Abstract of Master’s Dissertation
No.1
CourseThesis
Title

Master of TropicalMedicine

NameKazuaki Fukushima

Clinical characteristics of coronavirus disease 2019 (COVID-19) in a category-1
infectious diseases-designated hospital in Tokyo, a single-center retrospective
observational study

Abstract of Master’s Dissertation

Background: Coronavirus disease 2019 (COVID-19) has spread all over the world since
December 2019. The rapid increase in the number of infected people has led a devastating
impact on the medical field. Japan has experienced five waves in its epidemic curve due tovariant strain until December 2021. The impact of variants on the severity and death fromCOVID-19 has been reported overseas, but such data remains scarce in Japan.
Objectives: We aimed to clarify the social demographics and clinical characteristics of
COVID-19 patients in each epidemic wave from the first wave to fifth wave, to clarify the risk
factors for critical illness and death from COVID-19, and to determine whether there is anindependent association between each wave and clinical outcome.
Materials and Methods: This is a retrospective observational study of a single-center hospital.
From January 31, 2019, to October 31, 2021, patients who were admitted to Tokyo
Metropolitan Komagome hospital with a diagnosis of COVID-19 were recruited. Based on thenumber of newly reported daily cases in Tokyo, the patients were classified into five waves. We
collected medical data from the electronic medical record backwards. The severity isdetermined using the WHO classification. In the analysis of risk factors for severely ill patients,
these patients were further classified into critical and non-critical groups, death and survive
groups. Multivariate analysis performed Binomial logistic regression analysis by introducing
waves and vaccine history as remarkable variables in addition to the variables that weresignificant in univariate analysis.

Abstract of Master’s Dissertation
No.2
CourseMaster of TropicalMedicine

Name

Kazuaki Fukushima

Results: The total number of the patients was 1948. The median age was 53.0 years with
61.8% of males. Median age was lowest in the second wave (39 years) and highest in the third
wave (72 years). The proportion of cases that resulted in critical illness was significantly lowerin the second wave. The fatality rate was highest at 7.7% during the first wave and lowest at
1.9% during the fifth wave. The number of the patients and the proportion of the severity byage category were different by each wave, in particular, the number and the proportion ofseverely ill patients are largest in their 40s and 50s in the fifth wave. Older age, male, highBMI, the longer days from onset to admission, DM, and CKD were associated with critical
illness, on the other hand, older age, cancer, CKD, and immunosuppressant use wereassociated with death. Vaccine history was associated with protective effects for critical illness
and death. The first wave was associated with critical illness and death, and the fifth wave wasassociated only with critical illness, independently.
Conclusions: The risk of critical illness from COVID-19 was significantly higher in patientsduring the first and fifth wave even after adjusting for previously reported factors. However,
the risk of death was significantly higher only in patients during the first wave but not during
the fifth wave. This may reflect significant improvement of COVID-19 management andmedical care delivery system over the period.