SHABAS EL SHUHADA, Egypt — Abdel Gawad Ellabbad knows exactly how he was infected with hepatitis C.

As a schoolboy in this Nile Delta rice-farming village, his class marched to the local clinic every month for injections against schistosomiasis, a parasitic disease spread by water snails.

A nurse would boil the syringes, fill each with five doses and then jab five boys in a row with a single needle.

“I didn’t want that hot needle touching me, so I thought I’d be smart,” Mr. Ellabbad, 52, said. “I let the other guys go first.”

Six million Egyptians were infected with hepatitis C by unsterile needles during the country’s decades-long fight against schistosomiasis. The virus spread insidiously; today, at least 10 percent of Egyptians, nearly nine million people, are chronically infected, the highest rate in the world.