In the course of 1995–1998 the authors examined 114 complete families with one or more children aged 3–18 years for the presence of IgG antibodies against Helicobacter pylori (ELISA method). The investigation was focused on the problem in which family members of the investigated child („index case“) who live with them in a common household Helicobacter pylori infection is present. The objective was to find out whether the parents of Helicobacter pylori positive children suffer more frequen- tly from Helicobacter pylori infection than parents of Helicobacter pylori negative children and whether IgG against Helicobacter pylori positive children have more frequently positive mothers or fathers or both parents. Results: Serum IgG antibodies against H. pylori (ELISA) were examined in 114 „complete families“. The finding of S-IgG antibodies against H. pylori in the child of 114 complete three-member families (father, mother and one child – „index case“) depends statistically significantly on the finding of S-IgG antibodies against H. pylori in the parents at a significance level of p < 0.01. If both parents have serum S-IgG antibodi- es against H. pylori the relative risk (RR) that their children will be also positive is 1.84 and the confidence limit CI 95 % (1.40 < RR <2.42). The risk of H. pylori infection of children in families where both parents are positive is thus more than double as compared with children where both parents are negative. In families where both parents are positive as compared with families where only one parent is positive and one negative the RR is also significantly higher. This means that the group where both parents are S-IgG positive against H. pylori differs significantly from the other two groups (both parents negative or one positive and one negative). The finding of S-IgG antibodies against H. pylori of the child is significantly dependent (at a signifi- cance level of p < 0.001) on the finding in the mother. If the mother is S-IgG positive against H. pylori the RR that also the children will be positive is 1.74 (1.32 < RR < 2.30), i.e. almost 1.75 times greater than when the mother is negative. The finding of S-IgG against H. pylori in the child is also significantly dependent (at a significance level of p < 0.01) on the finding in the father. If the father is positive the RR that the children will be positive is 1.62 (1.19 < RR < 2.20). The RR is in this case somewhat lower than when the mother is positive. The difference between combinations mother/father is not statistically significant, i.e. it does not matter whether the father or the mother is positive, unless both are positive. The finding in the father depends significantly on the finding in the mother at a significance level of p < 0.01. This relationship between positivity of both parents living in a common household supports in a major way the hypothesis on the transmission of H. pylori infection among couples living together. The authors did not reveal statistically significant differences in the values of asses- sed antibodies for individual family members and positive and negative findings. Children who did not have antibodies against H. pylori were significantly younger as compared with their siblings. Conclusion: From the authors investigation of IgG antibodies against H. pylori ensues that H. pylori infection clusters in families and is transmitted. The relative risk of H. pylori infection in children from families where both parents are positive is more than double as compared with families where both parents are negative. If both parents are positive the relative risk of H. pylori infection in children is significantly higher as compared with families where only one parent is positive and one negative. Values of IgG antibodies against H. pylori are not affected by the child’s age. Infected children are significantly older than their IgG negative siblings.

        Key words: H. pylori infection – cumulation of H. pylori infection in families – IgG antibodies