Demographic and clinical information
Study personnel completed case report forms by interviewing parents or guardians and extracting clinical information from medical records, including radiographic and laboratory data. Demographic and clinical information collected included: underlying medical conditions (UMCs), gestational age, birth weight, mode of birth delivery [Caesarean section (C-section) or normal spontaneous vaginal delivery (NSVD)], child’s medical history including vaccination history, feeding, including supplemental vitamins, atopic history (asthma, allergic rhinitis or eczema) using the International Study of Asthma and Allergies in Childhood questionnaire12, family history of asthma, allergic rhinitis or eczema, current or history of breastfeeding, number of siblings, day care attendance, indoor pets, and household smoke exposure. Smoke exposure includes cigarette smoke and nargila, a form of smoking traditionally found in Middle Eastern cultures, in which tobacco is heated with charcoal and the resultant smoke is passed through a water basin before inhalation13. Subjects were considered to have UMCs if they had any of the following conditions: diabetes, heart disease, Down syndrome, kidney disease, sickle cell disease, cystic fibrosis, cancer, genetic/metabolic, cerebral palsy, neurological, mental retardation/developmental delay, seizure disorder, chronic diarrhoea (eg, >2 weeks), gastro-oesophageal reflux disease, immunodeficiency, asthma/reactive airway disease (RAD), liver disease and/or other. Data were entered into a standardized, secured database - REDCap (Research Electronic Data Capture) system (www.project-redcap.org)14.