Thoracic actinomycosis in the 21st century – A re-emerging infection: A case series from India

ABSTRACT Background: Thoracic actinomycosis is a rare, chronic granulomatous infection caused by Actinomyces species and is well known for mimicking tuberculosis, fungal infections, and malignancy. Although considered uncommon in the antibiotic era, recent reports suggest a re-emergence of this entity, possibly due to increasing immunocompromised populations and improved diagnostic techniques. Its nonspecific clinical and radiological features frequently lead to delayed diagnosis and inappropriate empirical therapy. Methods: We describe a case series of four patients diagnosed with thoracic actinomycosis at a tertiary care center in India. Clinical presentation, radiological findings, diagnostic modalities, treatment strategies, and outcomes were retrospectively analyzed. Results: The cases included middle-aged men and women presenting with nonspecific respiratory symptoms and non-resolving pulmonary infiltrates. Radiological appearances closely mimicked tuberculosis and malignancy. Definitive diagnosis was established using bronchoscopic biopsy, CT-guided biopsy, surgical excision, or sputum examination, demonstrating characteristic sulphur granules and branching filamentous organisms. All patients received prolonged courses of penicillin-group antibiotics. Treatment resulted in complete or near-complete radiological resolution and favorable clinical outcomes, with no mortality reported. Conclusion: Thoracic actinomycosis remains an important diagnostic consideration in patients with persistent pulmonary lesions, particularly in tuberculosis-endemic regions. Increased awareness and a high index of clinical suspicion are essential to prevent misdiagnosis and unnecessary invasive procedures or prolonged antitubercular therapy. Wider availability and use of bronchoscopic and minimally invasive diagnostic techniques may facilitate earlier recognition and effective treatment. Our experience supports the view that thoracic actinomycosis is a re-emerging infection that should be included in the differential diagnosis of non-resolving pulmonary infiltrates/cavities.