Autoantibodies/immunology; Autoimmune Diseases/immunology; Campylobacter Infections/complications; Enteritis/complications; Galactosylceramides/immunology; Gangliosides/immunology; Polyradiculoneuropathy/immunology; Adolescent; Adult; Aged; Antibodies, Bacterial/blood; Antibodies, Viral/blood; Antibody Specificity; Antigens, Bacterial/immunology; Autoantibodies/blood; Autoimmune Diseases/epidemiology; Autoimmune Diseases/etiology; Campylobacter Infections/immunology; Campylobacter Infections/microbiology; Campylobacter jejuni/classification; Campylobacter jejuni/immunology; Campylobacter jejuni/isolation & purification; Child; Child, Preschool; Comorbidity; Cytomegalovirus Infections/epidemiology; Cytomegalovirus Infections/immunology; Enteritis/immunology; Enteritis/microbiology; Europe/epidemiology; Feces/microbiology; Female; G(M1) Ganglioside/immunology; Herpesviridae Infections/epidemiology; Herpesviridae Infections/immunology; Herpesvirus 4, Human/immunology; Herpesvirus 4, Human/isolation & purification; Humans; Japan/epidemiology; Male; Middle Aged; Molecular Mimicry; Mycoplasma pneumoniae/immunology; Pneumonia, Mycoplasma/epidemiology; Pneumonia, Mycoplasma/immunology; Polyradiculoneuropathy/epidemiology; Polyradiculoneuropathy/etiology; United States/epidemiology