Viral infections may have clinically relevant phenotypical CPEs. For example, with the hepatitis C virus (HCV), liver steatosis is characteristic enough of the virus that it may be used to help identify the genotype, the genetic composition of the virus. HCV genotype 3 patients are significantly more likely to develop liver steatosis than those with genotype 1. Also, CPEs may be used during research to determine the efficacy of a new drug. An assay has been developed that screens the dengue virus's CPEs in order to assess cell viability.