Otago and Southland remain the only regions of New Zealand which have no confirmed cases of swine flu.
The southern-most confirmed case is in Ashburton.
Confirmed swine flu, or influenza A (H1N1), cases continue to rise nationwide, with more than 400 cases diagnosed, mostly in Auckland, Wellington and Canterbury.
Public Health South medical officer of health Dr Derek Bell said it was a matter of when, not if, swine flu would arrive in the region.
The increasing national numbers, along with more overseas visitors arriving in the South for the ski season, meant it was "only a matter of time" before the first cases were confirmed.
In the meantime, Otago health officials continue to prepare for swine flu hitting the South.
Health officials have flu centres ready in Dunedin, Queenstown and Invercargill in case family doctors become overwhelmed with numbers of patients with flu-like illness.
The centres, which will be called community-based assessment centres, will be staffed by Otago District Health Board and community-based doctors and nurses.
Venues for centres in other towns are also being confirmed.
If the centres are needed, they will enable health officials to separate people with flu-like illnesses from other patients. The centres would assess patients, provide advice, give anti-viral medication Tamiflu if appropriate and refer to other health services, such as hospital admission, if necessary.
In Dunedin, the centre would open in the former Bowling Green Tavern, and in Queenstown, the Lakes District Hospital staff accommodation building would be used.
They can be activated within 24 hours.
Public health staff continue to meet international flights at the airport to give information and advice to inbound passengers.
People who have flu-like symptoms should telephone their family doctor first or call the toll-free Healthline on 0800 611 116 for advice.
