Background: Nickel (Ni) oral consumption may elicit systemic reactions in patients affected by systemic nickel allergy syndrome (SNAS), including gastrointestinal symptoms, which in turn are associated with gut dysbiosis. We evaluated the effects of a low-Ni diet alone or in combination with the oral consumption of appropriate probiotics on Ni-sensitivity and urinary dysbiosis markers in SNAS patients. Methods: n = 51 patients with SNAS and concomitant intestinal dysbiosis were enrolled in the study. According to the urinary indican/skatole levels, quantified through a colorimetric and a high-performance liquid chromatographic method, respectively, patients were assigned to a dysbiosis type/grade and followed a low-Ni diet for three months. Along with the diet, 22 patients also consumed probiotics based on the dysbiosis type. In particular, a Lactobacilli- or Bifidobacteria-containing formulation was administered to patients with fermentative or putrefactive dysbiosis, respectively, while a broad-spectrum probiotic formulation containing both Lactobacilli and Bifidobacteria was administered to patients with mixed dysbiosis. After three months, patients were invited to repeat the Ni-stimulation and the dysbiosis tests. Results: The fermentative dysbiosis group represented the largest group followed by the mixed dysbiosis group, while only two patients had putrefactive dysbiosis. Overall, at three months of treatment in general (diet alone with or without probiotics), the Ni-sensitivity and dysbiosis levels were strongly ameliorated. The association of a low-Ni diet with a specific probiotic oral supplementation was significantly more effective in decreasing dysbiosis levels or reaching eubiosis than with diet alone. Conclusion: Our results, while confirming the benefits of a low-Ni diet in SNAS patients, strongly support that appropriate adjuvant treatment with probiotics significantly helps to improve intestinal dysbiosis or restore a healthy microbiota.

The COVID-19 outbreak disproportionately affected the elderly and areas with higher population density. Among the multiple factors possibly involved, a role for air pollution has also been hypothesized. This nationwide observational study demonstrated the significant positive relationship between COVID-19 incidence rates and PM2.5 and NO₂ levels in Italy, both considering the period 2016–2020 and the months of the epidemic, through univariate regression models, after logarithmic transformation of the variables, as the data were not normally distributed. That relationship was confirmed by a multivariate analysis showing the combined effect of the two pollutants, adjusted for the old-age index and population density. An increase in PM2.5 and NO₂ concentrations by one unit (1 µg/m³) corresponded to an increase in incidence rates of 1.56 and 1.24 × 10⁴ people, respectively, taking into account the average levels of air pollutants in the period 2016–2020, and 2.79 and 1.24 × 10⁴ people during March–May 2020. Considering the entire epidemic period (March–October 2020), these increases were 1.05 and 1.01 × 10⁴ people, respectively, and could explain 59% of the variance in COVID-19 incidence rates (R² = 0.59). This evidence could support the implementation of targeted responses by focusing on areas with low air quality to mitigate the spread of the disease.