Epidemiology

Acute appendicitis is among the most common causes of lower abdominal pain that brings patients to the emergency room; it is the most common diagnosis made in young patients admitted to the hospital with acute abdominal pain.​[2][7]

One systematic review of population-based studies reported the pooled incidence of appendicitis or appendectomy in the US in the 21st century to be 100 per 100,000 person-years; the estimated number of cases in the US in 2015 was 378,614.[10]​ Around 50,000 cases of acute appendicitis were treated in UK hospitals in 2020-2021.[11]​ Most cases occurred in the 20-59 year age group.[11] A large majority presented (46,297) as medical emergencies.[11] In the US, the overall lifetime risk of developing acute appendicitis is approximately 8% for males and 7% for females.​[12]​​

Data suggest a rapid increase in incidence in newly industrialized countries.[10] Acute appendicitis most commonly occurs between the ages of 10 and 30, with the highest incidence in children and adolescence.[7][13]​ There is a slight male to female predominance (1.4:1).[2]

Risk factors

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differences in the appendiceal microbiome

The gut microbiota refers to the trillions of microorganisms that live in the gastrointestinal tract.[22][23]​​​​ Some studies have identified significant differences in the appendiceal microbiome in patients with acute appendicitis compared to healthy controls.[24][25]​​​ Alterations in both the diversity and abundance of the gut microbiota may serve as one of the contributing factors to the onset of appendicitis.[24][26]​​ The gut microbiota also plays a crucial role in training and modulating the immune system.[23] Alterations in the gut microbiota composition may result in an aberrant immune response in the appendix, leading to inflammation and appendicitis.[23]

smoking

Children exposed to passive smoking have significantly increased incidence of acute appendicitis.[7][27] There is also an increased incidence of acute appendicitis in adult patients who smoke compared with adults who never smoked.[27][28]

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