Patterns of infections
The prevalence of serum markers of microbes transmitted through the oral route was higher in the non-atopic than atopic participants, with statistical significance for T gondii and hepatitis A virus (table ) even after adjustment for each other and for H pylori (not shown). Conversely, the presence of serum markers of all the six viruses transmitted by other routes was not associated with atopy (table ).
Prevalence of antibodies against selected infectious agents in 240 atopic and 240 non-atopic Italian military cadets. Values are numbers (percentages) of participants unless stated otherwise
In an attempt to verify whether the microbial agents had a cumulative effect we created two gradients (indexes) as a measure of lifetime cumulative exposure to T gondii, hepatitis A virus, H pylori, and to mumps, rubella, chickenpox, herpes simplex virus type 1, and cytomegalovirus; measles was excluded (prevalence exceeded 95%). After adjusting for relevant sociodemographic confounders, the odds of being atopic decreased linearly with cumulative exposure to H pylori, T gondii, and hepatitis A virus (P for linear trend <0.001) but not with cumulative exposure to the other viral infections examined (fig ).
Figure 1 Adjusted odds of being atopic according to cumulative indexes of exposure to T gondii, H pylori, and hepatitis A virus (P for linear trend 0.0010) or to mumps, rubella, chickenpox, herpes simplex virus type 1, and cytomegalovirus. Values were (more ...)
In the whole population sample, the frequency of high atopy was 2.7 times higher (20.1% v 7.8%, P=0.00012) among participants with no antibodies against T gondii, H pylori, and hepatitis A virus than among those with two or three positive results (table ). Additionally, cumulative exposure to T gondii, H pylori, and hepatitis A virus was inversely related to skin sensitisation to all allergens tested, except P judaica, and to allergic rhinitis or asthma (table ). Interestingly, allergic asthma was diagnosed in only 1 of 245 (0.4%) participants seropositive to at least two orofecal or foodborne infections (H pylori, T gondii, hepatitis A virus) and allergic rhinitis was diagnosed in only 16 of 245 (6.5%) versus 38 of 796 (4.8%) and 123 of 796 (15.5%) respectively in participants seronegative to H pylori, T gondii, and hepatitis A virus.
Atopy in 1659 Italian military cadets according to index of exposure to Toxoplasma gondii, Helicobacter pylori, and hepatitis A virus
Table 3 Skin sensitisation and respiratory allergies among 1659 Italian military cadets according to an index of exposure to Toxoplasma gondii, Helicobacter pylori, and hepatitis A virus. Values are numbers (percentages) of participants unless stated otherwise (more ...)
Exposure to orofecal and foodborne infections, total IgE concentration, and atopy
Geometric mean values for concentration of total IgE were only slightly higher (P=0.09) in participants not exposured to hepatitis A virus, T gondii, and H pylori, and this small difference tended to disappear after adjustment for atopy (table ). Multivariate analysis, adjusted for relevant sociodemographic factors and atopy, confirmed that the cumulative exposure to H pylori, T gondii, and hepatitis A virus was not associated with concentration of total IgE (not shown).
Concentrations of total IgE among 1659 Italian military cadets according to atopy and an index of exposure to Toxoplasma gondii, Helicobacter pylori, and hepatitis A virus. Values are geometric mean (SD) unless stated otherwise
We plotted the percentages of participants with atopy against intervals of total IgE concentration on a log scale (fig ). As expected, concentrations of total IgE were closely related to the prevalence rate of atopy in the whole population. The three other curves represent subgroups stratified according to index values of exposure to T gondii, hepatitis A virus, and H pylori. Interestingly, the prevalence of atopy increased with decreasing exposure to orofecal or foodborne infections within the three subgroups whose concentration of total IgE was between 160 kU/l and 1280 kU/l (fig ). For example, the frequency of atopic participants with concentrations between 160 kU/l and 320 kU/l was 28% (38 of 136) among those not exposured to T gondii, hepatitis A virus, or H pylori, and only 8% (3 of 38) among those exposured to at least two of these infections.
Figure 2 Relation between total IgE concentration and atopy according to cumulative exposure to T gondii, H pylori, and hepatitis A virus in 1659 Italian military cadets. Atopy is shown as the percentage of participants, grouped according to IgE concentration, (more ...)