Multimorbidity and SARS-CoV-2–Related Outcomes: Analysis of a Cohort of Italian Patients

Background: Since the outbreak of the COVID-19 pandemic, identifying the main risk factors has been imperative to properly manage the public health challenges that the pandemic exposes, such as organizing effective vaccination campaigns. In addition to gender and age, multimorbidity seems to be one of the predisposing factors coming out of many studies investigating the possible causes of increased susceptibility to SARS-CoV-2 infection and adverse outcomes. However, only a few studies conducted have used large samples. Objective: The objective is to evaluate the association between multimorbidity, probability to be tested, susceptibility, and severity of SARS-CoV-2 infection in the Piedmont population (Northern Italy, about 4 million inhabitants). For this purpose, we considered five main outcomes: access to swab, positivity to SARS-CoV-2, hospitalization, ICU admission, and death within 30 days from the first positive swab. Methods: Data were obtained from different Piedmont health-administrative databases. Subjects aged between 45 and 74 years and infections diagnosed between February and May 2020 were considered. Multimorbidity was defined both with the Charlson Comorbidity Index (CCI) and by identifying patients with previous comorbidities such as diabetes, and oncological, cardiovascular, and respiratory diseases. Multivariable logistic regression models (adjusted for age and month of infection and stratified by gender) were performed for each outcome. Analyses were also conducted by separating two age groups (45-59 and 60-74 years). Results: Out of 1,918,549 subjects, 85,348 performed at least one swab, 12,793 tested positive for SARS-CoV-2, 4,644 were hospitalized, 1,508 were admitted to the ICU, and 749 died within 30 days from the first positive swab. Individuals with a higher CCI had a higher probability of being swabbed but a lower probability of testing positive. We observed the same results when analyzing subjects with previous oncological and cardiovascular diseases. Moreover, especially in the youngest group, we identified a greater risk of being hospitalized and dying. Among comorbidities considered in the study, respiratory diseases seem to be the most likely to increase the risk of having a positive swab and worse disease outcomes. Conclusions: Our study shows that patients with multimorbidity, although swabbed more frequently, are less likely to result infected with SARS-CoV-2, probably due to greater attention on protective methods. Moreover, a history of respiratory diseases is a risk factor for a worse prognosis of COVID-19. Nonetheless, whatever comorbidities affect the patients, a strong dose-response effect was observed between an increased score of CCI and COVID-19 hospitalization, ICU admission, and death. These results are important in terms of public health because they help in identifying a group of subjects that are more prone to worse SARS-CoV-2 outcomes. This information is important for promoting targeted prevention and developing policies for the prioritization of public health interventions.