Other sources would included dust, clothing, pot plants(!), hands, hair, food, water and so on. A significant tightening of standard practices of hygiene for everyone entering the ward would also be helpful and have no doubt been in place since the cases were discovered.
Latest reports states that Aspergillus has been detected in several areas of the ward - presumably after swabbing surfaces open to the air (though the exact details are not stated). Specialist cleaners are being brought in to remove all traces of the fungus, so that suggests that was the only detected source of the infections. Equally importantly continuing efforts are being made to monitor the situation in an ongoing manner.