P. M. Matricardi et al. “Sibship Size, Birth Order, and Atopy in 11,371 Italian Young Men”. Journal of Allergy and Clinical Immunology 101, № 4, pt. 1 (1998); P. M. Matricardi et al. “Exposure to Foodborne and Orofecal Microbes versus Airborne Viruses in Relation to Atopy and Allergic Asthma: Epidemiological Study”. British Medical Journal (Clinical Research Ed.) 320, № 7232 (2000).