Viral haemorrhagic disease of rabbits (VHD), a potential biological control for wild rabbits in Australia and New Zealand, escaped from quarantined field trials on Wardang Island and spread to the mainland of Australia in October 1995. This study looked for any evidence of infection or illness in people occupationally exposed to the virus. Two hundred and sixty-nine people were interviewed and 259 blood samples were collected. Exposures to VHD-infected rabbits ranged from nil to very high. No VHD antibodies were detected in any of the 259 sera when tested by VHD competitive enzyme immunoassay, which had been validated with 1013 VHDV-specific antibody negative sera. A questionnaire designed to elicit symptoms of disease in a range of organ systems found no significant differences between illness in those exposed and those not exposed to VHD, nor could an association be found between exposure and subsequent episodes of illness. The findings are consistent with the view that exposure to VHD is not associated with infection or disease in humans.

1. A series of cases of repeated accidental vaccinal infections of vaccinia and vaccinoid types in subjects possessing strong or complete vaccinal immunity, is presented.

2. It is suggested that there is a similarity between such cases and the repeated infections on the hands of farm workers and milkers handling cows naturally infected with cowpox.

3. It is difficult to fit satisfactorily such facts into the framework of the modern theory of vaccinal immunity, but no explanation of the apparent discrepancy can be suggested.

Mud samples collected in June 1975 from the lakes, marshes and waterways of the Camargue were examined for Clostridium botulinum. The Grand Rhône and Petit Rhone were shown to contain types B and E, but of 44 samples taken from well distributed sites on the Ile de la Carmargue, only two (4·5%) were positive and these contained type E alone. The survey indicated a much lower prevalence of Cl. botulinum than any encountered in recent surveys of inland aquatic environments elsewhere.

Values are deduced for the efficiency of isolation against airborne particulates, e.g. micro-organisms, of a variety of ventilation systems. The calculated values show reasonable correspondence with the limited experimental data available. Much better control and indication of the air flow is necessary if high degrees of isolation are required.

Data were collected on 6578 patients diagnosed with AIDS at 52 clinical centres in 17 European countries during an 11-year period from 1979 to 1989. The centres were divided into four regions, North, Central, Southeast, and Southwest. Differences in the incidence of most AIDS-defining opportunistic infections and malignancies were found. After adjusting for known possible confounders, statistically significant differences between regions remained. Pneumocystis carinii pneumonia (PCP) was more common in Northern Europe, Kaposi's sarcoma and toxoplasmosis in Central Europe, cytomegalovirus retinitis in South-eastern Europe, and extrapulmonary tuberculosis in South-western Europe. These differences we attribute primarily to different degrees of exposure to the respective underlying pathogens. The prevalence of these and other micro-organisms will determine the clinical course of HIV infections in parts of Eastern Europe and elsewhere where the virus now is spreading.

The action of univalent and bivalent salts on bacteria in affeting the conductivity of thick emulsions of the meningococcus and B. coli demonstrates the important fact, that they alter the conductivity of these germs in the living condition, in a very definite manner. In this alteration, the predominant part is played by the cat-ion.

All monovalent cat-ions, with the exception of the H-ion, such as those of Na, K, Li, Rb, produce a rapid increase in conductivity or a fall in resistance. In its early stages this increase in conductivity is readily reversible in these solutions. If allowed to follow its due course, however, it leads finally to death in about two hours, when the bacterial cells no longer offer any resistance to the passage of the ions. The conductivity of the emulsion then becomes that of the fluid in which the emulsion has been suspended.

Bivalent cat-ions and the H-ion, on the other hand, at first produce a slight fall in conductivity or an increase in resistance, followed, swecondly, by an irreversible increase in conductivity which is slow and gradual resulting finally in death after 48 or more hours. This is shown by the car-ions of Ca, Sr, Ba, and Cd.

In a balanced solution such as sea-water, blood plasma, Ringer's solution, van't Hoff's solution, where a certain quantity of CaCl2 antagonises a larger amount of NaCl and KCl, the conductivity of bacterial emulsions undergoes no change, but remains constant.

Dead in distinction to living bacteria offer little resistance to the passage of ions of a solution. It would seem the relativity high resistance of the bacterial cell is due to some condition present in the living and absent in the dead state.

It has been shown by experiments on animals that the condition of increased conductivity of the cell is coupled with a loss of virulence in the case of some pathogenic bacteria. It is not clear from these experiments if this is due to the actual death of the germs in a monovalent salt solution, or to a detoxicating action of these solutions on the germs. It would seem there is some evidence for believing that the latter takes place, as the lost lethal power returns in the presence of a small trace of Ca. In bivalent salt solutions no loss of toxicity takes place. It has been pointed out that the action of monovalent and bivalent salts on bacteria offers a new explanation of certain experiments with gas gangrene organisms, where it is at present considered that the action of the salts are on the tissues of the animal and not on the bacteria.

Serological investigations were carried out on 147 patients with Paul—Bunnell positive infectious mononucleosis (IM) from the general population. All possessed antibody to the Epstein—Barr virus (EBV) and 63% showed serological evidence of recent infection. Contacts of 132 patients, 306 in all, were followed serologically; within 6 months of the index cases' illness twenty one contacts developed evidence of EBV infection or re-infection and of these five developed overt IM. The secondary attack rate of EBV infection among susceptible contacts was at least 19%; the corresponding figure for clinically apparent IM was 6%. EBY antibody prevalence among patients' siblings was significantly lower than among age-matched controls, suggesting that cases of IM come from families with a lower than normal previous experience of the virus. Of thirteen patients with persistently Paul—Bunnell negative ‘glandular fever’ four had serological evidence of recent EBV infection and two had probable cytomegalovirus mononucleosis. Recent EBV infection may have been associated with the illnesses of five of the remaining patients.

1. Streptococcus pyogenes multiplies readily in sterilized milk stored at 22 and 18° C., and more slowly at 15° C. In fresh raw milk this organism begins to multiply slowly only after 48–72 hours of storage at 18–22° C. In laboratory pasteurized milk the result is similar, but both commercially pasteurized milk and raw graded milk bottled for distribution sour too rapidly for multiplication to take place after artificial contamination. These facts suggest that widespread epidemics are rarely due to extensive multiplication of S. pyogenes in milk during commercial or household storage.

2. The initial degree of contamination of milk with S. pyogenes has no influence upon this organism's ability to multiply during storage.

3. The failure of S. pyogenes to multiply during storage is due to (a) its natural reluctance to grow at atmospheric temperatures, (b) the bacteriostatic action of the milk, and (c) the readiness with which saprophytic bacteria multiply at atmospheric temperatures.

4. It is contended that infected cows play a major part in the spread of milk-borne S. pyogenes epidemics, and relevant literature is quoted to support this view. It is urged that routine investigation of apparent milk-borne epidemics should include the immediate bacteriological examination of an individual sample of milk from every cow concerned in the supply under suspicion.

Botulism is a severe neuroparalytic disorder that can be potentially life-threatening. In Barcelona, Spain, no outbreaks had been reported in the past 25 years. However, in September 2011, two outbreaks occurred involving two different families. A rare case of Clostridium baratii which produced a neurotoxin F outbreak was detected in five family members who had shared lunch, and several days before that another family was affected by C. botulinum toxin A which was probably present in homemade pâté.

England has recently started a new paediatric influenza vaccine programme using a live-attenuated influenza vaccine (LAIV). There is uncertainty over how well the vaccine protects against more severe end-points. A test-negative case–control study was used to estimate vaccine effectiveness (VE) in vaccine-eligible children aged 2–16 years of age in preventing laboratory-confirmed influenza hospitalisation in England in the 2015–2016 season using a national sentinel laboratory surveillance system. Logistic regression was used to estimate the VE with adjustment for sex, risk-group, age group, region, ethnicity, deprivation and month of sample collection. A total of 977 individuals were included in the study (348 cases and 629 controls). The overall adjusted VE for all study ages and vaccine types was 33.4% (95% confidence interval (CI) 2.3–54.6) after adjusting for age group, sex, index of multiple deprivation, ethnicity, region, sample month and risk group. Risk group was shown to be an important confounder. The adjusted VE for all influenza types for the live-attenuated vaccine was 41.9% (95% CI 7.3–63.6) and 28.8% (95% CI −31.1 to 61.3) for the inactivated vaccine. The study provides evidence of the effectiveness of influenza vaccination in preventing hospitalisation due to laboratory-confirmed influenza in children in 2015–2016 and continues to support the rollout of the LAIV childhood programme.

These studies, carried out during the period 1940–2, were undertaken to test the relative merits of hypochlorous acid gas and sprayed solutions of sodium hypochlorite, when these systems are used as aerial disinfectants, and to ascertain the factors determining their efficiencies in this capacity. The ulterior motive was the use of such systems as a counter measure against the danger of air-borne infection. The more practical aspects of their large-scale application, in shelters and other compartments, have been the province of others of our colleagues and will be reported upon separately.

1. During a period of 1 year the incidence of infection with haemolytic streptococci was determined among children on admission to, and during residence in, the children's wards of University College Hospital, London.

2. The increased incidence among those in residence, 13·1% of whom acquired haemolytic streptococci during their stay, was due principally to outbreaks of infection by these organisms. By the slide agglutination method the majority of strains could be assigned to one or other of Griffith's thirty types and the presumed path of their spread studied.

3. The source of the infection in most of the outbreaks was not ascertain-able from the data collected, but in general it did not appear to be in the patients themselves.

4. With a few exceptions, isolation by cubicles was an effective measure in preventing the spread of haemolytic streptococci.

5. In general the haemolytic streptococci seemed to spread from patient to patient, though the exact mode of spread was not ascertained.

6. The clinical manifestations of infection by any one type of haemolytic streptococcus was varied, e.g. wound suppuration, sore throat, pyrexia, otitis media. Many of the infections were “latent”.

7. In addition to the haemolytic streptococcal outbreaks, there were two outbreaks of diphtheria (fifteen patients), two of Bact. sonnei dysentery (ten patients and one nurse), one of catarrhal jaundice (one patient and three nurses), six cases of intercurrent gastro-enteritis of infancy and one case of measles.

8. In all, at least 104 (or 18·9%) of the 551 patients of these wards developed intercurrent infections, manifest or latent, during their stay in hospital.

Salmonella Hadar ranks in the top ten serovars reported from humans in Switzerland. In this study, all 64 S. Hadar strains isolated from different patients from 2005 to 2010 in Switzerland were characterized by (i) assessing phenotypic antimicrobial resistance profiles using the disk diffusion method and (ii) by genotyping using pulsed-field gel electrophoresis (PFGE) in order to evaluate the relationship of the strains. The annual incidences varied between 0·32/100 000 in 2005 (highest incidence) and 0·065/100 000 in 2007 (lowest incidence). In total 71·8% of the isolates were resistant to nalidixic acid. Although 40·6% of the strains were resistant to the β-lactam antibiotic ampicillin, they remained susceptible to the third-generation cephalosporin cefotaxime. Genotyping revealed a primary cluster consisting of 42 strains, sharing a similarity of >92%, with a subcluster of 18 strains with indistinguishable patterns. Resistance profiles allowed further differentiation within this subcluster providing a link of two strains to an outbreak in Spain.

The epidemic of coronavirus disease 2019 (COVID-19) began in China and had spread rapidly to many other countries. This study aimed to identify risk factors associated with delayed negative conversion of SARS-CoV-2 in COVID-19 patients. In this retrospective single-centre study, we included 169 consecutive patients with confirmed COVID-19 in Zhongnan Hospital of Wuhan University from 15th January to 2nd March. The cases were divided into two groups according to the median time of SARS-CoV-2 negative conversion. The differences between groups were compared. In total, 169 patients had a median virus negative conversion time of 18 days (interquartile range: 11–25) from symptom onset. Compared with the patients with short-term negative conversion, those with long-term conversion had an older age, higher incidence of comorbidities, chief complaints of cough and chest distress/breath shortness and severer illness on admission, higher level of leucocytes, neutrophils, aspartate aminotransferase, creatine kinase and erythrocyte sedimentation rate (ESR), lower level of CD3+CD4+ lymphocytes and albumin and more likely to receive mechanical ventilation. In multivariate analysis, cough, leucocytes, neutrophils and ESR were positively correlated with delayed virus negative conversion, and CD3+CD4+ lymphocytes were negatively correlated. The integrated indicator of leucocytes, neutrophils and CD3+CD4+ lymphocytes showed a good performance in predicting the negative conversion within 2 weeks (area under ROC curve (AUC) = 0.815), 3 weeks (AUC = 0.804), 4 weeks (AUC = 0.812) and 5 weeks (AUC = 0.786). In conclusion, longer quarantine periods might be more justified for COVID-19 patients with cough, higher levels of leucocytes, neutrophils and ESR and lower levels of CD3+CD4+ lymphocytes.

In a previous communication (1921) experiments have been described showing the effect produced by continuously adding normal mice to a cage, the population of which is infected with bacilli of the group which includes B. gaertner and B. suipestifer. It was seen that under these circumstances the spread of infection progresses in a series of epidemic waves, and that the survival-time of any batch of mice varies according to the period at which they are introduced to the cage. It was further shown that, if such regular and continuous addition of susceptible animals be persisted in over long periods of time, all the micewill eventually succumb, while, if the addition of new individuals be discontinued, the epidemic will eventually subside, leaving a proportion of survivors who may remain in apparently good health over a considerable period.

Sera from 3163 patients were examined for growth-inhibiting and complement-fixing antibody to Mycoplasma hominis. The results were analysed in respect of the age and sex of the patients. Antibodies were found to be uncommon in young people but increased in frequency with age; they were present in old men but were less common in women over sixty-five. Patients attending V.D. clinics and prison inmates had a much higher incidence of antibody than hospital and ante-natal patients. Complement-fixing antibody was approximately three times as common as growth-inhibiting antibody in the sample examined; it was also more common in women than men but the overall incidence of growth-inhibiting antibody was the same in each sex. It was concluded that possibly growth-inhibiting antibody is produced in more severe infections and that it disappears from the serum more quickly than complement-fixing antibody.

The relationship between ocular toxoplasmosis and levels of toxoplasma specific antibodies was examined in 195 patients. Using clinical information collected by questionnaires, patients were divided into: 97 with ocular toxoplasmosis (group 1) and 98 with ocular lesions not due to toxoplasma (group 2). The geometric mean of dye test titres (±S.D. natural log titre) in group 1 was 53·2 (±0·95) compared with 24·6 (±1·11) in group 2 (P<0·001). Young females tended to have more active lesions compared with young males (P<0·05). There was an age-dependent difference in dye test titres between the groups (P<0·001). Group 1 showed a decline in titre with age compared with an increase in group 2. Ocular toxoplasmosis was diagnosed most frequently among 21–30 year olds. More group 1 patients had dye test titres [ges ]65 iu/ml than group 2 (P<0·05). Dye test titres [ges ]65 iu/ml support a diagnosis of ocular toxoplasmosis whereas lower titres suggest other causes for eye lesions.

It is now twelve years since it first became possible to study plague by modern methods, and yet no conclusion on its aetiology has been reached which has met with general acceptance. Two causes, as it seems to me, have chiefly contributed to this disappoinment. One consists in the appeal which has been persistently made to bacteriology for the lights which in fact are not in its power to shed; the other is neglect of the epidemiological method, or at least failure to apply it effectively. In consequence, a field has been occupied by the bacteriologist which could not be profitably laboured by him. The epidemiologist has not seriously disputed this usurpation of his domain, and for his apparent apathy he has not been without excuses of some weight.

The effects of various salts on the viabifity of T4 and T4 Bo phages during freezing and thawing have been studied. The effectiveness of different salts in causing inactivation or protection of phage during freeze—thawing was of the same order as has been observed for their effects on the conformational stability of macromolecules. There were two important contributory factors causing inactivation of phage during freeze—thawing: (i) concentration of solutes during freezing, and (ii) lowering the temperature, without change in salt concentration.

The viability of phage following storage at subzero temperatures was dependent on the storage temperature, the species of ions in the suspending medium and the initial salt concentration. Viability was greatest when phage had been initially suspended in dilute solutions.

Survival of T4 Bo phage, following cooling to subzero temperatures and rewarming, was greater in D2O solutions than in H2O solutions.

It was found that 20% glycerol completely protected against inactivation of T4 Bo phage, suspended in 3·5 molal NaBr, which were cooled to subzero temperatures and rewarmed in the absence of ice. Without added glycerol the viability of T4 Bo phage suspended in 3·5 molal NaBr, which were cooled to −20° C and rewarmed was less than 1%. This protective effect of glycerol is in contradiction to the accepted views of its mode of action in prevention of freezing injury.

This work has been supported in part by grants from the Medical Research Council and the Office of Naval Research under contract F 61052–68-C-0041.

A clinical trial was conducted in Argentina to determine the efficacy of clarithromycin plus lansoprazole for the treatment of Helicobacter pylori in duodenal ulcers and non-ulcer dyspepsia. PCR–RFLP was conducted on an 820-bp amplified product of the ureC gene of H. pylori to determine the genetic heterogeneity of 83 pretreatment and 21 post-treatment isolates. Twelve different restriction patterns were observed when digested with Sau 3A or Hha I, resulting in 40 different RFLP types. Comparison of isolates before treatment to after treatment showed that 20 of 20 patients had the same RFLP type. In addition, the presence of the cytotoxin-associated gene (cagA) and the vacuolating gene (vacA) were determined. All pretreatment isolates were positive for vacA whereas 75% of the pretreatment isolates were positive for cagA. The results of this study indicate that a high degree of heterogeneity exists among H. pylori and that infection is not limited to a small number of RFLP types.