Social encounter networks: characterizing Great Britain

A major goal of infectious disease epidemiology is to understand and predict the spread of infections within human populations, with the intention of better informing decisions regarding control and intervention. However, the development of fully mechanistic models of transmission requires a quantitative understanding of social interactions and collective properties of social networks. We performed a cross-sectional study of the social contacts on given days for more than 5000 respondents in England, Scotland and Wales, through postal and online survey methods. The survey was designed to elicit detailed and previously unreported measures of the immediate social network of participants relevant to infection spread. Here, we describe individual-level contact patterns, focusing on the range of heterogeneity observed and discuss the correlations between contact patterns and other socio-demographic factors. We find that the distribution of the number of contacts approximates a power-law distribution, but postulate that total contact time (which has a shorter-tailed distribution) is more epidemiologically relevant. We observe that children, public-sector and healthcare workers have the highest number of total contact hours and are therefore most likely to catch and transmit infectious disease. Our study also quantifies the transitive connections made between an individual''s contacts (or clustering); this is a key structural characteristic of social networks with important implications for disease transmission and control efficacy. Respondents'' networks exhibit high levels of clustering, which varies across social settings and increases with duration, frequency of contact and distance from home. Finally, we discuss the implications of these findings for the transmission and control of pathogens spread through close contact.     

Modelling seasonal variations in the age and incidence of Kawasaki disease to explore possible infectious aetiologies

The average age of infection is expected to vary during seasonal epidemics in a way that is predictable from the epidemiological features, such as the duration of infectiousness and the nature of population mixing. However, it is not known whether such changes can be detected and verified using routinely collected data. We examined the correlation between the weekly number and average age of cases using data on pre-vaccination measles and rotavirus. We show that age-incidence patterns can be observed and predicted for these childhood infections. Incorporating additional information about important features of the transmission dynamics improves the correspondence between model predictions and empirical data. We then explored whether knowledge of the age-incidence pattern can shed light on the epidemiological features of diseases of unknown aetiology, such as Kawasaki disease (KD). Our results indicate KD is unlikely to be triggered by a single acute immunizing infection, but is consistent with an infection of longer duration, a non-immunizing infection or co-infection with an acute agent and one with longer duration. Age-incidence patterns can lend insight into important epidemiological features of infections, providing information on transmission-relevant population mixing for known infections and clues about the aetiology of complex paediatric diseases.     

Infectious disease transmission and contact networks in wildlife and livestock

The use of social and contact networks to answer basic and applied questions about infectious disease transmission in wildlife and livestock is receiving increased attention. Through social network analysis, we understand that wild animal and livestock populations, including farmed fish and poultry, often have a heterogeneous contact structure owing to social structure or trade networks. Network modelling is a flexible tool used to capture the heterogeneous contacts of a population in order to test hypotheses about the mechanisms of disease transmission, simulate and predict disease spread, and test disease control strategies. This review highlights how to use animal contact data, including social networks, for network modelling, and emphasizes that researchers should have a pathogen of interest in mind before collecting or using contact data. This paper describes the rising popularity of network approaches for understanding transmission dynamics in wild animal and livestock populations; discusses the common mismatch between contact networks as measured in animal behaviour and relevant parasites to match those networks; and highlights knowledge gaps in how to collect and analyse contact data. Opportunities for the future include increased attention to experiments, pathogen genetic markers and novel computational tools.     

Interpretation of mixed sediment profiles by means of a sediment-mixing model and radioactive fallout

Chernobyl fallout provided a pulsed release to the environment and an opportunity to study sediment mixing processes in lakes. The paper presents the application of a mathematical modelling technique using a radionuclide as tracer. The model simulates the radionuclide profiles in sediments and computes the concentrations by solving numerically a one-dimensional mass-balance equation. The mixing-advection-decay model has been designed to include time-variable input capabilities and a depth-dependent mixing coefficient.     

Vertical mixing within the epilimnion modulates UVR-induced photoinhibition in tropical freshwater phytoplankton from southern China

1. The importance of vertical mixing in modulating the impact of UVR on phytoplankton photosynthesis was assessed in a tropical, shallow lake in southern China from late winter to mid‐spring of 2005. 2. Daily cycles of fluorescence measurements (i.e. photosynthetic quantum yield, Y) were performed on both ‘static’ and in situ samples. Static samples were of surface water incubated at the surface of the lake under three radiation treatments – PAB (PAR + UVR, 280–700 nm), PA (PAR + UV‐A, 320–700 nm) and P (PAR, 400–700 nm). In situ samples were collected every hour at three different depths – 0, 0.5 and 1 m. 3. The general daily pattern was of a significant decrease in Y from early morning towards noon, with partial recovery in the afternoon. Samples incubated under static conditions always had lower Y than those under in situ conditions at the same time of the day. 4. Under stratified conditions, no overall impact of UVR impact could be detected in situ when compared with the static samples. Further rapid vertical mixing not only counteracted the impact of UVR but also stimulated photosynthetic efficiency. 5. Based on these measurements of fluorescence, the mixing speed of cells moving within the epilimnion was estimated to range between 0.53 and 6.5 cm min⁻¹. 6. These data show that mixing is very important in modulating the photosynthetic response of phytoplankton exposed to natural radiation and, hence, strongly conditions the overall impact of UVR on aquatic ecosystems.     

Inferring patterns of influenza transmission in swine from multiple streams of surveillance data

Swine populations are known to be an important source of new human strains of influenza A, including those responsible for global pandemics. Yet our knowledge of the epidemiology of influenza in swine is dismayingly poor, as highlighted by the emergence of the 2009 pandemic strain and the paucity of data describing its origins. Here, we analyse a unique dataset arising from surveillance of swine influenza at a Hong Kong abattoir from 1998 to 2010. We introduce a state–space model that estimates disease exposure histories by joint inference from multiple modes of surveillance, integrating both virological and serological data. We find that an observed decrease in virus isolation rates is not due to a reduction in the regional prevalence of influenza. Instead, a more likely explanation is increased infection of swine in production farms, creating greater immunity to disease early in life. Consistent with this, we find that the weekly risk of exposure on farms equals or exceeds the exposure risk during transport to slaughter. We discuss potential causes for these patterns, including competition between influenza strains and shifts in the Chinese pork industry, and suggest opportunities to improve knowledge and reduce prevalence of influenza in the region.     

Social network- and community-level influences on contraceptive use: evidence from rural Poland

The diffusion of ‘modern’ contraceptives—as a proxy for the spread of low-fertility norms—has long interested researchers wishing to understand global fertility decline. A fundamental question is how local cultural norms and other people''s behaviour influence the probability of contraceptive use, independent of women''s socioeconomic and life-history characteristics. However, few studies have combined data at individual, social network and community levels to simultaneously capture multiple levels of influence. Fewer still have tested if the same predictors matter for different contraceptive types. Here, we use new data from 22 high-fertility communities in Poland to compare predictors of the use of (i) any contraceptives—a proxy for the decision to control fertility—with those of (ii) ‘artificial’ contraceptives—a subset of more culturally taboo methods. We find that the contraceptive behaviour of friends and family is more influential than are women''s own characteristics and that community level characteristics additionally influence contraceptive use. Highly educated neighbours accelerate women''s contraceptive use overall, but not their artificial method use. Highly religious neighbours slow women''s artificial method use, but not their contraceptive use overall. Our results highlight different dimensions of sociocultural influence on contraceptive diffusion and suggest that these may be more influential than are individual characteristics. A comparative multilevel framework is needed to understand these dynamics.     

Social contacts and the locations in which they occur as risk factors for influenza infection

The interaction of human social behaviour and transmission is an intriguing aspect of the life cycle of respiratory viral infections. Although age-specific mixing patterns are often assumed to be the key drivers of the age-specific heterogeneity in transmission, the association between social contacts and biologically confirmed infection has not previously been tested at the individual level. We administered a questionnaire to participants in a longitudinal cohort survey of influenza in which infection was defined by longitudinal paired serology. Using a variety of statistical approaches, we found overwhelming support for the inclusion of individual age in addition to contact variables when explaining odds of infection: the best model not including age explained only 15.7% of the deviance, whereas the best model with age explained 23.6%. However, within age groups, we did observe an association between contacts, locations and infection: median numbers of contacts (or locations) reported by those infected were higher than those from the uninfected group in every age group other than the youngest. Further, we found some support for the retention of location and contact variables in addition to age in our regression models, with excess odds of infection of approximately 10% per additional 10 contacts or one location. These results suggest that, although the relationship between age and incidence of respiratory infection at the level of the individual is not driven by self-reported social contacts, risk within an age group may be.     

An anthropometric and hematological comparison of sickle cell disease children from rural and urban areas

BACKGROUND:

Sickle cell disease (SCD) is a prevalent genetic disorder in India and the rural and urban areas experience distinctly different healthcare facilities. In view of this, a comparative study of SCD-SS pattern children of age 8–15 years from rural and urban areas of Wardha district of Central India was carried out using anthropometric and hematological parameters.

MATERIALS AND METHODS:

The data were collected using standard methods and the results showed a significant (P < 0.05) difference in the mean values for body weight, body mass index (BMI), hemoglobin, hematocrit, and white blood corpuscles (WBC). Statistical analysis of the data was done using SPSS 18.0 software. Individuals were screened by solubility test method. Sickle cell patterns (AS and SS) were determined by using electrophoresis technique.

RESULT:

The SCD-SS children from rural were significantly underweight than those from the urban area of Wardha district. BMI is a good indicator of nutritional status and BMI values of SCD children have less than desired.

CONCLUSION:

The study highlights an urgent need to conduct integrated investigations for SCD population of rural areas covering clinical, nutritional, and social aspects.     

Social transmission of nectar-robbing behaviour in bumble-bees

Social transmission of acquired foraging techniques is rarely considered outside of a vertebrate context. Here, however, we show that nectar robbing by bumble-bees (Bombus terrestris)-an invertebrate behaviour of considerable ecological significance-has the potential to spread through a population at the accelerated rates typical of social transmission. Nectar robbing occurs when individuals either bite through the base of a flower to 'steal' nectar (primary robbing) or use robbing holes that others have made (secondary robbing). We found that experience of foraging from robbed flowers significantly promoted the development of primary robbing in previously legitimate foragers, thus implying that the acquisition of nectar robbing by one individual will facilitate its adoption in others. Our findings suggest that the positive feedback effects of social transmission may potentially play an ecologically important role in the relationship between plants and pollinators.     

Different patterns of intestinal helminth infection among young workers in urban and rural areas of Alexandria Governorate, Egypt.

The process of urbanisation taking place in most developing countries is creating favourable conditions for an increase in prevalence of infections, especially with intestinal parasites, in the marginal areas of the towns. The present study was implemented in 1996 to assess the varying prevalence and intensity of infection among young workers in urban and rural areas of the same Governorate (Alexandria, Egypt). The sample comprised 408 male subjects, 8 to 19 years of age, in various occupations: 308 from urban areas, 67 from an industrialised village close to the desert, and 33 from a rural village. A quantitative diagnosis of intestinal helminth infections was made using the Kato-Katz technique, with a double reading of each slide. The results showed a higher prevalence (> 50%) and intensity of infection (indirectly measured as number of eggs per gram of faeces) than in previous studies. Furthermore, a higher prevalence and intensity of infection with Ascaris lumbricoides and Trichuris trichiura was detected in urban districts, as compared to rural areas. This difference was statistically significant. High crowding index, latrine shared with other families and no piped water inside the household, were more common in urban areas as compared with rural settlements and also associated with a higher intensity of infection by soil-transmitted helminths. The trend toward urbanisation seems to have caused deterioration of living conditions and sanitation standards in some areas of Alexandria city, with the most vulnerable people experiencing an increase in intestinal parasitic infections.     

Breeding of Tawny Owls Strix aluco in rural and urban habitats in southern Finland

Capsule The annual average breeding frequency, clutch size, offspring production and chick survival of Tawny Owls did not differ between rural and urban nesting territories.

Aims To determine whether the general intensity of human habitation in the territory affects breeding.

Methods Clutch size, offspring production, breeding frequency and prey abundance were determined from 210 rural and 60 urban nesting territories monitored between 1994 and 2006.

Results Fluctuations in the annual average clutch size did not differ between habitats. Clutch size and offspring production paralleled each other in rural habitats but not in urban ones. Annual average clutch size followed the regional spring abundance of small mammals in rural Tawny Owls but not in urban ones. The breeding frequency was higher after mild winters in rural environments but not in urban ones.

Conclusion Over an extended time period, rural and urban habitats were largely of equal quality. In urban environments, however, owls seem to be less affected by the pronounced regional abundance fluctuations of small mammals and weather conditions of the preceding winter that largely govern the breeding of owls elsewhere.     

BCG immunization age in urban and rural areas of Akita Prefecture, Japan

BCG immunization, utilizing whole-body coordination, is a highly cost-effective means of health intervention for preventing miliary tuberculosis (TB) and TB meningitis. In this study, we investigated the appropriate age by which a child should have completed his or her BCG immunization and discuss the current BCG immunization rate in Akita Prefecture, Japan. BCG immunization rates in urban and rural areas were 90.1% and 80.7%, respectively. Our immunization data were lower than the World Health Organization's (WHO) recommended rate. Immunization coverage rates in urban settings were higher than those in rural areas among infants four months to fifteen months of age, except for those six months old. We recommend: (1) completing BCG immunization by the age of twelve months, (2) preparing and educating parents for BCG immunization by means of a health policy, and (3) changing BCG immunization methods from group to individual inoculation. Immunization coverage rates may be increased or maintained to prevent miliary TB and TB meningitis.     

Social foraging: individual learning and cultural transmission of innovations

We present two stochastic models of individual and social learningthat count the number of individuals exhibiting a learned, resource-producingtrait in a group of social foragers. The novelty of our modelingresults from incorporating the empirically based assumptionthat rates of both individual and social learning should dependon the frequency of the learned trait within the group. Whenresources occur as clumps shared by group members, a naive individual'sacquisition of the skill required for clump discovery/productionshould involve opposing processes of frequency dependence. Theopportunity to learn via cultural transmission should increasewith the trait's frequency, but the opportunity for learningindividually should decrease as the trait's frequency increases.The results of the model suggest that the evolution of the capacityfor cultural transmission may be promoted in environments wherescrounging at resource clumps inhibits rates of individual learning.     

Comparison of fecal microflora of elderly persons in rural and urban areas of Japan

The Fecal microflora of 15 healthy elderly persons with a median age of 84 years in a rural area whose inhabitants tend to be long-lived (Yuzurihara-area, Uenohara, Yamanashi Prefecture) was compared with the microflora of individuals with a median age of 68 years in an urban area (Tokyo). The diet of the elderly persons in the Yuzurihara area is characterized by a high intake of dietary fiber. Total numbers of anaerobic bacteria were significantly smaller in the elderly persons in the Yuzurihara area than those in the Tokyo area. A significantly large number of bifidobacteria, but not of lecithinase-negative clostridia, was observed in the elderly persons in the Yuzurihara area. Large numbers and high incidences of bacilli and lecithinase-positive clostridia (mainly Clostridium perfringens) were found in the elderly persons in the Tokyo area. Twenty-five genera and over 81 species were isolated from the elderly persons in the Yuzurihara area, and 25 genera and over 92 species were isolated from the elderly persons in the Tokyo area. Furthermore, significantly larger numbers of Bifidobacterium adolescentis and Fusobacterium mortiferum strains were found in the Yuzurihara group, but significant reductions in the Bacteroides buccae-oris group, B. thetaiotaomicron, Bacteroides spp., C. coccoides, C. paraputrificum, and Clostridium spp. were observed in the same group. A significantly higher isolation rate of Bacillus subtilis was observed in the elderly persons in the Tokyo area. The difference in the fecal microflora between elderly persons in Yuzurihara and those in the Tokyo area might be due to a difference in the intake of dietary fiber.     

Use of mobile screening unit for diabetic retinopathy in rural and urban areas.

OBJECTIVES--To compare the effectiveness of a mobile screening unit with a non-mydriatic polaroid camera in detecting diabetic retinopathy in rural and urban areas. To estimate the cost of the service. DESIGN--Prospective data collection over two years of screening for diabetic retinopathy throughout Tayside. SETTING--Tayside region, population 390,000, area 7770 km2. SUBJECTS--961 patients in rural areas and 1225 in urban areas who presented for screening. MAIN OUTCOME MEASURES--Presence of diabetic retinopathy, need for laser photocoagulation, age, duration of diabetes, and diabetic treatment. RESULTS--Compared with diabetic patients in urban areas, those in rural areas were less likely to attend a hospital based diabetic clinic (46% (442) v 86% (1054), p < 0.001); less likely to be receiving insulin (260 (27%) v 416 (34%), p < 0.001 and also after correction for differences in age distribution); more likely to have advanced (maculopathy or proliferative retinopathy) diabetic retinopathy (13% (122) v 7% (89), p < 0.001); and more likely to require urgent laser photocoagulation for previously unrecognised retinopathy (1.4% (13) v 0.5% (6), p < 0.02). The screening programme cost 10 pounds per patient screened and 1000 pounds per patient requiring laser treatment. CONCLUSION--The mobile diabetic eye screening programme detected a greater prevalence of advanced retinopathy in diabetic patients living in rural areas. Patients in rural areas were also more likely to need urgent laser photocoagulation. Present screening procedures seem to be less effective in rural areas and rural patients may benefit more from mobile screening units than urban patients.