The nurse had twice gone into the room where Mr Garcia Viejo had been treated - to be directly involved in his care and to disinfect the room after his death. Both times she was wearing protective clothing.
It is unclear how the auxiliary nurse could have contracted Ebola.
The hospital was reported to have had extreme protective measures in place including two sets of overalls, gloves and goggles.
However, health workers told El Pais newspaper that the clothing used during the treatment of the two priests did not have level-four biological security, which is fully waterproof and with independent breathing apparatus.
Instead it was level two, the paper says, as photographs provided by staff indicated that the overalls worn did not allow for ventilation and the gloves were made of latex and bound with adhesive tape.