Rapid presumptive diagnosis of hantavirus cardiopulmonary syndrome by peripheral blood smear review

Hantavirus cardiopulmonary syndrome (HCPS) is a rare but frequently lethal acute zoonotic viral infection in rural North America. The rapidity of prog ression from febrile prodrome to cardiogenic shock and noncardiogenic pulmo nary edema requiring intensive care creates high diagnostic urgency and a n eed for a rapid screening tool. In this retrospective cohort study, 2 patho logists scored blinded peripheral blood smears from 52 patients with HCPS a nd 128 seronegative patients referred for diagnosis of suspected hantavirus infection. During the prodromal phase, thrombocytopenia was the only consistent abnorm ality and could be used to indicate hantavirus serologic testing. After the onset of pulmonary edema detected radiographically, the presence of 4 of 5 findings (thrombocytopenia, myelocytosis, hemoconcentration, lack of signi ficant toxic granulation in neutrophils, and more than 10% of lymphocytes w ith immunoblastic morphologic features) has a sensitivity for HCPS of 96% a nd a specificity of 99% and missed no patients with HCPS who required inten sive care. While each abnormality is commonly seen, the combination of at l east 4 of these CBC count data and peripheral blood smear findings can guid e early treatment and patient transport decisions until rapid, specific, se rologic testing becomes widely available.