Effused and Confused: A Case of Severe Adenovirus Pneumonia in a Teen.

Adenovirus is a common pathogen responsible for respiratory infections, including pneumonia, predominantly in pediatric populations but also in immunocompromised adults. This case report details an 18-year-old immunocompetent male presenting with severe lobar pneumonia and pleural effusion, initially suggesting a bacterial origin. Despite antibiotic treatment, the patient's symptoms persisted, prompting further investigation. The diagnostic approach included polymerase chain reaction testing on upper-airway specimens, pleural effusion, and bronchoalveolar lavage, which identified adenovirus as the causative agent. This diagnosis confirmed that adenoviral pneumonia could present with radiologic findings similar to bacterial infections, such as lobar consolidation and pleural effusion, which are typically considered suggestive of bacterial etiology. The successful identification of adenovirus from pleural effusion, previously reported in bronchoalveolar lavage or upper-airway specimens, is a novel aspect of this case, underscoring the importance of comprehensive diagnostic testing, especially in atypical or severe cases that fail to respond to empiric therapy. Antimicrobial therapy was continued to prevent secondary bacterial infections, but the primary treatment was supportive care. The patient showed significant clinical improvement and was discharged in stable condition after seven days, with no residual symptoms at follow-up. This case highlights the need for careful consideration of viral pathogens, particularly adenovirus, in the differential diagnosis of severe pneumonia, even in the presence of pleural effusion, to avoid unnecessary antibiotic escalation and guide appropriate management. Early viral identification and tailored treatment strategies are essential, particularly in cases that do not respond to conventional therapies. Furthermore, this case emphasizes the value of advanced diagnostic techniques in identifying less common pathogens and reducing the risks of unnecessary antibiotic use.