A group of infections that occur within the abdominal cavity.

IAIs are a common cause of gastrointestinal emergency procedures and responsible for high levels of morbidity and mortality. An uncomplicated IAI (uIAI) involves only a single organ and does not extend to the peritoneum, a two-layer membrane that lines the abdominal cavity. A complicated IAI (cIAI) involves more than one organ and infection of the peritoneal space, the gap between the two layers of the peritoneum, leading to abscesses or peritonitis.

Gram-negative and Gram-positive bacteria can cause IAIs and these can be drug-resistant.