Subject: IFST Position Statement on Foodborne Viral Infections

From: [email-masked] (J Ralph Blanchfield)
Date: Fri, 13 Sep 1996 23:20:13 GMT

Hello Everyone,

Herewith the IFST Position Statement on Foodborne Viral Infections,
dated 14 September 1996. 

It is  being posted on four food-related mailing lists, and two
newsgroups, for the benefit of those who subscribe to only one of
them. Usual apologies to those who subscribe to more than one of them
and will therefore receive more than one copy.

Regards

Ralph

FOODBORNE VIRAL INFECTIONS 

The Institute of Food Science & Technology, through its Public Affairs
and Technical & Legislative Committees has authorised the following
Position Statement, dated 14 September 1996, prepared by its
Professional Food Microbiology Group.

SUMMARY

Foodborne viral infections are caused mainly by two types of virus,
small round structured viruses (SRSVs) which cause gastroenteritis and
Hepatitis A virus which causes hepatitis. All foodborne viruses
originate from the human intestine and   contamination of food occurs
either during preparation by infected food handlers or by contact with
sewage sludge or polluted water. Control measures mainly depend on
staff education and good kitchen hygiene; food handlers suffering from
symptoms should be excluded from work immediately and all staff made
aware of the ease with which viral contamination is transmitted. The
use of clean water for irrigation of crops that are likely to be eaten
raw and cultivation of molluscan shellfish in sewage-free seawater are
also essential to prevent viral contamination of food.

THE PROBLEM

Foodborne viruses are a common but probably under-recognised cause of
gastroenteritis, and may often be the cause of outbreaks of illness.
The usual mode of transmission is from person to person. The greatest
risk of foodborne illness occurs from catering operations preparing
ready to eat foods; however foodborne spread is difficult to prove.
Most confirmed outbreaks of viral foodborne illness have been
associated with  the consumption of shellfish that had been harvested
>from  sewage-polluted waters.  

VIRAL FOODBORNE ILLNESS

The types of foodborne virus fall into two main groups:

(1)	Small, round, structured viruses (SRSVs), which include
Norwalk virus and cause gastroenteritis.

(2)	Hepatitis A virus, which causes hepatitis.

Other types of viruses which are occasionally implicated in foodborne
illness are astrovirus and rotavirus, but foodborne transmission of
these viruses is rare. 

Small, round, structured viruses (SRSV)

Illness caused by SRSVs is usually sudden in onset, and is
characterized by vomiting, diarrhoea and abdominal pain. Vomiting
frequently occurs without warning and may be projectile and
uncontrollable, whilst diarrhoea may be explosive. Incubation time is
usually 24 - 36 hours after eating an implicated food, but may be from
15 - 72 hours, depending on the number of virus particles consumed.
Duration of symptoms varies from 12 - 72 hours, but after the initial
uncontrollable onset may be relatively mild. Despite this sufferers
may feel debilitated for 2-3 weeks. 

Very few virus particles are needed to cause illness, and so the
attack rate in an outbreak can be very high, with the majority of
people who ate the contaminated food becoming ill. Because the viruses
multiply in the gut, a very large number of virus particles are
excreted during the illness (often more than 10 million per gram of
faeces or vomitus). As a result of the uncontrollable nature of the
symptoms, food can easily become contaminated by infected food
handlers, and secondary person-to-person spread is also common. 

Hepatitis A

Viral hepatitis has a long incubation period of 3 - 6 weeks, with
symptoms developing gradually. Symptoms include loss of appetite,
malaise, fever and vomiting, followed by jaundice. Illness usually
lasts a few weeks but may last several months, and is usually more
severe in adults than in children. Death may occur, particularly in
the elderly, but is very rare. Large numbers of virus particles may be
shed in the urine and faeces during the latter part of the long
incubation, before jaundice is apparent, but may be absent one week
after the onset of jaundice. 

SOURCE

Viruses require a host in order to multiply, and the original source
of all foodborne viruses is the human intestine. They cannot grow in
food. Contamination of food may occur either during preparation and
serving by infected food handlers, or by contact with sewage sludge or
polluted water. 

The main food type associated with foodborne viruses is molluscan
shellfish such as oysters, cockles and mussels, which are usually
found in shallow coastal or estuarine waters, commonly near sewage
outlets. Shellfish harvesting areas are classified according to the
level of faecal indicator bacteria present in the shellfish flesh; if
levels exceed the specification for direct consumption the shellfish
must be relayed in cleaner water, receive an approved heat treatment
or undergo a purification process (depuration) before sale. These
shellfish are filter feeders that can concentrate virus particles from
the surrounding water. Molluscs are either eaten raw or after a mild
heat process, which if poorly controlled may not inactivate virus
particles present. In addition, depuration cannot be guaranteed to
remove viruses, and outbreaks of viral gastroenteritis have been
attributed to depurated shellfish. Cultivation of molluscan shellfish
in clean water is therefore paramount in the control of viral
contamination. Although molluscs are the most clearly implicated
source of foodborne viral illness, they do not necessarily cause most
illness. 

Fruit and vegetables may act as vehicles of infection if fertilized
with sewage sludge or irrigated with sewage-contaminated water.
Guidelines issued by the World Health Organisation (WHO)  state that
fruit and vegetables to be eaten raw should not be fertilized with
sewage or irrigated with contaminated water. Apart from an outbreak of
Hepatitis A resulting from contaminated soft fruit, there are no
proven outbreaks associated with contamination of these foods at
source. Consumption of contaminated water and ice or their use in food
preparation may also cause viral illness. 

Contamination of food by infected food handlers is probably the most
common cause of viral foodborne illness. Food items such as salads and
dessert dishes that receive considerable handling during preparation
and are not given any further heat treatment before consumption are
often implicated in foodborne viral outbreaks. 

DETECTION

Detection of viruses in food is not possible in a routine laboratory
because of their requirement for a living host for growth. In
addition, the level of virus particles in a contaminated food is
usually very low. Specialist laboratories may achieve detection using
cell culture and complex extraction methods, but techniques currently
available are not suitable for routine application and recovery rates
remain poor. The use of the polymerase chain reaction (PCR) is being
developed for detection of SRSVs in foodstuffs implicated as the
source of outbreaks; this is still being evaluated and will not detect
all strains. 

Methods currently used for routine detection of SRSVs in faeces are
based on electron microscopy. In order to achieve detection at least
one million virus particles per gram of faeces need to be present, and
so only faecal samples obtained within 48 hours of the onset of
symptoms are suitable for examination for SRSVs. 
A recently developed PCR test is more sensitive than electron
microscopy and is able to detect SRSV in vomitus and in faeces up to 7
days after onset of symptoms. Use of this PCR test enables the
detection of more than 90% of SRSV infections, and also allows
characterization of the strains.   

Detection of Hepatitis A virus in faeces by electron microscopy is
usually not possible, because by the time jaundice occurs the peak of
excretion of virus particles has passed. Diagnosis is based on
detection of specific IgM and IgG antibodies in the blood serum or
saliva. 

SURVIVAL CHARACTERISTICS

Foodborne viruses are hardy, and may survive for prolonged periods in
foods or the food handling environment. They are highly resistant to
chilling, freezing, preservatives and ionising radiation. Hepatitis A
virus is rapidly destroyed by heating at temperatures above 85 deg C
and it is likely that SRSVs are also inactivated at this temperature.
Inactivation of viruses occurs at temperatures above 65 deg C at a
rate proportional to the temperature but also depends upon the
composition of the medium. They are resistant to acidic conditions (pH
3) and  therefore survive on acid fruits such as strawberries and
raspberries and processes such as pickling in vinegar or yogurt
production. They are also resistant to alcohol and high sugar
concentrations.

MANAGEMENT OF FOOD HANDLERS

Food handlers suffering from vomiting or diarrhoea should be excluded
>from  work immediately. They should not return to work until at least
48 hours after cessation of symptoms. After the initial onset of
symptoms, infection may be sufficiently mild to enable the food
handler to continue working. This must be prevented because even very
low numbers of virus particles may result in illness if transferred to
the food. Prevention of foodborne viral illness requires good staff
supervision and food handlers should be encouraged to report symptoms
of illness as soon as they occur. Staff should also be made aware that
they could transfer viral contamination to food via hands and clothing
following contact with an ill family member. There is no carrier state
associated with SRSVs.  

Hepatitis A is mainly spread by person-to-person transmission, but can
be spread by food handlers. Cases of viral hepatitis are most
infectious before jaundice is apparent, but exclusion of food handlers
>from  work for one week after the onset of jaundice is recommended.
There is no chronic carrier state. If food handlers are exposed to
Hepatitis A, those shown not to be immune by antibody testing may be
given prophylactic human normal immunoglobulin by injection.

CONTROL

Shellfish are an important cause of viral gastroenteritis. Cultivation
in clean waters is very important, as depuration procedures may not be
effective in eliminating viruses. Heat treatment to an internal
temperature of 85 - 90 deg C maintained for 90 seconds is required to
destroy viruses in molluscs, but careful control is necessary to
achieve this without toughening of the flesh. Consumption of uncooked
molluscs such as oysters remains a risk, as does cross-contamination
>from  contaminated shellfish to other food in the kitchen.

Contamination of foods other than shellfish will normally occur on the
surface of the food, where viruses will be more susceptible to heat
treatment. Heat processes commonly used in the food industry such as
heating to a core temperature of 70 deg C for two minutes will
significantly reduce the level of virus contamination, but may not
destroy all the viruses if the contamination level was very high.

The number of virus particles required to cause infection is very low.
Contamination of food with SRSVs by infected food handlers and
person-to-person spread occurs easily due to the very large numbers of
virus particles present in the stools and vomitus at the onset of
symptoms, and to the survival characteristics of the viruses.
Infection of personnel may take place by aerosol inhalation and
subsequent ingestion as well as the hand-to-mouth route. Thorough
handwashing with soap and warm running water and drying with
disposable towels or air hand dryers are essential to minimize spread
of contamination. 

If vomiting has occurred in the kitchen or factory, a rigorous
disinfection programme appropriate for viral decontamination of the
environment must be implemented. This is best achieved by using hot
water and detergent followed by a chlorine-based disinfectant at a
strength of 500 ppm available chlorine. Food that may have been
exposed to aerial contamination or handled by the ill person should be
destroyed unless it is to be heated above a core temperature of 85 deg
C following exposure. If contaminated food is not destroyed
cross-contamination and re-infection may occur. Any soiled clothing
should be rinsed to remove gross contamination, preferably into the
toilet bowl, and then laundered in a domestic or commercial washing
machine with a hot cycle. 

IMPLICATIONS FOR THE FOOD INDUSTRY

The prevention of foodborne viral illness depends heavily on  staff
education and a high level of awareness in the catering industry. If
payment is withheld during sickness staff will be reluctant to cease
working when symptomatic. However the cost of sickness benefit is
minimal compared with the potential costs incurred as a result of a
foodborne outbreak. 

FURTHER READING

Council Directive 91/492/EEC (1991). Health conditions for the
production and the placing on the market of live bivalve molluscs.
Official Journal of the European Communities L268: 1-14.

Mara, D. and Cairncross, S. (1991). Guidelines for the safe use of
wastewater and excreta in agriculture and aquaculture. WHO: Geneva.

Statutory Instrument No. 1263 (1989). The Sludge (Use in Agriculture)
Regulations 1989. HMSO, London.

Viral Gastroenteritis Sub-Committee of the PHLS Virology Committee
(1993).  Outbreaks of gastroenteritis associated with SRSVs. PHLS
Microbiology Digest 10: 2-8.

Working Party of the PHLS Salmonella Committee (1995). The prevention
of human transmission of gastrointestinal infections, infestations,
and bacterial intoxications. Communicable Disease Report 5: Review
No.11, R158 - R172.  

The Institute of Food Science & Technology (IFST) is the independent
professional qualifying body  for food scientists and technologists.
It is totally independent of government, of industry, and of any
lobbying groups or special interest groups. Its professional members
are elected by virtue of their academic qualifications and their
relevant experience, and their signed undertaking to comply with the
Institute's ethical 
Code of Professional Conduct. They are elected solely in their
personal capacities and  in no way representing organisations where
they may be employed. They work in a variety of areas, including
universities and other centres of higher education, research
institutions, food and related industries, consultancy, food law
enforcement authorities,  and in government departments and agencies.
The nature of the Institute and the mixture of these backgrounds on
the working groups drafting IFST Position Statements, and on the two
Committees responsible for finalising and approving them, ensure that
the contents are entirely objective.

IFST recognises that research is constantly bringing new knowledge.
However, collectively the profession is the repository of existing
knowledge in its field. It includes researchers expanding the
boundaries of knowledge and experts seeking to apply it for the public
benefit.  Its purposes are 

(1) to serve the public interest by furthering the application of
science and technology to all aspects of the supply of safe,
wholesome, nutritious and attractive food, nationally and
internationally;

(2) to advance the standing of food science and technology, both as a
subject and as a profession;

(3) to assist members in their career and personal development within
the profession;

(4) to uphold professional standards of competence and integrity
The Institute takes every possible care in compiling, preparing and
issuing the information contained in IFST Position Statements, but can
accept no liability whatsoever in connection with them.  Nothing in
them should be construed as absolving anyone from complying with legal
requirements. They are provided for general information and guidance
and to express expert professional interpretation and opinion, on
important food-related issues.

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J Ralph Blanchfield
Food Science, Food Technology & Food Law Consultant
Chair, IFST Member Relations & Services Committee
Web Editor, Institute of Food Science & Technology
IFST Web address: http://www.easynet.co.uk/ifst/ 
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