A rapid method for determining the presence of salmonella in food is described. It consists of pre-enrichment in buffered peptone water modified by the addition of dulcitol. and trimethylamine oxide, followed by selective enrichment in a selenite—cystine broth with similar modifications. Changes in the conductance of the selective enrichment broth are monitored continuously using a suitable impediometric instrument. Most of the Salmonella spp. tested gave a fast (˜100 μS/h) and large (> 600 μS) change in conductance, other enteric bacteria much less or no change. The assay is usually complete within 24 h. Samples of foodstuffs, naturally and artificially contaminated with Salmonella spp., were all correctly classified. Some strains of Citrobacter freundii produced a false positive conductance response, and they could not be selectively eliminated using antibiotics or cyanide. The conductance method is simple and easy to use, gives rapid results and involves less media and subculturing than is required for traditional methods.

Sixteen isolates of Escherichia coli were subjected to bacterial restriction endonuclease DNA analysis (BRENDA). Nine of these isolates were from an outbreak of human diarrhoea and produced stable toxin, the remaining seven were non-toxigenic strains from animal and human sources. The isolates from the outbreak produced indistinguishable DNA electrophoretic patterns in spite of their assignment to seven different H serotypes. Their BRENDA patterns were markedly different from the other isolates examined. These results support the epidemiological evidence that a single-strain outbreak had occurred, and they cast doubt on the value of H typing for this particular investigation.

The efficacy of iodophor germicides containing different concentrations of available iodine against transient (inoculated) bacteria and the natural hand microflora was compared with chlorhexidine gluconate (2 and 4%) liquid detergent (Hibitane), non-germicidal soap and a tap water rinse. The tap water rinse was ineffective compared with all other treatments. Only 4% chlorhexidine gluconate liquid detergent and iodophor containing 0·75% available iodine were significantly better than the non-germicidal soap for reduction of transient bacteria, Escherichia coli and Pseudomonas fluorescens, that had been inoculated onto hands. These agents also caused a significant reduction in the number of ‘natural’ micro-organisms released from hands after a standard 15 s hand wash. The low-concentration iodophor products and the product containing 2% chlorhexidine gluconate failed to give results significantly better than the non-germicidal control soap. Baird-Parker medium and standard aerobic plate counts were highly correlated (r = 0·82), so that for studies of Gram-negative bacteria inoculated onto hands as a transient microflora, counts on Baird-Parker medium give a reasonable indication of the natural (residual) hand microflora.

A study was made of the incidence of Neisseria meningitidis and N. lactamica in a school population; 2470 children aged between 5 and 7 years were studied from four schools in Alcala de Henares (Madrid). Nasopharyngeal swabs were taken in June, November and March, between 1979 and 1983.

In all the surveys except one, the proportion of carriers of N. lactamica was higher than that of N. meningitidis, reaching a ratio of about 2:1 in the complete study.

The predominant serogroup of meningococcus found was B (41%), with nongroupable strains reaching 43%. A study of serotypes within group B showed a predominance of nontypable strains (48·5%), while those strains considered to be most virulent (types 2 and 1, 8, 15) reached 40%.

Eighteen per cent of N. lactamica strains were observed to agglutinate with antimeningococcal sera whilst the remainder of the strains were rough. When these strains were studied with the antiscrum-agar technique, using antimeningococcal sera, a high percentage of strains cross-reacted with the meningococci. The susceptibility of strains to sulphadiazine, penicillin, ampicillin, chloramphenicol, rifampicin and spiramycin was determined.

Finally an analysis was made of the effect that an elevated colonization rate of N. lactamica might have on colonization by meningococi. The necessity of using fine epidemiological markers in tracing virulent strains in a population at risk is stressed. Selective prophylactic measures are also necessary.

The growth of coliform organisms on meat tissue from sheep carcasses processed in a commercial abattoir was investigated. The results indicated that for practical purposes the minimum temperature of growth of these organisms on meat may be taken as 8 °C. Equations were derived relating the generation time and the lag time of coliform organisms in raw blended mutton to the temperature at which the meat is held. Estimates of growth obtained with these equations were found to agree closely with the experimental results, especially at temperatures above 10 °C, and allowed the generation times and the lag times for all temperatures up to 40 °C to be calculated. These times were also found to agree closely with the times determined using a strain of Escherichia coli inoculated into blended mutton tissue. A strain of Salmonella typhimurium inoculated in the same way into blended mutton tissue gave longer generation and lag times at temperatures below 15 °C. Therefore, it is believed that the calculated tables of lag and generation times included in this paper can be used to determine the length of time raw chilled meat may be held afterwards at temperatures above the minimum temperature of growth without an increase in the number of any salmonella organisms present, and these times include a safety margin at each temperature.

The study indicates that the mandatory codes of practice presently applied in commercial abattoirs are too stringent. Maintaining the temperature of boning rooms at 10 °C or less does not appear to be necessary providing the meat is processed within the calculated time limits. A relaxation of the restrictions on boning room temperatures would decrease costs, increase worker comfort and safety and would not compromise the bacteriological safety of the meat produced.

A survey into the prevalence of salmonella organisms in sewage in the Borders Region of South-east Scotland is described. A total of 317 isolates representing 34 different serotypes were made, of which only 5 serotypes appeared in animals, supporting the view that the spreading of sewage sludge on to pastureland presents little risk to livestock provided the recommended guidelines are followed. Nevertheless, Salmonella typhimurium phage type 12, identified in sewage, was also recovered from animals in incidents on 11 farms, including 4 which had received sludge from this source. A further 48 isolates (13 serotypes) were obtained from the parallel monitoring of abattoir effluents, indicating that the background level of salmonella infection in the animal population appears to be low in comparison to that in humans.

The sequential acquisition of bacterial flora by premature neonates was studied during a 10 month period. Mean gestational age of the babies was 29·01 weeks and the mean birth weight was 1·728 kg. Escherichia coli and group B streptococci (GBS) colonized the umbilicus of 7 and 6 babies respectively, out of 23 studied, on the first day of life. E. coli and staphylococci were the predominant flora on the 6th day and they colonized 12 and 13 respectively. The oral flora was predominantly Gram-positive cocci, mainly Streptoccocus salivarius which was isolated from 17 out of 22 babies on the 6th day, viridians streptococci were isolated from 14 babies, Staphylococcus albus from 16 babies and group D streptococci from 11 babies. Candida spp. also colonized the oral cavities of 17 out of 22 babies on the 6th day. At the end of the first week of life, the faecal flora was predominantly anaerobic represented by Bifidobacteriurn spp., Bacterioides spp. and Clostridium spp. The commonest facultative faecal flora were E. coli, which was isolated from all the babies, and Strept. faecalis isolated from 20 babies. Early gut colonization by GBS, Bacteroides spp. and Clostridium spp. was noticed in more babies delivered vaginally than by caesarean section where colonization by these bacteria was relatively delayed. The use of prophylactic penicillin plus gentamicin in the special neonatal unit probably prevented systemic spread of any of the potential opportunistic pathogens during the study.

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.

Coumatetralyl was evaluated in the laboratory against Bandicota bengalensis and Rattus rattus. Feeding tests with 0·0375 % coumatetralyl baits produced 100 % mortality after a single day feeding period in B. bengalensis and after a 10–day period in R. rattus. The anticoagulant bait is less palatable in comparison to plain bait. In the case of R. rattus, LFP50 and LFP98 and their 95 % confidence limits were 3·89 (2·62–5·77) days and 11·22 (6·1–20·65) days respectively. Median period of survival and its 95% confidence limits of B. bengalensis and R. rattus were 4·7 (3·85–5·7) days and 11·2 (9·33–13·44) days respectively.

During the winter of 1982 concurrent outbreaks of influenza A and influenza B occurred. The epidemiology and clinical features of 151 cases referred during this time are described, and patients are discussed according to age and presenting clinical syndrome: croup was the commonest presentation in young children, a typical influenza syndrome predominated in young adults, while older patients were more likely to have lower respiratory tract infection. There was no significant difference between the clinical features of influenza A and influenza B. Unusual clinical features include rash, exudative tonsillitis and the need for myringotomy during the course of influenza.

Ether-treated influenza B haemagglutination inhibition (HI) antigen was used in a study of serum collections from three different epidemic seasons.

For diagnostic purposes, ether treatment increased the efficacy of the HI test by about 50 % over the conventional HI technique, raising it to the same level of sensitivity as the complement fixation (CF) test. The treatment reduced the specificity of the HI test, but its reliability in the diagnosis of influenza B infections was only slightly diminished. With regard to evaluation of the immune status of a given population, an HI test using ether-treated antigen from the epidemic influenza B strain seems to give more relevant information about the antibody level associated with protection than a conventional HI test using untreated virus antigen.

Surveillance of certain respiratory viral infections by applying immunofluorescence (IF) examinations to samples of nasopharyngeal secretions has been evaluated using a simplified procedure for the preparation of cell smears. Samples from 711 children living in different parts of Norway were examined during the winter 1982/83 and a positive diagnosis was made for 290 children (41%). Temporal epidemic peaks were observed for respiratory syncytial virus (RSV), parainfluenza virus type 3 and influenza virus. On the other hand, the monthly number of negative samples was almost constant throughout the period. Differences in timing of RSV outbreaks were observed between two regions in Norway. Compared to rapid IF diagnosis, RSV notifications obtained by serological examinations were delayed by several weeks. Rapid virus diagnosis by IF examinations with our simplified procedure for preparation of nasopharyngeal samples seems to be suitable for the epidemiological surveillance of respiratory viral infections, both for its simplicity of preparation of the samples and for its accuracy in defining the time of the actual virus infection. Nevertheless, the method is not without pitfalls; a close cooperation between those who take the specimens and the laboratory is essential, and the IF examinations should be performed by an experienced microscopist.

Recent evidence of bluetongue (BT) virus infection of livestock in scattered localities in the neotropics prompted a serologic survey of cattle in Colombia and Costa Rica. In Costa Rica 48·1% of 1435 bovine animals had BT virus antibody in the agar gel precipitation test (AGPT). In Colombia 51·8% of 635 cattle were AGPT-positive for BT virus. Antibody prevalence ranged from over 50% in the lowlands to 0% in Costa Rica and 19% in Colombian cattle above 2000 m altitude. Neutralization tests indicated that Costa Rican cattle had been exposed to BT virus types 6, 12, 14 and 17.

Mathematical models are developed to aid in the investigation of the implications of heterogeneity in contact with infection within a community, on the design of mass vaccination programmes for the control of childhood viral and bacterial infections in developed countries. Analyses are focused on age-dependency in the rate at which individuals acquire infection, the question of ‘who acquires infection from whom’, and the implications of genetic variability in susceptibility to infection. Throughout, theoretical predictions are based on parameter estimates obtained from epidemiological studies and are compared with observed temporal trends in disease incidence and age-stratified serological profiles.

Analysis of case notification records and serological data suggest that the rate at which individuals acquire many common infections changes from medium to high and then to low levels in the infant, child and teenage plus adult age groups respectively. Such apparent age-dependency in attack rate acts to reduce slightly the predicted levels of herd immunity required for the eradication of infections such as measles, when compared with the predictions of models based on age-independent transmission. The action of maternally derived immunity in prohibiting vaccination in infants, and the broad span of age classes over which vaccination currently takes place in the U.K., however, argue that levels of herd immunity of between 90 and 94 % would be required to eliminate measles.

Problems surrounding the interpretation of apparent age-related trends in the acquisition of infection and their relevance to the design of vaccination programmes, are discussed in relation to the possible role of genetically based variation in susceptibility to infection and observations on epidemics in “virgin” populations. Heterogeneous mixing models provide predictions of changes in serology and disease incidence under the impact of mass vaccination which well mirror observed trends in England and Wales.