In a recent paper by Miss Chick on “The Laws of Disinfection”, it was pointed out that disinfection of bacteria is strictly analogous to a chemical reaction in which individual bacteria play the part of molecules. Thus, if n be the number of bacteria present at any time t during dis-infection, , where K is a constant. Also, if K1, K2 are these constants for two different temperatures is also constant, i.e. Arrhenius' formula for the temperature coefficient of chemical reactions holds good in the case of bacteria as well. In addition to this, it was found that the relation between the concentration of the disinfectant and the time of disinfection (that is, the time required to reduce the original number of bacteria by a given percentage) might abe approximately expressed by the empirical law

where C is the concentration at time t.

Aedes aegypti female mosquitoes are capable of the mechanical transmission of lumpy skin disease virus (LSDV) from infected to susceptible cattle. Mosquitoes that had fed upon lesions of LSDV-infected cattle were able to transmit virus to susceptible cattle over a period of 2–6 days post-infective feeding. Virus was isolated from the recipient animals in 5 out of 7 cases. The clinical disease recorded in the animals exposed to infected mosquitoes was generally of a mild nature, with only one case being moderate. LSDV has long been suspected to be insect transmitted, but these findings are the first to demonstrate this unequivocally, and they suggest that mosquito species are competent vectors.

1. Outbreaks of mild food poisoning have been investigated in which heat-resistant Cl. welchii appeared to be the causative organism. The outbreaks were characterized by colic and diarrhoea without vomiting, commencing 8–20 hr. after ingestion of the contaminated food.

2. The strains of Cl. welchii concerned are only feebly toxigenic, and apart from the heat-resistance of their spores, and some colonial characters, fit well into Cl. welchii Type A. The toxin production and the serology of the strains is uniform within an outbreak.

3. Mild food poisoning similar to that seen in natural epidemics has been produced in volunteers by ingestion of cultures of heat-resistant Cl. welchii isolated from contaminated meat.

4. Infection is almost invariably due to meat which has been boiled, steamed, braised, stewed or insufficiently roasted, allowed to cool slowly, and eaten the next day, either cold or reheated.

5. Outbreaks of this kind should be prevented by cooking meat immediately before consumption; or, if this is impossible, by cooling the cooked meat rapidly and keeping it refrigerated until it is required for use.

The aetiological agent of an epizootic among Common Terns (Sterna hirundo) in South Africa in 1961 was isolated from several sick birds and named Tern virus. It was classified on the basis of antigenic and morphological properties as a strain of avian influenza virus, Myxovirus influenzae A/Tern/South Africa/1961. The strain-specific antigen of Tern virus was unrelated to all known influenza strains with the single exception of Chicken/Scotland/1959 virus and the two viruses may be regarded as variants of the same strain. This relationship raised the interesting epidemiological possibility of the spread of infection between sea-birds and domestic poultry because the Common Tern migrates between Europe and South Africa.

Environmental poliovirus surveillance (ENV) means monitoring of poliovirus (PV) transmission in human populations by examining environmental specimens supposedly contaminated by human faeces. The rationale is based on the fact that PV-infected individuals, whether presenting with disease symptoms or not, shed large amounts of PV in the faeces for several weeks. As the morbidity:infection ratio of PV infection is very low, this fact contributes to the sensitivity of ENV which under optimal conditions can be better than that of the standard acute flaccid paralysis (AFP) surveillance. The World Health Organization has included ENV in the new Strategic Plan of the Global Polio Eradication Initiative for years 2010–2012 to be increasingly used in PV surveillance, supplementing AFP surveillance. In this paper we review the feasibility of using ENV to monitor wild PV and vaccine-derived PV circulation in human populations, based on global experiences in defined epidemiological situations.

A fermentation-inhibition test for the measurement of growth-inhibiting anti-body to acid-producing mycoplasmas was performed in microtitre plastic plates. M. pneumoniae, M. fermentans and the Negroni agent were selected for study. Antibody could be titrated since specific antiserum inhibited mycoplasma growth and the concomitant production of acid, thus preventing a change in colour of phenol red which was incorporated in the growth medium. It was essential to use unheated horse serum as a component of the growth medium. The inhibitory effect of specific antiserum was much decreased when the horse serum was heat-inacti-vated, indicating the need for a heat-labile accessory factor. The additional use of unheated guinea-pig serum was essential for demonstrating the growth-inhibiting effect of specific antiserum on the Negroni agent. The test was reproducible, specific and sensitive. Sixteen-fold or greater antibody rises were demonstrated in paired sera from volunteers infected with M. pneumoniae. Tests with ninety-five random adult sera showed that 22% had antibody to M. pneumoniae at a titre of 1/5 or more and 13–5% had antibody to M. fermentans.

Recurrent epidemics of influenza are observed seasonally around the world with considerable health and economic consequences. A key quantity for the control of infectious diseases is the reproduction number, which measures the transmissibility of a pathogen and determines the magnitude of public health interventions necessary to control epidemics. Here we applied a simple epidemic model to weekly indicators of influenza mortality to estimate the reproduction numbers of seasonal influenza epidemics spanning three decades in the United States, France, and Australia. We found similar distributions of reproduction number estimates in the three countries, with mean value 1·3 and important year-to-year variability (range 0·9–2·1). Estimates derived from two different mortality indicators (pneumonia and influenza excess deaths and influenza-specific deaths) were in close agreement for the United States (correlation=0·61, P<0·001) and France (correlation=0·79, P<0·001), but not Australia. Interestingly, high prevalence of A/H3N2 influenza viruses was associated with high transmission seasons (P=0·006), while B viruses were more prevalent in low transmission seasons (P=0·004). The current vaccination strategy targeted at people at highest risk of severe disease outcome is suboptimal because current vaccines are poorly immunogenic in these population groups. Our results suggest that interrupting transmission of seasonal influenza would require a relatively high vaccination coverage (>60%) in healthy individuals who respond well to vaccine, in addition to periodic re-vaccination due to evolving viral antigens and waning population immunity.

The antigenic structure of Bordetella pertussis varies continuously with environmental conditions of growth and, under suitable conditions, any of three forms (or modes) with markedly different antigenic surfaces may be developed. High temperatures and certain ions, such as sodium, potassium, halides, formate and nitrate, favour growth like that on Bordet and Gengou's medium at 35° C. Low temperatures and other ions, such as magnesium, sulphate and mono- and dicarboxylic acids with more than two carbon atoms, favour growth with a markedly different antigenic structure and character. These two extreme forms have been called X mode and C mode respectively. A third mode (called I mode) is induced within a narrow range of intermediate temperatures and ion ratios. Bacterial cells in C mode, unlike those in X mode, do not agglutinate red-blood cells, are not haemolytic or agglutinable by heavy metal salts, have no surface antigen related to Bordetella parapertussis or B. bronchiseptica and are serotypically homogeneous.

The influence of ions is a function of their species and ratios and not of their absolute concentrations or total ionic strength. A number of ions has been arranged in a pattern. In this the influence of any salt is represented at the centre of a line joining its component ions, and a measure of the influence of any salt mixture is given by the position of its imaginary centre of inertia. (For calculating this, mass is represented by the product of salt concentration and conductance ratio and radius of gyration by distance.) The influences of ions and temperature appear not to interact since their combined influence is proportional to the sum of their separate influences.

The change from one mode to another (modulation) occurs without mutation or selection, is complete within 7–15 cell divisions and appears to stem from altered rates of synthesis of at least three kinds of antigen molecule. During the process of modulation, antigens not detectable by agglutination in any of the three equilibrium modes (X, I and C) may appear transiently at the surface.

Mutants may or may not modulate. Modulatable mutants may be distinguishable from the wild type in only one mode. Almost all convalescent antibodies are directed against X mode, but C-mode antibodies have been found in several adults with persistent cough and infection.

I wish particularly to thank Dr E. K. Andersen for her generous gifts of sera, Drs P. L. Kendrick, H. Proom, A. F. B. Standfast and A. J. H. Tomlinson for gifts of cultures and Mr M. Breach for his invaluable help in the preparation of media and sera. I am also indebted to the University of London Central Research Fund and the Governors of Westminster Hospital for grants towards the purchase of materials.

Influenza viruses circulate around the world every year. From time to time new strains emerge and cause global pandemics. Many national and international health agencies recommended the use of face masks during the 2009 influenza A (H1N1) pandemic. We reviewed the English-language literature on this subject to inform public health preparedness. There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission. There are fewer data to support the use of masks or respirators to prevent becoming infected. Further studies in controlled settings and studies of natural infections in healthcare and community settings are required to better define the effectiveness of face masks and respirators in preventing influenza virus transmission.

A dairy herd associated with Escherichia coli O157 infection in humans was studied for the 15 months following the outbreak to examine seasonal, age and management factors affecting faecal excretion of the organism and to determine the mode and frequency of milk contamination with the organism. Between May 1993 and July 1994, 28 visits were made to the farm to collect a total of 3593 rectal swabs from cows, heifers and calves and 329 milk samples. E.coli O157:H7 was isolated from 153 (4·3%) of 3593 bovine rectal swabs. The maximum prevalence at any one visit was 14% in lactating cows, 40% in non-lactating cows, 56% in calves and 68% in heifers. The prevalence in lactating cows, which was significantly lower than in the other groups, peaked during May–July 1993 and again briefly after the cattle were housed during November 1993 and then again during May 1994. Excretion rates of E. coli O157:H7 in lactating cows were highest during the first month after calving, falling during lactation and rising to another peak at 7 months postpartum. Between November 1993 and May 1994 there was no evidence of excretion in any group. Eighty-seven (74%) of the animals which excreted E. coli O157:H7 did so on only one occasion but 23 (32%) of 73 cows and heifers and 7 (16%) of 44 calves which excreted the organism did so on more than one occasion. E. coli O157:H7 was not isolated from milk taken from the bulk tank but it was isolated from individual milk samples (one milk jar and one fore-milk) from two animals previously shown to be faecal excretors of the organism. All isolates of E. coli O157:H7 obtained were of the same phage type, toxin genotype and plasmid profile.

We propose an analytical and conceptual framework for a systematic and comprehensive assessment of disease seasonality to detect changes and to quantify and compare temporal patterns. To demonstrate the proposed technique, we examined seasonal patterns of six enterically transmitted reportable diseases (EDs) in Massachusetts collected over a 10-year period (1992–2001). We quantified the timing and intensity of seasonal peaks of ED incidence and examined the synchronization in timing of these peaks with respect to ambient temperature. All EDs, except hepatitis A, exhibited well-defined seasonal patterns which clustered into two groups. The peak in daily incidence of Campylobacter and Salmonella closely followed the peak in ambient temperature with the lag of 2–14 days. Cryptosporidium, Shigella, and Giardia exhibited significant delays relative to the peak in temperature (~40 days, P<0·02). The proposed approach provides a detailed quantification of seasonality that enabled us to detect significant differences in the seasonal peaks of enteric infections which would have been lost in an analysis using monthly or weekly cumulative information. This highly relevant to disease surveillance approach can be used to generate and test hypotheses related to disease seasonality and potential routes of transmission with respect to environmental factors.

The objective of this study was to develop and apply a dynamic mathematical model of VZV transmission to predict the effect of different vaccination strategies on the age-specific incidence and outcome of infection. To do so a deterministic realistic age-structured model (RAS) was used which takes account of the increased potential for transmission within school aged groups. Various vaccine efficacy scenarios, vaccine coverages and vaccination strategies were investigated and a sensitivity analysis of varicella incidence predictions to important parameters was performed. The model predicts that the overall (natural and breakthrough) incidence and morbidity of varicella would likely be reduced by mass vaccination of 12-month-old children. Furthermore, adding a catch-up campaign in the first year for 1–11 year olds seems to be the most effective strategy to reduce both varicella incidence and morbidity (in the short and long term), though with the possible detrimental effect of increasing the incidence of zoster.

Two small flocks of egg-laying hens, naturally infected with Salmonella enteritidis. were housed in individual cages so that their eggs could be identified. During a longitudinal study where the contents of 1119 eggs were examined, 11 were positive for S. enteritidis. One isolate was phage type (PT) 33 the others were PT4. The production of infected eggs was clustered though intermittent. The positive eggs. which were produced by 10 of the 35 hens, were all found to contain fewer than 10 salmonellas. Some birds were also apparently carrying S. hadar PT14 as this organism was isolated from the contents of six Cracked eggs.

The cultural characteristics of 1220 Campylobacter strains from a variety of sources are described. Forty-two were identified as Campylobacter fetus ssp. fetus (Véron & Chatelain, 1973), 1120 as members of the C. jejuni/C. coli group, and 58 did not conform to any known description. Sixteen of the latter strains had the basic characteristics of C. fetus but were atypical in certain other respects. The other 42 strains had the thermophilic characteristics of the jejuni/coli group, but were resistant to nalidixie acid and had other features in common; it is possible that they represent a new species. They were isolated from 19% of locally caught wild seagulls but only occasionally from other animals and man.

Growth at 25 °C clearly distinguished strains of C. fetus from those of the jejuni/coli and the nalidixie acid-resistant thermophilic (NARTC) groups. Maximum growth temperature was less reliable for this purpose, and 43 °C was found to be better than the traditional 42 °C. By arranging the results of three tests (tolerance to 2,3,5-triphenyltetrazolium chloride, growth at 30·5 and 45·5 °C) serially in the form of a schema comprising nine categories, the jejuni/coli strains fell into two main groups resembling the Institute Pasteur C. jejuni and C. coli type strains, but these groups could not be clearly defined owing to the existence of strains with intermediate characteristics.

Most of the strains from cattle resembled C. jejuni, whereas those from pigs resembled C. coli; poultry strains occupied a more intermediate position. Strains from man and other animals were of mixed types, but most human strains resembled C. jejuni rather than C. coli. The type distribution pattern that most nearly matched that of human indigenous strains was given by a half-and-half mixture of strains from cattle and poultry.

This study examined the ethnic difference in the association between increased serum ferritin (SF) (>300 μg/l) and acute inflammation (AI) (C-reactive protein ⩾1·0 mg/dl) between black and white males aged ⩾20 years. Using data from the third National Health and Nutrition Examination Survey (NHANES III), we determined the risk for having elevated SF in black males (n=164) and white males (n=325) with AI present as well as black males (n=1731) and white males (n=2877) with AI absent. Black subjects with AI present were 1·71 times (95% CI 1·18–2·49), and 1·87 times (95% CI 1·46–2·40) more likely to have increased SF than AI absent blacks and AI present whites, respectively. Furthermore, with AI present, every increment of C-reactive protein, white blood cell count, serum albumin, lymphocyte count and platelet count was associated with higher odds of having elevations in SF in blacks than whites. Regardless of AI status, blacks were more likely to have elevations in SF than whites, and the prevalence of elevated SF was significantly higher in blacks than whites. This finding suggested that black males may respond to inflammation with a more aggressive rise in SF compared to white males. Future research is needed to investigate the underlying mechanisms.

Norovirus is the most frequent cause of acute infectious gastroenteritis and it is difficult to control in crowded environments like hospitals and nursing homes. Transmission depends on oral intake of virus deposited in the environment by infectious subjects. Data from volunteer studies indicate that virus concentrations in stool are highly variable, but systematic studies of the time-course of shedding and its individual variation are lacking. This paper quantifies norovirus shedding in a large population of 102 subjects, including asymptomatic shedders, and uses a longitudinal model to generalize shedding patterns. Enhanced surveillance for studies of transmission of norovirus in hospital outbreaks has yielded a considerable number of faecal samples from symptomatic and asymptomatic shedders, both from patients and staff. Norovirus concentrations were determined by real-time PCR. A quantitative dynamic model was fitted to the shedding data, in a multilevel Bayesian framework, to study the time-course of shedding and its variation. The results indicate that shedding in asymptomatic subjects is similar to that in symptomatic infections, both showing considerable variation in peak levels (average 105−109 /g faeces) as well as duration of virus shedding (average 8–60 days). Patients appear to shed higher numbers of virus than staff, for slightly longer durations, but the differences are too small to be significant. Given equal shedding, the greater contribution of symptomatic cases to transmission must be caused by their higher efficiency in spreading these viruses. The results of this study will be helpful for risk studies that need to quantify the deposition of virus in the environment.

The paper describes a maximum-likelihood method for the estimation of age-related changes in the per capita rate of infection, from case notification records or serological data. The methods are applied to records of measles incidence in the UK and USA, for which the estimated rates of infection tend to rise to a maximum value at around 10 years of age and then to decline in the older age-classes. Longer-term and seasonal trends are analysed by reference to changes in the estimated average age at infection; a statistic derived from a knowledge of the age-specific rates of infection. Future data needs in the epidemiological study of directly transmitted viral and bacterial diseases are discussed with reference to the detection and interpretation of age-dependent rates of disease transmission.

Broiler flocks on two Dutch poultry farms were screened weekly for the presence of Campylobacter in fresh caecal droppings during eight consecutive production cycles. Hatchery and fresh litter samples were taken at the start of each new cycle. Water, feed, insects, and faeces of domestic animals, present on the farms were also included in the sampling. Penner seretyping of isolates was used to identify epidemiological factors that contribute to Campylobacter colonization in the broiler flocks. Generally, broiler flocks became colonized with Campylobacter at about 3–4 weeks of age with isolation percentages of 100%, and stayed colonized up to slaughter. A similar pattern of serotypes was found within the various broiler houses on one farm during one production cycle. New flocks generally showed also a new pattern of serotypes. Most serotypes isolated from the laying hens, pigs, sheep and cattle were different from those isolated from the broilers at the same time. Campylobacter serotypes from darkling beetles inside the broiler houses were identical to the ones isolated from the broilers. No Campylobacter was isolated from any of the hatchery, water, feed or fresh litter samples. Conclusive evidence of transmission routes was not found, but results certainly point towards horizontal transmission from the environment. Horizontal transmission from one broiler flock to the next one via a persistent contamination within the broiler house, as well as vertical transmission from breeder flocks via the hatchery to progeny, did not seem to be very likely.

Between 1969 and 1990 strains of Staphylococcus aureus from 359 outbreaks and sporadic cases of staphylococcal food poisoning in the United Kingdom were examined in the PHLS Food Hygiene Laboratory for the production of enterotoxin. In a number of instances the incriminated foods were also examined for the presence of enterotoxin. Strains from 79% of incidents produced enterotoxin A alone or together with another enterotoxin. The level of S. aureus present in the foods ranged from no viable S. aureus detected to 1.5 × 1010 c.f.u./g with a median of 3.0 × 107 c.f.u./g. Enterotoxin was detected in foods in the absence of viable S. aureus in only two outbreaks and in both cheese was the implicated food. Meat. poultry or their products were the vehicle in 75% of incidents with ham and chicken most frequently implicated. Other foods included fish and shellfish (7%) and milk and milk products (8%). Most contamination took place in the home followed by restaurants and shops. Seventy-one percent of the incident strains were lysed by phages of group III or I/III.

A case control study comprising 282 cases and 319 matched controls was conducted in Denmark during 1996–7. Two estimates of the odds ratio (OR) were determined for each risk factor with and without ‘protective factors’ fitted into the final model. Consumption of undercooked poultry (OR 4·5; 8·2), consumption of red meat at a barbecue (OR 2·3; 4·1), consumption of grapes (OR 1·6; 2·8) and drinking unpasteurized milk (OR 2·3; 11·8) were identified as risk factors in both models. Frequent consumption of pork chops (OR 4·4) and daily contact with domestic animals and pets were identified as risk factors in one of the two models only. Finally, foreign travel was found to be a significant risk factor (OR 2·5). Seasonal and regional interaction was observed for several risk factors and the time elapsed from interviewing of cases to interviewing of controls seemed to influence the effect of certain seasonal dependent risk factors.