A five-year survey of blood donors suggests that about 1.5 million people in Japan have contracted hepatitis C virus (HCV), narrowing down an earlier, broader estimate, according to a health ministry study group.

The research found that 0.5 percent of around 3.48 million first-time donors between 1995 and 2000 were found to have HCV antibodies, the group from the Health, Labor and Welfare Ministry said in a presentation given at an informal meeting in Tokyo.

A study by the Japanese Red Cross Society estimates that 70 percent of all who have HCV antibodies actually carry the virus, and the remainder are those who carry antibodies as a result of having contracted HCV in the past.

The blood donor data cover those aged between 15 and 69. The group thus estimated from the nation's population data that in this age bracket, those with HCV total 885,000. Of these, some 760,000 are aged 40 or older.

The group also assumed that the infection rate is slightly higher for those of more advanced age, putting the estimated rate at 3 percent.

Given all these assumptions, the overall number of those infected with HCV comes to around 1.5 million in Japan, according to the group.

The previous estimate, produced by another group of health ministry experts, put the overall number of infected people at somewhere between 1 million and 2 million.

HCV causes hepatitis C, or disease of the liver, which often does not show symptoms in many people while becoming serious.

Hiroshi Yoshizawa, professor at Hiroshima University, who joined the latest ministry research, thus noted the importance of home doctors and hepatitis specialists working closely together so they can spot as many infected patients as possible through doctor visits.

Hepatitis C is transmitted primarily by blood and blood products, as in blood transfusions or intravenous drug use.