An estimated 83 people a year become seriously ill in Japan with listeriosis, a potentially fatal encephalitic disease caused by listeria bacteria found in soil and rivers, according to a recent study by the Health, Labor and Welfare Ministry.

Of the confirmed cases of listeriosis, around 10 percent have resulted in death, according to the report, compiled by a research team at the National Institute of Health Sciences.

Listeriosis symptoms resemble those of influenza, including fever. In serious cases, however, it can lead to cerebral meningitis or blood poisoning.

Since the 1980s, there have been numerous reports in the United States and Europe of groups of people becoming infected after consuming raw foods such as natural cheese and uncooked meat. The ministry plans to launch a study in fiscal 2004 into the possibility of infection via food product consumption.

"We need to quickly set up regulations on unheated food," a member of the research team said.

The team conducted the study in 2001 and 2002, contacting emergency hospitals with 100 or more beds that had treated listeriosis patients, receiving responses from 773 hospitals. The team then analyzed 95 serious cases of people hospitalized in 1995 or later.

It found that the nine who died were 60 or over, with many having weakened immune systems.

The survey found that healthy adults were less likely to develop listeriosis, while children under 10 or adults aged 60 or older comprised 76 percent of the infected. All cases were sporadic, with no instances of group infection.

On possible infection channels, research team chief Shizunobu Igimi said, "Infection is possible via contact with water or animals, but given overseas examples, it is reasonable to assume food" is the main cause.