[Chronic diseases and risk of symptomatic COVID-19: results of a case-population study on a sample of patients in the Local Health Unit 'Toscana Centro' (Tuscany Region, Central Italy)].

Background: the COVID-19 pandemic represents a challenge for health systems around the world, with just under 10,000 cases in Tuscany Region (Central Italy) and about 4,500 in the Local Health Unit (LHU) 'Toscana Centro', updated on 11 May 2020. The risk factors reported are several, including age, being male, and some chronic diseases such as hypertension, diabetes, respiratory and cardiovascular diseases. However, the relative importance of chronic diseases is still to be explored.

Objectives: to evaluate the role of chronic diseases on the risk to develop clinically evident (at least mild symptomatic) forms of SARS-CoV-2 infection in the population of the LHU Toscana Centro.

Design: case-population study.

Setting And Participants: 'case' is a subject with SARS-CoV-2 positive swab with at least mild clinical status, who lives in the LHU Toscana Centro area; 'controls' are all people residing in the LHU Toscana Centro area at 1 January 2020. People aged under 30 and patients living in nursing care homes are excluded from the analysis.

Main Outcome Measures: the analysis assesses the effect of gender, age, neoplasm, and the main chronic diseases on the onset of an infection with at least mild symptoms by calculating odds ratios (OR) by multivariate logistic regression models (to produce adjusted OR by potential confounders).

Results: among the 1,840 cases, compared to the general population, the presence of males and over-60-year-old people is greater. Almost all the considered chronic diseases are more frequent among the cases, compared to the general population. A chronic patient has a 68% greater risk to be positive with at least mild symptoms. Many of the considered diseases show an effect on the risk of getting COVID-19 in a symptomatic form, which remains even adjusting by other comorbidities. The main ones include heart failure, psychiatric disorders, Parkinson's disease, and rheumatic diseases.

Conclusions: these results confirm evidence already shown in other studies on COVID-19 patients and add information on the chronic diseases attributable risk in the population, referred to the symptomatic forms and adjusted by age, gender or the possible copresence of more diseases. These risk estimates should guide prevention interventions by health services in order to protect the chronic patients affected by the pathologies most at risk.