You're right @poodledoc. The Azithromycin is a known culprit for the few people on it longterm who develop higher millisecond rates of Long QT. It's an hERG blocker and tends to make people urinate out more potassium than normal.
(Does the name Poodledoc mean you are a veterinarian -- or do you just love dogs, like me?).
In Australia, the standard susceptibility testing they do is not fancy -- it usually first off just tests for susceptibility to Clarithromycin. Only if that's not susceptible then they try susceptibility to other meds. But I don't know about New Zealand where Heather is.
Annie