Between 1969 and 1974, 1467 packets (3309 samples) of pork sausages and sausage meat produced by two large and two medium sized manufacturers and several local butchers were examined for the presence of salmonellas. Of these, 435 packets (786 samples) were found to contain salmonellas, but there was a wide variation in the isolation rates according to the producer. The salmonella incidence in samples from several small and two medium sized producers was low (0–11%) while the results from the two large producers investigated showed a striking difference, the rate of salmonella contamination in the product of one was low (about 2%) and in that of the other consistently high (40–60%).

A comparison of liquid enrichment media, incubation temperatures and selective agar media was also carried out to determine the most efficient combination for the isolation of salmonellas from minced meat products. The results showed that (a) incubation of enrichment cultures at 43° C. yielded a consistently greater number of salmonella isolations than at 37° C., regardless of plating medium, (b) tetrathionate broth A (Rolfe) was superior to selenite broth as an enrichment medium at both 37 and 43° C. and (c) brilliant green agar gave better results than deoxycholate citrate sucrose agar and bismuth sulphite agar as a selective medium.

Endemic infection in male surgical wards has been studied during three periods. There was some infection due to gram-negative bacilli, though Staphylococcus aureus remained as the single most important pathogen even in the absence of epidemic spread. Beta haemolytic streptococci were isolated in large numbers from the lesions of four patients with deep wound infection. Changes introduced in the pattern of post-operative care reduced sepsis due to Staph. aureus, reduced the severity of wound infection and apparently decreased the need for antibiotic therapy. Patients who became infected were retained in hospital longer than those who escaped clinically apparent infection.

One hundred and fifty-six infections or episodes of infection associated with Pseudomonas aeruginosa in six hospitals over 14 months were investigated. Pyocine typing and serotyping suggested that 145 distinct episodes had occurred, caused by 78 different strains. During this period 15 distinct strains were isolated from the environment at one of the hospitals; 12 of these were apparently un-associated with infection in the same ward during the period, and 4 were of types not encountered in infective processes at any hospital. There appeared to be a rather higher proportion of unclassifiable pyocine inhibition patterns among the environmental strains; in general these strains also produced smaller amounts of haemolysin. If failure to produce haemolysin in vitro is correlated with lack of virulence in vivo, this may partially explain the sporadic nature of hospital infection with Ps. aeruginosa, despite the prevalence of strains of this species in the environment.

The recovery of virulence by means of reversion of a live streptomycin-dependent (Sm D) Salmonella typhimurium vaccine was studied in CD–I Swiss mice. Initially, a one–step Sm D mutant was obtained from a virulent streptomycin-sensitive (Sm S) S. typhimurium strain. Afterwards, two pools of streptomycin-independent (Sm I) revertants were prepared from the Sm D strain. The virulence of the Sm D strain and of the Sm I revertants was tested intraperitoneally. In the virulence testing the original suspension of the Sm I revertants, as well as their 1st and 10th passages on plain medium, medium + 50 μg. streptomycin/ml, and medium + 1000 μg. streptomycin/ml, were used. The results show that the Sm D mutant was avirulent, its avirulence being due to an intrinsic, genetic quality. The Sm I revertants, compared to the original Sm S strain, also displayed a lack of virulence. However, afterwards, the Sm I revertants behaved quite differently, according to their subsequent passages. Indeed, there was an increase in virulence after passages on plain medium, whereas after similar passages on medium containing the drug, the virulence not only failed to increase, but disappeared almost completely. Moreover, the passages on medium containing 1000 μg. streptomycin/ml, induced a return to the status of drug–dependence. The danger of recovery of virulence by means of revertants is evaluated.

The present experimental model offered the opportunity to study particular aspects concerning the avirulence stability of live streptomycin-dependent (Sm D) Salmonella vaccines, under conditions resembling human enteric fever. The results seem to indicate that, in practice, the risk of reversion to a virulent form during oral antityphoid vaccination with Sm D strains remains slight even after the interruption of concomitant streptomycin administration.

The epizootic range of Rift Valley fever in Kenya is defined from the results of virus isolations during epizootics, and from an extensive serological survey of cattle which were exposed during an epizootic. A study of the sera from a wide range of wild bovidae sampled immediately after the epizootic, showed that they did not act as reservoir or amplifying hosts for RVF.

Virus isolation attempts from a variety of rodents proved negative. Rift Valley fever did not persist between epizootics by producing symptomless abortions in cattle in areas within its epizootic range. A sentinel herd sampled annually after an epizootic in 1968 revealed not one single seroconversion from 1969 to 1974. Certain forest and forest edge situations were postulated as enzootic for Rift Valley fever, and a small percentage of seroconversions were detected in cattle in these areas, born four years after the last epizootic. This has been the only evidence for the persistence of the virus in Kenya since 1968, and may be a part of the interepizootic maintenance cycle for Rift Valley fever in Kenya, which otherwise remains unknown.

Ephemeral fever antibody was found in domestic cattle in Kenya across a wide range of ecological zones, from highland forests and grasslands to desert and semidesert thorn scrub. Antibody was found in several species of game animals, notably waterbuck and buffalo, where over 50% of the samples showed antibody to EF. Evidence was obtained to show that the virus had been cycling in these wild ruminant populations between epizootics in domestic cattle.

Laboratory studies showed that few rabbit fleas (Spilopsyllus cuniculi (Dale)) transmitted myxomatosis after removal from wild rabbits (Oryctolagus cuniculus (L)) that had been infected for fewer than 10–12 days, irrespective of the virulence of the myxoma virus strain involved. Rabbits infected with fully virulent (Grade I) strains died within 10–15 days and few fleas from these hosts became infective; averaging all the samples taken, 12% of the fleas were infective. Also, few fleas acquired infectivity on individual rabbits which recovered from infection with attenuated strains; the mean was 8% infective. Rabbits which died between 17 and 44 days after infection had higher proportions of infective fleas at all sampling times; the mean was 42% infective. Male and female fleas transmitted virus with equal efficiency.

For rabbits infected with any of the attenuated virus strains the mean percentage of infective fleas was inversely related to the survival time of the host. Rabbits infected with moderately attenuated strains (Grades IIIA and IIIB) had, on average, the highest proportion of infective fleas; hence such strains have a selective advantage and have become predominant under natural conditions in Britain. The changes that might occur if there is an increase in host resistance to myxomatosis are discussed.

Rhinovirus was recovered from the fingers of 16 of 38 volunteers and others, who were swabbed during the acute stages of their colds. Very low titres of virus were also recovered from 6 of 40 objects recently handled by infected volunteers, but not from the fingers of 18 non-infected subjects whose flat-mates were shedding virus. When rhinovirus from nasal secretions was dried on skin or other surfaces during laboratory experiments, approximately 40–99 % of infectivity was lost. Virus could be transferred from surface to surface by rubbing, the transfer being more efficient if it was carried out while the inoculum was still damp.

Volunteers could infect themselves if a moderately heavy dose (88 TCD50) of virus was inoculated on the finger and then rubbed into the conjunctiva or nostril, especially if the inoculum was still damp. From estimates of virus titres in nasal washings and on fingers, and of amounts transferred by rubbing, it was concluded that spread of colds is unlikely to occur via objects contaminated by the hands of the virus-shedder, but that a recipient might pick up enough virus on his fingers by direct contact with heavily infected skin or secretions to constitute a risk of self-inoculation via the conjunctiva or nostril.

A standard hand-wash sampling technique was compared with a simple fingerstreak sampling method in assessing the relative effectiveness of a number of alternative preparations used for disinfecting the surgeon's hands (alcoholic 0-5% chlorhexidine, alcoholic 0-1% tetrabrom-o-methyl phenol, a 4% chlorhexidine detergent solution, aqueous 0-5% chlorhexidine, 2% 'Irgasan' detergent solution and, as control, bar soap). There was a fairly good correlation between the results of assessment by the two methods after a single disinfection and after six disinfections, three on one day and three on the next. Significant differences were shown in 21 comparisons between treatments when the hand-wash sampling test was used, and 16 of these comparisons also showed a significant difference by the finger-streak test.

Staphylococcus aureus was found in hand samplings from 5 out of 8 nurses in the Burns Unit of Birmingham Accident Hospital by the hand-wash sampling method and from 2 of the same 8 nurses by the finger-streak method; the numbers were small, and no Staph. aureus were isolated from the same hands after 1 min. wash in 70 % ethyl alcohol. Similar sampling on 29 nurses in other wards showed Staph. aureus on 3 nurses (one in large numbers) by the hand-wash technique and on 1 nurse by the finger-streak test; in only 1 nurse whose hands showed Staph. aureus before disinfection was the organism found, by hand-wash sampling, after disinfection.

Parallel sampling of nurses' hands after washing with soap and water and after disinfection with 95 % ethanol showed larger numbers of Staph. aureus in a hospital for skin diseases than in a general hospital, and a lower incidence and somewhat lower density of Staph. aureus after ethanol treatment than after washing with soap and water; Gram-negative bacilli, on the other hand, were commoner on hands in the general than in the skin hospital, and present in much smaller numbers after disinfection with ethanol than after washing with soap and water.

Antibiotic sensitivity tests showed the frequent recurrence on the hands of some nurses of multi-resistant Staph. aureus with resistance patterns similar to those found in infective lesions in some of the patients; different sensitivity patterns were usually found in staphylococci isolated from the nose. Even in wards where many patients were infected, carriage by nurses' hands of a particular strain ofStaph. aureus did not seem to last for more than a few days.

Chickens in groups of 40 were infected orally with a nalidixic acid-resistant mutant of Salmonella typhimurium and then fed continuously on diets containing ampicillin, chloramphenicol, furazolidone, neomycin, oxytetracycline, polymixin, spectinomycin, streptomycin or a mixture of trimethoprim and sulphadiazine. The amount of S. typhimurium excreted in their faeces was estimated at intervals by culture on brilliant green agar containing sodium nalidixate, both direct and after enrichment in selenite broth; the amount of Escherichia coli excreted was estimated by culture on MacConkey agar. The feeding of diets containing 500 mg./kg. of ampicillin, furazolidone, neomycin, polymixin, spectinomycin or streptomycin or 100 mg./kg. of trimethoprim and 500 mg./kg. of sulphadiazine for 46 days reduced to a varying degree the amount of S. typhimurium and E. coli excreted, the greatest reduction in S. typhimurium being brought about by the last treatment. The effect was less obvious when the concentration of the antibiotics in the food was decreased fivefold. An important reason for the very limited effect of some of the antibiotics was the emergence of antibiotic-resistant populations of S. typhimurium and E. coli. High concentrations of antibiotic-resistant organisms also arose in the faeces of the chickens fed diets containing tetracyclines and chloramphenicol, treatments which had no apparent effect on the amount of S. typhimurium and E. coli excreted. Much of the antibiotic resistance encountered was determined by R factors, a particular R factor usually being found in the E. coli populations of individual chickens before it was found in their S. typhimurium populations. No S. typhimurium or E. coli were isolated that possessed R factors determining resistance to polymixin, furazolidone or trimethoprim. No S. typhimurium or E. coli were isolated that were polymixin-resistant and no S. typhimurium that were furazolidone-resistant. The few trimethoprim-resistant S. typhimurium isolated were thymine-dependent.

The feeding of diets containing the higher concentrations of trimethoprim/sulphadiazine, neomycin, furazolidone or ampicillin for 9 days reduced the amount of S. typhimurium excreted. After the withdrawal of these diets, the amount of S. typhimurium excreted increased to the numbers found in chickens given ordinary diets throughout; the chickens that had been given trimethoprim/sulphadiazine or furazolidone did not remain faecal excreters of S. typhimurium longer than the chickens that had been given ordinary diets. Similar results were obtained with trimethoprim/sulphadiazine when the start of the 9-day treatment period was delayed for an extra 9 days or when it was extended to 18 days.

Groups of 45 chickens were fed continuously on diets containing 10 or 100mg./kg. of different ‘growth-promoting’ antibiotics and infected orally with a nalidixic acid-resistant mutant of Salmonella typhimurium. The amount of S. typhimurium organisms excreted in their faeces was estimated by culturing them at weekly intervals and in a standard manner on plates of brilliant green agar containing sodium nalidixate, both direct and after enrichment in selenite broth.

All of four groups fed diets containing 100 mg./kg. of nitrovin in three different experiments excreted much larger amounts of S. typhimurium than did groups fed antibiotic-free diets. In some, but not all, experiments, larger amounts were also excreted by groups fed diets containing 10 mg./kg. of nitrovin or 10 or 100 mg./kg. of flavomycin or tylosin. Feeding diets containing 10 or 100 mg./kg. of virginiamycin or bacitracin either did not influence or slightly ncreased the amount of S. typhimurium excreted.

Two groups fed continuously on diets containing 100 or 500 mg./kg. of sulphaquinoxaline for 44 days excreted smaller amounts of the S. typhimurium organisms than did groups fed antibiotic-free diets; no sulphonamide-resistant organisms of the S. typhimurium strain were isolated from the faeces.

This study on Kenyan schoolchildren aims to elucidate the effect of contact with environmental mycobacteria on the development of specific delayed hyper-sensitivity. A series of 12 skin test reagents was employed; eleven of them were prepared from extracts of living mycobacteria and the last was the P.P.D. RT 23. Eight of the new tuberculins were prepared from mycobacteria recovered from the East African environment. A total of 8641 tests were carried out on 4320 children between the ages of 6 and 17 years in four townships. Two of these townships were in fertile agricultural areas and two were in the desert. Just over 80% of the children had received BCG immunization.

The results obtained showed that increasing age, geographical locality and BCG immunization all had a profound effect, and socioeconomic background had some effect, on the pattern of reactivity to the various reagents. The rationale behind the use of the series of new tuberculins and the results obtained with them are discussed in relation to the interacting effects of the factors complicating these results.

Nose and throat swabs, for culture of Haemophilus influenzae type b, and blood samples, for measurement of antibodies specific for that serotype, were collected from members of 28 families from which children had been admitted to hospital with acute H. influenzae type b infections (mainly meningitis or epiglottitis). The patients with meningitis were younger than those with epiglottitis and had more siblings, with a marked predominance of sisters. Investigations within a few days of admission of the affected children to hospital detected carriers of H. influenzae type b (19 altogether) in 13 of the 28 families, including 9 of the 13 families with 3 or more children. Members with raised antibody titres for H. influenzae type b (suggesting the presence of the organism for at least a few weeks) were found in 17 of the 25 families from which blood samples were obtained, including all 11 families with 3 or more children. Most of the patients probably acquired their infections from within their own families, and siblings under 11 years old were of predominant importance both as carriers and as potential sources of the patients' infections. Persistence of the organism within families for up to 6 months was demonstrated. Possible reasons for the difference in age-incidence between haemophilus meningitis and epiglottitis and for the occurrence of the former in babies with older sisters are suggested, and also a possible connexion between the results of this survey and the likely value of immunization against H. influenzae type b.