With a case-crossover design, a case's exposure during a risk period is compared to the case's exposures at referent periods. The selection of referents for this self-controlled design is determined by the referent selection strategy (RSS). Previous research mainly focused on systematic bias associated with the RSS. We additionally focused on how RSS determines the number of referents per risk, sensitivity to overdispersion and time-varying confounding.

We illustrated the consequences of different RSS using a simulation study informed by data on meteorological variables and Legionnaires’ disease. By randomising the events and exposure time series, we explored statistical power associated with time-stratified and fixed bidirectional RSS and their susceptibility to systematic bias and confounding bias. In addition, we investigated how a high number of events on the same date (e.g. outbreaks) affected coefficient estimation. As illustrated by our work, referent selection alone can be insufficient to control for a time-varying confounding bias. In contrast to systematic bias, confounding bias can be hard to detect. We studied potential solutions: varying the model parameters and link-function, outlier-removal and aggregating the input-data over smaller areas. Our simulation study offers a framework for researchers looking to detect and to avoid bias in case-crossover studies.

Influenza is a major human respiratory pathogen. Due to the high levels of influenza-like illness (ILI) in Zhejiang, China, the control and prevention of influenza was challenging during the 2017–2018 season. To identify the clinical spectrum of illness related to influenza and characterise the circulating influenza virus strains during this period, the characteristics of ILI were studied. Viral sequencing and phylogenetic analyses were conducted to investigate the virus types, substitutions at the amino acid level and phylogenetic relationships between sequences. This study has shown that the 2017/18 influenza season was characterised by the co-circulation of influenza A (H1N1) pdm09, A (H3N2) and B viruses (both Yamagata and Victoria lineage). From week 36 of 2017 to week 12 of 2018, ILI cases accounted for 5.58% of the total number of outpatient and emergency patient visits at the surveillance sites. Several amino acid substitutions were detected. Vaccination mismatch may be a potential reason for the high percentage of ILI. Furthermore, it is likely that multiple viral introductions played a role in the endemic co-circulation of influenza in Zhejiang, China. More detailed information regarding the molecular epidemiology of influenza should be included in long-term influenza surveillance.

In seeking a more satisfactory test than the conventional mouse-protection tests for the assessment of typhoid-paratyphoid vaccines in relation to their O and Vi antigens, it was decided to undertake a series of experiments with vaccines containing the somatic antigens of Salmonella paratyphi C and to use this organism to challenge mice thus immunized. Salm. paratyphi C contains the same Vi antigen as Salm. typhi and moreover it is capable of giving rise to a true infection in mice in contrast to the acute intoxication which follows a fatal dose of Salm. typhi.

Large doses, of the order of 100 × 106, of this paratyphoid organism injected intraperitoneally into mice resulted in acute intoxication with death in 24–72 hr., similar in every way to the picture with typhoid bacilli, but when the dose was reduced 100-fold or more an infective illness was set up which after an interval of 5–10 days or more, during which the organisms multiply freely in the tissues, terminated fatally. Typhoid bacilli do not produce a true infection in mice.

Living vaccines were prepared of Salm. typhi Ty6S (an almost pure Vi strain) and Salm. cholerae-suis (contains the same O-antigen complex as Salm.paratyphi C). These were used separately, and in combination, to immunize different batches of mice by the subcutaneous route against a subsequent intraperitoneal challenge with a Vi-positive culture of Salm. paratyphi C at both high- and low-dose levels. The different challenge doses were to assess the relative values of the 0 and Vi components in protecting against intoxication (high dose) and infection (low dose), respectively.

Against intoxication pure Vi vaccines were almost as effective as Vi + O vaccines, whereas pure O vaccines gave little or no protection.

Against fatal infection the combined Vi + O vaccine offered good protection and the pure O vaccine was but little inferior, whereas the pure Vi vaccine appeared to be without significant effect.

Quite small doses of Salm. paratyphi C administered by the intra-gastric route can give rise to a general infection in mice, but in order to obtain consistent results much larger doses were found necessary (about 300 x 106 organisms). Mice immunized with the same three vaccines and subsequently challenged by the intragastric route with this large dose showed significant protection throughout. The combined, O + Vi, vaccine did not appear to have any advantage over the pure O vaccine, but both were markedly superior to the pure Vi vaccine. Further experiments on the same lines are however necessary to see if the results obtained in this single experiment are reproducible.

The relationship of the above findings to the evaluation of agents employed in man for the prophylaxis of enteric fever and the need for further experimental work of a similar nature are discussed.

We wish to thank Dr F. Kauffmann for strains of Salm. paratyphi C, Lt-Col. T. E. Field, whose results we have freely quoted, and Dr S. Peto for advice on statistical evaluation of our results.

Methods of statistical analysis are presented for one or more dilution series experiments where the quantity of interest is the number of virus particles required to infect a cell. These methods are illustrated on several data sets drawn from the literature. Data from seven series, which have been used to support a two-particle model in the literature, are here shown to reject such a model decisively, whereas fifteen other experiments are found to be in excellent agreement with a one-particle model.

The studý of the Fusiformis necrophorus culture ‘132’ showed that new pure LI cultures could be isolated from it, which have already been maintained for one year and undergone more than 100 passages without reverting to their original type. The new cultures resemble the old L 1 strains from Streptobacillus moniliformis in every respect except for their strict anaerobiosis. It has been observed that swellings of the bacteria develop into large bodies not distinguishable from the elements of which the pure L 1 culture consists.

In the light of the new observations on Fusiformis necrophorus which are in full agreement with those of Dienes & Smith it is still not possible to disprove the symbiosis theory, for the newly established L 1 cultures have not reverted so far. Secondly, though it has been seen that L 1 forms develop from swellings of bacteria, the possibility that a parasite might behave in a similar way cannot be excluded.

On the other hand Dienes's opinion of the bacterial nature of the L 1 component cannot be disproved either. However, we know yet too little about the normal developmental cycle of bacteria to be able to decide whether the L 1 form is an independent entity or whether it may be a normal stage through which bacteria have to pass from time to time or whether it may represent a ‘loss-mutant’ which some bacteria might produce under not yet known conditions. If in the future the bacterial nature of the L1 could be convincingly proved we would be faced with the fact that bacteria can assume a form in which they grow as a thin shapeless slime containing nuclear structures arranged as bodies, rings or very finely dispersed particles—not the dumbbell pattern so characteristic for young bacteria of all kinds—and that further very small parts of the material (filterable granules?) are able to reproduce the L1 culture which at least can go on for many years without reverting into the bacterium from which it was derived.

Tularemia caused by the bacterium Francisella tularensis is a zoonotic disease. Tularemia is a common disease in the hare, and as a game species can be an important source of infection for humans. In this study, hares diagnosed with tularemia were examined with the aim to investigate whether the muscle (meat) had any pathological changes and/or contained F. tularensis. Real-time PCR and/or immunohistochemistry (IHC) detected the bacteria in muscle samples from 40 out of 43 investigated hares. IHC showed that bacteria were few and most commonly located in the peri- and endomysium. Histopathology showed occasional perimysial necroses and mild inflammation in association to the bacteria. Attempts to culture from 14 muscle samples were successful in two cases, both stored in the freezer <1 year. The result of this study shows that since F. tularensis is present in the muscle of infected hares, there is a risk for human infection when consuming undercooked hare meat. The risk is enhanced by the fact that some hares do not have easily detected gross lesions. The study contributes to a better understanding of sources of infection and risk factors for humans to contract tularemia.

Sera of Nigerians aged between 10 and 60 years were tested individually for their antibody to five strains of influenza A virus. The results showed a similar pattern to those which other investigators have found with sera collected in the U.S.A. and in this country. However, antibody to the swine and WS strains was found in younger individuals than was reported previously; and the distribution of antibody titres suggests that this represents antibody to minor antigens of more recent strains, rather than persistence of swine and WS viruses.

We should like to thank Dr C. H. Andrewes F.R.S. for his criticisms and Dr James S. Porterfield who sent the sera.

We describe an outbreak of echovirus 18 infection involving 10 patients in our neonatal intensive care unit (an attack rate of 33%). The mean age at the onset of illness was 26.8 days. Eighty percent were preterm infants. All were discharged home without sequelae. There were no differences in gestation age, birth weight, delivery mode, use of antibiotics, and parenteral nutrition between the enterovirus (EV) group and non-EV group, but the rate of breastfeeding was significantly higher in the EV group. Separation care and reinforcement of hand-washing seemed to be effective in preventing further spread of the virus. Visiting policy, hygiene practice, and handling of expressed breastmilk should be reinforced.

1. Streptolysin production by twenty-seven strains of haemolytic streptococci grown in a special buffered glucose serum-free broth has been compared and a very marked variation noted.

2. The anti-streptolysin titres in healthy individuals and in others at the commencement of illness showed a pronounced variation.

3. Throat infections with S. haemolyticus usually produced a rise in the level of circulating anti-streptolysin in the patients' blood, and this could be considered diagnostically significant.

4. Throat infections with haemolytic streptococci showed rather more rapid production and higher titres of anti-streptolysin than did skin infections such as erysipelas, and both throat and skin infections were greatly superior to uterine infections in this respect.

5. Neither the level of circulating anti-streptolysin at the commencement of infection nor the rate and height of response could be shown to have any bearing on the severity of the disease, except that a poor anti-streptolysin response was found in certain cases of relapses and toxic complications of throat infections. This appeared, however, to be merely indicative of a general poor antitoxic response and not to have any meaning by itself, except that in certain arthritic cases where the question of its importance was more open. No correlation whatsoever was noted between anti-streptolysin response and relapses and septic complications in erysipelas.

6. In general the anti-streptolysin response in infection appeared to depend more on the individual than on the site or severity of infection.

This review aims to assess the prevalence of malaria in pregnancy during antenatal visits and delivery, species-specific burden together with regional variation in the burden of disease. It also aims to estimate the proportions of adverse pregnancy outcomes in malaria-positive women. Based on the PRISMA guidelines, a thorough and systematic search was conducted in July 2023 across two electronic databases (including PubMed and CENTRAL). Forest plots were constructed for each outcome of interest highlighting the effect measure, confidence interval, sample size, and its associated weightage. All the statistical meta-analysis were conducted using R-Studio version 2022.07. Sensitivity analyses, publication bias assessment, and meta-regression analyses were also performed to ensure robustness of the review. According to the pooled estimates of 253 studies, the overall prevalence of malaria was 18.95% (95% CI: 16.95–21.11), during antenatal visits was 20.09% (95% CI: 17.43–23.06), and at delivery was 17.32% (95% CI: 14.47–20.61). The highest proportion of malarial infection was observed in Africa approximating 21.50% (95% CI: 18.52–24.81) during ANC and 20.41% (95% CI: 17.04–24.24) at the time of delivery. Our analysis also revealed that the odds of having anaemia were 2.40 times (95% CI: 1.87–3.06), having low birthweight were 1.99 times (95% CI: 1.60–2.48), having preterm birth were 1.65 times (95% CI: 1.29–2.10), and having stillbirths were 1.40 times (95% CI: 1.15–1.71) in pregnant women with malaria.

The aims of this study were to describe the trend of acquired syphilis in the city of Florence and its province over a 7-year period, to investigate sexual behaviours in the syphilis-infected population and to analyse syphilis/HIV co-infection. A total of 259 patients were classified according to age, sex and HIV infection. We estimated that from 2004 to 2008 cases increased by 248%. Most patients with concurrent HIV infection were male (31–45 years), but 40- to 60-year-old men who had sex with men predominated in both male and HIV-positive patients. Oral sex was identified as the most significant route of transmission, although most patients did not consider it so. Late-presenters with HIV accounted for 33% of HIV-positive patients: they were unaware of their HIV status and showed syphilis lesions only. In these cases, syphilis heralded the presence of HIV infection and allowed earlier diagnosis.

Since the 1990s, New Zealand (NZ) has seen an increasing incidence of paediatric skin infections leading to hospitalization. We sought to describe the epidemiology of these infections over time. Hospital discharge data were analysed for all children admitted to any NZ public hospital from 2004 to 2014. We found the age-standardized incidence of hospitalizations due to skin infections increased during this period from 522/100 000 in 2004 to a peak of 644/100 000 in 2011, after which it declined to 524/100 000 in 2014. This decline in incidence was driven primarily by the decline in hospitalization rates in high-risk groups including children living in the most deprived areas as well as Māori and Pacific children. Recent targeted policies focused on improving healthcare access through school-based and primary care-based interventions in these high-risk groups could potentially explain the decline in hospitalization rates. However, even with the closing of the inequality gap, significant socioeconomic and ethnic health disparities persist.

While searching for Escherichia coli O157 in the aquatic environment of Calcutta using an immunodetection procedure, we fortuitously detected five strains of Citrobacter braakii, which cross-reacted with the commercially available O157 polyvalent antiserum. The five C. braakii isolates gave positive results when a sensitive dot-ELISA was performed with E. coli O157 monoclonal antibody. Further, the O157 monoclonal antibody recognized the bands of proteinase K treated whole cells of lipopolysaccharide of all the C. braakii isolates. Apart from weak reactions with two or three of the DNA probes, all the C. braakii strains did not hybridize with the other probes spanning the minimum region required for O157 O-antigen biosynthesis. These strains did not possess any of the virulence genes that are commonly found in the Shiga toxin-producing E. coli (STEC) specially the serotype O157[ratio ]H7. Therefore, it appears that the serological cross-reaction between C. braakii and E. coli O157 antiserum is based on structural mimicry between the O-polysaccharide of C. braakii and E. coli O157.

The prevalence of many diseases in pigs displays seasonal distributions. Despite growing concerns about the impacts of climate change, we do not yet have a good understanding of the role that weather factors play in explaining such seasonal patterns. In this study, national and county-level aggregated abattoir inspection data were assessed for England and Wales during 2010–2015. Seasonally-adjusted relationships were characterised between weekly ambient maximum temperature and the prevalence of both respiratory conditions and tail biting detected at slaughter. The prevalence of respiratory conditions showed cyclical annual patterns with peaks in the summer months and troughs in the winter months each year. However, there were no obvious associations with either high or low temperatures. The prevalence of tail biting generally increased as temperatures decreased, but associations were not supported by statistical evidence: across all counties there was a relative risk of 1.028 (95% CI 0.776–1.363) for every 1 °C fall in temperature. Whilst the seasonal patterns observed in this study are similar to those reported in previous studies, the lack of statistical evidence for an explicit association with ambient temperature may possibly be explained by the lack of information on date of disease onset. There is also the possibility that other time-varying factors not investigated here may be driving some of the seasonal patterns.

The mumps vaccine is not included in the national immunisation programme (NIP) of approximately 80 countries including Japan. To investigate the vaccine's cost-effectiveness, we developed a dynamic transmission model for routine one- and two-dose mumps vaccination programs in Japan. We calculated the incremental cost-effectiveness ratio compared with a current programme over a projected 50-year period. We created a Japanese population model and performed dynamic simulation to estimate the number of patients enrolled in the current programme, the routine one-dose programme, and the routine two-dose programme over the next 50 years using the Berkeley Madonna program. We estimated the medical and social costs of natural mumps infections and vaccinations to analyse cost-effectiveness. Finally, we performed a sensitivity analysis with parameters including vaccine cost, vaccine efficacy, medical costs per case, social costs per case, incidence of adverse events and discount rate. Base case analysis showed that both the one-dose and two-dose programmes predominated and that quality-adjusted life years (QALYs) were saved, compared with the current programme. The medical costs, total cost and QALYs saved during the study period in the two-dose programme compared with the current programme were 217 billion JPY, 860 billion JPY and 184 779, respectively. The two-dose programme surpassed the one-dose programme throughout the study period. In all the scenarios of the sensitivity analysis, two-dose vaccination was better than the one-dose programme. This simulation confirmed that the routine two-dose vaccination programme was more cost-effective and QALY-saving than either the one-dose programme or the current programme. Because of the variability of the results between the various models, further simulations with different models should be conducted.

Shiga toxin-producing Escherichia coli (STEC) is a known food pathogen, which main reservoir is the intestine of ruminants. The abundance of different STEC lineages in nature reflect a heterogeneity that is characterised by the differential expression of certain genotypic characteristics, which in turn are influenced by the environmental conditions to which the microorganism is exposed. Bacterial homeostasis and stress response are under the control of the alarmone guanosine tetraphosphate (ppGpp), which intrinsic levels varies across the E. coli species. In the present study, 50 STEC isolates from healthy sheep were evaluated regarding their ppGpp content, cytotoxicity and other relevant genetic and phenotypic characteristics. We found that the level of ppGpp and cytotoxicity varied considerably among the examined strains. Isolates that harboured the stx2 gene were the least cytotoxic and presented the highest levels of ppGpp. All stx2 isolates belonged to phylogroup A, while strains that carried stx1 or both stx1 and stx2 genes pertained to phylogroup B1. All but two stx2 isolates belonged to the stx2b subtype. Strains that belonged to phylogroup B1 displayed on average low levels of ppGpp and high cytotoxicity. Overall, there was a negative correlation between cytotoxicity and ppGpp.

Hand hygiene (HH) performance on entering intensive care units (ICUs) is commonly accepted but often inadequately performed. We developed a simple, inexpensive module that connects touchless dispensers of alcohol sanitiser (TDAS) to the automatic doors of a paediatric ICU, and assessed the impact of this intervention on HH compliance of hospital staff and visitors. A prospective observational study was conducted over a 3-week period prior to the intervention, followed by a 4-week period post intervention. HH performance was monitored by a research assistant whose office location enabled direct and video-assisted observation of the ICU entrance. A total of 609 entries to the ICU was recorded. Overall HH performance was 46.9% (92/196) before and 98.5% (406/413) after the intervention. Our findings suggest that HH performance on entering an ICU can be improved via a mechanism that makes operation of an automatic door dependent on use of a TDAS system, and thus contribute to infection control.

Since the discovery of Legionnaires’ disease (LD), limited progress has been made in understanding the epidemiology of sporadic cases of LD. Outbreaks have confirmed that air conditioning and potable water systems can be sources of community-acquired LD. However, studying the association between water quality and LD incidence has been challenging due to the heterogeneity of water systems across large geographic areas. Furthermore, although seasonal trends in incidence have been linked to increased rainfall and temperatures, the large geographic units have posed similar difficulties. To address this issue, a retrospective ecological study was conducted in Washington, DC, from 2001 to 2019. The study identified aseasonal pattern of LD incidence, with the majority of cases occurring between June and December, peaking in August, October, and November. Increased temperature was found to be associated with LD incidence. In surface water, higher concentrations of manganese, iron, and strontium were positively associated with LD, while aluminum and orthophosphate showed a negative association. Intreatment plant water, higher concentrations of total organic carbon, aluminum, barium, and chlorine were positively associated with LD, while strontium, zinc, and orthophosphate showed a negative association. The results for orthophosphates and turbidity were inconclusive, indicating the need for further research.

The incidence of invasive infections due to Neisseria meningitidis in Israel is about 1/100 000 population annually. Three cases of meningococcal meningitis were reported in employees at a single plant; the first case appeared in March 2013 and the second and third cases appeared in December, almost 9 months later. N. meningitidis serogroup B was isolated from cerebrospinal fluid samples. Multilocus sequence typing assigned the three meningococcal isolates to ST10418, a new sequence type and a member of the ST32 clonal complex. The clonality was confirmed by performance of pulsed-field gel electrophoresis. Post-exposure antibiotic prophylaxis was administered to close contacts of the first case. Upon the diagnosis of the additional two cases, post-exposure prophylaxis was administered to all the plant employees. This report demonstrates the importance of combining public health measures and advanced laboratory studies to confirm clonality and to prevent further disease spread in a closed setting.

During the 5-year (1981–5) surveillance period, 2322 salmonella isolations were recorded from animals and other non-human sources in Peninsular Malaysia. This was an increase of 356% over the preceding 5-year period. The 83 serotypes isolated were recovered from 41 sources. Of these 34 were new serotypes bringing the total number of serotypes isolated from non-human sources to date up 97. Food animals and edible animal products accounted for 92·2% of the total isolations, with cattle and beef accounting for 70% of the total. Salmonella dublin was the most frequently isolated serotype, whereas S. typhimurium had the widest zoological distribution. More than 80% of the non-human salmonella serotypes have also been reported in man in this country.