Quinn R W
Yale J Biol Med. 1982 May-Aug;55(3-4):265-70.
The frequency and severity of streptococcal infections and their sequelae have declined dramatically in the past century, yet the prevalence of streptococcal infections is still high. The reasons for this decline must be intimately related to host resistance, virulence of the agent, and environmental factors, especially crowding. Close examination of these fundamental influences does not reveal any evidence that humans have become less resistant to streptococcal infections, but they react less violently. There is some evidence that the agent may have lost a degree of its virulence. The decline in morbidity and mortality due to streptococcal infections began long before antibiotics, especially penicillin, were available. However, penicillin has proved to be an important factor in prevention of streptococcal infections, especially in rheumatic fever prophylaxis. There are certain indications that repeated streptococcal infections due to similar M types, occurring in young children over the past several decades, have resulted in some degree of immunity as well as the possible evolution of less virulent, but not less infectious, strains of group A streptococci. Also, a decrease in crowding would be expected to result in fewer streptococcal infections. Although there are more people in the world than at any other time in the history of man, urban population density in the western world, at least, is less than in the late 1800s and early 1900s.
在过去的一个世纪里，链球菌感染及其后遗症的发生率和严重程度已大幅下降，但链球菌感染的患病率仍然很高。这种下降的原因必然与宿主抵抗力、病原体的毒力以及环境因素密切相关，尤其是拥挤程度。对这些基本影响因素的仔细研究并未发现任何证据表明人类对链球菌感染的抵抗力降低了，只是他们的反应没那么剧烈了。有一些证据表明病原体的毒力可能有所下降。在抗生素，尤其是青霉素问世之前很久，链球菌感染导致的发病率和死亡率就开始下降了。然而，事实证明青霉素是预防链球菌感染的一个重要因素，尤其是在预防风湿热方面。有某些迹象表明，在过去几十年里，幼儿反复感染相似M型的链球菌，已产生了一定程度的免疫力，以及A组链球菌可能进化出毒力较低但传染性不减的菌株。此外，预计拥挤程度的降低会导致链球菌感染减少。虽然现在世界上的人口比人类历史上任何时候都多，但至少西方世界的城市人口密度低于19世纪末和20世纪初。
