Helicobacter pylori is a Gram-negative, helix-shaped bacterium that colonizes the human stomach. More virulent type I strains are differentiated from the less virulent type II strains. The former have additional pathogenic factors, such as the vacuolating cytotoxin VacA and cytotoxin-associated CagA.

About half of the global human population is infected with H. pylori. The infection is often acquired in early childhood. In most cases, the infection is asymptomatic and remains undetected. However, about 10-15 % of those infected develop severe stomach diseases ranging from gastric ulcers to lymphoma and adenocarcinoma of the stomach. Left untreated, H. pyloriremains in the human stomach throughout an entire lifespan. Eradication is only possible with a combination of special antibiotics.

There are various invasive and non-invasive methods for the detection of 
H. pylori infections. Non-invasive serological analyses are easy to carry out and have high sensitivity and specificity. Antibodies against the bacterial pathogenicity factors, particularly CagA, are statistically more prevalent in serious infections. 

Specific antibodies against H. pylori are detectable by ELISA shortly after infection. The immune response to H. pylori generally begins with the formation of IgM antibodies, followed by an increase in the IgG and IgA antibody titres, which remain over the course of the infection.