 SCP-340 is produced by a human-specific virus, which preferentially colonizes the nasal cavities. The virus cannot be identified according to the Baltimore classification scheme, leading Foundation researchers to believe it was engineered by parties as yet unidentified. The presence of genes from both HIV and the SARS coronavirus supports this hypothesis. An incubation period, with a mean duration of three days, occurs upon initial exposure to the virus. Influenza-like symptoms will then develop. An increased production of mucus has been observed in all known cases, and will persist after other symptoms have ceased. Virulence is highest during the first five days of infection, but viral particles have been detected up to a month after exposure and foundation trials. Any time after infection, a high blood concentration of carbon dioxide will trigger production of SCP-340.