Numerical investigation of airborne transmission of respiratory infections on the subway platform

Underground subway platforms are among the world’s busiest public transportation systems,but the airborne transmission mechanism of respiratory infections on these platforms has been rarely studied.Here,computational fluid dynamics(CFD)modeling is used to investigate the airflow patterns and infection risks in an island platform under two common ventilation modes:Mode 1-both sides have air inlets and outlets;Mode 2-air inlets are present at the two sides and outlets are present in the middle.Under the investigated scenario,airflow structure is characterized by the ventilation jet and human thermal plumes.Their interaction with the infector’s breathing jet imposes the front passenger under the highest exposure risk by short-range airborne route,with intake fractions up to 2.57%(oral breathing)or 0.63%(nasal breathing)under Mode 1;oral breathing of the infector may impose higher risks for the front passenger compared with nasal breathing.Pathogen are efficiently diluted as they travel further,in particular to adjacent crowds.The maximum and median value of intake fractions of passengers in adjacent crowds are respectively 0.093%and 0.016%(oral breathing),and 0.073%and 0.014%(nasal breathing)under Mode 1.Compared with Mode 1,the 2nd mode minimizes the interaction of ventilation jet and breathing jet,where the maximum intake fraction is only 0.34%,and the median value in the same crowd and other crowds are reduced by 23–63%.Combining published quanta generation rate data of COVID-19 and influenza infectors,the predicted maximum and median infection risks for passengers in the same crowds are respectively 1.46%–40.23%and 0.038%–1.67%during the 3–10 min waiting period,which are more sensitive to ventilation rate and exposure time compared with return air.This study can provide practical guidance for the prevention of respiratory infections in subway platforms.

An Imported Case and an Infected Close Contact of the Omicron Variant of SARS-CoV-2—Guangdong Province,China,December 13,2021

On November 27,2021,a 67-year-old male returning from Canada via airplane was transferred to the central isolation hotel in Shanghai.During the quarantine,his 1st,4th,7th,and 14th days of specimens returned negative for severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),which causes coronavirus disease 2019(COVID-19).On December 11,he completed 14 days of centralized isolation and returned to Guangzhou from Shanghai via airplane,then he was closed-loop transferred to Yuexiu District for a 7-day home isolation.On December 12,the local Community Health Service Center routinely collected his throat swab and the result returned to COVID-19 positive on December 13,2021.He was transported to the Guangzhou Eighth People’s Hospital for isolated treatment by negative pressure ambulance on the same day.The patient had two inflamed lungs according to the chest computed tomography(CT)examination,but his most recently updated condition was stable.An estimated 600 close contacts were identified and were placed in centralized isolation.On December 16,one of the close contacts,a 70-year-old female also tested positive for COVID-19.She lived on the lower floor of the same type of apartment as the imported case and spent 19 hours in the same building.

First Imported Case of SARS-CoV-2 Omicron Subvariant BA.4-Guangdong Province,China,May 4,2022

On April 29,2022,a flight arrived at Baiyun International Airport,Guangzhou City,Guangdong Province,and departed from Amsterdam Schiphol Airport,Netherlands.After the first test of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)nucleic acid at the Baiyun International Airport,all passengers were admitted to a quarantine hotel for a routine 14-day medical observation.On April 30,one of the passengers(a 20-year-old Chinese female)was reported positive for coronavirus disease 2019(COVID-19),and then a nasopharyngeal swab sample was immediately retested on May 1 and reported positive.

An Imported Case of BA.2 Lineage of Omicron Variant COVID-19—Guangdong Province,China,December 28,2021

On December 19,2021,a 31-year-old male boarded a flight from Bhubaneswar,India to Mumbai,India,and then another flight from Mumbai to Muscat,Oman.On December 24,he returned from Muscat to Guangzhou by airplane and was transferred to a centralized isolation hotel in Foshan.He was sampled on the third day of the quarantine,and the result returned to be coronavirus disease 2019(COVID-19)positive on December 27,2021.He was transported to the Guangzhou Eighth People’s Hospital for isolated treatment by negative pressure ambulance on the same day.The case had two lungs focal inflamed according to the chest CT examination.

First Imported Case of SARS-CoV-2 Omicron Subvariant BA.2.12.1-Guangdong Province,China,April 30,2022

On April 23,2022,an international flight KQ880 from Nairobi,Kenya arrived at Guangzhou Baiyun International Airport,Guangzhou City,Guangdong Province.All passengers were transferred to the quarantine hotel for routine 14-day medical observation and regularly tested of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)nucleic acid.One of the patients,a 27-year-old Chinese male,reported positive SARS-CoV-2 nucleic acid on April 27,2022.The patient had a history of full coronavirus disease 2019(COVID-19)vaccination and denied exposure to other COVID-19 cases in the past 14 days.After diagnosis,he was transferred to Guangzhou Eighth People’s Hospital for treatment.

First Human Infection with Avian Influenza H9N2—Guangdong Province,China,2020

A case of avian influenza H9N2 was detected in a human in Zhuhai City,Guangdong Province through routine influenza surveillance on March 30,2020.The patient was a 3-year-old child who developed fever and cough on March 22.A pharyngeal swab was collected on March 23,and the novel coronavirus nucleic acid test was negative.On March 26,the pharyngeal swab was sent to Zhuhai CDC for influenza virus tests and was found to be H9 influenza A positive,and on March 30,Guangdong Provincial CDC reexamined the pharyngeal swabs as positive for influenza A(H9N2).