Do bacteria have a role in asthma development

The relationship between the microbial world and asthma is not well understood. Although we know that the most potent triggers of wheezing attacks are viruses, we do not understand whether and how they contribute to disease onset and progression. Even less is known about the relationship between asthma and bacteria. The clearest evidence stems from studying asthma exacerbations or wheezing episodes. In clinical studies viruses can be detected in up to 90% of such episodes 1, with rhinovirus being most commonly identified, followed by respiratory syncytial virus (RSV) in the first years of life. Other viruses such as parainfluenza, metapneumovirus, coronavirus, adenovirus, influenza and enteroviruses have also been implicated, mostly in older patients. In ∼10% of episodes multiple viruses were found 2. Most recently, the H1N1 virus has been reported to be more prevalent among asthmatics than other patients 3. In a recent high-risk birth cohort, children with wheezing illnesses triggered by rhinovirus infections early in life were at risk for the subsequent development of asthma up to 6 yrs of age 2. However, it remains unclear whether viral infections are causal factors for the new onset of disease by impacting on the host's immune response or whether they merely unmask a host's underlying susceptibility to develop asthma by triggering exacerbations. It has been proposed that asthmatics may have subtle deficiencies in their immune response resulting in reduced antiviral activity and increased susceptibility for viral infections, especially of the lower respiratory tract. Corne et al. 4 recruited 76 cohabiting couples where only one partner had asthma and compared the frequency, severity and duration of rhinovirus infection between them. The authors found that asthmatics develop more severe and longer lasting respiratory symptoms following rhinovirus infections than their spouses 4. Message et al. 5 experimentally infected adult …