The mechanisms of inactivation of aerosolized bacteriophage øX174 in atmospheres containing ozone, cyclohexene, or ozonized cyclohexene were studied by using 32P-labelled phage. The inactivation of the aerosolized phage in clean air or in air containing cyclohexene is due to damage of the protein coat since the deoxyribonucleic acid (DNA) extracted from the inactivated phage retains its biological activity. Inactivation of the phage in air containing ozone is mainly due to protein damage whereas inactivation in air containing ozonized cyclohexene is due both to protein and DNA damage. Sucrose gradient analysis shows that aerosolized inactivated øX174 releases unbroken DNA. In contrast, the DNA from phage øX174 inactivated by ozonized cyclohexene is broken.

The inactivation of aerosolized phage øX174-DNA was studied in the same atmospheres using 32P-labelled DNA. øX174-DNA aerosolized in clean air or air containing cyclohexene at 75% r.h. is inactivated by a factor of 2 in 30 min. The inactivated DNA is broken. Ozone as well as ozonized cyclohexene inactivates DNA very fast causing breaks in the molecule. This is in contrast with the intact bacteriophage in which ozone does not produce breaks in the DNA.

One hundred and thirty-three vanilla slices, purchased from shops in the West Yorkshire Metropolitan County, were examined to determine the numbers and types of bacteria present at the time of purchase. The surface colony count at 37 °C was > 103/g in 67/133 (50%) of the samples examined, Bacillus cereus being found at that concentration in 21·8%, coliform bacilli including E. coli in 5·3%, Staphylococcus aureus in 3·0% and Streptococcus faecalis in 0·8%. Thirty-four strains of B. cereus were serotyped and 11 (32%) of these were typable with the sera available.

Preparation of custard mixes in the laboratory suggests that the milk or milk powder used in the mix may be the major source of B. cereus in the final product. Many of the present methods of manufacture, distribution and storage allow organisms present in the custard at manufacture the opportunity to multiply and possibly reach numbers which present a risk of food poisoning.

Antibody to hepatitis B surface antigen was detected by radioimmunoprecipitation in 74 (5·5%) of 1336 staff members in a large general hospital in Edinburgh, in 14 (2·9%) of 480 volunteer blood donors in the area, and in 12 (6·1%) of 197 pregnant women attending for the first time at the ante-natal clinic in the hospital. Rates of antibody prevalence rose with age in the sample of hospital staff and in that of the blood donors, particularly among males. On the other hand, in the ante-natal patients antibody prevalence declined with age.

The rates in hospital staff were higher than those in blood donors of comparable age and sex, and high titres of antibody were more common in the staff group. However, no association was found between antibody prevalence and a history of clinical hepatitis, blood transfusion, or recognized contact with cases of hepatitis. Staff who had previously worked in an infectious disease hospital did not show increased antibody prevalence, indicating that simple isolation measures have been adequate to minimize exposure to hepatitis B.

No particular prevalence of infection was seen in physicians and surgeons, in the nursing staff, or in workers in clinical diagnostic laboratories, hospital administration or other areas. One group clearly showing increased antibody prevalence was staff currently working, or who had worked, in the Haemodialysis Unit; this correlated with the outbreak of dialysis-associated hepatitis in 1969–70. However, no evidence suggested that significant dissemination of infection had occurred to other defined groups of hospital staff. Elevated rates were also observed in a small sample of kitchen and portering staff, and in obstetric medical and nursing staff; the latter observations indicate a need for further investigation to identify unsuspected exposure to hepatitis B virus.

A study is described of influenza A anti-neuraminidase antibodies in the sera of young people of three different age groups. Each serum was individually absorbed with viruses containing the N2 neuraminidases of 1957, 1968 and 1972. Rabbit antisera prepared against the viruses were similarly absorbed. Results obtained with the animal sera suggested that these neuraminidases were antigenically distinct, but the human sera had a broader range of anti-neuraminidase activity and gave indication of asymmetric antigenic relationships. Earlier workers who surveyed anti-haemagglutinin antibodies reported that the virus of primary infection absorbed all antibodies, and the virus of secondary infection only those directed against itself. We too found that the virus of secondary infection absorbed only homologous anti-neuraminidase antibody. However, although the primary infecting virus did absorb some secondary antibody, this absorption was incomplete and it lessened with the lengthening of the time interval between the primary and secondary infecting viruses. A similar pattern was seen with anti-haemagglutinin antibodies.

Absorption of anti-neuraminidase antibodies from human sera proved much more difficult than absorption of anti-haemagglutinin antibodies particularly after repeated influenza virus infections. The relative rarity of antigenic shift in the neuraminidase subunit also creates problems in the interpretation of results of serum neuraminidase antibody surveys.

Saturation diving is an important and widely used technique in the Offshore Oil Industry. During 1974–5 two saturation dives in the North Sea were terminated because of outbreaks of incapacitating otitis externa, and others were disrupted. Pseudomonas aeruginosa was consistently isolated from the ears of affected divers. Because complex work schedules were threatened seven subsequent dives were subjected to microbiological monitoring and control. Colonization of the ear canal with P. aeruginosa or with other gram-negative bacilli occurred in 39 (67%) of the 58 divers studied, usually within 7 days of starting the dive. Data obtained by serotyping the isolations of P. aeruginosa suggested that a single infected diver may be the source of organisms which rapidly spread to his colleagues and throughout the living chambers, that the living chambers may constitute a reservoir of infection during and between dives, and that certain serotypes of P. aeruginosa are more likely than others to colonize the ear canal in the conditions of a saturation dive. The control measures used during the dives were only partially effective, but none of the divers suffered severe pain and all the dives were an operational success.

The surveillance programme described in an earlier report was used to monitor outbreaks of influenza in three successive winters. Influenza virus A was active in all of them, but the only major outbreak of influenza B was in 1973–4. The highest incidence of influenza A was in the 0–4 age group in all three winters, but schoolchildren bore the brunt of infections by influenza virus B.

A provisional serotyping scheme was used to type cultures of Bacillus cereus from 84 outbreaks of food poisoning in seven countries; 283 of the 337 (84%) cultures tested were typable.

In 35 of the 61 outbreaks associated with a vomiting-type syndrome, foods, clinical specimens or both yielded H-serotype 1 only. Type 1 strains together with other serotypes were isolated in seven outbreaks. In 14 outbreaks types 3, 4, 5, 8 or a mixture of serotypes were present. Untypable strains were isolated in five outbreaks.

Two of the nine diarrhoeal-type outbreaks yielded serotype 1 only. Types 2, 6, 8, 9, 10 and a mixture of type 12 and an untypable strain appeared to be responsible for one outbreak each.

Although 16 of the 18 recognized serotypes were present among cultures of B. cereus from various routine foods, only 156 of the 400 (39%) isolates tested were typable.

Fresh human and bovine milk are bacteriostatic in vitro for only some (milk-sensitive) strains of E. coli. The addition of bicarbonate to the test system potentiates the bacteriostasis so that otherwise milk-resistant strains are inhibited. By titration of the bicarbonate in the milk, it is possible to determine the minimum concentration that will activate milk against a milk-resistant strain but be ineffective in boiled milk, i.e. it potentiates a heat-labile system in milk and does not merely exert a direct toxic effect. This concentration is lower for human milk than for cows‘ milk and can be reduced even further by the addition of more iron-binding protein.

Lactoferrin and bicarbonate may be present in the gut of the newborn. In an attempt to imitate conditions in the infant gut, we therefore reinvestigated, in vitro and in the presence of added bicarbonate and transferrin, the bacteriostatic activity against E. coli of fresh breast-milk, commercial bottle-milk, and mixtures of these as fed to infants in this study. The results, and information about events in vivo deduced from the ratio of milk-sensitive to milk-resistant strains of E. coli isolated from babies‘ stools, suggest that neonatal intestinal secretions may contribute to the bacteriostatic activity of their feeds so that (1) in fully breastfed babies all strains of E. coli are inhibited to the same extent; there is no selection on the basis of milk sensitivity and equal numbers of strains resistant and sensitive to milk are found in the stools; (2) in fully bottle-fed babies E. coli is not inhibited since the milk is non-bacteriostatic and again there is no selection; (3) in babies fed at the breast but bottle-milk supplemented, only milk-sensitive strains are inhibited; milk-resistant strains are not, and preferentially colonize the large intestines.

Three South-Asian rodent pest species were tested for susceptibility to anticoagulant rodenticides. Wheat flour containing 0·025% warfarin, 0·0375% coumatetralyl or 0·005% difenacoum was fed to 260 Tatera indica, 140 Nesokia indica and 81 Bandicota bengalensis for 1–56 days. Tatera was about as susceptible to anticoagulants as Rattus rattus has been reported to be. Nesokia and Bandicota were extremely variable: though the majority were highly susceptible, the slopes of the dose-mortality curves were close to zero. The difenacoum diet appeared to be more toxic than the warfarin diet to all three species, but less toxic than the coumatetralyl diet to Tatera and Nesokia. All of the anticoagulants were eventually lethal to all of the animals tested.

RSV complement fixation antibodies were established in 200 paired maternal and cord blood sera. Geometric mean titres in cord sera were significantly higher than in maternal sera. The differences did not depend on the virus strain used. Half of the paired sera (taken at random) were also submitted to microneutralization tests. No differences were found between geometric mean titres in maternal and cord sera.

Rubella haemagglutination inhibiting (HAI) antibody titres were determined in 54 seronegative women and 31 naturally immune women after vaccination and revaccination with Wistar RA27/3 strain rubella vaccine administered by the intranasal or subcutaneous routes or revaccination with the Cendehill strain administered subcutaneously. In addition, HAI antibody titres were determined in 46 seronegative schoolgirls after vaccination with the Cendehill strain and revaccination with the RA27/3 strain.

All seronegative women vaccinated with the RA27/3 strain developed antibody, peak titres being reached 6 weeks after vaccination. Six months after vaccination with the Cendehill strain, 45 (98%) of the 46 seronegative girls had developed antibody, but 11 (24%) had not reached their peak titre by 6 weeks, suggesting a slower response than that elicited by the RA27/3 strain. Revaccination did not induce significant antibody responses in the seronegative women vaccinated 6 months previously with RA27/3 but 4 naturally immune women developed an eightfold increase in antibody. In 10 (22%) of 46 schoolgirls previously vaccinated with the Cendehill strain a significant rise in antibody followed revaccination with RA27/3. These results provide further evidence of the more rapid antibody responses elicited by the RA27/3 vaccine in comparison with the Cendehill vaccine.

An outbreak of natural rubella occurred in 1972 and 97 cases were confirmed serologically. The clinical disease was more common in older school-children and in adults. More males than females were affected in the 11–15 age group, the sex ratio being 18:12; this may be explained by the routine vaccination of girls of this age group as part of the national programme which began in 1970. The significance of the persistence of high HAI antibody titres after natural infection and the effect of the epidemic on the serological status of the population are discussed.

Six serologically negative sows were infected by intranasal instillation of porcine cytomegalovirus (PCMV) between 31 and 85 days of pregnancy. Four sows showed an afebrile anorexia and lethargy 14–25 days after infection and all 6 developed significant increases in indirect immunofluorescent (IIF) antibody titres within 35 days. Virus was recovered from nasal and/or cervical swabs from 2 sows during life and from lung macrophage cultures after death.

At term the sows were killed and their fetuses harvested by caesarean section. The number of mummified and stillborn fetuses increased from 4/63 in 6 previous litters to 18/60 in the 6 present litters. Nine of 43 fetuses born alive were reared in isolators for up to 6 weeks but the majority were killed for examination on the day of birth. Virus was isolated from 16 piglets from 4 of the 6 litters examined; it was isolated most frequently from lungs and liver but also from spleen, kidney, brain and nasal mucosa. Unsuckled day-old pigs had insignificant IIF titres, irrespective of whether they were excreting virus or not. The 5 congenital excretors which were reared all died within 7 days but no deaths occurred among their 4 litter-mates. Post-natal infection of 2 of these piglets reared in contact with congenitally infected pigs was suggested by the recovery of virus from nasal swabs 17 and 27 days after birth and the subsequent rise in IIF titre to 1/256 by day 42.

Human milk has a bacteriostatic effect on Escherichia coli in vitro. The milks of 40 mothers were tested for this effect against E. coli isolated from their stools, from those of their own babies, and from those of babies not breast-fed. The milks had a direct bacteriostatic effect, not dependent on complement, on some but not all the strains of E. coli. Breast-fed babies receiving supplementary bottle feeds were colonized with milk-resistant strains, whereas bottle-fed babies and, surprisingly, babies completely breast-fed were colonized equally with milk-sensitive and milk-resistant strains, as were the mothers. These results suggest that the bacteriostatic effect of human milk, demonstrable in vitro does sometimes operate in vivo.

The antibacterial activity of human milk is not influenced by the O, H or K antigens of E. coli and is effective against other Gram-negative organisms, e.g. Salmonella, Klebsiella, Proteus.

A comparison of homologous and heterologous rates of neutralization demonstrated that antigenic relationships of foot-and-mouth disease virus strains could be differentiated quantitatively by the kinetics of neutralization method described previously (Rweyemamu, Booth & Pay, 1977). Conventional formulae for r, R and D values could be applied to results obtained by this method. It was demonstrated that results analysed this way gave R values which were similar to those obtained with other neutralization test methods but which were generally smaller than those obtained with complement fixation test results. It was demonstrated that there were wide differences between the vaccine strains tested as demonstrated by R value relationships. An examination of r values, however, demonstrated that antisera to the Moz 1/70 strain were highly reactive with most of the virus strains from Central and Southern Africa. The selection of FMD virus strains with a wide serological range for vaccine production is discussed.

The faeces of nine subjects eating mainly at home were collected at regular intervals over periods ranging from 2–5 months. Although a large number of serotypes of E. coli were isolated, the variety per subject was lower than is usually found. In most subjects only a limited number of serotypes persisted over most of the periods of study while many serotypes were only isolated on single occasions.

A very high proportion (75%) of the pigs slaughtered in Hong Kong were found to be infected with salmonellas. Seven serotypes including Salmonella choleraesuis were isolated but the majority (91%) were S. anatum and S. derby. These serotypes, especially S. anatum and S. derby, had been isolated frequently from clinical cases, symptomless carriers and in this study from abattoir workers, suggesting that the pig was a significant source of human salmonella infection.

The majority of pigs slaughtered are imported and the high level of apparent infection was thought to be due to cross-infection during transport of the pigs under stress. S. anatum and S. derby were also isolated from pigs on local farms but the incidence was threefold lower. Scalding the pigs at 60 °C for 5 min caused no great reduction in the degree of superficial contamination. The two predominant serotypes were isolated from the tank and from drain swabs, and also from the latter held under scalding tank conditions. Thus, in spite of the introduction of hygienic slaughter under modernized conditions employing an automatic conveyance system, 55% of the carcasses were superficially contaminated after dressing before despatch to customers. Control of infection before slaughtering would appear crucial and a more thorough rinsing or washing of the dressed carcasses desirable.

A study of the kinetics of inactivation of foot-and-mouth disease virus type SAT 2 strains revealed that in most cases the rate of neutralization was not rectilinear. Deviations from first-order kinetics observed represented biphasic or parabolic and stepwise reactions. The initial rate was rapid and showed no lag phase or shoulder. The effects of deviations from linearity could be minimized by dilution of antiserum to a suitable extent. Treatment of virus–antibody mixtures with anti-species globulin resulted in enhancement of the rate of neutralization of homologous and heterologous reactions without significantly altering the relation between the two. This treatment also considerably reduced the amount of the persistent fraction. In attempt to disaggregate virus it was observed that sodium dodecyl sulphate inhibited neutralization of virus by specific antiserum.

Between 1968 and 1975, well over 3000 samples of pig faeces and 407 samples of pig mesenteric glands were examined for salmonellas. A very wide range of serotypes was isolated. The material from this survey was used to evaluate certain aspects of salmonella isolations. The factors studied were: selective motility enrichment, size of inoculum of faeces, comparison of drain swab with animal sample and comparison of selenite F broth with Muller–Kauffmann tetrathionate broth. The conclusions drawn from these investigations allowed an efficient routine to be developed during the survey.

Stools from 183 babies under 2 years of age admitted to Ruchill Hospital with diarrhoea were examined by electron microscopy, virus culture, bacterial culture and light microscopy. As far as possible, several stools were examined from each patient and the results showed rotaviruses, astroviruses and other viruses in association with symptoms, as well as the expected bacterial pathogens. Examination of several stools from the same patient also showed that in this age group the viral flora of the gut changes rapidly and that the viruses seen by electron microscopy were only rarely grown in cell culture and vice versa. This phenomenon was particularly noted with adenoviruses. In 30% of cases no microbial pathogen was identified and in the remainder the presence of the infecting organism did not always coincide with the symptoms. It is concluded that, with viruses at least, presence of the organism does not constitute proof of causation.