Viral infections are often self-limiting, which is why it is sufficient to treat the symptoms, and laboratory diagnostic tests are usually not performed. Bacteria such as Yersinia and Campylobacter, however, may cause immunologically mediated secondary diseases, e.g. reactive arthritis. Here, serological tests may support the diagnosis. Infections with Helicobacter pylori may cause chronic active gastritis and complications such as gastroduodenal ulcer disease, stomach carcinoma or lymphoma. Antibody detection is recommended in suspected cases of non-acute or chronic infection. Parasitic pathogens such as Schistosoma and Strongyloides stercoralis can also cause gastrointestinal symptoms with chronic courses. Direct and indirect methods are applied for diagnostics. In general, specific antibody detection is suitable to support the diagnosis in suspected cases of chronic courses or secondary diseases, but not for diagnostics in acute cases.