Disease mapping method comparing the spatial distribution of a disease with a control disease.

Small-area methods are being used in spatial epidemiology to understand the effect of location on health and detect areas where the risk of a disease is significantly elevated. Disease mapping models relate the observed number of cases to an expected number of cases per area. Expected numbers are often calculated by internal standardization, which requires both accurate population numbers and disease rates per gender and/or age group. However, confidentiality issues or the absence of high-quality information about the characteristics of a population-at-risk can hamper those calculations. Based on methods in point process analysis for situations without accurate population data, we propose the use of a case-control approach in the context of lattice data, in which an unrelated, spatially unstructured disease is used as a control disease. We correct for the uncertainty in the estimation of the expected values, which arises by using the control-disease's observed number of cases as a representation of a fraction of the total population. We apply our methods to a Belgian study of mesothelioma risk, where pancreatic cancer serves as the control disease. The analysis results are in close agreement with those coming from traditional disease mapping models based on internally standardized expected counts. The simulation study results confirm our findings for different spatial structures. We show that the proposed method can adequately address the problem of inaccurate or unavailable population data in disease mapping analysis.

On the impact of residential history in the spatial analysis of diseases with a long latency period: A study of mesothelioma in Belgium.

Mesothelioma is a rare cancer caused by exposure to asbestos. Belgium has a known long history of asbestos production, resulting in one of the highest mesothelioma mortality rates worldwide. While the production of asbestos has stopped completely, the long latency period of mesothelioma, which can fluctuate between 20 and 40 years after exposure, causes incidences still to be frequent. Mesothelioma's long incubation time affects our assessment of its geographical distribution as well. Since patients' residential locations are likely to change a number of times throughout their lives, the location where the patients develop the disease is often far from the location where they were exposed to asbestos. Using the residential history of patients, we propose the use of a convolution multiple membership model (MMM), which includes both a spatial conditional autoregressive and an unstructured random effect. Pancreatic cancer patients are used as a control population, reflecting the population at risk for mesothelioma. Results show the impact of the residential mobility on the geographical risk estimation, as well as the importance of acknowledging the latency period of a disease. A simulation study was conducted to investigate the properties of the convolution MMM. The robustness of the results for the convolution MMM is assessed via a sensitivity analysis.

Air pollution and self-perceived stress and mood: A one-year panel study of healthy elderly persons.

BACKGROUND AND OBJECTIVES: Previous studies have suggested that air pollution is associated with depression and anxiety symptoms. Here, we investigate the association between personal exposure to NO2 and perceived stress and mood in a panel of healthy elderly persons. METHODS: In a one-year panel study, we included 20 healthy volunteers (10 male-female couples aged 58-76 years) with air pollution and health parameters measured every two months (120 observations). We measured personal exposure to NO2 in the previous 5 days, perceived stress using the Perceived Stress Scale (PSS) and positive and negative affect with the Positive and Negative Affect Schedule (PANAS). We used linear and Poisson mixed models to evaluate the associations between the health outcomes and NO2 adjusted for age, sex, temperature in the previous 5 days, sunlight in the previous day and physical activity (daily average number of steps on the previous week). Also, the interaction terms between NO2 and physical activity were tested. We report % changes for PSS scores and unit changes (ß) for positive and negative affect, and their 95% confidence intervals (CI), for changes in 10 µg/m3 of NO2. RESULTS: After adjustment, an increase by 10 µg/m3 in NO2 concentrations was associated with a decrease of 1.3 points in the positive affect (95% CI -2.49 to -0.17) and an increase of 0.11 points in the negative affect (95% CI 0.02 to 0.20). The association with positive affect was stronger when physical activity was below median value of 9,362 steps per day (ß = -2.68; CI: 4.87 to -0.49); p-value for interaction was 0.08. No statistically significant associations were observed with perceived stress. CONCLUSION: Short-term exposure to air pollution may produce non-pathological alterations in mood in healthy elderly population.

Asbestos bodies in bronchoalveolar lavage in the 21st century: a time-trend analysis in a clinical population.

OBJECTIVES: Asbestos bodies (AB) in bronchoalveolar lavage (BAL) can be detected by light microscopy and their concentration is indicative of past cumulative asbestos exposure. We assessed clinical and exposure characteristics, as well as possible time trends, among patients in whom AB had been quantified in BAL. METHODS: BAL samples obtained from 578 participants between January 1997 and December 2014 were available for analysis. The processing of samples and the microscopic analysis were performed by a single expert and 76% of samples came from a single tertiary care hospital, allowing clinical and exposure data to be extracted from patient files. RESULTS: The study population (95% males) had a mean age of 62.5 (±12.4) years. AB were detected in 55.2% of the samples, giving a median concentration of 0.5 AB/mL (95th centile: 23.6 AB/mL; highest value: 164.5 AB/mL). The AB concentration exceeded 1 AB/mL in 39.4% and 5 AB/mL in 17.8%. A significant decrease from a geometric mean of 0.93 AB/mL in 1997 to 0.2 AB/mL in 2014 was apparent. High AB concentrations generally corresponded with occupations with (presumed) high asbestos exposure. AB concentrations were higher among patients with asbestosis and pleural plaques, when compared with other disease groups. Nevertheless, a substantial proportion of participants with likely exposure to asbestos did not exhibit high AB counts. CONCLUSIONS: This retrospective study of a large clinical population supports the value of counting AB in BAL as a complementary approach to assess past exposure to asbestos.

Hotspots of malignant pleural mesothelioma in Western Europe.

Malignant pleural mesothelioma, a highly invasive tumour, has been epidemiologically linked to an occupational or environmental exposure to asbestos. Although asbestos has been widely used in diverse industrial applications and in construction, some industrial sectors have been affected much more than others. The objective of this review was to describe the existence of clusters of malignant pleural mesothelioma in Western European countries, based on epidemiological studies published between 2000 and 2015. MEDLINE (PubMed) and Embase were searched for relevant studies on spatial clustering of mesothelioma in Western European countries. Eventually, 16 different studies published between 2000 and 2015 were selected for a comprehensive analysis. Relevant studies on spatial clustering of mesothelioma were found for Belgium, the Netherlands, the United Kingdom, Germany, France, Spain, Italy and Denmark. Clustering of pleural mesothelioma was found mainly around shipyards (16 studies) and asbestos cement industries (10 studies). Although malignant pleural mesothelioma may be found throughout Western Europe, the present study indicates specific areas with higher past and also probable future incidence.

Disease mapping of zero-excessive mesothelioma data in Flanders.

PURPOSE: To investigate the distribution of mesothelioma in Flanders using Bayesian disease mapping models that account for both an excess of zeros and overdispersion. METHODS: The numbers of newly diagnosed mesothelioma cases within all Flemish municipalities between 1999 and 2008 were obtained from the Belgian Cancer Registry. To deal with overdispersion, zero inflation, and geographical association, the hurdle combined model was proposed, which has three components: a Bernoulli zero-inflation mixture component to account for excess zeros, a gamma random effect to adjust for overdispersion, and a normal conditional autoregressive random effect to attribute spatial association. This model was compared with other existing methods in literature. RESULTS: The results indicate that hurdle models with a random effects term accounting for extra variance in the Bernoulli zero-inflation component fit the data better than hurdle models that do not take overdispersion in the occurrence of zeros into account. Furthermore, traditional models that do not take into account excessive zeros but contain at least one random effects term that models extra variance in the counts have better fits compared to their hurdle counterparts. In other words, the extra variability, due to an excess of zeros, can be accommodated by spatially structured and/or unstructured random effects in a Poisson model such that the hurdle mixture model is not necessary. CONCLUSIONS: Models taking into account zero inflation do not always provide better fits to data with excessive zeros than less complex models. In this study, a simple conditional autoregressive model identified a cluster in mesothelioma cases near a former asbestos processing plant (Kapelle-op-den-Bos). This observation is likely linked with historical local asbestos exposures. Future research will clarify this.

Emergence of human G2P[4] rotaviruses containing animal derived gene segments in the post-vaccine era.

The introduction of Rotarix into the Belgian immunization program in June 2006 coincided with an increase of the relative prevalence of G2P[4] strains. However, the genetic composition of these persistent G2P[4] strains has not been investigated. Therefore, we have investigated the NSP4 gene of 89 Belgian G2P[4] strains detected between 1999 and 2013, covering both pre- and post-vaccination periods. The NSP4 genes were divided over seven separate clusters of which six were more closely related to animal than to human strains. The NSP4 genes that clustered more closely to animal DS-1-like strains were isolated after 2004-2005 and were found throughout multiple seasons. Complete genome sequencing of 28 strains identified several other gene segments that clustered more closely to animal than to human DS-1-like strains. These findings suggest that frequent interspecies reassortments may have played a role in the spread of G2P[4] rotaviruses in the post-vaccination period in Belgium.