Nationwide epidemiological survey of acute pancreatitis in Japan, 2021: the impact of the COVID-19 pandemic and revised clinical guidelines.

Objectives: This study aimed to clarify the current clinico-epidemiological characteristics of acute pancreatitis (AP) in Japan.

Methods: We conducted a two-stage nationwide survey of patients with AP treated at selected hospitals in 2021, during the COVID-19 pandemic. The first stage estimated the total number of AP patients, while the second collected detailed clinical data.

Results: The estimated number of AP patients requiring hospitalization was 61,080, with an overall incidence rate of 49 per 100,000 persons, decreasing from 78,450 in 2016. Detailed clinical data were obtained for 4,375 patients, including 1,362 (31.1%) classified as severe. The male-to-female ratio was 2.0, with mean ages at onset of 60.1 years for males and 65.4 years for females. The three major causes were alcohol (31.2%), gallstones (22.5%), and idiopathic etiology (22.1%). The AP-associated in-hospital mortality rate was 2.1% in all AP and 5.3% in severe cases, down from 6.1% in the 2016 survey. Antibiotics were administered to 61.2% of mild cases, a significant reduction from 94.5% in 2016. Enteral nutrition was provided to 56.9% of severe cases, up from 31.8% in 2016. Among 124 patients undergoing interventional drainage for walled-off necrosis, 57 were treated using a step-up approach. Notably, no patients underwent upfront surgery as the initial treatment.

Conclusions: During the pandemic, the estimated number of AP cases requiring hospitalization declined for the first time in nearly four decades. Mortality in severe cases improved, and adherence to clinical guidelines on prophylactic antibiotics and enteral nutrition also improved, indicating enhanced management of AP in Japan.