On February 22, 2020, 215 adults (of the 3711 passengers and crew on board the cruise ship Diamond Princess) were recruited, of which nine (4%; 95% CI 2-8) were positive for SARS-CoV-2 by RT-qPCR or serology and were hospitalized. Of these nine patients, RT-qPCR on nasopharyngeal swab was positive in eight patients (89%; 57-99) at baseline. All nine patients were positive for anti-RBD IgG on days 8 and 12. 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 exhibited frosted glass peripheral multifocal changes on a high-resolution scanner, typical of COVID-19. Five patients (56%; 27-81) with frosted glass modifications on a high-resolution scanner had higher anti-nucleoprotein IgG ODD values on days 8 and 12 and higher anti-RBD IgG ODD values on day 12 compared to patients without frosted glass modifications. Six (67%; 35-88) patients remained asymptomatic throughout the 14-day quarantine period.
The setting of the cruise ship provided an unusual opportunity to study viral shedding and seroconversion of SARS-CoV-2, mimicking the onset of a community epidemic. Passengers who are exposed to the virus could seroconvert while remaining asymptomatic with a high viral load, and they could continue to shed the virus. High-resolution computed tomography (CT) scans have also been used to make a clinical diagnosis and detect asymptomatic lung infections. A combination of RT-qPCR and serology should be performed to detect community outbreaks and to effectively perform contact tracing.
Strength of evidence Weak
- Case series. - N=215. - The study period was limited by the 14-day quarantine period.
To study the sequential excretion of SARS-CoV-2 and the specific antibody response in this cohort of passengers quarantined in Hong Kong.
Adult passengers (≥18 years old) from Hong Kong who had been on board the cruise ship Diamond Princess, moored in Yokohama, Japan, were recruited in February 2020. All participants had been found negative for SARS-CoV-2 by RT-PCR 4 days prior to disembarkation and were transferred to quarantine in a public area in Hong Kong, where they were recruited. All adult passengers aged 18 years and older were screened and were given the option to participate in the study. There were no exclusion criteria. Participants were prospectively screened by quantitative RT-PCR (RT-qPCR) of nasopharyngeal and pharyngeal swabs, and serum IgG and IgM against the internal nucleoprotein and receptor binding domain (RBD) of the SARS-CoV-2 peak surface protein at departure (at entry into quarantine) and on days 4, 8 and 12 of quarantine.