The staff member was a lodge attendant who was cleaning at Glade House at the time.
Ultimate Hikes is an operator of multi-day guided walks on the Milford and Routeburn tracks. It also offers private lodges for customers while they walk.
"We've been planning since the start of the season, and have protocols in place that we have in conjunction with the Southern District Health Board.
"Because of distancing and those protocols, all walking groups and lodge staff are regarded as causal contacts.
"All of those who were there at the time just need to monitor their symptoms and get tested if they have any."
They said future walks will still go ahead and they will contact all those with bookings.
Glade House has been closed and people will be walked to the next lodge.
Covid-19 has spread quickly in the south with dozens of cases now reported in Queenstown and a number in Dunedin.
A Gore Main School class is self-isolating after a pupil tested positive at the weekend.
Nine new cases were reported today in Nelson Marlborough and Canterbury and 30 were reported in the Southern region.
