Cytologic findings in effusions from patients with SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is associated with "flu-like" upper respiratory tract symptoms and pneumonia. Body cavity effusions develop in a subset of patients with advanced disease. Although SARS-CoV-2 is known to be present in certain body fluids (eg, blood) of COVID patients, it remains unclear if body cavity fluids are sites of infection. Our aim was to characterize the cytologic and clinical findings in COVID-19 patients with effusions.

A record search for all cases of body cavity effusion cytology in SARS-CoV-2 positive patients from March 1, 2020, to September 1, 2020, was performed. Clinical history, fluid chemical analysis, cytologic findings, and patient outcomes were recorded. All cytology slides were reviewed. In situ hybridization (ISH) targeting SARS-CoV-2 spike protein transcript (V-nCoV2019-S) was performed on cell block material in all cases.

A total of 17 effusion cytology cases were identified among 15 COVID patients, including 13 pleural, 2 pericardial, and 2 peritoneal. Most (13 of 15) patients were hospitalized for COVID complications. Eight patients died during hospitalization, 7 from COVID complications. All fluids were transudative by protein criteria. Lymphocytic or histiocytic inflammation predominated in 12 of 17 cases. Five exhibited hemophagocytosis. No viral cytopathic changes or extra-medullary megakaryocytes were seen. Viral RNA was not detected in any case by ISH.

Body cavity effusion is an ominous finding in patients with advanced COVID-19 disease. Such effusions tend to be transudative with lymphohistiocytic inflammation, and commonly exhibit hemophagocytosis, an otherwise rare finding in effusion cytologies. No direct infection of cellular elements by SARS-CoV-2 was identified by ISH.