Chlamydia pneumoniae and asthma
I read with interest the recent report by Cook et al 1 in which they report that, compared with hospital controls, outpatients with chronic severe asthma had significantly more C pneumoniae antibody titres (IgG 64–256 and/or IgA ≥8) indicating previous infection, whereas unselected patients admitted to hospital for acute asthma attacks had titres similar to controls. They also found that serological evidence of acute (re)infection (presence of IgM, a fourfold change in titre, and/or IgG titre ≥1:512) was equal among groups.
These data are in accord with previous evidence suggesting an important role for chronic C pneumoniae infection as a promoter of asthma symptoms but a lesser role for acute infection as a cause for asthma exacerbations.2 An additional recent report of positive therapeutic responses to antibiotics in severe steroid dependent asthmatic patients (aged 13–65) further supports the possibility that antibody titres indicative of “previous infection” may also indicate persistent chronic infection.3
Acute primary (presence of IgM) or secondary (fourfold change in titre without IgM) C pneumoniae infection has been reported to initiate asthma in previously non-asthmatic individuals.4 Since the incidence of asthma in adults is very small (around one per 1000 per year) it is likely that most of the acute exacerbations occurred in patients who had had previous wheezing episodes. It would be interesting to know whether Cook et al can retrospectively identify any patients who had their very first wheezing episode; this might be easier in general practice than in a hospital based study.
