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Clinical characteristics of COVID-19 in 104 people with SARS-CoV-2 infection on the Diamond Princess cruise ship: a retrospective analysis

Our take —

Outbreak investigations that examine factors associated with asymptomatic or pre-symptomatic COVID-19 are important to understand the clinical features and disease pathogenesis of the virus. Findings from this study highlight serum lactate dehydrogenase, lymphopenia, age, and consolidation on CT scan as potential predictors of disease severity, but due to the small sample size and potential for selection bias, these results should be interpreted with caution and more research in this area is warranted.

Study design

Retrospective cohort

Study population and setting

This retrospective review of medical records at the Self-Defense Forces Central Hospital in Tokyo, Japan included 104 laboratory-confirmed SARS-CoV-2 cases originating on the Diamond Princess cruise ship. Patients were admitted between February 11 and February 25, 2020, and followed either until they were discharged or until study end on February 26, 2020. These patients accounted for approximately 15% of the laboratory-confirmed SARS-CoV-2 cases from the Diamond Princess cruise ship.

Summary of Main Findings

Upon admission, 43 (41%) patients did not have symptoms, 41 (39%) had mild presentation, and 20 (19%) had severe disease (clinical symptoms of pneumonia requiring oxygen therapy). By the end of the study, 10 of the 43 patients who had initially been admitted without symptoms had developed symptoms (3 of whom progressed to severe COVID-19). Of the 41 patients who had initially been admitted with mild disease, five progressed to severe COVID-19. Baseline serum lactate dehydrogenase levels were elevated among the 10 patients who were admitted without symptoms at baseline but later developed symptoms, compared to asymptomatic cases (i.e., those who never developed symptoms). Among the eight patients who had been admitted with no or mild symptoms upon admission but then progressed to severe COVID-19, all had radiological abnormalities on CT prior to emergence of pneumonia-like symptoms. Comparing patients with mild and severe COVID-19 at the end of observation, there were no differences in sex, comorbidities, clinical signs, or symptoms. However, patients with severe COVID-19 at the end of observation were older, had higher lymphocyte counts, and more consolidation on CT.

Study Strengths

Participants with laboratory-confirmed SARS-CoV-2 who were asymptomatic, pre-symptomatic, and mildly symptomatic were followed to examine predictors of symptom onset and severe disease.


The small sample of patients included in this study accounted for only 15% of cases from the Diamond Princess cruise ship. Triage and referral patterns of passengers aboard the ship to different medical institutions could have resulted in selection bias. Short follow-up and differing periods of observation with unknown time between infection and symptom onset may have resulted in missed symptoms (i.e. symptoms prior to hospital admission) or symptom onset after study end (only 29% of patients were discharged by February 26).

Value added

The authors claim that this is the first study to examine predictors of symptomatic illness among patients with initially asymptomatic, laboratory-confirmed SARS-CoV-2.

This review was posted on: 4 July 2020