在流行病學中,SIR模型可以用來解釋一個疾病傳染過程,包括易受感染期(Susceptible)、傳染期(Infectious)、復原或死亡期(Recovered),但此模型只能適用於那些沒有潛伏期的疾病。後來有人提出了SEIR模型來改善了這個情況,它將疾病的潛伏期考慮進去,使得一個疾病傳染過程分成四個部分,包括易受感染期(Susceptible)、感染期(Exposed)、傳染期(Infectious)、復原或死亡期(Recovered),利用此模型可以計算出一個評估疫情嚴重程度的指標—基本再生數(R0)。 基本再生數(R0)指的是在一個易受感染的群體中每一個原發性疾病平均可以傳染的人數,當R0>1時,認為這個疾病有爆發流行的趨勢;當R0<1時,則認為此疾病較沒有流行的疑慮。一般而言,R0越大越有可能產生嚴重的疫情,也越難以控制。根據過去的資料顯示,天花的R0為5至7,SARS的R0為2至5,而台灣2007年的結核病疫情其R0為1.6至4.8,顯示了台灣結核病有爆發流行的可能。
In epidemiology,SIR model can be used to explain a disease transmission process,including the Susceptible(S)、Infectious(I) and Recovered(R).However,this model can only apply to those who have no incubation period of the disease,then the SEIR model was be derived to improve SIR model.This model takes into account the incubation period of disease.It makes four parts of disease process, including the Susceptible(S)、Exposed(E)、Infectious(I) and Recovered(R).Basic reproduction number R0 can be calculated by the SEIR model,and it is represent how serious of epidemic. Basic reproductive number R0 means the average number of secondary cases generated by a primary case in a pool of mostly susceptible individuals.When R0>1,the epidemic tend to outbreaks;If R0<1,where have less possible for outbreaks of epidemic.By the past data,the value of smallpox R0 is 5 to 7 and the value of SARS R0 is 2 to 5.In Taiwan 2007,the value of tuberculosis is R0 is 1.6 to 4.8,it means the tuberculosis epidemic may be outbreak.