To investigate the distribution of pathogenic bacteria in patients with chronic obstructive pulmonary disease (COPD) complicated with pulmonary infection, and to analyze the effect of related serum cytokine levels on the clinical outcome of patients.

From February 2015 to February 2017, a total of 178 patients with COPD complicated with pulmonary infection were treated in Heji Hospital Affiliated to Changzhi Medical College. Virus identification was done by nine respiratory tract viruses fluorescent labeling PCR. The species of bacteria were identified by BD BACTEC^? FX40 automatic bacterial identification instrument. Serum interleukin (IL-6 and IL-10), interferon (IFN-α and IFN-γ) and tumor necrosis factor (TNF-α and TNF-β) were detected by enzyme linked immunosorbent assay (ELISA); while the effect of the above indexes on the clinical outcome of COPD patients complicated with pulmonary infection were analyzed, respectively.

Total of 178 patients with COPD were divided into virus infection group (36 cases, 20.22%) and bacterial infection group (142 cases) according to the detected pathogen. Among the 142 cases with bacterial infection, 47 (26.41%) patients were with Gram-positive bacteria infection and 95 (53.37%) with Gram-negative bacteria infection. The levels of serum IL-6, IL-10, IFN-α, IFN-γ, TNF-α and TNF-β in bacterial infection group were significantly higher than those of virus infection group, all with significant differences (all P < 0.001). The levels of IL-6, IL-10, IFN-α, IFN-γ, TNF-α and TNF-β of patients with hospitalization days ≥ 7 days and the died cases were significantly higher than those with hospitalization days < 7 days and the survivors, respectively, all with significant differences (all P < 0.001). The results of Logistic regression analysis showed that elderly, Global Initiative for chronic obstructive lung disease (GOLD) grade (3/4), Gram-negative bacterial infection and high level of IL-6 were all important factors affecting the short-term clinical outcome of patients (P = 0.01, 0.01, 0.04 and 0.03). And elderly, GOLD grade (3/4), smoking history, hospitalization days ≥ 7 d, forced expiratory volume in the first second (FEV1) (% predictive value) were important factors for the long-term clinical outcome of the patients (all P < 0.05).

Gram-negative bacteria infection is most common among patients with COPD complicated with pulmonary infection. COPD and complicated with pulmonary infection is the most common infection of Gram-negative bacteria. Due to the different kinds of pathogenic bacteria, the levels of cytokines such as IL, IFN and TNF vary greatly; among whom, IL-6 has a significant effect on the short-term clinical outcome of patients.