Background and Objectives:
The COVID-19 pandemic has hit worldwide. Italy was one of the first European countries to be severely affected. Many factors can play relevant roles in SARS-CoV-2 infection, both in virus replication and in activating the host’s immune system. This case-control study aims to assess the possible relationship between SARS-CoV-2 infection, evaluated through antibody response and the main socio-demographic, occupational, clinical-anamnestic and biochemical factors, in a population mostly residing in the Modena province (northern Italy) and mainly composed of workers.

Methods:
Enrolment was performed among subjects who voluntarily underwent serological testing. Subjects with antibody positivity for IgM and/or IgG (cases) and a similar number of negatives (controls), matched by sex, age and Italian region or foreign country of birth, were selected. Additional parameters (zinc/iron/copper/chromium/nickel, vitamins D/B12, folates, triglycerides, LDL/HDL/total cholesterol) were determined. Moreover, a questionnaire on the main relevant sociodemographic occupational and clinical data was administered through telephone interviews.

Results:
A total of 405 subjects have been enrolled, 166 cases (mean age 50.6±12.4 years), 71 (42.8%) men and 95 (57.2%) women, and 239 controls (mean age 50.6±11.6 years), 106 (44.3%) men and 133 (55.7%) women. The smokers’ percentage was significantly lower in cases (12.7%) compared to controls (20.6%). Among cases a higher percentage of subjects with diabetes (2.4% _vs _0.8%) and a lower percentage of persons affected by respiratory diseases (9.7% _vs_ 12.6%) were found. By analysing biochemical data, a lower median serum level of folates was detected among cases.

Conclusion:
Our results suggest an inverse association of SARS-CoV-2 infection evaluated through antibody response with smoke and also with folates serum level. The first association, also observed in other studies, is controversial due to the role of potential confounding factors. Regarding the inverse association with folates, a recent study shows that folates bind and inactivate a viral protease.