Background-Cesarean delivery may alter neonatal immune responses and increase the risk of atopy. Studies of the relation between cesarean delivery and allergic diseases in children not selected on the basis of a family history of atopy have yielded inconsistent findings.

Among children with parental history of asthma or allergies, current mouse exposure is associated with increased risk of wheeze during the first 7 years of life. Early mouse exposure was associated with early wheeze and atopy later in life.

Recent studies have shown that mouse allergen is prevalent and potentially important in both urban and suburban environments, particularly in homes of subjects with asthma sensitized to this allergen. 1-4 However, little is known about the relation of sensitization to mouse allergen to asthma morbidity in adults with asthma outside the occupational laboratory setting. In this study, we evaluated whether sensitization to mouse allergen is a cause of morbidity in women with asthma from a range of socioeconomic back-grounds from a large metropolitan area in the United States.This study involved women who were screened for participation in the Epidemiology of Home Allergens and Asthma Study, which has previously been described in detail 5-7 (see this article's Online Repository at www.jacionline.org). This analysis includes 853 women for whom serum IgE to mouse allergen was measured. The study was approved by the Human Research Committee of the Brigham and Women's Hospital. Information on race was determined from the woman's response to questions asking her in which ethnic or racial groups she would classify herself (white, black, Hispanic, Asian, or other) as previously described 5 (see this article's Online Repository at www.jacionline.org). Other demographic and socioeconomic variables were obtained from screening questionnaires and have been previously described. 7A serum sample drawn at screening was analyzed for total IgE and IgE specific to a panel of allergens using the UNICAP system (Pharmacia, Uppsala, Sweden). 7 Furthermore, sera were assayed for IgE to mouse urinary allergen (Pharmacia ImmunoCAP e88) and to recombinant Mus m 1 (Mus musculus) using the streptavidin technique. 8 Results for recombinant Mus m 1 showed a strong quantitative correlation with IgE antibody to mouse allergen (r = 0.92; P< . 001). We defined sensitization to each allergen as CAP class level 1 or above (≥0.35 IU/mL).Each woman was asked detailed questions regarding her current and past history of respiratory disease, as previously described. 9 In the screening questionnaire, women were asked, "Has a doctor ever said that you have asthma?" These women were asked questions regarding asthma morbidity in the past 12 months. A bout of asthma lasting 1 week or more was defined as E-mail: wanda.phipatanakul@childrens.harvard.edu.. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript "prolonged illness," treatment in a hospital emergency room (ER) for asthma was defined as "use of a hospital ER," use of an oral steroid for asthma exacerbation was defined as "use of steroid," and having wheezing or whistling in the absence of a cold (upper respiratory viral infection) was defined as "wheeze without a cold." A positive response to any of the above defined asthma morbidity indicators ("prolonged illness," "use of hospital ER," "use of steroid," and "wheeze without a cold") was defined as "overall asthma morbidity."The univariable analysis was conducted using χ 2 for categorical variables and 2-tailed t...