Fearing a potential AIDS explosion, Japan will step up its monitoring of people infected with the deadly disease by conducting a more thorough study into infection trends.

The Health, Labor and Welfare Ministry's move comes in the wake of a sharp rise in the number of people suffering sexually transmitted diseases, such as chlamydia and gonorrhea.

Ministry officials said they also hope to establish a method to estimate the number of infected people who are not counted in the tally.

It is believed there are about 10,000 unreported AIDS cases in Japan. One of the reasons for this high number is that many people are unaware they have been infected.

It is also difficult for the ministry to track the number of infected people because it lacks relevant data, such as the source of infection.

Half of the new cases in 2002 were contracted through male homosexual activity. But it is unknown whether this marks a rise or that more people are undergoing AIDS tests.

The ministry plans to set up a task force of epidemiology experts to come up with ways to collect more data.

The number of AIDS cases has been rising since the ministry began tracking the disease in 1985.

As of the end of 2002, there were about 5,100 infections and about 2,600 people with full-blown AIDS, according to ministry statistics. This tally excludes the estimated 1,400 patients infected with AIDS via tainted blood products.

In 2002, the reported cases of chlamydia and gonorrhea rose by about 1.6 times from 1999 figures. Experts say this is evidence that people are not using condoms and have multiple sexual partners.

The rapid spread of AIDS throughout Asia is sparking concern that there could be a huge outbreak in Japan.