Unexplained autumn increases in hospital admissions for asthma have been reported in many countries, including the United States, Canada, England and Wales.To investigate the role of infection, the association was tested between hospital admissions for asthma and respiratory infections among preschool children in Metropolitan Toronto, Canada during the period 1981 to 1989. The seasonal pattern in overall hospital utilization was assessed by admissions for nonrespiratory diseases. Time series analysis was used to remove potentially confounding temporal trends and the influence of correlated errors.A fourfold increase in asthma admissions occurred between July and October unaccompanied by similar increases in nonrespiratory admissions. Admissions began increasing during the third week of August, peaked during the third week in September, and slowly decreased during November and December. After adjusting for serial correlation, trends, climate, ambient air pollution and aeroallergens, the seasonal pattern of respiratory infection explained 14% of the variance in asthma admissions.Based on seasonal patterns, respiratory infection is the major identifiable risk factor for the large autumnal increase in asthma admissions.

Background: Considerable interest exists in the potential therapeutic value of dietary supplementation with the omega-3 fatty acids. Given the interplay between pro-inflammatory omega-6 fatty acids, and the less pro-inflammatory omega-3 fatty acids, it has been thought that the latter could play a key role in treating or preventing asthma. The purpose was to systematically review the scientific-medical literature in order to identify, appraise, and synthesize the evidence for possible treatment effects of omega-3 fatty acids in asthma.

Our objective was to determine whether methotrexate is an effective steroid-sparing agent for patients with severe asthma. Published reports of controlled trials assessing the use of methotrexate in asthma were identified by a search of the MEDLINE, EMBASE, CINAHL, Biological Abstracts on CD, and Current Contents databases. Bibliographies from identified studies and from review articles were manually searched. Published and unpublished reports in any language were identified and assessed for inclusion in the meta-analysis. We selected randomized, double-blind, placebo-controlled trials in which low-dose methotrexate was administered to corticosteroid-dependent asthmatics, and oral steroids were subsequently tapered according to the patients' clinical status. Data were extracted independently by two reviewers. For all eligible trials, the mean reduction in oral corticosteroid dose, the mean change in FEV1, and the standard deviations, were calculated for the treatment and control groups. Data concerning side-effects of therapy were also extracted. Data from 12 studies, reporting on a total of 250 patients, were pooled using a weighted average method, with weights proportional to the inverse of the variance of the treatment effect. Compared to placebo, the use of methotrexate was associated with a pooled 6.0% improvement in FEV1 (95% CI, 1.0-11%) and an 18.2% reduction in oral steroid use (95% CI, 11.7-24.7%). This corresponded to a 3.3 mg day-1 greater reduction in oral steroid use for patients taking methotrexate than for those taking placebo (95% CI, 2.1-4.4 mg day-1). Gastrointestinal complications and transient increases in liver enzymes were more common in patients randomized to methotrexate. Three potentially life-threatening side-effects (two pneumonias and one liver dysfunction) occurred in 159 patients randomized to methotrexate vs. none in those patients on placebo. It was concluded that methotrexate allowed a modest reduction in oral corticosteroid compared to patients receiving placebo. The benefit is relatively small, however, and should be balanced against the potential for side-effects associated with the use of methotrexate.