Microbiological characteristics of pleural infection in adults: A 10-year retrospective study from a tertiary respiratory care hospital.

Introduction: Pleural infection is a high-mortality disease with a rising incidence in the past two decades. The knowledge of the main causative organisms is an important step for appropriate treatment. This study aims to describe etiologic and antibiotic resistance features of non-tuberculous pleural infections in adults in a tertiary care center specializing in the treatment of respiratory diseases.

Methods: This retrospective study was conducted at the microbiology laboratory of Abderrahmen Mami pneumology and phthisiology hospital, Ariana, Tunisia from January 2014 to December 2023. Pleural fluid samples were collected from adult patients with pleural effusion, from any cause, admitted to the different clinical services. Bacterial isolation and identification were performed by conventional techniques. The disk diffusion and the Vitek 2 methods were used for the susceptibility testing.

Results: During the study period, 5235 pleural fluid specimens were included. The sex ratio M/F was 2:1, and the median age was 57 years (interquartile range: 43-68 years). Culture was positive in 9.6 % of all cases, and in 31.4 % of purulent pleural fluids. The Gram stain had 41.5 % (95 % CI 35.6-47.6) sensitivity and 99.8 % (95 % CI 99.6-99.9) specificity in detecting microorganisms. A pleural fluid leukocyte count >10,000/mL showed a sensitivity of 51.4 % (95 % CI 47.7-55.8) and a specificity of 91.7 % (95 % CI 90.8-92.4). A total of 544 microorganisms were isolated. The main causative microorganisms were viridans streptococci group (32.1 %), Enterobacteriaceae (25.3 %), Staphylococcus aureus (10.2 %), and anaerobes (9.3 %). Among Enterobacteriaceae, 19 % were resistant to third-generation cephalosporins and 6.4 % to carbapenems. The resistance to penicillin G was detected in 19 % of the viridans streptococci group. Methicilline Resistant Staphylococcus aureus percentage was 14.2 %.

Conclusion: Conventional culture yielded 31.4 % positivity in purulent pleural fluids, and Gram-positive organisms were the leading cause of non-tuberculous pleural infections in adults over the past ten years. These results highlight the need for new molecular methods to improve culture-negative empyema diagnosis.