Waitematā DHB concedes it has had complaints about ill-fitting masks that are supposed to protect staff from Covid-19.
The DHB's launched an investigation into the use of PPE (personal protective equipment) after three of its nurses contracted the virus.
It has stood down 57 staff and is tracing everyone who's had contact with the infected nurses.
According to the DHB the nurses had access to full PPE, it was worn at all times and the DHB has yet to confirm where and how they caught Covid-19.
Waitematā DHB's deputy chief executive Dr Andrew Brant says he doesn't yet understand how this has happened.