FLORENCE, Italy (Reuters Health) - Poorly cleaned glass syringes used to administer the polio vaccine in the 1950s and 60s could have spread the hepatitis C virus from person to person in southern Italy, researches from Italy's National Cancer Institute suggested this week.

The accidental spread of the virus might explain why southern Italy has a particularly high rate of the chronic liver disease, suggest Dr. Maurizio Montella and colleagues.

In the mid 1950s and 1960s, an injected vaccine known as the Salk vaccine was used to protect against the crippling disease polio. In southern Italy, reusable glass syringes were used to deliver the vaccine until the new oral version, known as the Sabin vaccine, was introduced in 1965. The authors' theory is that the syringes, if not properly sterilized, may have spread the hepatitis C virus.

Montella told Reuters Health Wednesday there was already some indirect evidence linking the glass syringes used for the older vaccine to high hepatitis C rates.

"The phenomenon is circumscribed to certain areas -- where glass syringes were widely used, there is an increase of hepatitis C cases," he said.

To look closer at the link, he and others drew on a previous investigation that included a sample of 1,908 people aged 30 to 60 years.

The subjects were originally enrolled as healthy "controls" in another study. They were known not to have used intravenous drugs or to have had blood transfusions, both of which can spread the disease.

Tests showed that seven percent of men and five percent of women aged 40 to 49 years had antibodies to hepatitis C, suggesting infection with the virus. People born between the 1940s and early 1960s were nearly three times as likely as younger subjects to have the virus, they reported in this month's Journal of Medical Virology.

Overall, about six percent of older adults had been infected with the virus compared with about two percent of those aged 30 to 39.

The prevalence of hepatitis C is about 1.8 percent in the U.S. and ranges from 0.5 percent to nine percent in Western Europe.

"This is indisputable data, and it is linked to the years when the Salk polio vaccination was administered," Montella said. "The high rate of HCV is most likely attributable to a misuse and reuse of needles and glass syringes being inadequately sterilized."

Because chronic hepatitis C infections may not cause any symptoms, "it will be useful to inform the population of southern Italy about the implication to their future health," the authors write in the article.

About four million people in the United States and 150 million worldwide have hepatitis C, an infection of the liver that is spread by contact with blood and other body fluids.

About 20 percent of people infected with the virus will develop severe and potentially fatal liver damage, or cirrhosis, which in turn increases a person's risk of liver cancer.

SOURCE: Journal of Medical Virology 2003;70:49-50.