Degree

CYTOTOXICITY

CULTURE CONDITIONS

0

Absent

Discontinuous cytoplasmic granules; without cell lysis

1

Slight

Up to 20% of cells are vaguely round, without cytoplasmic granules; lysed cells are occasionally present

2

Mild

Up to 50% of cells are round, devoid of cytoplasmic granules, without extensive cellular lysis, and with empty areas between cells

3

Moderate

Up to 70% of layers contain rounded or lysed cells

4

Severe

Almost complete destruction of cellular layers