Continuous source outbreak of campylobacteriosis traced to chicken.

Poultry is a source of human campylobacteriosis, but a large continuous source outbreak, heretofore, has not been attributed to both a single source of poultry and single serotype of Campylobacter. Here we report an outbreak of C. jejuni affecting 6 catering college trainees and 13 patrons of a restaurant in southern England. An epidemiological investigation successfully tracked the outbreak source to the farm of origin. Frequency of occurrence of campylobacters and outbreak serotype distribution were determined in index cases, the local population, and local chicken suppliers. The source farm was investigated and the effect of interventions assessed. A single outbreak serotype of C. jejuni was isolated from trainee chefs, patrons, and chicken supplied to the college by Wholesaler A. The Campylobacter isolation rate for Wholesaler A was 89% (98% outbreak serotype), compared to 40% for non-Wholesaler A (10% outbreak serotype). The isolation rate for 14 months averaged 85% (99% outbreak serotype) in chickens grown on two farms (X and Y) supplying Wholesaler A, contributing approximately 40% to all local cases. In the research reported here, a specific strain and hygiene practice were found to be important for understanding transmission of Campylobacter from poultry to humans in this outbreak.

Modification of the standard method used in the United Kingdom for counting Escherichia coli in live bivalve molluscs.

The standard method for counting Escherichia coli in live bivalve molluscs is labour intensive and takes three days to obtain a result. Modifications to the standard method were investigated in a collaborative trial conducted in five centres. No significant difference was found between results based on the presence of acid at 24 hours (h) in first stage tests and those based on the presence of acid and gas after 48 h (standard method). The use of the chromogenic medium BCIG (5-bromo-4-chloro-3-indolyl-beta-D glucuronide) agar incubated at 44 degrees C to confirm first stage tests was also found to give equivalent results to conventional confirmation tests. The preferred, modified method removes the presence of gas as a criterion of detection, uses a chromogenic agar medium to confirm the presence of E. coli, and gives results within 48 h. A distribution of simulated samples and selected strains of E. coli to other laboratories using the PHLS external quality assurance scheme for shellfish found no significant difference between results obtained by the standard and modified methods.

Microbial ecology of Campylobacter jejuni in a United Kingdom chicken supply chain: intermittent common source, vertical transmission, and amplification by flock propagation.

A study of Campylobacter jejuni on a broiler chicken farm between 1989 and 1994 gave an estimated isolation rate of 27% (3,304 of 12,233) from a 0.9% sample of 1.44 million broiler chickens from six to eight sheds over 32 consecutive rearing flocks comprising 251 broiler shed flocks. During the study, C. jejuni was found in 35.5% of the 251 shed flocks but only 9.2% (23 of 251) had Campylobacter isolates in successive flocks, with 9 of those 23 sheds having the same serotype between consecutive flocks, indicating a low level of transmission between flocks. Analysis of a systematic sample of 484 of 3,304 (14.6%) C. jejuni isolates showed that 85% were of 10 serotype complexes but 58% were of 3 serotype complexes, indicating a high degree of strain similarity throughout the entire study. The three commonest types were detected in 8 of 32 flocks during the 5-year study period, suggesting an intermittent common external Campylobacter source. This hypothesis was tested by a retrospective cohort analysis of C. jejuni rates and types by reference to hatchery supplier of the 1-day-old chicks. Isolation rates of C. jejuni and frequency distribution of types were determined in 6-week-old broiler chickens identified by the hatchery supplying the original chicks. The isolation rate of C. jejuni in broilers, supplied by hatchery A, was 17.6%, compared to 42.9% (P < 0.0001) for broilers reared from chicks supplied by hatchery B. In two instances, when both hatcheries were used to stock the same farm flock, Campylobacter isolates were found only in those sheds with chicks supplied by hatchery B. Thus, the frequency distribution of Campylobacter types for chickens supplied by the two hatcheries over the 5-year period showed marked dissimilarity. These findings suggest that the isolation rate and type of Campylobacter isolates in broiler chickens was associated with the hatchery supplying chicks. The lack of diversity of types and the intermittent high positivity of sheds is evidence for a common source of C. jejuni introduced by vertical transmission rather than contamination at the hatchery or during transportation.

Factors affecting results obtained with European Community tests for pasteurized milk sampled at the heat treatment establishment.

A total of 3000 samples of pasteurized milk taken at the heat treatment establishment over a 1-year period were examined for the presence of phosphatase and by a plate count at 30 degrees C, a coliform count at 30 degrees C, and a plate count at 21 degrees C after pre-incubation of the sample for 5 days at 6 degrees C, performed as prescribed in EC Directive 85/397/EEC. Samples were also examined for presence of Listeria species. Of 2690 samples (1713 from small dairies and 977 from large commercial premises) received at 4 degrees C or less, 96 (3.6%) has a plate count at 30 degrees C exceeding 30,000 organisms per ml, 608 (22.6%) contained 1 or more coliforms per ml, and in 1327 (49.3%) the pre-incubated count exceeded 100,000 organisms per ml. Thirty two samples from 23 dairies contained phosphatase. Listeria species were detected in 25 samples; only three of these strains were identified as Listeria monocytogenes. Results were analysed to determine relationships between factors which might affect test results. Samples from small dairies showed significantly higher coliform counts and pre-incubated plate counts than did those from large commercial premises. They were also more likely to contain phosphatase or Listeria species. Samples were significantly more likely to contain coliforms when taken in the July-September quarter or if received in glass containers.

The occurrence of Listeria species in milk and dairy products: a national survey in England and Wales.

A total of 4172 samples of milk, cheese and other dairy products were examined over a 1-year period for the presence of Listeria species. Strains of Listeria were found most frequently in soft, ripened cows milk cheese; 63 out of 769 (8.2%) samples contained Listeria monocytogenes, 25 samples contained species other than L. monocytogenes, and 18 samples contained both L. monocytogenes and other Listeria spp. Eleven samples of pasteurized cows milk (1.1%) from four dairies contained L. monocytogenes, and other Listeria spp. were isolated from a further five samples. Goats and ewes milk and their products, yogurt, cream and ice cream also occasionally contained Listeria spp. Levels of Listeria were usually low, but 20 samples of cheese contained more than 1000 cfu/g. Most strains of L. monocytogenes belonged to serotype 1/2 (58%) or serotype 4b (33%).

Frequency of isolation of campylobacter spp., Yersinia spp. and salmonella spp. from small mammals from two sites in Southern Britain.

Small wild mammals were trapped at two sites in the United Kingdom: Skomer Island, Dyfed and a farm in Dorset. Faecal samples were collected from 43 rodents of two species on Skomer and tested for the presence of Yersinia. Samples of faeces and of material from the terminal ileum were collected from 141 animals of eight species in Dorset and tested for Campylobacter, Yersinia and Salmonella. In addition some samples of spleens from the Dorset animals were tested for Campylobacter. Four typable isolates of Campylobacter were obtained from the Dorset site, two from spleens from shrews and two from intestinal contents from a bank vole. Nineteen isolations of Yersinia were made from the Skomer animals and seventeen from animals in Dorset. No isolations of Salmonella were made from any of the animals sampled.

The source of Yersinia spp. in pasteurized milk: an investigation at a dairy.

Pasteurized bottled milk supplied by a single dairy was frequently found to be contaminated with Yersinia spp. Investigations were carried out at the dairy in an effort to pinpoint the source of these organisms. Viable counts obtained from milk bottle rinses indicated that bottle washing was often unsatisfactory, and on one occasion Y. frederiksenii was isolated from the pooled rinse water of six bottles. Samples of milk were taken on arrival at the dairy and at various stages following pasteurization. Heat resistance tests carried out on strains of yersinia isolated from pasteurized milk indicated that they would not survive the pasteurization process. However two strains of yersinia were isolated from a sample of milk taken immediately after pasteurization but before bottling. The thermograph indicated that the time/temperature conditions applied during pasteurization were adequate. The presence of yersinia strains in the milk at this stage therefore suggests that undetectable levels of raw milk were being allowed to contaminate the pasteurized milk. The absence of yersinia in cartoned samples produced on the same day as contaminated bottled samples indicated that environmental contamination of the bottle filler valve also may have occurred at times. Results of this investigation indicate that increased vigilance is required to ensure proper operation of pasteurizers and bottle washers.

Excretion of Yersinia spp. associated with consumption of pasteurized milk.

Yersinia enterocolitica biotype 1, serotype O.10K was isolated from 19 patients in the paediatric wards of a district general hospital over a period of 3 months. Fifteen cases were patients on the medical ward. Shortly afterwards, Y. enterocolitica biotype 1, serotype O.6, 30 was isolated from a further 17 patients on this ward in 1 month. The same serotypes of Y. enterocolitica were isolated from the pasteurized milk supplied to the ward. Epidemiological evidence indicated that contaminated pasteurized milk was the source of the yersinia organisms excreted by the patients.

The occurrence of Listeria monocytogenes in cheese from a manufacturer associated with a case of listeriosis.

A case of listeriosis was associated with the consumption of a soft cheese produced in England. Goats cheese and other products from the same food manufacturer were examined for the presence of Listeria over the following 11 months. Listeria monocytogenes was isolated from 16 of 25 cheese samples on retail sale, 12 of 24 cheese samples obtained directly from the factory, and from shelving within the plant. Phage-typing of 68 isolates of L. monocytogenes from cheese samples and the factory showed that 66 (97%) were indistinguishable from the strain isolated from the patient's cerebrospinal fluid and stool. L. monocytogenes was not isolated from seven goats milk or two yoghurt samples. Listeria innocua was isolated from 10 cheese samples, two of which contained no other species of Listeria. Levels of L. monocytogenes shortly after production were low (less than 10/g), but were higher (10(5)-10(7) cfu/g) in six of the 16 cheese samples obtained from retail outlets. Multiplication of L. monocytogenes was demonstrated in cheeses contaminated at the factory and held at 4 degrees C in the laboratory.

The use of alkalinity and incubation at 9 degrees C for improved recovery of Yersinia spp. from faeces.

Recovery of Yersinia enterocolitica and related strains from faecal samples enriched in 1% buffered peptone water (pH 7.2) and incubated at 4 degrees C for 7-21 days was compared with recovery from 1% peptone water buffered to pH 8.0 and incubated over the temperature range 4-26 degrees C. Best recovery was obtained by use of the alkaline medium incubated at 9 degrees C. Greatest recovery was obtained after incubation for 10-14 days, but most strains (greater than 75%) were recovered after 1 week.

An appraisal of methods used in the examination of retail samples of cows milk.

The use of the methylene blue test for the examination of cows milk was investigated in an inter-laboratory survey. A poor relationship was found between results of these tests and total viable counts. Coliforms were detected in a large number of pasteurized milks, indicating frequent post-pasteurization contamination. No relationship was found between the results of the methylene blue test and the presence of coliforms. Results from this survey highlight the need for reappraisal of the methylene blue test as a statutory method for the examination of milk. A total viable count and coliform test are suggested for providing information regarding dairy hygiene and the quality of the product at the point of retail sale.

The microbiology of cooked prawns and shrimps on retail sale.

In an inter-laboratory survey, 148 samples of cooked prawns and shrimps were obtained at the point of sale to the consumer. Salmonellae and Vibrio parahaemolyticus were not detected. Yersinia enterocolitica was isolated from three samples. Results for total viable count and presence of Escherichia coli and Staphylococcus aureus complied well with available guidelines for imported cooked prawns, suggesting that the risk of food poisoning from retail samples of these foods in the South of England is minimal.

The microbiology of selected retail food products with an evaluation of viable counting methods.

In an inter-laboratory survey, the pour plate, surface spread, agar droplet and spiral plate methods were used in parallel with the surface drop method for enumeration of micro-organisms in foods. Good agreement was obtained between all surface methods of enumeration, but there was poor agreement between molten agar methods and the surface drop method. A total of 1143 samples of food that were ready for consumption at the point of retail sale were examined. Eight types of food products were chosen: meat pasties, sausage rolls, real-cream slices, synthetic-cream slices, mayonnaise-based coleslaws, faggots, patés and continental sausages. The results of this survey suggest that the upper limit for an acceptable viable count should vary according to the food product. Salmonellae were not isolated on any occasion. Potentially harmful organisms were not isolated at levels expected to constitute a public health hazard. Information concerning the nature of the product, the total viable count, the presence or absence of pathogenic, toxigenic or indicator organisms, the spectrum of the bacterial flora and the relative predominance of each organism must all be considered when assessing the microbiological acceptability of retail 'ready to eat' products.

Tryptophan disposition in psychiatric patients before and after stress.

Non-esterified fatty acid and total and free tryptophan were determined in the plasma of psychiatric patients unselected with respect to psychiatric diagnosis and in the plasma of normal subjects before and after physiological and psychiatric tests. Retarded patients had significantly low total and free tryptophan values which correlated negatively with agitation. Total tryptophan fell significantly after testing in the non-retarded subjects. The only biochemical abnormality significantly associated with a diagnosis of primary depression was the rise of plasma non-esterified fatty acid after testing. Thus, tryptophan abnormalities were associated more with psychiatric rating scores than with diagnoses.

The effect of adrenaline on human platelet MAO activity.

Platelet monoamine oxidase (MAO) activity was determined before and after the subcutaneous administration of adrenaline to nine healthy volunteers. Significant increases were found 15 min and 1 hr after adrenaline in the enzymatic activity with benzylamine acting as substrate. Increases were also found in all but two samples in the activity towards tyramine. Such increases may be part of a general response to "stress", and, if so, need to be taken into account when interpreting changes in platelet MAO activity in psychiatric patients.

The acute effects of oral (--)-tryptophan in human subjects.

1 The psychotropic effects of a single oral dose of (--)-tryptophan (5 g) in human volunteers were investigated using a series of physiological and psychological tests. 2 Self-ratings of mood showed increase in drowsiness but no euphoria was detected. 3 Severe initial nausea occurred and headache increased; other bodily symptoms were unaffected. 4 Trptophan caused increased activity in the slow wavebands of the EEG but did not alter the other physiological measures. 5 The levels of total and free tryptophan in the plasma increased 8 and 20 fold respectively to peak levels 2 h after ingestion.