Objective  To analyze the early clinical characteristics of coronavirus disease 2019 (COVID-19) cases in different age groups, and provide references for the early identification, treatment and management of COVID-19 cases, prevention of the progression of illness and further effective prevention and control of COVID-19.

  Methods  Our study included COVID-19 cases in all the provinces, except Hubei, in China reported through national COVID-19 online reporting system from 19 January to 9 March, 2020. Descriptive method was used to analyze and compare the early clinical symptoms, clinical severity, laboratory and imaging features and the underlying diseases of the COVID-19 cases.

  Results  Our study analyzed 12 647 confirmed cases, including 196 cases aged 0–5 years old (1.5%), 508 cases aged 6–17 years old (4.0%), 5 491 cases aged 18–44 years old (43.4%), 4 004 cases aged 45–59 years old (31.7%) and 2 448 cases aged ≥60 years old (19.4%), the median age of the cases was 45 years interquartile range (IQR): 33–56). There were 102 deaths, the case fatality rate was 0.8%. No death was reported in cases under 17 years old. The proportions of severe and critical cases in age group ≥60 years were 18.7% and 10.6% respectively, highest in all age groups, and the case fatality rate was 3.6%. The cases were mainly mild (62.2%) and moderate (37.1%) in age group <17 years. The proportion of severe cases under 5 years (1.0%) was higher than that of cases aged 6–17 years (0.6%), there were no critical cases in cases under 17 years old. The proportions of the cases with decreased white cell count and decreased lymphocyte count in age group 0–17 years were lower than those in age group ≥18 years significantly ( χ²=225.037, P<0.001, χ²=479.737, P<0.001). The proportion of the cases with CT-indicated pneumonia in age group 0–17 years old was 44.7%, lower than that in age group ≥18 years (76.1%) significantly ( χ²=397.322, P<0.001). The proportions of the cases with running nose (13.3%) and vomiting (2.6%) in age group under 5 years old were highest in all age groups, and the proportions of the cases with increased white blood cell count (24.3%), increased lymphocyte count (51.0%) and increased lymphocyte percentage (66.9%) were also highest in all age group under 5 years old. The proportions of the cases with joint muscle pain (12.4%), headache (12.3%), sore throat (11.9%) and diarrhea (5.1%) in age group 18–44 years were highest. The proportions of the cases with dry cough (34.3%) and chest tightness (8.1%) was highest in age group 45–59 years. The highest proportions of the cases with abdominal pain (1.1%), conjunctival congestion (7.7%), diarrhea (5.4%) and nasal obstruction (10.2%) were reported in age group ≥60 years. The cases with underlying diseases were mainly aged ≥60 years, accounting for 41.0%, and the proportion of the severe cases with underlying diseases (19.6%) were higher than that of the severe cases without underlying diseases (11.1%) significantly (χ²=451.301, P<0.001).

  Conclusion  The proportions of severe cases and deaths were highest in age group ≥60 years, the proportion of severe cases with underlying diseases were higher than that of the severe cases without underlying diseases. There were significant differences in early clinical characteristics of COVID-19 cases among different age groups. The proportions of the cases with decreased white blood cell count, decreased lymphocyte count and CT-indicated pneumonia in age group 0–17 year were lower than those in age group ≥18 years. The proportions of the cases with running nose, vomiting, increased white blood cell count, increased lymphocyte count and increased lymphocyte percentage were highest in age group under 5 years old. The proportions of the cases with joint muscle soreness, headache, diarrhea and sore throat were highest in age group 18–44 years. The proportions of the cases with dry cough and chest tightness were highest in age group 45–59 years. Abdominal pain, conjunctival congestion, nasal obstruction and chest pain mainly occurred in cases aged ≥60 years. The early clinical characteristics of COVID-19 provided references for the early identification and diagnosis of the disease, prevention of the progression of illness, and further prevention and control.