2.1 Patients epidemiological history and chronic diseases
Based on the information collected, patients in the severe group have higher average age of 61.3 years and more chronic diseases. In the severe group, 44 patients had residential/contact history to Wuhan/Hubei epidemic areas while 4 patients had contact history with confirmed cases. 2 patients had neither been in Wuhan/Hubei or in contact with any confirmed case. 34 patients have at least one type of chronic diseases, including hypertension, diabetes, coronary heart disease, arrhythmia, COPD and hepatitis B. 13 of them have two or more underlying diseases. Six patients turned to critical state and three of them died. Two died cases were with either hypertension or COPD while the third case had no chronic disease history. The other three critical cases had chronic disease history of hypertension or diabetes, or both. Other patients were discharged upon recovery. The average course of disease was 4.9 days while average length of hospitalization was 29 days.
In the mild group, 53 patients had residential/contact history to Wuhan/Hubei epidemic areas. 13 patients had contact history with confirmed cases. 7 patients had no epidemiological history. 13 of the patients have at least one type of chronic diseases, including hypertension, diabetes, emphysema, tuberculosis, hyperlipemia, hepatitis B and cirrhosis at decompensation stage. 2 patients have two underlying chronic diseases. All of the patients in the mild group were discharged upon recovery. The average course of disease was 3.6 days while average length of hospitalization was 19 days. (Table S1)
2.2 Inter-group comparison of the levels of multiple organ function indices
From the results of biochemical test and blood routine tests, significant differences in the levels of multiple organ function indices were seen between the severe group and the mild group. Statistically, positive t or z value represents a higher mean/median value of the index level in the severe group comparing to the mild group, and vice versa. The higher the absolute t or z value, the more different in the index level between the two groups and the lower the p-value. (Table 1)
Significantly lower oxygenation index was detected from the severe group comparing to the mild group. Levels of liver function indices, alanine aminotransferase (ALT) and aspartate aminotransferase(AST), are significantly higher, while level of albumin is lower in the severe group. Elevated concentrations of immune system function indices including C-reactive protein(CRP), procalcitonin(PCT), erythrocyte sedimentation rate (ESR), neutrophil count and interleukin–6 (IL–6) but lower lymphocyte count were also observed in the severe group. Longer plasma prothrombin time (PT) and activated partial prothrombin time (APTT), higher level of D-Dimer and lower platelet counts were detected from the severe group. Kidney function index, creatinine(Cr), and heart function index, troponin(Tnl), were also increased in patients with severe syndromes. No difference was observed from other indices between the two groups in statistical perspective. (Table 1, details in Table S1) These results are possibly indicating altered functions of major organs and systems including the heart, the liver, the kidney, the immune system and the blood coagulation system as the severity of the infection increased.
2.3 Inter-group comparison of categorical variables
By converting quantitative variables to categorical variables, the ratio of abnormalities in each category was analyzed between the two groups. Statistically, the proportion of patients with abnormal level of each index were compared between the two groups. Higher x2 value represents larger difference between the two groups. Based on the comparison, there were more male patients in the severe group which aligned with the result of previous research study. There are higher proportions of patients with altered lymphocyte count, D-dimer level, albumin level, aspartate aminotransferase level, procalcitonin level, C-reactive protein level, erythrocyte sedimentation rate and interleukin-6 level in the severe group. More patients in the severe group have bilateral lung involvement and altered heart function in the severe group comparing to the mild group. Other indexes are not significantly different in statistical perspective. (Table 2, details in Table S1) This showed that COVID-19 infection have more extensive influence to organ function indices in the severe group.
2.4 Effects of underlying diseases on the blood indices
There are more patients with underlying diseases in the severe group comparing to the mild group. Thus, further analysis according to these underlying diseases was done to examine the effects of these underlying diseases on the variation of blood indices between the two groups. By comparing between the blood index levels quantitatively and qualitatively between patients with underlying diseases in the two groups, it was found that Cr, PCT, CRP, N, ESR, IL_6, PT, D_DIC were significantly higher in the severe group while levels of PLT and ALB were significantly higher in the mild group.(Table 3) This showed that underlying disease is indeed a factor affecting the severity of COVID-19 infection. Blood index levels were then compared respectively according to hypertension and diabetes which are most common underlying diseases observed from the patients. Elevated levels of PCT, CRP, N and decreased levels of PLT and ALB were observed from patients with diabetes in the severe group, where level of N increased both quantitatively and as a categorical variable. (Table 3) For those patients with hypertension in the severe group, levels of Cr, PCT, CRP, and ESR were significantly increased while levels of PLT and ALB were decreased, where levels of CRP, ESR and ALB were varied both quantitatively and as a categorical variable. (Table 3) Such results specifically highlighted the possibility of the influence of underlying diseases on the organ functions in the COVID-19 patients.