To explore the clinical diagnosis experience of pleural effusion caused by paragonimus infection, so as to avoid misdiagnosis or delayed diagnosis.

The clinical data and treatment of 6 patients with exudative pleural effusion caused by paragonimus infection in the Department of Respiratory and Critical Care Medicine of Taihe Hospital of Shiyan City from May 2018 to December 2022 were analyzed, retrospectively. Data included the demographic characteristics, clinical symptoms, exposure history, laboratory results, pleural fluid cytology, pleural biopsy histopathology, intradermal test for paragonimus-specific antigen, outcome of antiparasitic treatment and follow-up results of 6 patients were collected, respectively.

Three male and three female patients were enrolled, with a mean age of (46.5 ± 5.1) years old. The absolute count and percentage of eosinophils in peripheral blood elevated to varying degrees (12.6%-54.0%). Cytological examination of pleural fluid of four patients showed a small to large number of eosinophils. Four patients underwent thoracoscopic pleural biopsy, of which 3 patients showed extensive eosinophilic infiltration in the interstitium, 1 patient showed parasite eggs and 1 patient showed nonspecific inflammation. There were 4 cases among the 6 patients had a history of intaking fresh water crabs or stream water. Meanwhile, 6 patients were positive in intradermal test of paragonimus-specific antigen (IDTPA) and serum enzyme-linked immunosorbent assay (ELISA) for paragonimus antibody. Paragonimus infection in extrapulmonary organs was excluded and pleural effusion caused by paragonimus was confirmed. All the 6 patients received oral praziquantel treatment (25 mg/kg, 3 times a day, continuous 3 days as a course of treatment, intermittent 7 days and then the second course). Chest computed tomography (CT) showed reduced or disappeared pleural effusion after treatment.

In the diagnosis of unexplained pleural effusion, paragonimus infection should be highly suspected in patients with elevated eosinophils in peripheral blood, pleural fluid, or pleural tissue, and with a history of raw freshwater crab or stream water intaking, especially in patients from areas which paragonimus infection is endemic.