Taipei, May 5 (CNA) Some of the recently confirmed COVID-19 cases at the Taiwanese carrier China Airlines (CAL) and an airport hotel in Taoyuan are connected, but the source of the cluster infection remains unclear, the Central Epidemic Command Center (CECC) said Wednesday.

The CECC made the link after carrying out genome sequencing of the viruses in cases connected to Novotel Taipei Taoyuan International Airport Hotel and CAL, one of Taiwan's major airlines, said CECC official Lo Yi-chun (羅一鈞).

Over the past two weeks, 11 CAL cargo pilots, a flight attendant, and relatives of the pilots have tested positive for COVID-19.

At Novotel, which is located in CAL's complex in Taoyuan and is used to quarantine the airline's flight crews, five employees and three of their family members have also tested positive.

On Wednesday, Lo confirmed that some of the CAL cases were linked to those at Novotel, as indicated by matching genome sequences of the viruses found in the five Novotel employees, two of their family members, four CAL pilots, and one of their relatives.

Three of the four pilots had stayed at Novotel prior to testing positive, while the fourth had flown with one of the three, according to Lo.

This means that some of the cases at CAL and at Novotel are part of the same cluster infection, Lo said.

Other CAL pilots who have contracted the disease but whose viruses have a different genome sequence most likely contracted the disease outside the cluster, Lo said, adding that the CECC will conduct further sequencing to confirm that theory.

Although the CECC is now sure that the two groups of cases are connected, it has not yet determined the source of the infections or how the virus had spread among the patients, said Health and Welfare Minister Chen Shih-chung (陳時中), who heads the CECC.

As the CECC continues its investigation, the mandatory quarantine period for CAL flight crews will be extended from three days to five, and additional protocols will be announced Thursday, he said.