During the period 1971–4, Torulopsis glabrata formed 42% of yeasts isolated from 5677 clinical specimens from patients with cancers, diabetes mellitus, chronic renal failure, pregnancy or major surgical operations complicated by mycotic infections. The significance of T. glabrata in these patients is discussed.

The method of path analysis is described in detail. Application of this analytical technique in the interpretation of causal relationships in complex biological systems is demonstrated using data from an epidemiological study of echinococcosis in New Zealand. The results identified the major causal pathways determining Echinococcus granulosus prevalence in dogs, based on multiple regression analysis of a linear causal model constructed from prior biological and epidemiological knowledge. Only ethnic and sheep husbandry variables had important direct effects on prevalence in the North Island of New Zealand, with some climatic factors (maximum temperature and relative humidity) and soil porosity acting indirectly through animal husbandry practices. It is suggested that path analysis, by permitting interaction between epidemiological theory and statistical analysis, provides a valuable additional tool to epidemiologists for the study of causal relationships among variables in multivariate systems.

The factors influencing the rate of progress in Echinococcus granulosus control in New Zealand were analysed by hydatid control area using stepwise multiple regression techniques. The results indicated that the rate of progress was related positively to initial E. granulosus prevalence in dogs and the efficiency with which local authorities implemented national control policy, and negatively to the Maori proportion in the local population and the number of dogs per owner. Problems in analysis of the New Zealand data are discussed and improved methods of monitoring progress in hydatid disease control programmes are described.

A model activated sludge treatment plant was used which was functionally very similar to a full scale plant. It was inoculated with poliovirus either continuously or with a single dose and the amounts of virus in the influent, mixed liquor and effluent were monitored regularly. The distribution of the virus in the liquid and solid phases of the mixed liquor was very unequal with about 85% of the virus associated with the suspended solids fraction. Only small amounts of virus were recovered from the effluent and after inoculation was stopped virus rapidly became indetectable. The efficiency of the plant with regard to removal of virus was closely related to its capacity to remove suspended solids and the adsorption of virus to solids and its inactivation is briefly discussed.

Using the microthread technique the survival of Escherichia coli MRE 162 in open air was measured in different parts of The Netherlands.

The presence of bactericidal compounds (open air factor = OAF) could be demonstrated on several days and quantitated in relative units of OAF concentration.

In the absence of ozone the OAF concentration was always low. In the presence of ozone the OAF concentration was dependent on wind direction. At the selected microthread exposure sites air from areas with high traffic intensity contributed more to OAF production than air from industrial areas. OAF production is probably related to the nature of hydrocarbons in the air.

The effects of ozone and ozonized olefins on aerosol survival of bacteriophage øX174 were studied. The ozone concentrations used were between 0 and 110 parts/109, giving decay rates up to 0·03 min−1. The olefins used were trans-2-butene and cyclohexene in concentrations of 500 parts/109 and 2·4 parts/106, respectively. Olefins alone have no effect, whereas in combination with ozone, decay rates of 0·1 min−1 and higher were obtained. The results are discussed in relation to the viricidal effect of open air.

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.

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.

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.

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.

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.

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.

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.

The results of testing 7060 human serum specimens obtained in the Province of Ontario, Canada, were analysed for the presence of antibodies to Toxoplasma gondii. Of these samples 38% were serologically positive at a titre of 1/16 or greater. The age-specific rates climbed from 2·7% in infants between 6 months and 1 year of age, to about 50% in individuals aged 25 years or over. Variations in prevalence were noted between different areas within the province and evidence is put forward to show that an inverse relation exists between urban size and toxoplasma prevalence. Seasonal and annual variations were not shown to be significant. On the basis of a very small sample of specimens, cat ownership did not appear to cause a significant increase in the risk of acquiring this infection.

A series of outbreaks of skin sepsis among meat handlers in England during 1974 and 1975 afforded an opportunity to study the group-A streptococci commonly isolated from the lesions. Few of these streptococci could be M typed with existing antisera. Intensive study of strains from two outbreaks of sepsis in one abattoir in Shropshire led to the recognition of three new provisional M types. The streptococci were first sorted according to T-typing pattern and ability to produce opacity factor. Opacity-factor producing strains with the same T pattern were then screened for inhibition of opacity production by the sera of convalescents from the same outbreak. Finally, M antisera were made in rabbits against representative cultures.

Sera against the three new provisional types were used to re-examine streptococci from 20 other outbreaks or incidents of sporadic infection among meat handlers. This increased the proportion of typable strains from 3% to 55%. Two of the new provisional types (nos. 2015 and 1658; both T25/Imp 19, opacity-factor positive) were confined to the Shropshire outbreak, but the third (no. 2681; T14, opacity-factor negative) was found among strains from meat workers in eight other geographically distinct areas. In all, 31% of 131 distinct strains from meat workers, but less than 1% of 2816 strains from other British sources, belonged to provisional type 2681. Thus, in Britain, one M-type of group-A streptococcus appears at present to be almost exclusively associated with sepsis in meat workers.

The phage-typing scheme of Callow (1959) has been extended. The original number of types was 34; this has now risen to 207. Tables are presented which show the provisional type designations and the definitive designations now being introduced.