If the
balance between agent and host favors the agent, infection (and in some instances, disease) will
occur. This relationship among the agent, the route or mechanism of transmission, and the
host is referred to as the chain of infection. Control and prevention of infection depend on sufficient understanding of the dynamics of
these interrelating factors.Characteristics of the agent or host are frequently seen as
independent factors. However, it is necessary to consider both the host and the agent together in any
discussion of the
relationship resulting in infection and disease. For example, smallpox was a disease of dramatic human
suffering; historically, it was one of the most feared of all infectious diseases.
Yet, the ability of the smallpox virus (variola virus) to infect and cause disease
only in humans and subhuman primates was an important consideration in approaches to control and prevention (i.e., vaccination of
the human population).[75] Consideration of the smallpox virus as highly virulent was
tempered by the fact that inoculation of this virus into many animal species did
not result in infection. In contrast, most Salmonella serotypes can cause mild to
severe infection in humans and in a variety of animal species. A notable exception is Salmonella
typhi, which causes
infections only in humans. Therefore, any description of the characteristics for either the
agent or the host must be understood in the context of their interrelationship.傳播鏈（管制對象三元素）Chain
of infection
病原 Infectious Agent
病人（感染或移生）
醫療工作人員、家屬
傳播
易感宿主
侵入性醫療處置
免疫抑制藥物
抗微生物制劑
慢性疾病等生理狀態微生物散播途徑
呼吸道：空氣傳播、飛沫傳播
接觸：直接接觸病人及其血體液分泌物，或接觸被污染之環境（含儀器、設施）
共同媒介
蟲媒感染管制策略
1、瞭解貯存窩
2、實施依部位之管制措施以避免由移生進展到感染
3、調整宿主（免疫狀態等）風險因素