Hepatitis B has four subtypes. In his investigations Chen found that among citizens of Taiwan, who originate from all over China, those of northern Chinese origin hosted the North China subtype. Even their children, who were born and raised in Taiwan, carried the same subtype. From this Chen inferred that the main source of infection of hepatitis B in Taiwan is not the greater environment, but the family.
B 型肝炎有 4 種亞型，陳定信在調查中發現，在各省籍雲集的台灣，華北人到了台灣，身上的 B 肝病毒卻還是華北亞型，甚至連他們在台灣土生土長的子女也都屬同一亞型，由此推知，台灣 B 肝的主要感染源不是來自大環境，而是家庭。