The virus is blood-borne, and the most common source of infection is needle-sharing among people who use illicit drugs. In the United States before 1992, when a test became available to screen donated blood, many cases were caused by transfusions. In countries where the blood supply is not screened, transfusions still pose a risk. Needlestick injuries and other hospital accidents may also cause some cases.

There is no vaccine to prevent the infection, so treatments have long been eagerly sought.

The drugs covered in the new report include two blockbusters, Sovaldi and Harvoni, both made by Gilead Sciences and priced at $1,000 a pill, with billions of dollars in sales. Sovaldi was approved in 2013, and Harvoni in 2014. These drugs and other antivirals can cure the disease in 12 weeks in many patients.

Earlier drugs were less effective, had to be taken for much longer and had harsh side effects that left many patients unable to finish the course of therapy.

About 250,000 people took the newer drugs in 2015, the report said, at tremendous expense: $55,000 to $125,000 per patient. In those treated during the year ending June 30, 2016, the report identified 524 with liver failure, 165 of whom died. Of those with liver failure, 386 were from outside the United States. An additional 1,058 had severe liver injury, and in 761 the drugs appeared not to work.

But whether the drugs were to blame is not known. The problems were observed by doctors who suspected drugs were the cause, but that does not prove cause and effect. And details about the patients’ medical histories were not available.

A spokesman for Gilead, Mark Snyder, wrote in an email, “We closely assess both post-marketing safety reports as well as safety data from our clinical trials on an ongoing basis and have found no suggestion of a causal relationship between Sovaldi or Harvoni and liver failure.”

He added that Gilead’s drugs had been approved for people with severe liver disease from hepatitis C, and that some would inevitably suffer liver failure despite the best treatment.