Minor allele frequencies between groups were compared with a test of binomial proportions. The null hypothesis was that there was no difference in minor allele frequency between the cases and the reference sample. A priori groups examined in subgroup analyses included previously healthy case-patients, case-patients <5 years old, case-patients with invasive bacterial co-infection, and case-patients with sudden death. Differences in length of illness were evaluated with the Kaplan-Meier estimator with differences tested with the log-rank statistic. Tests of signifi cance were based on a 2-sided test with α = 0.05. Tests of departure from Hardy-Weinberg equilibrium for the reference sample have been published (10) . Analyses were conducted in SAS version 9.2 (SAS Institute, Cary, NC, USA).