How can blood be contageous when it dries and you clean it i thought all stds and disease are dead from sitting out for awhile?

Because it is: Blood born STD's include the hepatitis B virus, that has been shown to remain potentially infectious for more than 6 months.Only a minute blood particle is needed to for transfer. Persons acquiring Heb B from a needle stick cleaning out an abandoned crack house learned the hard way.Each germ has its own limit if present in dried blood, but all body fluids should be considered a potential threat.