Inclusion Criteria:

Mayo Site

• Children born in Olmsted County between 1997–2016. with age of 3-26 years old.
• Research authorization for using medical record for research.
• Children who have received medical care at only Mayo Clinic.

Sanford Children's Hospital (for Aim 4 only)

• Children who were born between November 1, 2011, and December 31, 2018.

Exclusion Criteria: 

• No research authorization for using medical record for research.*
• Non-Olmsted County residents defined by non-Olmsted County address in medical record within one year prior to last follow-up date as of data abstraction.*
• Insufficient medical record to ascertain asthma status or other variables.
• Children who left the community before the age of 3 years because API requires medical history at least during the first 3 years of life.*
• Adopted children (lack of information on a family history of parents which is one of API criteria).
• Conditions making asthma ascertainment difficult (tracheobronchial foreign body at or about the incidence date of asthma, bullous emphysema or pulmonary fibrosis, PiZZ alpha1-antitrypsin, cystic fibrosis, hypogammaglobulinemia (IgG<2.0 mg/mL), other immunodeficiency disorder (or conditions identified by the International Union of Immunological Societies at index date of AIICs), primary ciliary dyskinesia, bronchiectasis, or COPD if it is present) and other major chest disease (severe kyphoscoliosis or bronchiectasis) which will be identified by ICD code and free text search.
• Immunodeficiency or immunosuppressive therapy:  Patients who had received immunosuppressive or immunoglobulin therapy or transfusion within twelve months prior to index date of AIICs except corticosteroid burst therapy for asthma exacerbation. 
• Children who weigh below 17 kg (the volume of blood taken from the donors is minimized to be less than 3 mL/kg bodyweight for a venipuncture).*
• A history of malignancy at index date of AIICs.

* Applied to Mayo site study only.