COHORT A  Inclusion Criteria:  6- 60 months of age Diagnosed with possible Kawasaki disease (even if they do not fulfil the criteria below for Kawasaki disease) by the treating clinician based on the 2004 AHA guidelines Appropriate guardian of patients are able and willing to provide blood samples per protocol Appropriate guardian of patients are able to comprehend and willing to sign and date the written informed consent document(s) and any applicable medical record release documents for the study  Exclusion Criteria:  Patient with comorbidities likely to influence gene expression, such as immunosuppressive treatments, Have a medical condition which, in the opinion of the investigator, should preclude enrollment into the study. Have participated or be currently participating in a clinical research study in which an experimental medication has been administered  COHORT B  Inclusion Criteria:  6- 60 months of age Diagnosed with febrile illness but without Kawasaki disease presentation criteria Appropriate guardian of patients are able and willing to provide blood samples per protocol Appropriate guardian of patients are able to comprehend and willing to sign and date the written informed consent document(s) and any applicable medical record release documents for the study  Exclusion Criteria:  Patient with comorbidities likely to influence gene expression, such as immunosuppressive treatments, Have a medical condition which, in the opinion of the investigator, should preclude enrollment into the study. Have participated or be currently participating in a clinical research study in which an experimental medication has been administered  COHORT C  Inclusion Criteria:  6- 60 months of age no recent history of fever or immunization Appropriate guardian of patients are able and willing to provide blood samples per protocol Appropriate guardian of patients are able to comprehend and willing to sign and date the written informed consent document(s) and any applicable medical record release documents for the study  Exclusion Criteria:  Patient with comorbidities likely to influence gene expression, such as immunosuppressive treatments, Have a medical condition which, in the opinion of the investigator, should preclude enrollment into the study. Have participated or be currently participating in a clinical research study in which an experimental medication has been administered