Section 2: Epidemiological data of COVID-19 (from DOI: 10.1016/j.clim.2020.108427)
From publication: "COVID-19 pathophysiology: A review" published as Clin. Immunol.; 2020 Apr 20 108427. DOI: https://doi.org/10.1016/j.clim.2020.108427
Section 2: Epidemiological data of COVID-19
A large number of studies so far are reports based on experiences in China. At the beginning of the outbreak, COVID-19 cases were mostly observed among elderly people. As the outbreak continued, the number of cases among people aged 65 years and older increased further, but also some increase among children (< 18 years) was observed. The number of male patients was higher initially, but no significant gender difference was observed as case number increased. The mean incubation period was 5.2 days. The combined case-fatality rate was 2.3%. The risk factors of in-hospital death were studied using the data of two hospitals in Wuhan. Older age, higher sequential organ failure assessment (SOFA) score and d-dimer >1 mug/mL on admission were shown to be risk factors in the multi-variable analysis. In the univariable analysis, the presence of coronary artery disease, diabetes and hypertension was also considered to be risk factors. The study of 85 fatal COVID-19 patients with median age of 65 years in Wuhan showed that the majority of patients died from multi-organ failure as respiratory failure, shock, and ARDS were seen in 94%, 81%, and 74% of cases, respectively. As in line with the high prevalence of multi-organ failure, high d-dimer levels, fibrinogen and prolonged thrombin time were seen in severe diseases.
Following the outbreak in China, SARS-CoV-2 has spread worldwide. As of early April 2020, the reported number of COVID-19 patients is highest in the U.S., followed by Spain, Italy, Germany, France and China. Italy was significantly affected after the outbreak of China. Fatality rate was also higher in elder population as in Chinese series. The report from Italy showed the case-fatality rate of 7.2%, which was three times as high as the one in China. Although the case-fatality rate of patients aged 70 years or older was higher in Italy, it was very similar between age 0 and 69 years in both countries. As 23% of Italian was aged 65 years or older, the high case-fatality in Italy was somewhat explained by the demographic characteristics. The data from US and other countries is available in the number of resources. We expect to learn experiences more from individual countries in the forthcoming future.
From the beginning of this outbreak, the percentage of children within the total COVID-19 patients was small. According to the data of the Chinese Center for Disease Control and Prevention (China CDC) from February 2020, children younger than 10 years of age and within the age of 11-19 years occupied 1% each of the total cases. Considering this age group represents 20% of the total population, this may indicate less prevalence of COVID-19 in pediatric population. However, this may be underestimation of actual incidence in pediatric population if less tests were undertaken in children due to less symptoms. One confounding factor is that schools in China were closed for most of the epidemic due to the Chinese New Year holidays, which might have contributed to less exposure among children. In the report of 2134 pediatric patients with COVID-19 from the China CDC, 4.4%, 50.9%, 38.8%, and 5.9% of patients were diagnosed as asymptomatic, mild, moderate, or severe, respectively. The definition of asymptomatic, mild, moderate, severe and critical is summarized in Table 1 . In contrast, 18.5% of adult patients had severe diseases. Infants were most vulnerable to severe type of infection; the proportion of severe and critical cases was 10.6%, 7.3%, 4.2%, 4.1% and 3.0% for the age group of <1, 1-5, 6-10, 11-15 and >=16 years, respectively. The case-fatality rate of age group 0-9 and 10-19 was 0% each. In Italy, COVID-19 patients of age 8-18 years occupied only 1.2%. The case-fatality rate of age group 0-9 and 10-19 was 0% and 0.2%, respectively, which was similar to Chinese experience. In the data from the Korean CDC on late March, 6.3% of all cases tested positive for COVID-19 were children under 19 years of age. On April 6, 2020, the US CDC released the study of 2572 COVID-19 cases among children younger than 18 years. Of all reported cases in the US, this occupied only 1.7% of the total cases, even though this age group makes up 22% of US population. Overall, the data suggested that children were less symptomatic than adults as in Chinese reports. Among the children for whom complete information was available, only 73% developed fever, cough, or shortness of breath. That's compared to 93% of adults reported in the same time frame, between the ages of 18 and 64 years. The estimated hospitalization rate for children aged 1 to 17 was 14% at most. In contrast, infant accounted for the highest percentage of hospitalization (15-62%), which was again similar to the data from Chinese CDC. Despite the overall favorable outcome for pediatric population, a number of deaths have been reported in US and other countries, and further information needs to be obtained.
Regarding the severity of COVID-19, there is a growing interest in the relationship between the severity of disease and gender. Although the Chinese series showed equal number of cases between males and females, the data suggested that more men than women suffered from severe disease and died. The data from other countries demonstrated similar results. Adverse outcomes of COVID-19 were associated with comorbidities, including hypertension, cardiovascular disease, and lung disease. These conditions are more prevalent in men and linked to smoking and drinking alcohol. Sex-based immunological differences were pointed out as another potential explanation. In addition, the study to examine factors influencing the adoption of protective behaviors, specifically within the context of pandemics, found that women were about 50% more likely to practice non-pharmaceutical behaviors, such as hand washing, face mask use and avoiding crowds compared to men, which may be in part responsible.
