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Introduction |
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| 1. |
Hepatitis A is an infectious disease affecting
the liver caused by hepatitis A virus (HAV). |
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| 2. |
Food borne transmission through faecal-oral
route is the most important mode of transmission for hepatitis
A. |
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| 3. |
Hepatitis A may be asymptomatic, or
produces acute symptoms depending on the age of the infected
persons. Adults exhibit more severe symptoms while infants usually
show no signs. |
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| 4. |
The incubation period of the disease
ranges from two to six weeks. Symptoms can include fatigue,
poor appetite, nausea, vomiting, diarrhoea, abdominal discomfort,
jaundice and tea-coloured urine. |
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| 5. |
Because of its unique habitat and
special feeding mechanism, shellfish especially bivalve shellfish
is an important vehicle responsible for transmission of hepatitis
A. |
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Risk Assessment and Public Health Significance
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| 1. |
Shellfish is a broad term for all aquatic animals
that have a shell of some kind. It generally divided into four
groups namely crustaceans (examples: crabs, crayfish, lobster,
and shrimp), gastropods (examples: abalone, limpet, snail, and
whelk), bivalves (examples: oysters, clams, mussels, and scallops),
and cephalopods (examples: octopus, squid, and cuttlefish). |
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| 2. |
Shellfish living in water contaminated by sewage
can carry the HAV. Because bivalve shellfish are filter feeders,
they absorb food particles and nutrients by filtering out the
seawater. Hence they tend to concentrate the virus present in
the polluted water. Man may contract hepatitis A after consumption
of contaminated shellfish that has not been thoroughly cooked.
Consumption of bivalve shellfish, like cockles, oysters and
clams, is strongly associated with hepatitis A outbreaks. |
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| 3. |
Attention to environmental, food and personal
hygiene can prevent hepatitis A. When handled properly, shellfish
is as safe to eat as any other source of food. |
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| Control Measures and Surveillance Findings |
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| 1. |
Under the Public Health and Municipal Services
Ordinance, Cap.132, fresh or frozen shellfish is classified
as a restricted food item, which is subject to licensing control.
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| 2. |
At the import level, we strongly encourage importers
to obtain health certificates issued by health authorities of
the countries of origin certifying that each imported consignment
of shellfish is fit for human consumption. |
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| 3. |
When a consignment of shellfish arrives at entry
points, it may be subject to inspection or sampling by us. If
the importer concerned is unable to present a health certificate
for inspection, we may take samples from the consignment for
examination before its release. |
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| 4. |
We take regular samples of shellfish both from
the retail outlets and at the entry points for testing of HAV.
From 1999 to June 2000, 809 samples of shellfish (including
734 samples of bivalve shellfish) were taken for HAV testing.
92 samples (11.4%) were found unsatisfactory. All these unsatisfactory
samples were bivalves. The surveillance findings reflected that
bivalve is more vulnerable to HAV contamination than other groups
of shellfish. |
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Advice to the Public
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| 1. |
Buy only those shellfish which are fresh, with
intact shell and free from abnormal odour. |
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| 2. |
Do not buy shellfish from illegal hawkers and
unlicensed food premises. |
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| 3. |
Scrub and rinse the shellfish in clean water. |
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| 4. |
All shellfish should be cooked at boiling temperature
for not less than five minutes before eating. |
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| 5. |
Mud oysters should not be eaten raw. |
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| 6. |
If possible, remove the shells before cooking
as they impede heat penetration. |
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| 7. |
Remove the viscera of the shellfish before cooking.
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| 8. |
When having hotpot, use separate chopsticks and
utensils for handling raw and cooked food to avoid cross contamination.
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| Advice to the Trade |
| 1. |
Do not obtain the supply of shellfish from unreliable
sources. |
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| 2. |
Importers should obtain health certificates from
the relevant health authorities certifying the safety of each
consignment of shellfish. |
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| 3. |
Observe good manufacturing, preparation and hygiene
practices. |
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| 4. |
Observe hygienic practice during food preparation
and storage. |
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Risk Assessment Section
30 December 2000
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