By James Rodgers BBC News

More than 70 people, mostly children, contracted the virus, apparently from infected blood transfusions.

It is not known how the defendants are expected to respond to the charges.

The trial is being held behind closed doors; even the street in which it is taking place has been cordoned off, according to reports from Shymkent.

Court officials will not�give any details of the proceedings, but they have confirmed that the trial is under way and expected to last for several months.

Local media reports say that 21 medical personnel face charges linked to the presence of HIV-infected blood in the city's blood banks.

Prosecutors allege that the accused purchased blood from donors who had themselves not been tested for HIV.

The defendants are further alleged to have reused disposable medical equipment.