables were contaminated with virus.

With NLV, projectile vomiting is probably a major source of cross infection following aerosol distribution into the environment (see Food Safety & Hygiene February 2001).

The potential for secondary transmission via environmental surfaces in semi-closed communities was demonstrated following a wedding reception where an outbreak of NLV gastroenteritis affected 50 per cent of guests. On investigation it was found that the previous day a kitchen assistant had vomited in a sink that was subsequently used for preparing vegetables eaten by the wedding guests. Transmission of infection occurred despite apparent cleaning and sanitising of the sink after the vomiting incident.

As with other enteric viruses hepatitis A virus is shed from an infected person in large numbers and is able to survive on environmental surfaces and be readily transferred by hands.

These authors recommend a risk assessment approach to hygiene starting from the premise that homes and other settings always contain potentially harmful microbes. Good hygiene is about targeting measures in the places and at the times that matter in order to limit risks of exposure. For both the hands and environmental surfaces, hygiene can be achieved by physical removal of organisms from the surface.

In many instances such as the hands and cooking and eating utensils, appropriate risk reduction can be achieved using detergent and hot water followed by rinsing. Biocides that have activity against both enveloped and non-enveloped viruses include chlorine and iodine releasing agents, peracetic acid and ozone. Effectiveness depends on the virus, the surface carrier, the presence of interfering substances, and contact time.

Although these compounds can be used for disinfection of environmental surfaces they are generally too irritant for use on the skin.

Recommendations for hand washing (and drying) can be found in a number of previous issues of Food Safety & Hygiene including November 1997 and November 1998.

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Prepared by Keith Richardson and Rachel Jackson
Food Science Australia
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