Diagnostic Dilemma of Herpes Simplex Virus Type 1 Pneumonia or Colonization: A Case Report.

Herpes simplex virus type 1 (HSV1) pneumonia presents diagnostic challenges due to there being no gold-standard criteria currently. Specimens from bronchoalveolar lavage can increase specificity, and cytohistological examination can prove virus infection. Patients with high viral load have been reported with poor outcomes and benefited from antiviral agent. We describe an 80-year-old man with severe pneumonia who initially showed improvement without antiviral therapy, despite viral inclusion bodies on sputum cytology and positive HSV1 polymerase chain reaction from sputum, though subsequent clinical deterioration due to infection necessitated intensive care. This case highlights the complexities of diagnosing and managing HSV1 pneumonia, emphasizing the importance of integrating clinical suspicion, radiological imaging, and laboratory tests for timely therapeutic decisions in critically ill patients.