Delayed infection, family size and malignant lymphomas

Background-The annual incidence of non-Hodgkin's lymphomas (NHL) is increas ing by 3%-4% in different parts of the developed world. Excesses of NHL hav e been observed in populations exposed to immunosuppressants and to HIV, bu t these causes do not explain the increasing trends. It is suggested that d elayed infection could explain NHL trends, through an impairment of the Th1 /Th2 lymphocyte patterns. Methods-In a population-based study on 1388 patients with NHL, 354 with Hod gkin's disease (HD) and 1718 healthy controls, the age of first occurrence of bacterial and viral diseases was investigated. Clinical records were per used in one centre to check the anamnestic data. Findings-The age of occurr ence of bacterial and viral diseases was significantly higher among NHL pat ients than in the controls. The association between later age at first bact erial or viral disease was limited to small families (OR= 1.95; 95% confide nce intervals 1.26, 3.00, for age 4-8 at first infection; OR=1.91; 1.19, 3. 06, for age 9+, compared with less than 4). The association was more obviou s for bacterial diseases (possibly for the lower degree of misclassificatio n). High grade lymphomas showed the strongest association. The later age of occurrence of bacterial or viral diseases in NHL patients is consistent wi th a higher incidence of lymphomas observed in higher social groups. No cle ar association was found between HD and age at first bacterial or viral dis eases. Interpretation-It is proposed that delayed infection could explain the incr easing NHL trends, through an impairment of the Th1/Th2 lymphocyte patterns . The model of delayed infection has been proposed also to explain increasi ng prevalence rates of asthma.