Epidemiological relationships between the common cold and exacerbation frequency in COPD

Higher exacerbation incidence rates in chronic obstructive pulmonary disease (COPD) are associated with more rapid decline in lung function and poorer quality of life, yet the mechanisms determining susceptibility to exacerbation remain ill-defined. The same viruses responsible for common colds are frequently isolated during exacerbations. The current authors hypothesised that exacerbation frequency may be associated with an increased frequency of colds, and investigated whether increased exacerbation frequency was associated with increased acquisition of colds, or a greater likelihood of exacerbation once a cold has been acquired. A total of 150 patients with COPD completed diary cards recording peak expiratory flow, and respiratory and coryzal symptoms for a median 1,047 days. Annual cold and exacerbation incidence rates (cold and exacerbation frequency) were calculated, and the relationships between these variables were investigated. This analysis is based on 1,005 colds and 1,493 exacerbations. Frequent exacerbators (i.e. those whose exacerbation frequency was greater than the median) experienced significantly more colds than infrequent exacerbators (1.73 versus 0.94.yr(-1)). The likelihood of exacerbation during a cold was unaffected by exacerbation frequency. Patients experiencing frequent colds had a significantly higher exposure to cigarette smoke (46 versus 33 pack-yrs). Exacerbation frequency in chronic obstructive pulmonary disease is associated with an increased frequency of acquiring the common cold, rather than an increased propensity to exacerbation once a cold has been acquired.