Respiratory tract infection (RTI) is a significant cause of asthma exacerbation. This study explored clinical characteristics and the incidence of respiratory pathogens in patients with asthma exacerbations before the COVID-19 pandemic. 

We recruited the asthmatic patients treated in participating hospitals for exacerbation. Conventional sputum culture was used for typical bacteria. In addition, we used commercially available multiplex polymerase chain reaction (PCR) tests to detect atypical pathogens such as atypical respiratory bacteria and viruses.

Four hundred fifty-six patients were enrolled in this study. About half of the exacerbation occurred in the winter, and a quarter developed in the spring. Almost all patients (97%) were hospitalized for about 10.0 days.

The respiratory pathogen was detected in 53% of the patients. One hundred twelve patients (24.6%) had positive results for bacteria. Viruses were detected in 170 (37.3%) patients (Figure). Among the bacterial pathogen, pneumococcus was the most frequently isolated. Influenza A virus was the most common viral pathogen, followed by rhinovirus. Although the bacterial infection rate was relatively low, 90.0% of patients were given antibiotics. 

Our study showed that RTI caused about half of the hospitalized asthma exacerbations. Pneumococcus and influenza A were the most frequently isolated bacteria and viruses. A well-designed prospective study is needed to validate our findings.