Background: Several infectious lung diseases often develop in patients with Rheumatoid arthritis (RA), especially during immunosuppressive medication, including disease-modifying anti-rheumatic drugs (DMARDs). The present study aimed to determine the role of respiratory tract bacterial infection in RA activity.
Methods: Blood and sputum samples were collected from 31 patients with RA and 12 healthy subjects as control. The bacterial isolates were isolated and identified in collected sputum by biochemical tests and Vitec 2 system.
Results:  In the present study, thirty-one patients with RA were compared with 12 healthy subjects.  Eight patients with RA were not infected with pathogenic bacteria (RA-NIPB) (25.8%). Twenty-three RA patients were infected with pathogenic bacteria (RA-IPB) (74.19%). From 23 RA-IPB, 10 RA patients were infected with Staphylococcus aureus, 6 RA patients were infected with Klebsiella pneumonia, 4 RA patients were infected with Streptococcus pneumoniae, and 3 RA patients were infected with Pseudomonas aeruginosa. No pathogenic bacteria were isolated from the sputum of a healthy subjects. There was no significant difference between RA-NIPB and RA-IPB in terms of the level of disease activity score DAS28.
Conclusion: The current study showed that patients with RA have a higher incidence of being infected with pathogenic bacteria than the healthy control group. No significant effect of bacterial species infection on the level of DAS28. The present study is the pioneer study that showed no effect of bacterial respiratory infections and different RA treatments on RA disease activity.