In the 1990s, blood selling became popular in Henan and other parts of Central China, especially among poor farmers as a means to earn extra money. Many blood collecting stations operated illegally and used unsanitary practices for blood collection, including:  - Pooling and reinjection of blood  - Unclean spinning of blood  - Shared needles As a result, estimates of 60-80% of the adult population is infected with HIV in numerous villages. The exact extent of the tragedy remains unknown; estimates of up to one million are infected in Henan province.