Oyster-associated outbreaks of Norovirus gastroenteritis in Singapore.

Outbreaks of gastroenteritis associated with the consumption of raw imported half-shelled frozen oysters occurred in Singapore between 16 Dec 2003 and 04 Jan 2004. A total of 305 cases were reported with clinical symptoms of diarrhoea (94%), abdominal cramps (72%), vomiting (69%) and fever (54%). The median incubation period was 30.8h and the duration of illness was 2-3 days. The overall relative risk of oyster consumption was 14.1 (95% CI: 8.3-24.0, P<0.001). Stool and oyster samples tested negative for common bacterial pathogens, including Vibrio parahaemolyticus. However, stool samples were positive for the presence of Norovirus group II RNA via RT PCR while oyster samples indicated the presence of Norovirus particles by electron microscopy. The clinical and epidemiological features were suggestive of Norovirus gastroenteritis and were subsequently confirmed by laboratory tests of stools and implicated oysters. Steps have been taken to ensure that food outlets do not thaw frozen oysters and serve them raw.

Random amplified polymorphic DNA (RAPD) fingerprints for identification of red meat animal species.

The random amplified polymorphic DNA (RAPD) method was used to generate fingerprint patterns for 10 meat species: wild boar, pig, horse, buffalo, beef, venison, dog, cat, rabbit and kangaroo. A total of 29 10-nucleotide primers, with GC contents ranging from 50-80%, were evaluated for their specificity and efficiency. The fingerprint patterns that were generated were found in some cases to be species-specific, i.e. one species could be differentiated from another. The advantages and disadvantages of using RAPD-PCR for the identification of red meat species are also discussed.

Restriction fragment length polymorphism (RFLP) of Salmonella organisms.

Genetic relatedness of 20 Salmonella isolates comprising 16 serotypes was analysed by restriction endonuclease digestion of the total DNA with six endonucleases individually. The rDNA fingerprints generated by EcoRI were more polymorphic, each serotype showed a unique fingerprint sharing several core (monomorphic) bands with several polymorphic bands. Eight characteristic NciI rDNA fingerprints were found. Similar rDNA RFLP patterns were observed in strains of Salmonella from different serotypes.

Pyaemia in pigs.

Pyaemia is by far the most important cause of condemnation in pigs slaughtered in Singapore abattoirs. Between 1983 and 1987, 1757 from a total of 4,899,731 pigs were condemned by meat inspectors for pyaemia, accounting for 0.036% of the total condemnations. The common post-mortem findings of affected pigs during the 5-year period are presented. Abscesses were most commonly seen in the liver (22%), spleen (21%), gastrohepatic lymph node (20%) and bronchial lymph node (17%). Pseudomonas pseudomallei was the most predominant organism isolated, accounting for 39% of the pyaemic cases. The public health significance of abscesses in pigs is discussed with particular reference to melioidosis.