Purpose: The proportion of atypical pathogens in patient with AECOPD within mainland China is unknown. The objectives of this study were to determine the distribution of atypical pathogens among Chinese patients with AECOPD, to evaluate the clinical characteristics of different atypical pathogen infections, and to compare different detection methods for atypical pathogens.
Patients and Methods: Specimens were collected from patients with AECOPD from March 2016 to November 2018 at eleven medical institutions in eight cities in China. Double serum, sputum, and urine samples were obtained from 145 patients. Serological and nucleic acid tests were used to assess for Mycoplasma pneumonia  and Chlamydia pneumoniae ; serological, urinary antigen, and nucleic acid tests were applied to detect Legionella pneumophila . The clinical characteristics of atypical pathogen-positive and -negative groups were also compared.
Results: The overall positivity rate for Mycoplasma pneumoniae  was 20.69% (30/145), with the highest rate being 20.00% (29/145) when determined by passive agglutination.The overall positive rates for Chlamydia pneumoniae  and Legionella pneumophila  were 29.66% (43/145) and 10.34% (15/145), respectively. The most common serotype of Legionella pneumophila  was type 6. The maximum hospitalized body temperature, ratio of eosinophils, C-reactive protein (CRP) level, and procalcitonin (PCT) level of the Mycoplasma pneumoniae -positive group were significantly higher than those of the Mycoplasma pneumoniae -negative group. Patients in the Chlamydia pneumoniae -positive group smoked more, had higher proportions of comorbidities and frequent aggravations in the previous two years than those in the Chlamydia pneumoniae -negative group. Furthermore, the forced expiratory volume in one second to forced vital capacity (FEV₁/FVC) ratio assessment of lung function was higher, and the concentration of arterial blood bicarbonate (HCO₃⁻) was lower in the Legionella pneumophila -positive group than in the Legionella pneumophila -negative group.
Conclusion: Overall, atypical pathogens play an important role in AECOPD. Regarding the testing method, serological testing is a superior method to nucleic acid testing.
Keywords: COPD, exacerbations, Mycoplasma pneumoniae , Chlamydia pneumoniae , Legionella pneumophila