A medical staff member informs residents of the dos and don'ts for COVID-19 tests at the Pidu District Hospital of Traditional Chinese Medicine in Pidu District of Chengdu, capital of southwest China's Sichuan Province, Dec. 10, 2020. Chengdu reported zero increase in new domestically transmitted COVID-19 cases and asymptomatic cases from 9 p.m. Tuesday to 6 p.m. Wednesday, while citywide nucleic acid tests are continuing, local authorities said.  (Xinhua/Shen Bohan)

A Sichuan Airlines international cargo flight pilot was diagnosed as an imported COVID-19 case on Monday evening. He attended a wedding feast with 300 guests in Jiangyou of Mianyang, a neighboring city of Chengdu, before he was confirmed as infected with the coronavirus.

The pilot, surnamed Gao, 26, also completed a flight between Chengdu and Jinan of East China's Shandong on December 9 during quarantine. Epidemiological investigations show that he had no contact with passengers on the flight or staff at Jinan airport, the Jinan Center for Disease Control and Prevention announced Tuesday. 

As he had disembarked to refuel at the airport, an airport fuel worker has been put under quarantine. A staff member at the airport, a close contact of the pilot's contacts, and passengers of particular concern on the flight have also been quarantined.

China's Civil Aviation Administration (CAAC) has set up an expert team to investigate the case and find out the cause of the infection, and especially the infection risk, Xiong Jie, a CAAC official said at a press conference on Wednesday. 

CAAC will further strengthen supervision and refine epidemic control measures to block the spread of the coronavirus through aviation, Xiong said.

The screening operation is ongoing. All 25 close contacts of the pilot, including 22 close contacts in Jiangyou, will remain in quarantine for medical observation, Mianyang authority announced on Tuesday.

A customer service employee from Sichuan Airlines said that the company is investigating the case, the Beijing News reported. 

The hotel in Jiangyou, where the wedding was held, has since been closed. More than 100 guests and employees in the hotel underwent nucleic acid testing on Tuesday morning.

The close contacts who attended the wedding banquet are currently being investigated, and no one has yet returned a positive nucleic acid test result.

As of noon on Tuesday, Jiangyou has collected samples from 289 local residents and 95 environmental samples for testing. 91 people have returned negative nucleic acid test results.

The community in Chengdu where the pilot lives was locked down on Tuesday. All residents in two apartment buildings will be required to remain in their homes; their daily necessities will be delivered by the community's housekeeper; and all food delivery staff will not be allowed to enter the community, the Sichuan Daily reported.

Gao arrived in Chengdu on November 29 from Los Angeles and underwent his quarantine in a designated place.

During his quarantine, Gao returned negative nucleic acid test results and completed the flight between Chengdu and Jinan on December 9. After that, he continued his quarantine until December 12. 

Gao then drove to Jiangyou of Mianyang city, close to Chengdu, to attend a wedding feast with 300 guests.

On Sunday, Gao went to West China Hospital for medical treatment, where his CT check returned an abnormal result. His nucleic acid test also returned positive before he was diagnosed with COVID-19.

Concerns were initially raised as to how Gao could fly before he completed his mandatory quarantine period. However, the latest epidemic control guidelines released by CAAC allows aircrews to continue to fly if they can meet certain conditions.

For international and regional cargo flights, the crew members who strictly follow the relevant epidemic control requirements during their missions and have not spent the night abroad are exempt from centralized or home isolation and can continue to perform their duties, according to the CAAC guidelines on airlines and airports released on November 26.

Crew members who spend nights abroad but engage in closed management quarantine while overseas can be exempt from isolation and continue to work as long as they return negative nucleic acid test results, the guideline says.