The World Health Organization (WHO) says at least 150 million patients live with the hepatitis C virus (HCV). According to an article in Hepatology​, a journal of the American Association for the Study of Liver Diseases, one genotype of HCV accounts for nearly half of these cases.

Researchers from the United Kingdom analyzed more than 1,200 medical studies from 1989—the time that HCV was discovered—through 2013 and then combined these results with estimates on HCV prevalence from the WHO Global Burden of Disease project. They found that HCV genotype 1 accounted for approximately 46% of all cases. Specifically, more than 83 million people are infected with genotype 1 HCV, one-third of whom live in East Asia.

“One possible hypothesis for the current global distribution of genotype 1 is the chance association of subtypes 1a and 1b with the international dissemination of contaminated blood and blood products during the twentieth century,” prior to HCV’s discovery in 1989, the article states.

Genotype 3, which claims 54 million cases, was the second most prevalent at 30%, followed by genotypes 2, 4, and 6, which together totaled nearly 23% of all cases. Genotype 5 represented less than 1% of these cases.

Although genotypes 1 and 3 are most prevalent worldwide, genotypes 4 and 5 tended to predominate in lower-income countries. According to the WHO, HCV-associated liver diseases cause approximately 350,000 to 500,000 deaths annually worldwide.

“While the HCV infection rate is decreasing in developed countries, deaths from liver disease secondary to HCV will continue increasing over the next 20 years,” the study’s lead co-author Dr. Jane Messina, with the University of Oxford in the U.K., said in a statement. “Understanding the global trends in the genetic makeup of HCV is the focus of our study and imperative in developing new treatment strategies that may save millions of lives around the world.”

The study represented data from 117 countries, about 90% of the global population.