1 INTRODUCTION
On December 12, 2019, 27 pneumonia cases of unknown cause emerged in Wuhan, Hubei, China.1 The etiological agent was identified as a novel coronavirus and later renamed as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by the International Committee on Taxonomy of Viruses (ICTV).2-4 Community transmission is now evident, and it is clear that SARS-CoV-2 is a highly contagious virus.5 Until 9 May 2020, the coronavirus disease 2019 (COVID-19) has wreaked havoc in 210 countries and territories, affected more than 3.8 million cases and 265,862 deaths around the world.6 SARS-CoV-2 infection induces pneumonia, acute respiratory distress syndrome and death, particularly in vulnerable populations such as elderly adults and those with chronic medical conditions, such as cardiovascular diseases, diabetes, respiratory diseases, hypertension and malignancy.7Knowledge on SARS-CoV-2 infection in children is still yet to be fully developed and only limited studies on pediatric patients are currently available.8-12
According to the Chinese expert consensus on the diagnosis, treatment and prevention of SARS-CoV-2 infection in children (2nd Version), pediatric COVID-19 cases are classified to five clinical types with different severities: 1) asymptomatic infection; 2) acute upper respiratory infection (AURI); 3) mild pneumonia; 4) severe pneumonia; 5) critical pneumonia.13 In contrast to infected adults, most infected children appear to have a milder clinical course.8 Asymptomatic infections are not uncommon. Despite that the clinical features of COVID-19 pediatric patients have been established so far, the difference between children with pneumonia and without pneumonia (asymptomatic and AURI), in aspects of clinical features, laboratory findings, immunological changes and outcomes, were not reported. In addition, the allergy status, and the information of the allergic diseases-related laboratory findings of these patients, have not been reported yet. Allergic diseases are common and with increasing prevalence in children.14-16 Previous studies showed virus infection is one of the triggers for the exacerbation of asthma.17 However, there was limited information about the association between asthma and coronaviruses infection, especially SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV).18,19 Most animal models established for the research of SARS-CoV and MERS-CoV are also found less relevant to asthma.20 On the other hand, atopic sensitization had no effect on the severity of viral pneumonia in children, as shown in a multi-center prospective study, but the history of allergic diseases such as atopic dermatitis, food allergy and drug allergy were associated with severe pneumonia.21 In a previous study on 140 adult COVID-19 cases, allergic diseases and asthma showed much less prevalence compared to population levels, suggesting that allergy is not a predisposing factor for SARS-CoV-2 infection.22
This study aims to investigate the clinical and laboratory characteristics of hospitalized COVID-19 pediatric patients, and to reveal the relationship between SARS-CoV-2 infection, immune response and allergic status, with a special focus on disease severity and allergy in patients.