The inverse association of salmonellosis in infancy with allergic rhinoconjunctivitis and asthma at school-age: a longitudinal study

Background: Respiratory allergies are inversely related to early acquisition of food-borne and fecal-oral infections, consumption of unpasteurized milk, early exposure to stables and high endotoxin concentrations in a farming environment. We tested therefore if infection by Salmonella in early life can protect from development of respiratory allergies later in life. Methods: During 2003, we studied two groups of Sardinian children (age 6-18 years) who had been hospitalized before 4 years of age (during 1989-2001) with non-typhoid salmonellosis (n = 148) or acute enteritis of nonbacterial etiology (NB-enteritis) (n = 167). Allergic rhinoconjunctivitis (AR) and asthma were evaluated by telephonic interview with a ISAAC questionnaire; participants reporting AR and/or asthma were further examined through a complete diagnostic work-up to objectively confirm or exclude current disease. Kaplan-Meier curves and Cox proportional hazard models were used to analyze the role of different types of enteritis on the risk of developing allergic rhinoconjunctivitis or asthma over time. Results: Children who had been hospitalized with salmonellosis had a lower prevalence of allergic rhinoconjunctivitis (eight of 148, 5.4%vs 23 of 167, 13.8%; P = 0.019) or asthma (five of 148, 3.4%vs 21 of 167, 12.6%; P = 0.006) than those who had been hospitalized with NB-enteritis. The proportional hazard of salmonellosis for asthma was 0.23 (95% CI: 0.08-0.67; P < 0.01) and for allergic rhinoconjunctivitis was 0.40 (95% CI: 0.17-0.95; P = 0.04), after adjusting for confounders. Discussion: The strength of the observed associations suggests that Salmonella may contribute to shape the natural history of respiratory allergies. However, further studies are needed to test in other settings the association observed in Sardinian children. We speculate that clinical or subclinical infection by Salmonella may contribute to the atopy protective influence of a traditional farming environment or of areas endemic for food-borne and fecal-oral infections. Food hygiene and prevention of salmonellosis must remain however a public health priority.