There is one new Covid-19 case in managed isolation.

A second worker at the Sudima managed isolation facility tested positive yesterday, and was a close workplace contact of the case reported on Monday.

Both cases came into contact with the international mariners while carrying out their duties at the facility, including some of the 31 who tested positive for Covid-19.

The individual tested negative following routine testing on Thursday, October 29, and is asymptomatic but was retested after Monday's positive result.

One of the workers visited a Chemist Warehouse at a busy shopping mall, Ministry of Health officials have warned.

Chemist Warehouse South City, in central Christchurch, was added to the Ministry of Health's location of interests. These locations may be for casual contacts of Covid-19 community cases.

"While risk from these locations is most often very low, casual contacts are asked to monitor their health and get medical advice from their GP or Healthline if they become unwell," the ministry said today.

A Covid-19 case visited the Chemist Warehouse between 3.45pm and 4pm last Friday. The Chemist Warehouse is part of a major shopping mall complex.

No other shops or parts of the centre have been flagged by the ministry.

Meanwhile, a high school student is a close contact of Monday's new community case.

The Canterbury District Health Board sent a letter to Cashmere High School parents on Tuesday confirming the student was a close contact.

The student had tested negative and was isolating at home.

"Students and staff do not need to be tested unless they have symptoms of Covid-19, and they do not need to self-isolate," it said in the letter.

Director general of health Dr Ashley Bloomfield. Photo / NZ Herald

First health worker case linked to infected Russian seamen

Earlier today director general of health Dr Ashley Bloomfield told Newstalk ZB's Mike Hosking genomic testing had shown an exact match with the infection found in five of the Russian and Ukrainian seamen who are at the Sudima Airport Hotel in managed isolation.

He said the results were linked to the first health worker who became ill. Despite testing negative for Covid on Thursday, the woman became symptomatic on Saturday and tested positive for Covid-19.

A second health worker working alongside the sick female health worker who is now isolating at home with a teenager has since tested positive.

Bloomfield said the fact that the genomic testing linked the case back to the Sudima outbreak meant there was little fear of a fresh Covid strain unchecked in the community.

He said while there was strict infection control measures inside the facility incursions were always a possibility.

He added he had a high level of confidence the latest cases of health workers becoming infected did not pose a wider threat to others outside the quarantine facility.