Hypothesis: For 50 years in the developed world, autoimmune and allergic disease incidence has increased by 3-5%/yr. Several such chronic diseases are life threatening. For some, symptoms can be controlled, but treatments have side-effects. This rapid increase and the less than 50% concordance in monozygotic twins, indicates environmental causes. The "hygiene hypothesis" proposed a relation with decreased pathogen exposures, which are normally rare. Changes in exposure to ubiquitous non-pathogenic bacteria, particularly the abundant and heavily immunosurveilled gut commensals, seem more relevant. Model system: Difficulties in relating gut microbiota species to allergic and autoimmune diseases include: the microbiota being ubiquitous yet individual specific, multiple protective/culprit acting at a distant, non-sterile and poorly accessible site, disease appearance being disconnected from infection period, rarety of some of the diseases and presence of genetic susceptibility. We therefore want to examine whether there is any evidence that increasing exposure to broad spectrum antibiotics during early childhood increases the chance of developing some of the most common allergic diseases: asthma and perhaps eczema and allergies.

Specific hypothesis to be examined (Aims): Examine whether early life (before 3 yrs of age) single or repeated exposure(s) to broad-spectrum antibiotics correlates with increased risk of developing increasingly severe asthma, eczema and allergies.