The Madlanga Commission faces further delays as IDAC head Andrea Johnson's testimony is postponed due to illness, raising questions about the reliability of medical certificates submitted by witnesses.

The number of key witnesses ending up in hospital just before they have to appear before the Madlanga Commission is growing.

Several witnesses have either submitted sick notes or been hospitalised, with the head of the Investigating Directorate Against Corruption (IDAC), Andrea Johnson, being the latest casualty.

Her testimony on Monday was postponed after she took ill. Johnson was rushed to hospital while travelling to the hearing and subsequently submitted a medical certificate. However, the commission found the medical certificate to be lacking in detail.

IDAC head Advocate Andrea Johnson IDAC head Advocate Andrea Johnson