A quantitative method for testing serum diphtheria antitoxin levels was set up using a diphtheria antitoxin radioimmunoassay (RIA). The results of this RIA correlated well with the Schick test in 554 subjects and with intradermal neutralization tests in guinea-pigs in a small group of subjects. The RIA was suitable for use on blood collected by fingerprick on to a disc of standard chromatography paper. These discs could be stored at room temperature for at least 1 month. If storage for more than 6 months was required –20 °C was found to be better. Experience with this RIA in a total of 2349 subjects indicated that it is more accurate, rapid and less costly than Schick testing. The RIA should prove to be the preferred method for testing diphtheria immunity in population surveys.

In a population of approximately 300000 there were 150 illnesses attributable to chlamydial infection from January 1975 to June 1983 and nearly all were presumed due to Chlamydia psittaci. Diagnosis was based on the complementfixation (CF) test, the disadvantages of which are discussed, especially anamnestic responses.

There were 73 cases of pneumonia, 37 febrile respiratory infections, 35 miscellaneous conditions and five asymptomatic seropositive contacts.

The annual number of cases was lowest in 1976 (3) and increased to a maximum in 1980 (28) followed by a sustained high level. No seasonal variation was observed.

A presumptive bird source was present in only 17% and detailed consideration of cases in one rural practice suggests that the infection may possibly be more endemic than zoonotic.

This paper presents three different methods of estimating the number and age distribution of individuals susceptible to pertussis in England and Wales. The first approach is an extrapolation from data in the prevaccine era, the second is based upon theoretical consideration of the transmission dynamics of pertussis, and the third is a detailed cohort analysis of available notification and vaccination data. Each of these analyses suggests that the total number of people susceptible to pertussis infection in England and Wales has remained at 3–4 million for the past 40 years, despite the increase and changes in numbers vaccinated. The effect of vaccination has been to reduce the incidence of infection and disease, but not to reduce the number of susceptibles. These findings, which are consistent with ‘mass action theory’, could be tested by an appropriately designed seroepidemiological survey.

The prevalence of scropositivity to Legionella spp. was studied in inmates and staff members of two geriatric hospitals (Rahel and Sinai); attendants to a geriatric Day Club; and 26 old people with entirely independent households. The sera were examined by indirect immunofluorescence with antigens of six Legionella species (L. pneumophila, L. longbeachae, L. micdadei, L. gormanii, L. dumoffii and L. bozemanii). A titre of ≥ 256 to at least one antigen was obtained in 30·5% of patients and 35·7% of staff members from Rahel; 12·1% of patients and 17·2% of staff members from Sinai; 9·1% of attendants to the Day Club; and none of 26 old people with their own households. All the positive patients from Rahel reacted with L. pneumophila, but only four of seven of the positive patients from Sinai did so; none of the seropositive subjects from the Day Club reacted with this agent.

The results indicate intramural exposure to agents of legionellosis, at least for the Rahel Hospital.

The application of Preston enrichment broth to isolation of ‘thermophilic’ campylobacters from water has been investigated. Enrichment substantially increased the yield of such organisms. The optimum timing for subculturing the broth was after 48 h incubation. Despite the addition of aerotolerant supplement to the broth the number and variety of isolates was greater when the broth was incubated microaerically than when it was incubated in air.

Growth and survival of four Campylobacter jejuni strains in yolk, in liquid whole egg and in white during aerobic storage at 37, 20 and 4 °C was followed. In 48 h at 37 °C the coll counts of C. jejuni increased by about 3 log10 units in yolk and 1·60–3·3510 log units in liquid whole egg. The growth of C. jejuni was slightly better in yolk than in liquid whole egg. At 20 °C during 48 h the cell counts decreased by about 0·5–1·5 log10 units in yolk and in liquid whole egg. At 4 °C the decrease in cell counts after 21 days ranged from 1 to 2 log10 units, except for one strain, KH 3, which could not be detected after 14 days storage in yolk. In liquid whole egg the cell counts of this strain also decreased considerably during storage.

In white the number of inoculated C. jejuni cells decreased rapidly. The killing effect of white was shown to be temperature-dependent; at 37 and 20 °C no positive samples were detected after 24 h and at 4 °C no positive samples were found after 48 h.

A total of 289 non-O1 Vibrio cholerae (NVC) strains and 20 rough V. cholerae (RVC) strains isolated in an endemic area were tested for antibiotic resistance and for transferable R-plasmids. Twenty three per cent of NVC and 40% of the RVC isolates were found to be resistant to one or more drugs. Eight NVC and four RVC strains possessed multiple drug resistance, varying from four to eight drugs. The common spectrum found in NVC isolates were chloramphenicol and streptomycin (CS) or chloramphenicol, streptomycin, tetracycline and ampicillin (CSTA). Resistance to sulphamethoxazole (Su) and to trimethoprim (Tm) was encountered infrequently. In RVC isolates in addition CSTASuTm determinants, resistance markers to aminoglycosides kanamycin, gentamicin and neomycin were also found. Eighteen of the 27 V. cholerae strains with two or more resistance determinants transferred them en bloc to Escherichia coli K12. The level of resistance in the recipient strain was equal to or greater than that of the donor vibrio strains. Most of the strains possessing solitary resistance markers were unable to transfer them. βlactamase production could be demonstrated in 92·8% of the ampicillin resistant strains. None of the strains was resistant to nalidixic acid or furazolidone. The results emphasize the importance of antimicrobic susceptibility determination of V. cholerae isolates, regardless of the serotypes, before commencing chemotherapy.

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.

The development of the normal intestinal microflora of the small intestine, caecum and large intestine of specific pathogen-free (SPF) chickens, was studied in the period from hatching to 84 days of age.

No bacteria were detected in any of the sites at hatchery (day 1), but by day 3 significant levels of faecal streptococci and coliforms were isolated from all sites. The flora of the small intestine was limited to faecal streptococci and coliforms for the first 40 days and then lactobacilli became established and dominated the flora.

A large variety of facultative and strictly anaerobic organisms colonized the caecum. Many of these species were transient and were only present for a limited period; after 40 days the flora stabilized to consist predominantly of faecal streptococci, Escherichia coli, Bacteroides spp. and Lactobacillus sp.

The flora of the large intestine was composed of organisms also present in the small intestine or the caecum.

These findings differ from previously published studies on conventionally reared chickens in that the number of species isolated and the population levels of organisms are much lower. This probably reflects the absence of continuous environmental challenge to the chickens because of the housing and feeding facilities in which the chickens were maintained.

A prospective study identified 785 pregnant women who had been shown to possess complement fixing antibodies against cytomegalovirus (CMV) during a previous pregnancy. As these women were thus known to have been immune prior to their subsequent conception, their neonates were examined for evidence of congenital CMV infection. Specimens were obtained from 725(92%) of the neonatcs and congenital infection was found in only one (0·14%). The elder sister of the infected child was also shown, by retrospective testing of her stored cord serum for specific IgM antibodies, to have been infected in utero. Thus, one woman was identified who had delivered consecutive siblings congenitally infected with CMV. We conclude that some women have a propensity for intra-uterine transmission of CMV, despite being immune prior to conception, and speculate that such women may have acquired their infections perinatally.

The levels of cytopathic enteroviruses at two wastewater-treatment works were monitored over a period of 9 months. The maximum level of virus at works 1 was 72500 p.f.u. l-1 and at Avorks 2,57500 p.f.u. l-1. Examination of process efficiency showed an overall reduction of 63% for works 1 and 26 % for works 2 when used without lagooning. When lagooning was employed at the second works, virus reduction was 97%. Individual treatment processes showed poor reduction of virus levels. Sedimentation and rapid sand filtration had no significant effect on levels whilst both percolating filtration and activated sludge showed some reduction. Only lagooning resulted in substantial reductions of virus levels.

Studies were carried out in South America to assess the effect of maternally derived antibody (MDA) on the responsiveness of calves to FMD vaccination. It was found that calves with MDA did not merely fail to respond to vaccination, but that their serum titres were depressed. This depression was proportional to the level of pre-existing MDA at the time of vaccination and following primary vaccination it persisted for a least 60 days. High MDA titres interfered with both primary and secondary responses. Animals with relatively low MDA titres were able to respond to vaccination, or at least to be sensitized so that on revaccination they showed a satisfactory response. The half-life of MDA was shown to be approximately 22 days, suggesting that under field conditions significant MDA titres are likely to persist for 4–5 months. A trial carried out in Brazil in which the primary course of two inoculations, 4 weeks apart, was initiated when the calves were 5–6 months of age, resulted in the reduction of FMD in the calf population from 11% to 0·9% over a 12-month period. The use of vaccination programmes of this type to lessen the incidence of FMD in young bovines is discussed.

A micro test for the detection of rubella IgG antibody by passive haemolysis in free solution (MIH) is presented. The technique is reproducible, sensitive, simple to perform and economical in the use of reagents. Identical results were obtained in all but one of 408 tests on serum specimens screened for rubella antibody at 15 i.u./ml by the MIH and haemagglutination inhibition (HI) techniques. The quantitative potential of the MIH test and the relative merits of the MIH, HI and radial haemolysis (RH) procedures for rubella screening are discussed.

Twenty-nine boys in a boarding school were present during a large outbreak of influenza A H1N1 in 1978 when 27 were infected, 21 with clinical influenza. These boys were bled annually and were still in school when another outbreak of influenza A H1N1 occurred in 1983. Twentythree of them were reinfected but only nine had symptoms. These results are compared with the experience of a similar group of boys in the early years of the influenza A H3N2 era.