The number of reported cases of food poisoning and food-borne disease continues to increase in most countries. The published figures are recognized as being only a small fraction of the true total and the problem is clearly both very large and international.

Of the variety of micro-organisms responsible for outbreaks, Salmonella spp. are by far the most frequently incriminated and in the United Kingdom these organisms cause over 90% of cases (Epidemiology, 1986). The almost universal presence of these organisms in certain common foods, their ability to grow in a wide variety of foodstuffs over a substantial temperature range, the ease with which dissemination occurs from person to person and the prolonged period of excretion following recovery are the properties which, taken together, distinguish Salmonella spp. from other food-poisoning organisms. It is because of these characteristics that salmonellas are really the only food-poisoning organisms in which human beings as carriers pose potential problems as sources of outbreaks. This review is, therefore, confined to a consideration of the practical significance of the faecal carriage of salmonellas by asymptomatic food handlers, to an evaluation of the degree of risk, if any, that such a person may pose and to an assessment as to whether the time and money devoted to the investigation and exclusion of such persons is well spent.

Campylobacters isolated from human, animal and environmental sources during the investigation of a milk-borne outbreak, an incident involving goats' milk and an outbreak associated with puppies were serotyped using the Penner and Lior schemes and biotyped using the Preston scheme. Application of these three methods to the incident strains demonstrated that heterogenicity amongst similar strains exists. This study has confirmed the need to use at least two typing methods when investigating epidemiologically-related strains and we suggest that a combination of a serotyping scheme and an extended biotyping scheme is the most useful.

Coagulase-negative staphylococci isolated from blood or spinal fluid during a period of 1 year in a department of neurosurgery, were analysed by biotyping, antibiotic resistance pattern and plasmid profiles. Altogether 41 isolates from 19 patients were studied. About 90% of the isolates were Staphylococcus epidermidis. The antibiotic resistance pattern seemed to be closely related to antibiotic usage in the unit. Most common was resistance to penicillin (63%), trimethoprimsulphamethoxazole (49%) and cloxacillin (39%) while resistance to gentamicin was seen in only one strain.

In several cases species and antibiograms were identical in isolates from different patients. Plasmid pattern analysis could then be used for identification of different strains. In one instance, plasmid pattern and restriction enzyme analysis confirmed that two patients probably were infected by the same strain.

An epidemiology analysis of a series of 12 Aeromonas hydrophila infections, including six of septicaemia, which occurred on several wards of one hospital during the summer of 1982 is presented. The hypothesis that the hospital water could be the source of these infections was supported by the isolation of 1–10 motile aeromonads per ml in most of the water samples collected from various points on the hospital water system. Electrophoretic esterase typing was used as an epidemiological screening method to determine the relationship between bacterial strains isolated from the patients and those from water samples. The epidemiology of A. hydrophila infection in the hospital was found to be complex. Amongst the 15 strains of A. hydrophila isolated from patients were 8 zymotypes, while amongst the 126 strains from the water samples there were 37. In some cases, several zymotypes were isolated simultaneously from the same tap water. On one ward, the same zymotype was found in 2 patients and in 2 water samples. The prophylactic measures taken in 1982–5 to avoid oral contamination of immunocompromised patients with infected hospital water have significantly reduced the number of cases of septicaemia. This success has constituted additional retrospective evidence for the water-borne origin of these infections.

Restriction enzyme fingerprinting was applied to 72 transferable trimethoprim resistance plasmids to examine aspects of their epidemiology and molecular relatedness.

These plasmids had previously been divided into 25 groups according to differences in mol. wts and in antimicrobial resistance determinants. Restriction enzyme fingerprinting allowed the plasmids to be further divided into 44 different groups. The groups based on molecular weight and resistance patterns often, but not invariably, corresponded with those based on restriction enzyme fingerprints. Some plasmids with the same mol. wt and resistance pattern had different digest fingerprints and conversely, although more rarely, plasmids which differed in molecular weight by as much as 10 MDa or in resistance pattern by one resistance marker, had indistinguishable fingerprints.

The plasmids were initially divided into three broad categories according to which restriction enzymes gave fingerprints of 6–20 fragments. These categories differed in the molecular weights of the plasmids contained, the numbers of resistance markers, and the proportions of the plasmids which carried transposon Tn7.

Some plasmids were more widespread and persistent than others with the same mol. wt and resistance pattern but with a different restriction enzyme fingerprint.

Thus, application of this technique has shown the trimethoprim resistance plasmids studied to be more diverse than was indicated by determination of mol. wt and resistance pattern, and has indicated changes in the plasmid pool over the 3 years during which they were collected.

Samples were collected at two abattoirs from four sites on pig carcasses as they were being placed in a chiller. Bacteriological examination showed that no single sampling site could be used to assess the microbiological status of pig carcass surfaces. Sampling from multiple sites on a carcass may be required to assess the degree of contamination by different bacteria. It is suggested that the hygiene of slaughtering and dressing of pig carcasses at an abattoir cannot be assessed on a single visit and that a number of visits are necessary to establish a hygiene pattern.

The intradermal inoculation of four badgers with small numbers of Mycobacterium bovis resulted in localized lesions with ulceration which slowly healed by 5 months after inoculation. Lesions of generalized tuberculosis were seen in three badgers, one of which died at 17 months post-inoculation and in the remaining two killed 22 months post-inoculation. In the fourth badger lesions were confined to the draining lymph node of the inoculation site but M. bovis was isolated from the liver. Monthly clinical sampling of faeces, urine, tracheal aspirate and inoculation site exudates detected only the excretion of M. bovis from the inoculation site of one badger. There were marked seasonal variations in body weight but significant weight loss was observed during the second year in all four badgers, particularly prior to death. Four badgers inoculated intratracheally with a similar inoculum of M. bovis and another two control badgers showed no evidence of infection with M. bovis.

Swabs and water samples from a hospital water system were cultured for legionellae over an extended period. Legionella pneumophila serogroup 1, including outbreak associated strains, were isolated in small numbers from approximately 5% of these samples despite implementation of the current DHSS/Welsh Office regulations. No cases of nosocomial legionnaires' disease were proven during the study. Physical cleaning and chemical sterilization of taps, and replacement of washers with ‘approved’ brands did not eradicate the organisms. Eradication of legionellae in hospital water supplies appears to be unnecessary in preventing nosocomial legionnaires' disease provided the current DHSS/Welsh Office recommendations are implemented.

Optimal conditions were determined for performing antibody measurements (ELISA), lymphocyte transformation tests and, to some extent, skin tests in badgers. These parameters, together with the bacteriological and pathological studies reported previously (Pritchard et al. 1987), were used to follow the course of intradermal and intratracheal challenge of badgers with bovine tubercle bacilli. Two challenge doses were used for each route of infection and two animals received each dose. None of the four animals challenged by the intratracheal method showed any evidence of infection, suggesting that adult badgers may have some resistance to challenge by this method. All four animals challenged intradermally developed lesion of tuberculosis.

Immunologically the disease passed through three phases. There was an early phase in which lymphocyte transformation to whole BCG steadily and significantly increased, and skin tests to tuberculin became positive but there was little change in antibody levels. This was followed by an intermediate phase of variable skin responses, fluctuating lymphocyte transformation and significant increase in antibody levels. The final phase, which was only seen in two animals with extensive disease, was associated with changing skin reactions and falling lymphocyte responses, together with a sudden increase in antibody levels.

This paper presents the first formal evidence of cell-mediated immunity to tuberculosis in the badger, which may delay onset and prolong the survival of challenged animals.

The Salmonella Reference Centre in Johannesburg received 14059 strains of human origin between 1979 and 1984. A significant proportion (6·3%) proved to belong to subspecies II. The majority were cultured from faecal material, usually associated with symptoms related to the gastrointestinal tract. They comprised 884 isolates, represented by 203 serotypes, of which 45 were new serotypes.

The poor hygienic conditions found in many rural areas, together with possible contamination of food and water by wild animals, may contribute to the greater frequency of human S.II infections and the widespread occurrence of unusual serotypes in man in this geographic region.

During the period 1968–85 shigella organisms were isolated from stool specimens of 1562 patients attending Tygerberg Hospital, situated in the south-western province of the Cape of Good Hope of the Republic of South Africa. Shigella flexneri (72% of patients) was the commonest subgroup identified. Sh. sonnei was the second-commonest isolate (20%), with smaller number of Sh. boydii (5%) and Sh. dysenteriae (3%). Sh. dysenteriae has not been isolated since 1979. In 1985 30% of isolates were resistant to ampicillin and 52% to trimethoprim-sulphamethoxazole. During this period 12 cases of shigellaemia were seen, 11 in young infants less than 13 months of age who were malnourished in 6 cases. The single adult had had a previous gastrectomy and splenectomy.

The aim of this study was to establish the risk of acquiring common respiratory and gastrointestinal illness for paediatric nurses. Using self-administered questionnaires, student nurses at two children's hospitals and students at one school of medical technology reported biweekly the number of minor illnesses, symptoms, and indicators of severity of infection over a 3-year period (1975–8). Although a systematic bias was evident with some symptoms, others appeared to be quite reliable. The following four syndromes were defined to estimate the risk: upper respiratory syndrome (URS), lower respiratory syndrome (LRS), respiratory and gastrointestinal syndrome (RGS), and gastrointestinal syndrome (GS). Surveillance days were allocated to groups with high- or low-intensity contact with children. The incidence of all illnesses was 2·9 per person-year in the low-intensity contact group and 4·4 per person-year in the high-intensity contact group. The reported incidence of LRS and RGS in the high-intensity contact group was 1·55 times higher than in the low-intensity group (P < 0·001). LRS and RGS incidence was similar in nurses at both schools. During low contact periods it corresponded to that of the medical technologists.

Twelve herds of dairy cows were examined by rectal swabbing for the presence of Campylobacter jejuni. Ten herds were positive with the incidence of colonized animals ranging from 10 to 72% of those tested. With the exception of the two negative herds where mains water only was consumed, all animals drank from rivers or streams when grazing. There was no relationship between total and coliform counts and the presence of C.jejuni in raw milk. However, milk from one farm that consistently gave positive results had significantly higher Escherichia coli counts than other samples.

A total of 181 samples of irrigation water from the farmlands of Granada were examined for the presence of Salmonellaspp. At the same time 849 samples of the crops from these farmlands and of vegetables sold in city market-places were studied. Sampling was done regularly over the period of study which ran from March 1981 to February 1983. Isolates from these sources were compared with 93 salmonellas isolated from human pathological material at various hospitals of the city of Granada from 1979–80, and again from 1981–3.

The most commonly isolated serotypes of human origin were S. typhimurium and S. enteritidis. In irrigation waters and in crops, S. typhimurium, S. kapemba, S. london and S. blockley were found to be the most common. The results indicate a close relationship between the isolates from the irrigation waters and those from the vegetables, but their relationship to prevalent human infections is less clear.

We assembled an international collection of strains from sporadic and epidemic human infection with Streptococcus zooepidemicus (Lancefield group C) for laboratory study. Cultural and physiological characteristics of the isolates were determined, including biotyping with the API 20 STREP test kit and susceptibility testing with penicillin, erythromycin and tetracycline. The strains were examined for bacteriocin production and sensitivity and typed with a specially developed group-C streptococcal bacteriophage system incorporating a panel of 14 phages. Results of these tests gave useful discrimination between many of the strains: differences were shown between each of the major outbreak strains, including those complicated by post-streptococcal glomerulonephritis.

Serious group C streptococcal infection may be caused by S. zooepidemicus and isolates should be identified to species level; the application of a typing scheme such as this may help to distinguish epidemiological patterns of infection.

The occupational risk of acquiring minor respiratory infections for paediatric student nurses was estimated by performing serological examinations with influenza A, B, C, parainfluenza, mumps, respiratory syncytial virus, adenovirus and Mycoplasma pneumoniae at 6-month intervals over a period of 4 years in paediatric student nurses at two schools of nursing and students at one school of medical technology, litre increases against all tested agents occurred 1·86 times more often in the student nurses than in the medical technology students, the most frequent agents in both groups being influenza A and B. No difference in the relative distribution of the agents could be verified in the two occupational groups. Data on the protective value of pre-infectious antibody levels for influenza A, B, and coronavirus OC43 and on the importance of the spread of single agents among classmates are presented.

Isolations of salmonellas from humans and food products are recorded for the period 1981–5 and an attempt has been made to investigate the relationship between serotypes isolated from humans and those from meat products.

The predominant serotypes isolated from humans were Salmonella typhimuriunu S. enterilidis and S. virchow. S. typhimurium was commonly isolated from a range of meat products. S. derby was one of the most common serotypes isolated from tripe and sausages but was relatively uncommon in humans.

Salmonellas were found in < 0·5% of most cooked meat products apart from tripe and udder (3·2%) and pet foods (12·4%). Isolations from raw meats ranged from 3 % for pork to 28% for poultry.

Incidents of salmonella infection in humans in Manchester increased between 1981 and 1984 but decreased during 1985.

Three unrelated severe infections with Streptococcus zooepidemicus occurred in England in 1985. The first patient developed septic arthritis, which has not been recorded before with this organism. The second died with septicaemia, pneumonia and post-streptococcal glomerulonephritis, the only record so far of nephritis following sporadic S. zooepidemicus infection and of nephritis and systemic sepsis in the same patient. The third patient experienced septicaemia during pregnancy but recovered without complications. A likely animal source of infection was found in only one case.