The COVID-19 belongs to the category of "epidemic disease" in TCM. The main syndrome elements are damp, heat, poison (toxin), stasis and Qi deficiency, and it is obvious that the pathogenic dampness leads to diseases. The winter of Wuhan is characterized by cold and humid climate. It is a subtropical monsoon climate in Wuhan. Wuhan has developed water system, abundant rainfall and humid climate; the warm winter in Wuhan and the cold and wet weather at the end of the year formed the external conditions of diseases caused by pathogenic dampness and epidemic evils. According to the theory of Yellow Emperor's Inner Canon and the discourse of famous virtuous of past dynasties, the nature of COVID-19 is "Yin Syndrome". In light of the clinical manifestation, climate, season and regional characteristics of COVID-19 outbreak, academician Tong Xiaolin ^[13] proposed that COVID-19 be treated from the perspective of "cold-dampness pestilence". The COVID-19 is caused by toxin of pestilence. The pathogenesis is characterized by that cold and heat are mixed, deficiency and excess are seen together, evil is flourishing and vital Qi is declining; the disease is lingering, the pathogenic toxins run through the whole process, and the lung, heart and kidney are affected. The treatment should be based on cold and dampness. The therapeutic method can be warming Yang, supporting right, transforming rheum, dissipating cold, dispelling dampness, and resolving toxin. "Treatise on Febrile Diseases" said: "When the vital Qi is relatively vigorous, there are fever and aversion to cold, and it is exterior Yang Syndrome (greater Yang disease); when Qi and blood decline, there are chills without fever, and it is exterior Yin Syndrome (lesser Yin disease)". According to the analysis of clinical research ^[14], most COVID-19 patients had low fever, or no fever, suggesting that the disease is mainly Yin Syndrome.

In this paper, according to the statistics, totally there are 204 Chinese medicines; Poria cocos had the highest use frequency of 225 times, followed by Herba Pogostemonis (219) and Rhizoma Atractylodis Macrocephalae​ (187). Experts believe that the three aspects of TCM etiology and pathogenesis are cold, dampness and epidemic toxin, and dampness is involved in the development and changes of diseases. Therefore, pathogenic dampness is the most important core ^[15] of disease onset, development and change. Poria cocos is a kind of diuretic and detumescence medicine with sweet/light taste and flat nature. It belongs to the heart, lung, spleen and kidney meridians, and can disinhibit water and percolate dampness, strengthen the spleen and calm the heart. In our hospital, the use frequency of Poria cocos was the most, which reflects that the treatment pays attention to dispelling dampness. The minimum dose is 6g, and the maximum dose is 50 g. According to the Pharmacopoeia, the conventional dose is 10-15 g. For example, in "Treatise on Febrile Diseases" and "Synopsis of Golden Chamber" authored by Zhang Zhongjing, the single dose of Poria cocos varies widely, ranging from 1.25 to 40 g. The dosage of Poria cocos can be divided into small dose (< 10 g), medium dose (10 - 20 g) and large dose (> 20 g). Small dose of Poria cocos can invigorate the spleen and remove dampness, dissipate phlegm and stop diarrhea; its medium dose can promote diuresis, regulate Qi, calm heart and calm palpitation; its large dose can promote diuresis and detumescence, calm stomach and stop vomiting. In treating COVID-19, it should be applied in different levels of dose in view of different patients, syndromes, and formulas, etc. As for Herba Pogostemonis (Huoxiang in Chinese), "Materia Medica Account (Ben Cao Shu in Chinese)" ^[16] said: "It is used in dispersing cold and dampness, treating exogenous cold pathogen, cold and heat of malaria and other diseases". Wei Xiaolu ^[17] showed that the main medicinal component of Herba Pogostemonis is agastache oil. When sensitive strains of virus were screened in vitro, agastache oil showed anti-adenovirus effect, and its mechanism may be to prevent virus from adsorbing cells by destroying virus gene. Rhizoma Atractylodis Macrocephalae has the function of invigorating spleen and supplementing spleen Qi, which can help spleen to move Qi and disinhibit water, and promote water and liquid transport, so as to achieve the effect of eliminating and transforming dampness.

As for TCM efficacy in treating COVID-19, heat clearing, detoxicating, dampness eliminating, phlegm resolving, water disinhibiting and damp percolating are prominent. These reflect the medication characteristics of cold-dampness pestilence. According to Stab Method Theory in Plain Questions (Su Wen), "the healthy Qi is stored in the body, and the evil can not invade". It shows the struggle process of healthy Qi and evil Qi in the human body. When the healthy Qi is sufficient, it can fight against the evil and expel the residual evil. Meanwhile, the heat clearing and dampness transforming drugs are used to eliminate the residual heat pathogen, so as to prevent the bandits from staying in the closed door, which has the effect of supporting the healthy without retaining the evil, expelling the evil without injuring the right, and promoting the recovery from disease. The novel coronavirus infection induces inflammation storm, which is an important factor leading to a rapid deterioration of the disease. It is also the cause of high mortality in the elderly patients. Many drugs for clearing away heat and detoxification have the function of inhibiting inflammatory factors ^[18], but the specific mechanism of inhibiting the inflammatory storm needs further study.功效统计分析，在治疗新冠肺炎其中以清热解毒、燥湿化痰、利水渗湿药为主，体现了寒湿疫的用药特点。《素问·刺法论》云：“正气存内，邪不可干”，说明正气与邪气在人体斗争的过程，正气充足，与邪抗争，驱逐余邪，同时以清热药、化湿药清除残存余热之邪，防止闭门留寇，起到扶正而不留邪，驱邪而不伤正之功效，促进疾病恢复。新型冠状病毒感染导致的“炎症风暴”是导致病情急转直下的重要因素，也是老年人病死率高的原因，有研究^[18]表明，许多清热解毒的药物具有抑制炎症因子分泌的作用，但是能否抑制炎症风暴的具体的机制需要进一步的研究。