SARS-CoV-2 shedding and seroconversion among passengers quarantined after disembarking a cruise ship: a case series

Ivan Fan-Ngai Hung, Vincent Chi-Chung Cheng, Xin Li, Anthony Raymond Tam, Derek Ling-Lung Hung, Kelvin Hei-Yeung Chiu, Cyril Chik-Yan Yip, Jian-Piao Cai, Deborah Tip-Yin Ho, Shuk-Ching Wong, Sally Sau-Man Leung, Man-Yee Chu, Milky Oi-Yan Tang, Jonathan Hon-Kwan Chen, Rosana Wing-Shan Poon, Agnes Yim-Fong Fung, Ricky Ruiqi Zhang, Erica Yuen-Wing Yan, Lin-Lei Chen, Charlotte Yee-Ki Choi, Kit-Hang Leung, Tom Wai-Hin Chung, Sonia Hiu-Yin Lam, Tina Poy-Wing Lam, Jasper Fuk-Woo Chan, Kwok-Hung Chan, Tak-Chiu Wu, Pak-Leung Ho, Johnny Wai-Man Chan, Chak-Sing Lau, Kelvin Kai-Wang To, Kwok-Yung Yuen
Lancet Infectious Diseases 2020 June 12

BACKGROUND: A cruise ship is a closed-off environment that simulates the basic functioning of a city in terms of living conditions and interpersonal interactions. Thus, the Diamond Princess cruise ship, which was quarantined because of an onboard outbreak of COVID-19 in February, 2020, provides an opportunity to define the shedding pattern of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and patient antibody responses before and after the onset of symptoms.

METHODS: We recruited adult (≥18 years) passengers from Hong Kong who had been on board the Diamond Princess cruise ship docked in Yokohama, Japan in February, 2020. All participants had been found to be negative for SARS-CoV-2 by RT-PCR 4 days before disembarking and were transferred to further quarantine in a public estate in Hong Kong, where they were recruited. Participants were prospectively screened by quantitative RT-PCR (RT-qPCR) of nasopharyngeal and throat swabs, and serum IgG and IgM against internal nucleoprotein and the surface spike receptor-binding protein (RBD) of SARS-CoV-2 at baseline (upon entering quarantine) and on days 4, 8, and 12 of quarantine.

FINDINGS: On Feb 22, 2020, 215 adults were recruited, of whom nine (4%; 95% CI 2-8) were positive for SARS-CoV-2 by RT-qPCR or serology and were hospitalised. Of these nine patients, nasopharyngeal swab RT-qPCR was positive in eight patients (89%; 57-99) at baseline. All nine patients were positive for anti-RBD IgG by day 8. Eight (89%; 57-99) were simultaneously positive for nasopharyngeal swab RT-PCR and anti-RBD IgG. One patient who was positive for anti-RBD IgG and had a negative viral load had multifocal peripheral ground-glass changes on high-resolution CT that were typical of COVID-19. Five patients (56%; 27-81) with ground-glass changes on high-resolution CT were found to have higher anti-nucleoprotein-IgG OD values on day 8 and 12 and anti-RBD IgG OD value on day 12 than patients without ground-glass changes. Six (67%; 35-88) patients remained asymptomatic throughout the 14-day quarantine period.

INTERPRETATION: Patients with COVID-19 can develop asymptomatic lung infection with viral shedding and those with evidence of pneumonia on imaging tend to have an increased antibody response. Positive IgG or IgM confirmed infection of COVID-19 in both symptomatic and asymptomatic patients. A combination of RT-PCR and serology should be implemented for case finding and contact tracing to facilitate early diagnosis, prompt isolation, and treatment.

FUNDING: Shaw Foundation Hong Kong; Sanming-Project of Medicine (Shenzhen); High Level-Hospital Program (Guangdong Health Commission).

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