Drug resistance, molecular epidemiological characteristics and risk factors for secondary MRSA infection in elderly patients with chronic obstructive pulmonary disease

OBJECTIVE To explore the drug resistance, molecular epidemiological characteristics and risk factors for secondary methicillin-resistant Staphylococcus aureus (MRSA) infection in elderly patients with chronic obstructive pulmonary disease (COPD). METHODS A total of 160 elderly COPD patients who were complicated with secondary infection and treated in Hospital of Changchun University of Technology from May 2020 to May 2022 were enrolled in the study. The etiological test, identification of MRSA and drug susceptibility testing were carried out for the enrolled patients. The risk factors for the secondary MRSA infection in the COOPD patients were analyzed, and the drug resistance genes and virulence genes in the MRSA strains were detected by polymerase chain reaction (PCR). RESULTS Totally 257 strains of pathogens were isolated from the patients, among which Pseudomonas aeruginosa and S.aureus were dominant.Totally 28 patients had MRSA infection, the isolation rate of MRSA was 60.87% (28/46), and the rest of 132 patients had non-MRSA infection. The drug resistance rate of the MRSA strains to β-lactams was 100.00%, and the drug susceptibility rates to vancomycin, teicoplanin and linezolid were 100.00%. The positive rates of fnbA, hla and hld were the highest (100.00%) among the virulence genes in the MRSA strains; the positive rate of mecA was the highest (100.00%) among the drug resistance genes. The proportions of patients with course of disease no less than 3 years, diabetes mellitus, mixed infection, endotracheal/intonation, mechanical ventilation, intensive care unit (ICU) stay, length of hospital stay no less than 7 days before isolation of strains, use of antibiotics no less than 5 times/year and use of immunosuppressants were significantly higher in the MRSA group than in the non-MRSA group (P<0.05). Complication with diabetes mellitus and use of antibiotics were the risk factors for secondary MRSA infection in the elderly patients with COPD (P<0.05). CONCLUSION The incidence of secondary MRSA infection is high among the elderly patients with COPD. The MRSA strains are resistant to most of the antibiotics and carry with multiple drug resistance genes and virulence genes, therefore, it is necessary to attach great importance to the high-risk MRSA infection patients with diabetes mellitus and use of antibiotics no les than 5 times/year and reasonably use antibiotics.