You have 1 mL of nasal wash from patients infected with SARS-CoV-2 virus. You follow the standard plaque-forming assay protocol to determine the number of infectious particles per mL. You have performed a 1 in 10 dilution series. After 6 serial dilutions, you added 0.1 mL from your 10^-4, 10^-5, and 10^-6 dilutions to MDCK cells growing in wells of cell culture plates. You obtain 12 plaques and 3 plaques in the wells of cells inoculated with 10^-5 and 10^-6 dilutions, respectively. What is the concentration of the virus in the nasal wash?