Impact of viral infection on acute exacerbation of asthma in out-patient clinics: a prospective study

The prevalence of viral infection triggering asthma exacerbation and its impact on the symptoms and duration of exacerbation are unclear.Asthma and healthy control subjects were recruited from the First Affiliated Hospital of Guangzhou Medical University between February 2012 and February 2013. Nasal swabs were collected, and respiratory viruses were detected by polymerase chain reaction (PCR). All patients completed questionnaires and a lung function test. Some were followed up for 4 weeks, and symptom changes were evaluated via asthma diaries.In total, 70 patients with acute asthma exacerbations were recruited. Among them, 34 patients (48.6%) completed the 4-week follow-up study. Another 65 patients with stable asthma and 134 healthy volunteers were also included in this study. The rate of positive viral detection via PCR in acute asthma exacerbation patients was 34.2% (24/70), which is significantly higher than that of stable asthma (12/65; 18.5%; P=0.038) and normal control patients (18/134; 13.4%; P0.001). Among the viral-positive subjects, the number of viral copies was significantly higher in acute asthma exacerbation patients [(5.00±4.63) ×10(7) copies/L] (mean ± SD) than those in stable asthma patients [(1.24±1.44) ×10(6) copies/L; P0.001] or in healthy controls [(1.44±0.44) ×10(6) copies/L; P0.001], whose viral loads were not significantly different from one another (P=0.774). During the 4-week follow-up period, the cough scores on days 1 and 3 were significantly higher in the viral-positive group than in the viral-negative group (day 1: P=0.016; day 3: P=0.004). However, there were no significant differences between these two groups for other tested symptoms, such as dyspnea and total recovery time (P0.05).Respiratory viruses may be involved in acute asthma exacerbations, inducing more prominent and persistent cough symptoms.