A mobile laminar cross-flow unit for surgery has been evaluated by the use of an experimental bacterial aerosol of Escherichia coli in different concentrations, generated at several different sites. A separate ventilation system, mounted underneath the table, produced an almost downward directed curtain of sterile air along both sides of the table. When the velocity of the air stream, discharged by the cross-flow unit, was adjusted at 0·50 m./sec. at 2 m. from the filter face (at the head end of the operation table), the surface of the table could be maintained free of bacterial settling, even after aerosolization of heavily concentrated suspensions of 108 bacteria/ml. at different sites outside the enclosure and underneath the table as well.

The bactericidal activity of RBA 777 has been found to vary with both the cultural and environmental test conditions against Pseudomonas aeruginosa and to a lesser extent against Staphylococcus aureus. These variations may explain certain anomalies in earlier work regarding the activity of chloroxylenol-based products. The addition of EDTA to RBA 777 has brought about an improvement in the performance against P. aeruginosa and this activity is confirmed in vivo. Previous reports have already illustrated this potential and the evaluations of the new antibacterial agent DA 136 confirms and extends these results to its performance under adverse conditions, often associated with the hospital environment.

A survey was conducted in seven hospitals to assess the risk of cross-infection with the highly infectious air-borne diseases, varicella-zoster and measles, in isolation wards of different design. Existing wards and isolation techniques were found to afford a high degree of protection, but there was considerable variation in the incidence of cross-infection related to ward structure, ward practice and the availability of trained staff. Recommendations are made for the design of new isolation wards and for safe practice.

In the present study rubella HI antibodies were determined in cases of congenital malformation and bad obstetric history to determine the role of rubella in such cases in India, as it has been reported to be rare in Japan in contrast to Western countries. The incidence of antibodies was statistically significant in cases of congenital eye, c.n.s., visceral and miscellaneous malformations and cases of spontaneous abortion and still-birth compared with controls of matching age groups. This is further supported by the demonstration of IgM antibodies in seven cases of congenital malformations and ten cases of spontaneous abortion. Our findings show that congenital rubella is not rare in India.

Experiments were carried out to assess the reduction rate of two salmonella strains (S. eastbourne and S. typhimurium) in chocolate bars. After artificial contamination of chocolate, after ‘conching’, with about 106S. eastbourne/g. this organism was still recovered after 9 months storage. The strain of S. typhimurium was less resistant. Both serotypes died off more rapidly in bitter chocolate than in milk chocolate.

After contamination with a smaller dose (about 103/g.) with these two serotypes, similar differences were observed.

As part of the bacteriological quality control programme of the Public Health Laboratory Service, we were asked to investigate the possibility of providing simulated water samples for distribution to the laboratories. For this purpose it was necessary to find some means whereby suspensions of coliform organisms and Escherichia coli could be kept relatively stable in number at room temperature for a period of 7–10 days. This, it was finally found, was best achieved by adding selected strains of the organisms to improved formate lactose glutamate medium (Gray, 1964) without the lactose but with added boric acid to a final concentration of 1·8%.

The procedures adopted in the successful quality control programme are described.

Various sampling techniques to determine the aerobic, E. coli and Entero-bacteriaceae counts and to detect the presence of salmonellas were compared. As a simple method for the detection of salmonellas a modified Surkeiwicz procedure using both drip and rinse water is advocated. To evaluate hygiene during processing, determination of the number of Enterobacteriaceae in pieces of skin from the ventral, lateral and breast region is preferred.

The immunizing activity of ribosome preparations derived from Brucella abortus strain 19 cells was examined in guinea-pigs and mice. After subcutaneous injections of Br. abortus ribosomes in Freund's incomplete adjuvant, both mice and guinea-pigs developed immunity to challenge by virulent Br. abortus 544 organisms which was at least as effective as the protection conferred by live strain 19 vaccine. Both mice and guinea-pigs also developed agglutinating and complement-fixing antibodies and delayed hypersensitivity to Br. abortus antigens. Conversely, ribosome preparations elicited delayed hypersensitivity reactions on intracutaneous injection into guinea-pigs chronically infected with Br. abortus or Br. melitensis.

On injection into rabbits, Br. abortus ribosomes incorporated in incomplete adjuvant induced high titres of agglutinins, complement fixing antibodies and precipitins for Br. abortus antigens. On immunochemical examination, the ribosome preparations were not grossly contaminated with antigens derived from the cell surface. They were chemically complex, however, and in addition to RNA contained numerous protein components identified by disk electrophoresis. The nature of the components responsible for conferring protection against Br. abortus was not determined.

The antibacterial effectiveness of hand antiseptics commonly used in wards was studied by laboratory and in-use tests and their acceptability assessed by means of a questionnaire passed to hospital staff. To determine the immediate and long-term antibacterial effects of the preparations the in-use tests were performed by groups of students. The greatest immediate reduction in bacterial counts on hands was obtained by products containing chlorhexidine. The longterm antibacterial effect was recorded with emulsions containing 3% hexachlorophane, 2% Irgasan CF3R or 4% chlorhexidine when used constantly on several consecutive days. Considerable discrepancies were recorded in the antibacterial effectiveness of some preparations when comparing laboratory and in-use test results. Therefore it is suggested that antiseptics should be tested by in-use tests which more closely resemble practical conditions before their use, or further trial, in hospital.

A review of 194 cases of enteric infection in Scotland during 1967–74, is reported. Diagnosis was confirmed by the laboratory isolation of Salmonella typhi (64 cases), S. paratyphi A (3) and S. paratyphi B (127), from blood or faeces; 174 persons were clinically ill and 20 were symptomless infections.

Most patients (81·0%) were under 35 years of age, with the highest incidence occurring among young adults of 15–24 years, many of whom had been travelling overseas. One-third of all cases (65) were imported infections; the remaining 129 patients had not been outside the United Kingdom. A significantly greater proportion of typhoid infection (54·7%) was contracted overseas, in contrast to paratyphoid B with only one-fifth of cases (21·2%) being imported; all three cases of paratyphoid A were imported. The geographic distribution of origin of imported infections is discussed, along with the frequency of organisms belonging to different phage types.

Two deaths occurred, one of which was the result of complications of paratyphoid fever. All other patients responded well to treatment, although two persons continued to excrete and became chronic carriers.

A few examples are given of episodes of particular epidemiological interest.

It is expected that in future years there will be a continued increase in the proportion of imported infections as more persons travel overseas, concurrent with the continuing decline in the number of chronic carriers resident in the British Isles.

Contamination of a laboratory environment with pathogenic or non-pathogenic micro-organisms may be relevant to safety of technicians and quality of technical performance. Two widely separated incidents in 1968 and 1974 initiated a study of aspects of the laboratory environment. Water-baths, water of syneresis and portions of salmonella cultures spurting out of the sterilizing flame were examined. The water of water-baths was shown to be contaminated from the fluid cultures incubated in them. This raised questions of potential cross-contamination and reporting of false positives. Water of syneresis was sometimes contaminated with salmonellas. A few quantitative counts were made. The range of counts varied between 16 salmonellas per ml. and 13,000,000 salmonellas per ml. Five hundred portions of salmonella cultures and 571 portions of Shigella sonnei cultures which had spurted from the sterilizing flame were examined. All these samples failed to grow salmonellas or shigellas.

Precautions necessary to avoid environmental contamination are briefly discussed.

A thymine-requiring (thy−), trimethoprim-resistant (tmpr) mutant isolated from the faeces of chickens experimentally infected with Salmonella typhimurium and treated with a mixture of trimethoprim and sulphadiazine was less virulent for chickens than the parent strain and a thy+tmps revertant prepared in vitro from the mutant. The difference in chicken-virulence was more noticeable when the strains were administered orally than when they were administered subcutaneously. All tmpr mutants prepared in vitro from four other salmonella strains were also thy−; those tested were less virulent for chickens and mice than their parent strains. After oral infection, thy− salmonella organisms were found much less commonly in the alimentary tract of chickens then were thy+ organisms. This was especially so in the caeca, the principal site of colonization of both the thy+ and thy− organisms. Relatively high concentrations of thymine or related compounds were found in the contents of all regions of the alimentary tract of chickens except the caeca; the caeca usually contained low or undetectable concentrations.

The thy− salmonella strains would not grow on one brand of brilliant green agar because of its deficiency in thymine; their colonial appearance on other kinds of media used for isolating salmonellae from clinical material was often ‘un-salmonella-like’.

The indirect immunofluorescent technique has been used to detect and titrate the specific immunoglobulins in serum specimens from 154 infants with confirmed or suspected congenital rubella. IgM antibody was stained more efficiently in sucrose density gradient fractions than in whole serum and was detected in this way in 27 out of 40 patients with confirmed congenital rubella at ages ranging from birth to 2 years. It was present in 48 out of 50 serum specimens during the first 6 months of life and in 11 out of 38 specimens obtained at ages between 6½ months and 2 years. IgM antibody was therefore estimated to persist for about 6 months in the majority of cases and up to 2 years in a few individuals. IgM antibody was also detected by this method in 11 out of 114 infants with suspected but unconfirmed congenital rubella at ages up to 5 months. The total concentrations of IgM were above the normal range in nearly all sera taken from confirmed cases during the first 3 months of life and in half the specimens obtained between the ages of 3 and 6 months.

IgG antibody was detected by fluorescent staining of whole serum in all patients with congenital rubella. Geometric mean titres increased during the first 3 months of life and then declined slowly. IgA antibody was not detected, except in two patients in whom traces were present at the age of 6 months, and the total concentrations of IgA were usually within normal limits.

Fluorescent staining of fractions showed that the sedimentation characteristics of rubella IgG and IgM antibodies were the same in infants as in adults. The peak IgM fractions never contained IgG antibody, and the presence of specific IgM in these fractions could usually have been safely inferred from their HAI titres. Fluorescent staining, however, was more sensitive and frequently detected IgM antibody in fractions which had no definite HAI activity.

Fluorescent staining of whole serum for IgM antibody was less distinct, and often unsuccessful, even in specimens in which specific IgM was detected in the fractions. The addition of IgG- to IgM-containing fractions caused depression of IgM staining and suggested that failure to detect IgM antibody in whole serum was partly due to competitive inhibition by specific IgG.

A longitudinal, virological and serological study of pigs in two herds with respiratory disease showed that infection by porcine cytomegalovirus (PCMV) was universal in both.

Virus excretion usually began when piglets were between 3 and 6 weeks of age and reached a maximum between 5 and 8 weeks; it was usually no longer detectable at 11–12 weeks. Antibody demonstrable in indirect immunofluorescence (IIF) tests was present to moderate or high titre in all piglets at 2–3 weeks. This was presumed to be maternal in origin as it declined in titre between 2–3 and 5–6 weeks. After this fall the majority of piglets showed seroconversion as a result of virus infection. One group of 12 pigs in which infection occurred earlier than usual showed a very poor antibody response, which, nevertheless, persisted through to week 27.

The findings are discussed with relation to porcine atrophic rhinitis and cytomegalovirus infection in other species.

The serological examination of over 900 rhinovirus strains isolated in Britain over a 10-year period has demonstrated a wide variety of different serotypes. Their seasonal and temporal distribution are described and discussed.

A procedure for combining evidence from different biological assays is shown to be equivalent both to generalized least-squares and to maximum-likelihood estimation. By appropriate nesting of hypotheses, the likelihood function can be used to test the agreement between the assays and to obtain probability limits for the combined estimate of potency. The properties of these limits are examined, with particular reference to the situation, unusual but not impossible in practice, in which the values of relative potency that they define consist of several disjoint segments instead of a single interval. The connexion with general theory of estimating linear functional relations is pointed out.