Space-time analysis of testicular cancer clusters using residential histories: a case-control study in Denmark

Though the etiology is largely unknown, testicular cancer incidence has seen recent significant increases in northern Europe and throughout many Western regions. The most common cancer in males under age 40, age period cohort models have posited exposures in the in utero environment or in early childhood as possible causes of increased risk of testicular cancer. Some of these factors may be tied to geography through being associated with behavioral, cultural, sociodemographic or built environment characteristics. If so, this could result in detectable geographic clusters of cases that could lead to hypotheses regarding environmental targets for intervention. Given a latency period between exposure to an environmental carcinogen and testicular cancer diagnosis, mobility histories are beneficial for spatial cluster analyses. Nearest-neighbor based Q-statistics allow for the incorporation of changes in residency in spatial disease cluster detection. Using these methods, a space-time cluster analysis was conducted on a population-wide case-control population selected from the Danish Cancer Registry with mobility histories since 1971 extracted from the Danish Civil Registration System. Cases (N=3297) were diagnosed between 1991 and 2003, and two sets of controls (N=3297 for each set) matched on sex and date of birth were included in the study. We also examined spatial patterns in maternal residential history for those cases and controls born in 1971 or later (N= 589 case-control pairs). Several small clusters were detected when aligning individuals by year prior to diagnosis, age at diagnosis and calendar year of diagnosis. However, the largest of these clusters contained only 2 statistically significant individuals at their center, and were not replicated in SaTScan spatial-only analyses which are less susceptible to multiple testing bias. We found little evidence of local clusters in residential histories of testicular cancer cases in this Danish population.

Spatiotemporal trends of cases of pandemic influenza A(H1N1)pdm09 in Argentina, 2009-2012

The aim of this paper was to analyze the spatiotemporal variations of cases of influenza A(H1N1)pdm09 in Argentina. A space-time permutation scan statistic was performed to test the non-randomness in the interaction between space and time in reported influenza A(H1N1)pdm09 cases. In 2009, two clusters were recorded in the east of Buenos Aires Province (May and June) and in the central and northern part of Argentina (July and August). Between 2011 and 2012, clusters near areas bordering other countries were registered. Within the clusters, in 2009, the high notification rates were first observed in the school-age population and then extended to the older population (15-59 years). From 2011 onwards, higher rates of reported cases of influenza A(H1N1)pdm09 occurred in children under five years in center of the country. Two stages of transmission of influenza A(H1N1)pdm09 can be characterized. The first stage had high rates of notification and a possible interaction with individuals from other countries in the major cities of Argentina (pattern of hierarchy), and the second stage had an increased interaction in some border areas without a clear pattern of hierarchy. These results suggest the need for greater coordination in the Southern Cone countries, in order to implement joint prevention and vaccination policies.

Epidemiological Characteristics and Spatial-Temporal Clusters of Hand, Foot, and Mouth Disease in Zhejiang Province, China, 2008-2012

Hand, foot and mouth disease (HFMD) is one of the major public health concerns in China. Being the province with high incidence rates of HFMD, the epidemiological features and the spatial-temporal patterns of Zhejiang Province were still unknown. The objective of this study was to investigate the epidemiological characteristics and the high-incidence clusters, as well as explore some potential risk factors. The surveillance data of HFMD during 2008-2012 were collected from the communicable disease surveillance network system of Zhejiang Provincial Center for Disease Control and Prevention. The distributions of age, gender, occupation, season, region, pathogen's serotype and disease severity were analyzed to describe the epidemiological features of HFMD in Zhejiang Province. Seroprevalence survey for human enterovirus 71 (EV71) in 549 healthy children of Zhejiang Province was also performed, as well as 27 seroprevalence publications between 1997 and 2015 were summarized. The spatial-temporal methods were performed to explore the clusters at county level. Furthermore, pathogens' serotypes such as EV71 and coxsackievirus A16 (Cox A16) and meteorological factors were analyzed to explore the potential factors associated with the clusters. A total of 454,339 HFMD cases were reported in Zhejiang Province during 2008-2012, including 1688 (0.37%) severe cases. The annual average incidence rate was 172.98 per 100,000 (ranged from 72.61 to 270.04). The male-to-female ratio for mild cases was around 1.64:1, and up to 1.87:1 for severe cases. Of the total cases, children aged under three years old and under five years old accounted for almost 60% and 90%, respectively. Among all enteroviruses, the predominant serotype was EV71 (49.70%), followed by Cox A16 (26.05%) and other enteroviruses (24.24%) for mild cases. In severe cases, EV71 (82.85%) was the major causative agent. EV71 seroprevalence survey in healthy children confirmed that occult infection was common in children. Furthermore, literature summary for 26 seroprevalence studies during 1997-2015 confirmed that 0-5 years group showed lowest level of EV71 seroprevalence (29.1% on average) compared to the elder children (6-10 years group: 54.6%; 11-20 years group: 61.8%). Global positive spatial autocorrelation patterns (Moran's Is>0.25, P<0.05) were discovered not only for mild cases but also for severe cases, and local positive spatial autocorrelation patterns were revealed for counties from the eastern coastal and southern regions. The retrospective space-time cluster analysis also confirmed these patterns. Risk factors analyses implied that more EV71 and less sunshine were associated with the clusters of HFMD in Zhejiang Province. Our study confirmed that Zhejiang Province was one of the highly epidemic provinces in China and that the epidemiological characteristics of HFMD were similar to other provinces. Occult infection in elder children and adults was one of the important reasons why most HFMD cases were children aged under-five. Combining the results of spatial autocorrelation analysis and the space-time cluster analysis, the major spatial-temporal clusters were from the eastern coastal and southern regions. The distribution of pathogens' serotypes and the level of sunshine could be risk factors for, and serve as an early warning of, the outbreak of HFMD in Zhejiang Province.

Geographical spread of influenza incidence in Spain during the 2009 A(H1N1) pandemic wave and the two succeeding influenza seasons

The aim of this study was to monitor the spatio-temporal spread of influenza incidence in Spain during the 2009 pandemic and the following two influenza seasons 2010-2011 and 2011-2012 using a Bayesian Poisson mixed regression model; and implement this model of geographical analysis in the Spanish Influenza Surveillance System to obtain maps of influenza incidence for every week. In the pandemic wave the maps showed influenza activity spreading from west to east. The 2010-2011 influenza epidemic wave plotted a north-west/south-east pattern of spread. During the 2011-2012 season the spread of influenza was geographically heterogeneous. The most important source of variability in the model is the temporal term. The model of spatio-temporal spread of influenza incidence is a supplementary tool of influenza surveillance in Spain.

Spatio-temporal correlation networks of dengue in the state of Bahia

BACKGROUND

Dengue is a public health problem that presents complexity in its dissemination. The physical means of spreading and the dynamics of the spread between municipalities need to be analyzed to guide effective public policies to combat this problem.

METHODS

This study uses timing varying graph methods (TVG) to construct a correlation network between occurrences of reported cases of dengue between cities in the state of Bahia-Brazil. The topological network indices of all cities were correlated with dengue incidence using Spearman correlation. A randomization test was used to estimate the significance value of the correlation.

RESULTS

The correlation network presented a complex behavior with a heavy-tail distribution of the network edges weight. The randomization test exhibit a significant correlation (P < 0.0001) between the degree of each municipality in the network and the incidence of dengue in each municipality.

CONCLUSIONS

The hypothesis of the existence of a correlation between the occurrences of reported cases of dengue between different municipalities in the state of Bahia was validated. The significant correlation between the node degree and incidence, indicates that municipalities with high incidence are also responsible for the spread of the disease in the state. The method proposed suggests a new tool in epidemiological control strategy.

Relative risk estimates from spatial and space-time scan statistics: are they biased?

The purely spatial and space-time scan statistics have been successfully used by many scientists to detect and evaluate geographical disease clusters. Although the scan statistic has high power in correctly identifying a cluster, no study has considered the estimates of the cluster relative risk in the detected cluster. In this paper, we evaluate whether there is any bias on these estimated relative risks. Intuitively, one may expect that the estimated relative risks has upward bias, because the scan statistic cherry picks high rate areas to include in the cluster. We show that this intuition is correct for clusters with low statistical power, but with medium to high power, the bias becomes negligible. The same behavior is not observed for the prospective space-time scan statistic, where there is an increasing conservative downward bias of the relative risk as the power to detect the cluster increases.

Retrospective space-time cluster analysis of whooping cough, re-emergence in Barcelona, Spain, 2000-2011

A retrospective, space-time study of whooping cough cases reported to the Public Health Agency of Barcelona, Spain between the years 2000 and 2011 is presented. It is based on 633 individual whooping cough cases and the 2006 population census from the Spanish National Statistics Institute, stratified by age and sex at the census tract level. Cluster identification was attempted using space-time scan statistic assuming a Poisson distribution and restricting temporal extent to 7 days and spatial distance to 500 m. Statistical calculations were performed with Stata 11 and SatScan and mapping was performed with ArcGis 10.0. Only clusters showing statistical significance (P <0.05) were mapped. The most likely cluster identified included five census tracts located in three neighbourhoods in central Barcelona during the week from 17 to 23 August 2011. This cluster included five cases compared with the expected level of 0.0021 (relative risk = 2436, P <0.001). In addition, 11 secondary significant space-time clusters were detected with secondary clusters occurring at different times and localizations. Spatial statistics is felt to be useful by complementing epidemiological surveillance systems through visualizing excess in the number of cases in space and time and thus increase the possibility of identifying outbreaks not reported by the surveillance system.

Dynamic spatiotemporal trends of dengue transmission in the Asia-Pacific region, 1955-2004

Background

Dengue fever (DF) is one of the most important emerging arboviral human diseases. Globally, DF incidence has increased by 30-fold over the last fifty years, and the geographic range of the virus and its vectors has expanded. The disease is now endemic in more than 120 countries in tropical and subtropical parts of the world. This study examines the spatiotemporal trends of DF transmission in the Asia-Pacific region over a 50-year period, and identified the disease’s cluster areas.

Methodology and Findings

The World Health Organization’s DengueNet provided the annual number of DF cases in 16 countries in the Asia-Pacific region for the period 1955 to 2004. This fifty-year dataset was divided into five ten-year periods as the basis for the investigation of DF transmission trends. Space-time cluster analyses were conducted using scan statistics to detect the disease clusters. This study shows an increasing trend in the spatiotemporal distribution of DF in the Asia-Pacific region over the study period. Thailand, Vietnam, Laos, Singapore and Malaysia are identified as the most likely clusters (relative risk = 13.02) of DF transmission in this region in the period studied (1995 to 2004). The study also indicates that, for the most part, DF transmission has expanded southwards in the region.

Conclusions

This information will lead to the improvement of DF prevention and control strategies in the Asia-Pacific region by prioritizing control efforts and directing them where they are most needed.

Spatial and temporal clustering of isolated cleft lip with or without cleft palate in Poland

BACKGROUND

Geographic variation in the prevalence of isolated cleft lip with or without cleft palate may be due to exogenous environmental factors or genetic variation. In this study, we aim to evaluate the prevalence of isolated cleft lip with or without cleft palate in Polish urban and rural environments in order to identify geographic areas with high prevalence (defect clusters).

METHODS

We use all cases of congenital malformations reported to the Polish Registry of Congenital Malformations in the years 1998-2008 from the total population of 2,362,502 births.

RESULTS

We detect a strong signal of increased prevalence of isolated cleft lip with or without cleft palate in a single region of Poland, the Dolnośląskie voivodeship. Furthermore, we demonstrate a statistically significant prevalence differences between the urban and rural areas within this region. Through our comprehensive spatiotemporal analysis, we precisely define the cluster of the highest risk that comprises the eastern part of this voivodeship.

Temporal variation in United States firearm injuries 1993-2008: results from a national data base

BACKGROUND

There are few studies that address temporal variation in firearm associated injuries. It was the purpose of this study to analyze the temporal variation in the types and patterns of injuries associated with firearm use from a national data base.

METHODS

The database used was the Inter-University Consortium for Political and Social Research Firearm Injury Surveillance Study 1993-2008. Emergency department visits associated with firearm use were analyzed for month and day of the week for various demographic variables. Statistical analyses were performed using SUDAAN 10™ software to give national estimates. Temporal variation by month or day was assessed using histograms, circular distributions, and cosinor analyses. Variation by month and day combined were analyzed using three dimensional contours.

RESULTS

There were an estimated 1,841,269 injuries. Circular analyses demonstrated a non-uniform distribution for all parameters for both month and day of injury (p less than 0.001). The overall peak was September 15 with several exceptions. Injuries from BB guns had a peak on May 22, a diagnosis of a foreign body on July 11, and patients aged 10 to 14 years on April 9.The peak day was always Saturday/Sunday when significant variation existed. There were many different patterns for month and day combined. Some were "a rapidly rising high mountain starting at sea level" (hunting), or others a "series of mountain ranges starting from a high plain or steppe" (hospital admissions).

CONCLUSIONS

This study provides altogether new information regarding temporal variation for injuries associated with firearms in the USA. These results can be used to assist medical resource allocation and prevention campaigns. Education campaigns can be emphasized before the peaks for which prevention is desired (eg. BB gun prevention campaigns should be concentrated in March, prior to the April/May peak).

A multilevel model for spatially correlated binary data in the presence of misclassification: an application in oral health research

Dental caries is a highly prevalent disease affecting the tooth's hard tissues by acid-forming bacteria. The past and present caries status of a tooth is characterized by a response called caries experience (CE). Several epidemiological studies have explored risk factors for CE. However, the detection of CE is prone to misclassification because some cases are neither clearly carious nor noncarious, and this needs to be incorporated into the epidemiological models for CE data. From a dentist's point of view, it is most appealing to analyze CE on the tooth's surface, implying that the multilevel structure of the data (surface-tooth-mouth) needs to be taken into account. In addition, CE data are spatially referenced, that is, an active lesion on one surface may impact the decay process of the neighboring surfaces, and that might also influence the process of scoring CE. In this paper, we investigate two hypotheses: that is, (i) CE outcomes recorded at surface level are spatially associated; and (ii) the dental examiners exhibit some spatial behavior while scoring CE at surface level, by using a spatially referenced multilevel autologistic model, corrected for misclassification. These hypotheses were tested on the well-known Signal Tandmobiel® study on dental caries, and simulation studies were conducted to assess the effect of misclassification and strength of spatial dependence on the autologistic model parameters. Our results indicate a substantial spatial dependency in the examiners' scoring behavior and also in the prevalence of CE at surface level.

Residential mobility and breast cancer in Marin County, California, USA

Marin County (California, USA) has among the highest incidences of breast cancer in the U.S. A previously conducted case-control study found eight significant risk factors in participants enrolled from 1997–1999. These included being premenopausal, never using birth control pills, lower highest lifetime body mass index, having four or more mammograms from 1990–1994, beginning drinking alcohol after age 21, drinking an average two or more alcoholic drinks per day, being in the highest quartile of pack-years of cigarette smoking, and being raised in an organized religion. Previously conducted surveys provided residential histories; while Ǫ statistic accounted for participants’ residential mobility, and assessed clustering of breast cancer cases relative to controls based on the known risk factors. These identified specific cases, places, and times of excess breast cancer risk. Analysis found significant global clustering of cases localized to specific residential histories and times. Much of the observed clustering occurred among participants who immigrated to Marin County. However, persistent case-clustering of greater than fifteen years duration was also detected. Significant case-clustering among long-term residents may indicate geographically localized risk factors not accounted for in the study design, as well as uncertainty and incompleteness in the acquired addresses. Other plausible explanations include environmental risk factors and cases tending to settle in specific areas. A biologically plausible exposure or risk factor has yet to be identified.

Space-time clustering characteristics of tuberculosis in China, 2005-2011

OBJECTIVES

China is one of the 22 tuberculosis (TB) high-burden countries in the world. As TB is a major public health problem in China, spatial analysis could be applied to detect geographic distribution of TB clusters for targeted intervention on TB epidemics.

METHODS

Spatial analysis was applied for detecting TB clusters on county-based TB notification data in the national notifiable infectious disease case reporting surveillance system from 2005 to 2011. Two indicators of TB epidemic were used including new sputum smear-positive (SS+) notification rate and total TB notification rate. Global Moran's I by ArcGIS was used to assess whether TB clustering and its trend were significant. SaTScan software that used the retrospective space-time analysis and Possion probability model was utilized to identify geographic areas and time period of potential clusters with notification rates on county-level from 2005 to 2011.

RESULTS

Two indicators of TB notification had presented significant spatial autocorrelation globally each year (p<0.01). Global Moran's I of total TB notification rate had positive trend as time went by (t=6.87, p<0.01). The most likely clusters of two indicators had similar spatial distribution and size in the south-central regions of China from 2006 to 2008, and the secondary clusters in two regions: northeastern China and western China. Besides, the secondary clusters of total TB notification rate had two more large clustering centers in Inner Mongolia, Gansu and Qinghai provinces and several smaller clusters in Shanxi, Henan, Hebei and Jiangsu provinces.

CONCLUSION

The total TB notification cases clustered significantly in some special areas each year and the clusters trended to aggregate with time. The most-likely and secondary clusters that overlapped among two TB indicators had higher TB burden and risks of TB transmission. These were the focused geographic areas where TB control efforts should be prioritized.

[Spatio-temporal pattern of larvae and eggs of gastrointestinal nematodes in cattle pastures in Veracruz, Mexico]

The spatial and temporal distribution of gastrointestinal nematodes of cattle has been little studied in Mexico. Previous studies have described periods of higher larval presence, vertical and horizontal migration in grasslands, and the frequency of adult nematodes; as well as the effect of pasture trichomes on the migration and survival of Haemonchus larvae. The aim of this study was to determine the time-space layout and spread of gastrointestinal nematode larvae on pasture, and to estimate the effect of ivermectin applied to cattle on the time-dependent abundance of their eggs in a ranch in Veracruz. To determine the spatio-temporal arrangement, monthly morning grass samples were obtained from 30 sampling points from July 2008 to June 2009. Third stage larvae (L3) from each point were counted, and aggregation patterns were estimated through variance/mean and negative binomial K indices. Additionally, the number of eggs per gram in cattle feces was determined, from samples with (CI) and without ivermectin (SI), using standard techniques. A total of 20 276 L(3) larvae were recovered in the pasture, of which an 80% corresponded to Haemonchus contortus. The highest nematode density with more than 5 000L(3)/kgDM was detected in October 2008, and the lowest in February and March 2009. The L3 showed an aggregated spatial pattern of varying intensity throughout the year. The number of eggs in the stool was not reduced with the ivermectin application to cattle, which suggested a failure of control. However, the highest parasite loads were observed from July to November 2008. We concluded that the application of ivermectin was not effective to control nematodes eggs, and that L3 populations fluctuated on pasture for ten months, providing an infection source to grazing animals afterwards.

[Vertebrate mortality in the Guanare-Guanarito road, Portuguesa state, Venezuela]

Roads directly or indirectly affect the structure, dynamics and function of ecosystems that they traverse. Most studies on the effect of roads on wildlife focus on the evaluation of mortality of vertebrates by vehicle collisions. Despite the extensive road network that exists in Venezuela, studies of wildlife mortality in them are scarce. In this paper, we analyzed the temporal and spatial pattern of vertebrate's collisions along the road Guanare-Guanarito, in Portuguesa state. We travelled 26 times between these towns (74 km) to localize dead vertebrates, at a speed of 50-60km/h. of those trips were conducted from March 13 to October 26, 2010, and 10 additional trips from December 7, 2009 to December 14, 2010; these ones, with the aim to include months and seasons that were insufficiently sampled during the first period. The elapsed time between trips varied from 14 to 37 days. The total distance traveled was 1 924 km. Dead animals found amounted 464 individuals, 66 of them were birds (25 identified species), 130 mammals (15 species) and 268 reptiles (18 species). The species with the highest number of individuals were the snake Leptodeira annulata (n=119), the oppossum Didelphis marsupialis (n=39) and the spectacled caiman Caiman crocodilus (n=33). Excluding domestic animals, the rate of road-killed vertebrates was 0.2282 indiv./km, a figure 28.3% higher than previous studies in the same road. Changes in the relative number of collisions for some species, respect to the numbers reported 20 years ago, were linked to the increase in traffic flow and changes in land use. Road segments with collision rates higher than expected by chance were identified. Collition by cars may be the principal cause of mortality for species like the tamandua (Tamandua tetradactyla) and the giant anteater (Myrmecophaga tridactyla), the last considered a vulnerable species. Some basic measures are proposed to reduce wildlife mortality on the road.

[Spatial variations in motorcycle registrations and the mortality of motorcycle users due to traffic injuries in Argentina]

Although pedestrians, cyclists and motorcyclists account for nearly half of those killed in traffic accidents in the world, little is known about the geographical distribution patterns of these vulnerable roadway users. Using spatial scan statistics techniques, the spatiotemporal variations in the mortality of motorcycle users in Argentina were analyzed for the period 2001-2010, as well as the spatial variations in mortality and motorcycle registration from 2007-2010. Two space-time clusters with a high risk of death for motorcycle riders were identified during the second half of the study period. Overall, there was a spatial relationship between motorcycle registrations and the mortality of the users of these vehicles in the northern-central region of Argentina. The results of this study indicate the need to reinforce primary prevention policies focused on motorcycle users in this region of the country, especially in areas with high population density.

Spatial variations in motorcycle registrations and the mortality of motorcycle users due to traffic injuries in Argentina

Although pedestrians, cyclists and motorcyclists account for nearly half of those killed in traffic accidents in the world, little is known about the geographical distribution patterns of these vulnerable roadway users. Using spatial scan statistics techniques, the spatiotemporal variations in the mortality of motorcycle users in Argentina were analyzed for the period 2001-2010, as well as the spatial variations in mortality and motorcycle registration from 2007-2010. Two space-time clusters with a high risk of death for motorcycle riders were identified during the second half of the study period. Overall, there was a spatial relationship between motorcycle registrations and the mortality of the users of these vehicles in the northern-central region of Argentina. The results of this study indicate the need to reinforce primary prevention policies focused on motorcycle users in this region of the country, especially in areas with high population density.

[Spatial-temporal analysis on the distribution of infected snail at the village level in Anhui province, 2006-2012]

OBJECTIVE

The characteristics of spatial-temporal distribution on infected snails were analyzed at the village level in Anhui province, 2006-2012.

METHODS

Data on the distribution of infected snails from 2006 to 2012 in Anhui province was collected. Spatial database was established by ArcGIS 9.3. Retrospective spatial-temporal cluster analysis was done by SaTScan 9.1.1 at the village level.

RESULTS

Eight areas with increased risk and distributed along the upstream to downstream of Yangtze and connecting branch rivers, were found having infected snails, from 2006 through 2012, including one area in 2006, five in 2006-2008, one in 2007-2009 and one in 2009-2011, respectively. Proportion on the number of areas with infected snails decreased from 6.2% in 2006 to 0.5% in 2012.

CONCLUSION

The spatial-temporal distribution of infected snail was not random but there appeared significant clusters. The trend seemed to be declining in Anhui province, between 2006 and 2012. Areas being detected as snails positive were important for the schistosomiasis control program to be carried out in Anhui province.

Spatial-temporal analysis of drink-driving patterns in Hong Kong

Normally, bars and restaurants are the preferred locations for drinking. Therefore, there is concern that the roads in bar and restaurant areas could have a higher probability of drink-drivers and alcohol-related road crashes. Many studies have been conducted to model the association between drinking locations and the prevalence of drink-driving, so that cost-effective enforcement strategies can be developed to combat drink-driving. In this study, a cluster analysis approach was applied to model the spatial-temporal variation of drink-driving distribution in Hong Kong. Six spatial-temporal clusters of drink-driving distribution emerged from the data: (i) bar and restaurant area, weekend-overnight; (ii) bar and restaurant area, other timespan; (iii) urban area, weekend-overnight; (iv) urban area, other timespans; (v) rural area, weekend-overnight; and (vi) rural area, other timespans. Next, separate zero-inflated regression models were established to identify the factors contributing to the prevalence of drink-driving for each of the six recognized clusters. The results indicated that drivers in rural areas tend to consume more alcohol than those in urban areas, regardless of the time period. In addition, both seasonal variation and vehicle class were found to determine the breath alcohol concentration (BrAC) levels among drivers.

Temporal distribution and weather correlates of Norway rat (Rattus norvegicus) infestations in the city of Madrid, Spain

Urban Norway rats are challenging pests, posing significant health and economic threats. Implementing ecologically based integrated rodent management (EBIRM) programmes relies primarily on the understanding of ecological relationships between rodents and their environments, with emphasis on the processes influencing rodent populations in the target ecosystem. We investigated the temporal distribution of urban Norway rat infestations in Madrid, Spain, and tested for the association of such infestations with temperature, relative humidity and precipitation by fitting a multivariate Poisson generalized linear model to a 3-year (2006-2008) daily time series of 4,689 Norway rat sightings. Norway rat infestations showed a marked seasonality, peaking in the summer. Most Norway rat sightings were reported on Mondays. Minimum temperature and relative humidity were positively associated with Norway rat infestation, whereas the association with precipitation was negative. The time series was adequately explained by the model. We identified previously unrecognized time periods that are more prone to Norway rat infestation than others and generated hypotheses about the association between weather, human outdoor activity, resource availability, rodent activity and population size. This provided local authorities engaged in preserving urban ecosystem health with basic research information to predict future rodent outbreaks and support the implementation of EBIRM programmes in urban areas.

How do childhood diagnoses of type 1 diabetes cluster in time?

Background

Previous studies have indicated that type 1 diabetes may have an infectious origin. The presence of temporal clustering—an irregular temporal distribution of cases—would provide additional evidence that occurrence may be linked with an agent that displays epidemicity. We tested for the presence and form of temporal clustering using population-based data from northeast England.

Materials and Methods

The study analysed data on children aged 0–14 years diagnosed with type 1 diabetes during the period 1990–2007 and resident in a defined geographical region of northeast England (Northumberland, Newcastle upon Tyne, and North Tyneside). Tests for temporal clustering by time of diagnosis were applied using a modified version of the Potthoff-Whittinghill method.

Results

The study analysed 468 cases of children diagnosed with type 1 diabetes. There was highly statistically significant evidence of temporal clustering over periods of a few months and over longer time intervals (p<0.001). The clustering within years did not show a consistent seasonal pattern.

Conclusions

The study adds to the growing body of literature that supports the involvement of infectious agents in the aetiology of type 1 diabetes in children. Specifically it suggests that the precipitating agent or agents involved might be an infection that occurs in “mini-epidemics”.

Numerical simulation of a susceptible-exposed-infectious space-continuous model for the spread of rabies in raccoons across a realistic landscape

We introduce a numerical model for the spread of a lethal infectious disease in wildlife. The reference model is a Susceptible-Exposed-Infectious system where the spatial component of the dynamics is modelled by a diffusion process. The goal is to develop a model to be used for real geographical scenarios, so we do not rely upon simplifying assumptions on the shape of the region of interest. For this reason, space discretization is carried out with the finite element method on an unstructured triangulation. A diffusion term is designed to take into account landscape heterogeneities such as mountains and waterways. Numerical simulations are carried out for rabies epidemics among raccoons in New York state. A qualitative comparison of numerical results to available data from real-world epidemics is discussed.

Social and spatial processes associated with childhood diarrheal disease in Matlab, Bangladesh

We develop novel methods for conceptualizing geographic space and social networks to evaluate their respective and combined contributions to childhood diarrheal incidence. After defining maternal networks according to direct familial linkages between females, and road networks using satellite imagery of the study area, we use a spatial econometrics model to evaluate the significance of correlation terms relating childhood diarrheal incidence to the incidence observed within respective networks. Disease was significantly clustered within road networks across time, but only inconsistently correlated within maternal networks. These methods could be widely applied to systems in which both social and spatial processes jointly influence health outcomes.