Purple Pleural Effusion due to Acinetobacter baumannii Infection: A Rare Case Report

Pleural effusion (PE) is a frequent clinical condition with diverse etiologies including heart failure, infections, and malignancies. While the color of pleural fluid is rarely considered diagnostic, unusual discolorations may offer important clinical clues. We report what appears to be only the third documented case of purple PE (PPE) in the medical literature. This case was associated with Acinetobacter baumannii infection, a rarely reported cause of PPE, providing additional insight into its potential pathophysiology.

A 54 year-old obese male with multiple comorbidities-including COPD, heart failure, and recent pulmonary embolism-was admitted with acute respiratory failure. He was found to have a right-sided PE requiring drainage. Initial fluid analysis revealed an exudative, lymphocyte-predominant effusion with no evidence of infection. However, the fluid in the drainage bag gradually turned deep purple, and Acinetobacter baumannii was later isolated from the catheter and collection bag. The patient was treated with colistin and meropenem, with full clinical recovery and resolution of discoloration.

Although the exact mechanism remains unclear, PPE may share pathophysiologic pathways with Purple Urine Bag Syndrome, involving bacterial metabolism of tryptophan-derived compounds. This case highlights the importance of visual inspection of pleural fluid and emphasizes that unusual discoloration-while not diagnostic in itself-should prompt thorough microbiological and biochemical evaluation.

Unusual pleural fluid discoloration should prompt immediate microbiological evaluation, as it may indicate infection with uncommon or multidrug-resistant organisms, even in the absence of typical infection signs.