Acute idiopathic pericarditis during a national lockdown to prevent transmission of SARS-COVID-19

Background: Idiopathic acute pericarditis is often presumed to have a viral cause. We hypothesized that if acute viral infection was the cause, the incidence of acute ‘idiopathic’ pericarditis would decrease during a public health lockdown introduced to prevent the spread of SARS-COVID-19 in New Zealand when acute viral infections decreased by 75% to 99%. Methods: Hospitalization for acute ‘idiopathic’ pericarditis during 5 months of the national public health lockdown were compared to 54 months before the COVID-19 pandemic from administrative data. Results: The hospitalization rate for acute pericarditis was similar before (n = 1364, 24.8 cases/30 days) compared to during the public health lockdown (n = 132, 25.8 cases/30 days), +4% 95 % confidence interval −25 % to +30 % (P = 0.67). Conclusion: These observations do not support the hypothesis that acute viral infection is the cause for most cases of acute idiopathic pericarditis.