Figure 5. Ultrastructural characteristics of a bronchial alveolar lavage (BAL) from a patient with severe acute respiratory syndrome. A) Infected cells from a BAL specimen, showing numerous cytoplasmic and extracellular virions (arrowheads). Note the region of double-membrane vesicles (arrow), a common feature of coronavirus-infected cells. B) At higher magnification, double-membrane vesicles (arrow) are shown to contain diffuse, granular material. Bars, 1 μm.