The Hasselt Appendicitis Immunology and Environmental Study (HAPPIEST) aims at characterizing factors that influence the development and severity of acute appendicitis. In a cohort of 300 patients and 300 controls, environmental factors as well as genetic make-up of the innate immune system, focusing mainly on pattern recognition, will be analyzed in order to gain insight in their relative importance in the pathology of appendicitis. Furthermore, populations of micro-organisms present in the gut of patients will be characterized, and the interaction between relevant micro-organisms and the innate immune system will be analyzed.

Inclusion Criteria:

• Acute appendicitis
• Appendectomy within 7 days after onset of symptoms
• Signed informed consent

Exclusion Criteria:

• Appendectomy 7 days or more after onset of symptoms
• Participation in any clinical investigational drug study within 4 weeks of screening
• Severe, life-threatening disease with a life expectancy of less than 2 months.

Patients are asked to participate after presenting with acute appendicitis at the emergency room of Jessa Ziekenhuis, Hasselt. If the patient fits the criteria, and informed consent is signed, the patient is included in the study.