Inhalation of asbestos fibres is detrimental to human health. The toxicity of asbestos has been known since the early twentieth century and linked almost exclusively to pleural mesothelioma
. However, this is just one of the 10 clinical conditions that currently define Asbestos Related Diseases (ARD)
Asbestos is a mineral whose main characteristics are incombustibility and thermal isolation. As a result of these properties, asbestos is used in a wide range of applications in almost every industrial sector
Workers at fibre cement plants, painters, carriers of asbestos materials and construction workers are the population with the highest risk of exposure to asbestos fibres
ARD is a group of 10 conditions that originate from the inhalation and subsequent deposit of asbestos fibres in the pulmonary parenchyma and which affect mainly the respiratory system. Following the most widely accepted guidelines
[2, 6], ARD are classified in two groups (malignant and non-malignant) which include diseases of the lung parenchyma, the pleura and the bronchi.
Asbestos toxicity is related to its fibrous structure, since studies have demonstrated that pulverized asbestos does not cause disease
. Due to individual susceptibility factors, the development of ARD cannot be ruled out in individuals with low intensity exposure to asbestos
[8, 9]. The study of risk and protective factors of ARD can be hindered by the latency period, which can be as prolonged as 40 years
In addition to its fibrogenic properties, asbestos is a carcinogen.
 The most widely accepted oncological model is the dose–response without a safety level.
[8, 11] Fibrogenic and carcinogenic properties are related, particularly in the amphibole type of asbestos. The role of amphibole asbestos as a co-carcinogenic agent has been shown in the development of mesothelioma and in other pulmonary neoplasms
. The risk of malignant mesothelioma increases with age and depends on when first exposure started. These factors are also closely associated with the level of exposure, continuity of exposure, and latency period
The main risk factor to develop ARD is inhalation of asbestos fibres as a result of work exposure. However, not everybody that has been or is exposed to asbestos develops ARD. A main difficulty in the study of ARD is the lack of information related to exposure history in the medical records and the lack of awareness of the workers themselves. In addition, the late age at diagnosis due to the time lag between exposure and clinical manifestations is another factor that explains the significant number of ARD cases that are not considered a work-related disease
. A large number of ARD worldwide are still not considered or notified as a work-related disease
Asbestosis, asbestos-related lung cancer and mesothelioma are classified in Spain as work-related diseases in the Royal Decree 1995/1978 of 12th of May
. Nevertheless, the actual morbidity and mortality caused by ARD are still largely unknown, mainly due to the scarce notification of these cases as work-related conditions
Fibre inhalation when living near an asbestos source, living together with an asbestos worker that brought asbestos fibres in the work clothes, the domestic use of products manufactured with asbestos and simple environmental exposure constitute non-work related exposures that can also cause ARD. The association with simple environmental exposure is better known for mesothelioma than for asbestos-related lung cancer
[17–20]. The incidence of benign ARD cases that originate from environmental exposure has hardly been investigated. Moreover, no data on the incidence of additional ARD in patients already suffering from any form of ARD exist, and no studies on the protective factors of ARD have been published.
The association of asbestos with ARD is modified by tobacco consumption. Indeed, smokers exposed to asbestos are at higher risk of developing radiologic signs of asbestosis than non-smokers
. Also, asbestosis itself is a risk factor for lung cancer
. To date, no definite association between tobacco consumption and mesothelioma has been found
It is generally accepted that the spontaneous incidence of mesothelioma is very rare, close to 1 new case/million inhabitants/year
. However, this figure has been now reviewed and increased to 3 new cases/million inhabitants/year
. In the province of Barcelona, the incidence of mesothelioma estimated from mortality data of residents equals 8.3 cases/million inhabitants/year in men, and 4.7 cases/million inhabitants/year in women. These figures are much higher in Barcelona’s neighbouring towns of Cerdanyola del Vallès, with 18.4 cases/million inhabitants/year, and Ripollet, with 17.6 cases/million inhabitants/year
A recent study on all types of ARD in our area show an incidence of 95 cases/million inhabitants/year and a prevalence of 910 cases/million inhabitants/year; in particular, the incidence and prevalence of mesothelioma are 30 and 10 cases/million inhabitants/year, respectively
. The severity of pleural mesothelioma and the possibility of an upward trend in the incidence of ARD
 are the leading motives for the research team to undertake the current project, in continuity with our previous work.
The plausibility of asbestos as the cause of ARD will be strengthened with the case–control design of this project. Also, the creation of two parallel cohorts for comparison over time will constitute the basis for future research.
Asbestos-related diseases, and non-malignant ARD specifically, are poorly understood causes of morbidity and mortality. Indeed, the course of these conditions in our study population is unknown. The transition of ARD from non-malignant to malignant has not been elucidated, and few prospective studies that address this question have been published
Up-to-date data on the impact of asbestos exposure on morbidity and mortality and on the risk and protective factors of the exposed general population are needed. Our working hypothesis is that within the group of ARD patients that develop a new ARD, a significant number of non-malignant ARD cases will develop into malignant ARD. The pattern of geographical distribution of new ARD cases requires a study with a case–control design.
The experience of the research team suggests that over 75% of ARD cases are diagnosed within the primary care network, since it is the best and most accessible gateway to the National Health System. Thus, the primary care network becomes a comprehensive setting to conduct this type of study.
The analysis of mortality in ARD cases is another relevant aim of this project. In addition to the difficulties in obtaining a final certain diagnosis, ARD must compete with other diseases as the underlying cause of death certification.
The concordance between the underlying cause of death in the Statistical Bulletin and final hospital discharge records is a fundamental quality measurement of our National Health System
. Health services use within the National Health System is an essential research area. However, in our setting it is as yet underdeveloped for primary care
, particularly in relation to ARD. We therefore aim to analyze the impact of ARD on health services through direct costs (financial burden for high cost health conditions) using the prevalence method, together with burden of disease, which combines mortality with health outcomes
The study of risk and protective factors associated with ARD, new ARD in patients with one or more previous diagnosis of ARD (additional ARD) and the space-time clustering of ARD patients in specific geographical areas generate the following working hypotheses:
Lifestyles and individual susceptibility influence the course of asbestos-related diseases.
Clinical parameters will change in 50% ARD patients every year, and for the three years of duration of the study.
10% of patients diagnosed with one or more ARD will present some new ARD (additional ARD) during the three years of the study.
Environmental exposure determines the geographical clusters of ARD cases in the study area.
The protocolized follow up of all ARD patients facilitates the management of the disease and decreases the health expense allocated to ARD (burden and costs of the disease).
ARD as the underlying cause of death certification coincides with the mortality found in the population of the study area.
The main objective of this project is the identification of protective and risk factors associated with new cases of ARD and with additional ARD, and to characterise ARD’s geographical clustering.
To identify the lifestyles and associated morbidity that might determine ARD incidence.
To quantify the proportion of ARD cases which present changes in the clinical parameters on a yearly basis during the three years of duration of the study.
To quantify the proportion of ARD cases that present an additional ARD during the three years of duration of the study.
To describe the geographical clustering of ARD cases in the study area, determined by exposure factors and individual susceptibility.
To analyze the effectiveness of the management and control of ARD through a specific protocol and its impact in the reduction of the health budget allocated to ARD (burden and costs of ARD).
Finally, to describe the level of agreement between ARD as the underlying cause of death stated in death certificates and final hospital discharge records.