Sarcoidosis in an Italian province. Prevalence and environmental risk factors

Abstract

Background and aim: Sarcoidosis is a systemic granulomatous inflammatory disease whose causes are still unknown and for which epidemiological data are often discordant. The aim of our study is to investigate prevalence and spatial distribution of cases, and identify environmental exposures associated with sarcoidosis in an Italian province.

Methods: After georeferentiation of cases, the area under study was subdivided with respect to Municipality and Health Districts and to the altitude in order to identify zonal differences in prevalence. The bioaccumulation levels of 12 metals in lichen tissues were analyzed, in order to determine sources of air pollution. Finally, the analysis of the correlation between metals and between pickup stations was performed.

Results: 223 patients were identified (58.3% female and 41.7% male of total) and the mean age was 50.6±15.4 years (53.5±15.5 years for the females and 46.5±14.4 for the males). The mean prevalence was 49 per 100.000 individuals. However, we observed very heterogeneous prevalence in the area under study. The correlations among metals revealed different deposition patterns in lowland area respect to hilly and mountain areas.

Conclusions: The study highlights a high prevalence of sarcoidosis cases, characterized by a very inhomogeneous and patchy distribution with phenomena of local aggregation. Moreover, the bioaccumulation analysis was an effective method to identify the mineral particles that mostly contribute to air pollution in the different areas, but it was not sufficient to establish a clear correlation between the onset of sarcoidosis and environmental risk factors.

Fig 1. Study area, residential localization of sarcoidosis patients and location of the sampling stations, numbered as in Table 1.

The inset shows the location of Parma in the Italian peninsula. Data from OpenStreetMap visualisation.

Fig 2. Graphic representation of the sarcoidosis prevalence for municipality (MDs) and health districts (HDs).

In the upper right, graphic representation of the sarcoidosis mean prevalence health districts groups compared using ANOVA to Fisher (Significance is expressed with different letters [a, b] and by level of significativity expressed by p values <0.005).

Fig 3. Histogram representing the mean prevalence of sarcoidosis as function of the altitude, obtained grouping together MDs over intervals of 50 meters of altitude.

The highest and lowest values of prevalence in the municipalities belonging to each interval are indicated by the bars; a square symbol identifies the median value in each group. The values of the aggregate prevalence for each group are indicated by crosses.

Fig 4. Heat map of distribution of sarcoidosis cases the Parma area.

The color-scale from low blue (equal to 1) to red (equal to 8) displays the number of patients resident within a range of 500 meters from each considered point on the map of the area under study. Data from OpenStreetMap visualisation.

Fig 5. Histogram of the prevalence in the quarters of the Parma town.

The inset shows the location of quarters in the town.

Fig 6. Heat-Plot representing the correlations among different stations computed from the concentrations of the metals under study and associated dendrogram obtained from the hierarchical clustering analysis of the same data computed using a distance based on Pearson correlation coefficients and complete linkage.

The associations for which the value of correlation is significant (p value < 0.05) are marked with an asterisk.