The Capital District Health Authority says it could be several weeks before all hospital mattresses with mould are replaced.

The problem was discovered earlier this month and affected mattresses were destroyed.

Now, the authority is doing an audit of all beds to determine if the problem is widespread. The audit is expected to be completed by the end of this week but spokesperson Peter Graham said replacing mattresses could take weeks.

Kim Strong, an indoor air and mould expert, said all you need for mould to grow is humidity and time.

capital-bed_852x479_1-4col

A plastic covering is placed over the beds to protect patients. (CBC)

"The environment potentially could have simply been humid for any one of a number of reasons and may be not even humid now, the problem may have developed in the summer and not been discovered until now," he said.

"I would recommend Capital Health find out first what kinds of moulds are there."

Capital Health says it doesn't know what caused the mould.

Graham said all mattresses have covers that are moisture and vapour-proof so patients shouldn't worry because any mould is sealed inside.

"Mould is only dangerous if it's airborne so in the instances where mould has been found within the mattress cover, on the mattress, it actually doesn't pose a direct hazard to a patient," he said.

Capital Health said more than 1,000 mattresses will be examined as part of the audit.