In sensitivity analyses to address possible misclassification of our Lyme disease definition, inferences were similar to the main analysis when we required disseminated cases to have positive serology (IgG or IgM, 45% of disseminated cases) (Additional file 1: Table S5), or an antibiotic order within 30 days before or after the diagnosis date (Additional file 1: Table S6). The gene discussed is CD40LG; the disease is Lyme disease.