A detailed study is made of methods available for estimating the significance of difference in degree of pollution of water by conform bacteria and of obtaining practically useful estimates of such differences.

For estimating the significance of a difference in a single pair of samples it was considered preferable to employ as the variate the difference in the total number of fertile tubes, or n.f.t., rather than the difference in the so-called most probable number of bacteria per 100 ml. A table (Table 3) is included by which the significance of any difference in n.f.t. may be determined at a glance. The variate is also useful in determining whether a series of differences may be regarded as homogeneous and such as might be expected to arise by chance in a high proportion of trials if corresponding members in a series of pairs of samples had been taken from sources identical as to their degree of pollution. Table 5 is included to facilitate the application of a comprehensive test of identity, in degree of pollution, of the members of each pair of samples.

The application of the binomial distribution in testing the significance of consistency in sign of a series of differences is explained, and Table 13 is included to facilitate the application of the binomial for a series of pairs twenty or less in number. The use of the normal distribution as an approximation to the binomial for pairs over twenty in number is explained.

The distribution of differences in the logarithms of the ‘most probable number of bacteria per 100 ml.’, or m.p.n., between samples in a certain series, A, and those of another series, B, in an experiment carried out by Dr L. F. L. Clegg, was found to be approximately normal in form. Thus the normal test of the mean logarithmic difference in m.p.n. is applicable and the t-test is applicable to a small series of differences. The advantages of employing the logarithmic difference as the variate are pointed out.

All tests applied to Dr Clegg's data agree in showing that the degree of pollution estimated from the results of a certain method, B, was higher than that indicated by the results of another method, A. According to method A the tubes were inoculated and- incubated at once at 44° C, while according to method B the inoculated tubes were incubated at 37° C, those proving fertile at that temperature being used for inoculating fresh tubes which were then incubated at 44° C. The mean ratio, B : A was found to be 1·416 and the 0·025 points of the distribution were found to be B : A = 9·6, A : B = 4·8 respectively.

The choice of a level of significance is discussed.

The results of the application of some statistical tests of significance to data from a control experiment are discussed. In this experiment the members of each pair of samples were taken from the same water sample and treated by identical methods.

The methods of replacing a difference by the corresponding value of the normal abscissa and of applying the normal test of significance of a mean to the mean of such normal abscissae is explained. This method is applied in testing the significance of a mean difference in n.f.t. and in testing the significance of a mean error from zero.

The theoretical bases of tests of the significance of differences in m.p.n. and in n.f.t. are compared.

The advantage of knowledge of the exact distribution of a single difference in tests of the significance of a series of differences is explained and examples are given which demonstrate this advantage very clearly.

The combination of results taken at different times and places for testing the significance of time or locality effects is explained and a, suggestion is made as to the use of replicated observations when the value of P for each observation is known.

The growth of an enterotoxin A producing strain of Staphylococcus aureus in corned beef was investigated. In the inoculated 6 lb. canned product the bacteria spread throughout the meat and attained high numbers. The rate of spread of the organisms was related to the temperature and length of storage of the cans and the numbers of bacteria inoculated. Cans which had been stored for more than four months showed high counts of the bacteria throughout the meat. It was noted that with the long term contaminated product counts of S. aureus on some selective media may give falsely low results.

Numbers of S. aureus on meat inoculated by handling after removal from the can were initially extremely variable. More uniform distribution and higher counts were attained only if the meat was exposed for some hours at ambient temperature or above. The significance of the results to the investigation of outbreaks of food poisoning suspected of being associated with canned corned beef is discussed.

A high incidence of resistance to trimethoprim has been shown in the normal faecal flora in a population in south India. The dihydrofolate reductase (dhfr) genes mediating transferable resistance to trimethoprim have been identified. Unusually, in this study, the dhfr V was shown to be the predominant resistance gene (dhfr V 50% of tranaconjugants, dhfr Ia 30%), the dhfr Ib was also detected being distinguished from the dhfr V by an oligo-probe. However, when non-transferable resistance was considered, the dhfr Ia was the most prevalent of the dhfrs identified. All those plasmids harbouring the dhfr Ia were shown to possess Tn7. All the plasmids that probed positive for the dhfr V and the dhfr Ib were shown to be associated with the integrase of the Tn21-like transposons, but 8 of the dhfr V genes were not associated with the Tn21 resolvase. The dhfr IV was shown to be present in all seven plasmids that produced low level trimethoprim-resistance. The dhfr V. first characterized in Sri Lanka, would seem to have a local distribution in this region of Asia but is distinguishable from the dhfr Ib only by the use of an oligo-probe.

Many writers having observed that cases of acute rheumatism are not distributed evenly throughout the year, much study has been devoted to the possible relationship between these variations and meteorological conditions.

The effect of a community intervention programme of antibiotics and meningitis vaccine on pharyngeal carriage of Neisseria meningitidis was investigated. Carriage rates were determined in pupils at both secondary schools (ages 11–18 years) included in the community intervention programme and compared with two schools outside the area matched for socio-economic status. A total of 1869 pupils were studied 6 months after the programmes, and 2457 pupils after 11 months.

Six months after the programme was completed there was a 72% reduction in pharyngeal carriage of Neisseria meningitidis in pupils attending the schools in the intervention area compared with pupils in the control schools. After 11 months this difference persisted in the 11–14 age group but not in the 15–18 age group. No resistance to the antibiotics used in the programme was found.

A community intervention programme of antibiotics and vaccine for the control of meningococcal disease led to a long-term reduction in Neisseria meningitidis carriage in some age groups.

This prospective, multicentre study was conducted during 2–30 April 2001 in the internal medicine/infectious diseases services in France and included data from 1858 hepatitis C virus (HCV)-infected patients, half of whom were HIV co-infected. The aims were to outline the type of pre-therapeutic evaluation of HCV infection performed (HCV RNA, genotype, liver biopsy); determine the proportion and characteristics of patients receiving antiviral treatment; and determine if any changes in these parameters had occurred between 1995 and 2001. Patients whom had a complete pre-therapeutic evaluation (39%, 709/1834) and received antiviral treatment (38%, 690/1830) were more likely to have abnormal liver biochemistry, cirrhosis and cryoglobulinaemia (P<0·001). Injecting drug users and HIV-co-infected patients were less likely to have a complete pre-therapeutic evaluation or receive antiviral treatment (P<0·001). A complete pre-therapeutic evaluation was more often performed in 2001 than in 1995 (39% vs. 6%, P<0·001), including qualitative HCV RNA testing (91% vs. 68%, P<0·001), genotyping (59% vs. 7%, P<0·001) and a liver biopsy (60% vs. 29%, P<0·001). The frequency of anti-HCV treatment approximately doubled between 1995 and 2001 (20% vs. 38%, P<0·001). Although adherence to consensus recommendations regarding pre-therapeutic evaluation is not ideal, a substantial improvement has occurred since 1995. Nevertheless, means of increasing the availability of antiviral therapies, particularly for patients with HIV co-infection or injecting drug use, require further study.

In May 2011, the Center for Disease Control and Prevention of a Chinese county found a rapid increase in the number of hepatitis A case notification; these were traced to an outbreak in an elementary school. Twenty-eight cases aged between 7 and 13 years with onset between 7 May and 8 June were serologically confirmed. Network method was conducted to reconstruct an outbreak network and to quantify the relative importance of those involved in the outbreak. A case-control study was used to study the association between the outbreak and putative risk factors. The network analysis suggested this was a disseminated outbreak originating from a 4-year-old boy with propagated spread. Evidence from the case-control study supported consumption of well water as a potential risk factor; however, this was unable to be established through field investigation. Outbreak networks can be used to identify the possible source of infectious disease outbreak, especially when the environmental investigation information is negative or not available.

The social networks of 49 ethnic Vietnamese injecting drug users (IDUs) and 150 IDUs of other ethnicities recruited in Melbourne, Australia, were examined for ethnic differences in distribution of hepatitis C virus infection risk using social network analysis and molecular epidemiology. Vietnamese IDUs were more highly connected than non-Vietnamese IDUs, and more likely to be members of dense injecting sub-networks. More related infections were detected in IDUs with discordant ethnicities than were captured in the social network data; nonetheless, most dyads and most IDU pairs with related infections had matching ethnicity, confirming that mixing was assortative on that criterion. Mixing was not obviously dissortative by risk; low-risk Vietnamese IDUs injected more frequently than did correspondingly low-risk non-Vietnamese IDUs, but results for other measures were reversed or equivocal. Network measurements suggest that ethnic Vietnamese IDUs are at elevated risk of blood-borne infection, a conclusion supported by their relatively high HIV prevalence.

The process of physical growth in children is manifested by changes in their size, mass and shape. Changes in size are ascertained by measurement, usually, of the standing height of the child, but occasionally of the sitting height, and sometimes, also, of the chest circumference and the width between the hips. Changes in mass are detected by weighing, whilst changes in shape, which are due to unequal rates of growth in height and in mass, are estimated by methods referred to later.

It is greatly to be desired that the causes of the decline of tuberculosis, which has been so striking a feature in the history of that disease in recent times, should be clearly ascertained; for only through an understanding of their nature and relative importance can our efforts to accelerate that decline hope to succeed.

The fact that the blood of ordinary laboratory animals exerts a very marked bactericidal effect upon the Bacillus typhosus and the Spirillum cholerae asiaticae, while it exerts little or no effect upon the Staphylococcus and Streptococcus pyogenes, has hardly received the attention which it would seem to merit in view of the circumstance that these facts involve the important problem as to whether the blood exerts its bactericidal action upon pathogenic organisms generally, or only upon certain species of such micro-organisms.

A descriptive study was performed between 1 January 2010 and 31 December 2011 to estimate the incidence of norovirus outbreaks in hospitals and nursing homes in Catalonia (Spain). Epidemiological surveys were done for each outbreak. Norovirus was confirmed using RT–PCR. The incidence of outbreaks/106 person-years by centre, and the attack rate, were calculated. Statistically significant differences were calculated using odds ratio (ORs) and 95% confidence intervals (CIs). Person-to-person transmission was responsible for 81·5% (22/27) of outbreaks. The incidence in the population was 156·7 outbreaks/106 person-years. The incidence by centre was 1·3% per year and was greater in hospitals (2·6%) than in nursing homes (0·9%) (OR 3·2, 95% CI 1·5–6·9). The global attack rate in residents and staff was 34·7% (816/2348). The mortality rate was 0·25% (2/816). Genogroup GII.4 caused 66·7% of outbreaks. Norovirus GII.4 outbreaks cause significant morbidity affecting both patients and staff.

Epidemiological analysis of Klebsiella strains from nosocomial infections needs a simple, stable and reproducible technique of typing. We have evaluated three bacteriocin typing methods for Kiebsiella spp. by means of 15 bacteriocin-producing strains, with special reference to stability and reproducibility.

With the three methods indicator strains and clinical strains were retyped on different days under constant test procedures. Stability of bacteriocins was tested by titration immediately after preparation and after 4 weeks of storage at –70°C. Thereafter, reproducibility of typing was tested by means of these freshly prepared bacteriocin lysates and of portions of the same lysates stored at –70 °C. A moderate reproducibility was obtained with one method after two typing experi ments: 79.2% and 61.3% for indicator strains and clinical strains respectively. The other two methods gave a much lower reproducibility of 38 .5% and 32.5 % for indicator strains and of 11.1% and 25.5% for clinical strains after two experiments.

The reproducibility decreased after retyping three, four or five times. These methods are simple to perform but their usefulness for epidemiological studies is doubtful. Possible causes of the lack of reproducibility of the methods are discussed.

A study was conducted to characterize the risk of Plasmodium vivax infection in the Lacandon forest, southern Mexico. Blood samples and questionnaire data were collected in 1992. Malaria cases (n = 137) were identified by the presence of symptoms and a positive thick blood smear. The control group included individuals with negative antibody titres and no history of malaria (n = 4994). From 7628 individuals studied, 1006 had anti-P. vivax antibodies. Seroprevalence increased with age. Risk factors associated with infection included: place of birth outside the village of residence (odds ratio, OR 11·67; 95% CI 5·21–26·11); no use of medical services (OR 4·69, 95% CI 3·01–7·29), never using bed-nets (OR 3·98, 95% CI 1·23–12·86) and poor knowledge of malaria transmission, prevention and treatment (OR 2·30, 95% CI 1·30–4·07). Health education represents the best recommendation for controlling the disease in the area.

Infection with hepatitis A virus (HAV) in patient with chronic liver disease (CLD; due to hepatitis B or hepatitis C) may cause severe disease and fulminant liver failure. This study aimed to determine the seroprevalence of HAV antibodies in patients infected with HCV or HBV in Iran (Jahrom city). A total of 159 patients with underlying CLD were recruited between September 2012 and February 2013. Serum samples were collected from each patient and tested for anti-HAV using enzyme-linked immunosorbent assay (ELISA). The overall seroprevalence of total anti-HAV was 79·2%. Patients aged 20–30 years had the lowest (28·3%) anti-HAV seropositivity and those aged >50 years had the highest (95%) seropositivity. The overall prevalence of anti-HAV in patients with chronic HCV and HBV infection was 93·7% and 77·1%, respectively. The anti-HAV seropositivity in liver cirrhosis patients was 100% compared to CLD patients. Because of low HAV immunity in younger CLD patients, vaccination against HAV should be considered.

We propose a rather simple model, which fits well the weekly human influenza incidence data from England and Wales. A standard way to analyse seasonally varying time-series is to decompose them into different components. The residuals obtained after eliminating these components often do not reveal time dependency and are normally distributed. We suggest that conclusions should not be drawn only on the basis of residuals and that one should consider the analysis of squared residuals. We show that squared residuals can reveal the presence of the remaining seasonal variation, which is not exhibited by the analysis of residuals, and that the modelling of such seasonal variations undoubtedly improves model fit.

Preparations of influenza virus A0 PR 8/34 and A 2 Malaysia/68 have been studied in the electron microscope. They were similar in appearance to preparations made by others. Each preparation was degraded by Triton N 101. The process of degradation appeared to be different from that observed using ether and, by inference, a number of other agents.

Chlamydia pneumoniae infection is said to be associated with obesity. We studied the association between C. pneumoniae infection and inflammation and increased BMI in 891 Finnish military recruits. IgG seropositivity in arrival and departure serum samples during 6–12 months of military service was considered as persistence of antibodies and a possible indication of chronic infection. Persistently high C-reactive protein (CRP) level (elevated on arrival and departure) (OR 2·2, 95% CI 1·3–3·9), and persistent C. pneumoniae antibodies (OR 2·1, 95% CI 1·5–2·8) were significant risk factors for overweight (BMI ⩾25 kg/m2). In addition, those who had persistent antibodies and persistently elevated CRP levels, or those who had either of them, had a significantly higher BMI (kg/m2) compared to those who had neither of them (25·8 vs. 24·6 vs. 23·5, respectively; P<0·001). These results provide new information about the association between possible chronic C. pneumoniae infection and obesity in young men.

Pneumonia leads to considerable morbidity and mortality in nursing home residents with dementia. We assessed pneumonia incidence based on data from three different studies: (1) real-time national surveillance of healthcare-associated infections in nursing home residents in 2009–2015; (2) a randomized controlled trial in 2012–2015 to assess effects of a practical guideline in nursing home residents with dementia and pneumonia; and (3) a study in 2007–2010 to assess quality of dying in newly admitted nursing home residents with dementia. In national surveillance data, pneumonia incidence was calculated separately for psychogeriatric and somatic beds, as a proxy for residents with and without dementia. Weekly pneumonia incidence was significantly lower per 1000 psychogeriatric beds (3·9; 95% confidence interval (CI) 3·2–4·6) compared with 1000 somatic beds (5·7; 95% CI 5·1–6·3). Annual incidence per 1000 psychogeriatric beds was similar in national surveillance (range 78·9–117·1) and the trial (range 71·0–94·3), and significantly higher in newly admitted dementia residents (range 267·3–363·2). The incidence was highest during the first months after admission when compared with residents with longer stay. In conclusion, follow-up of pneumonia in newly admitted dementia residents may result in higher incidence, possibly due to higher risk in this population.

1. Glycine, alanine, and several isomers of alanine, DL-glutamic acid and DL-aspartic acid, when added to fresh guinea-pig serum and allowed to stand on the bench for half an hour, will protect the complement of this serum from destruction by heating at 55 and 56° C. for half an hour, but most of the complement activity is destroyed by heating at 57° C. and it is completely destroyed at 58° C. after half an hour.

2. Derivatives of glycine do not have any protective effect.

3. Various substances of high molecular weight, that might be described as ‘protective colloids’ do not have any protective effect.

4. How these amino-acids when added to serum alter the heat-lability of the complement is not understood.