RIYADH, 11 April — The Riyadh Medical Complex has discovered that four people who donated blood to the complex’s blood bank last year were HIV positive.

Laboratory tests also revealed that 906 blood donors — out of a total of 25,125 — during the same period were suffering from serious liver infections such as Hepatitis B and Hepatitis C, according to a hospital source.

The tests found that 496 of the Saudi donors were suffering from Hepatitis B and 60 from Hepatitis C, while 190 non-Saudis had Hepatitis B and 160 Hepatitis C.

Hepatitis B and C are transmitted through blood transfusion and sexual contact. The source made clear that these diseases could not spread through saliva, but wounds or cuts in the mouth might lead to infection.

Hepatitis C is considered less dangerous than B, though the former causes liver cirrhosis. There is no vaccination against the C strain.

About 11,000 Saudis are likely to have contracted HIV, according to World Health Organization estimates. Recent reports said that at least 225 AIDS patients had been receiving treatment at King Faisal Hospital in Riyadh.