At the turn of the 20th century, physicians became more aware of pneumococcus, its relationship to pneumonia, and the increasing mortality rates associated with the illness. During this period, published papers which detailed the impact of pneumonia in the U.S. began to appear in medical journals. In 1900, pneumonia (and influenza) was the leading cause of infectious disease death and the third leading cause of overall death in the U.S.
By 1909, Ludwig Handel and Franz Neufeld of the Robert Koch Institute for Infectious Diseases in Berlin had developed a technique to categorize the different strains of pneumococci. Between 1915 and 1945, research focused on increasing the understanding of the structure of the S. pneumoniae bacteria, its ability to cause disease, and the impact of disease on humans. By 1940, more than 80 types of S. pneumoniae had been identified and described. S.pneumoniae was noted to be genetically diverse and identifiable by its unique outer capsule surrounding the bacteria. This capsule was found to be crucial in maintaining the pneumococci’s ability to cause infection because it prevented other cells from devouring it, in a process known as phagocytosis. The prevalence of a particular serotype (strain) was found to be dependent on geographical location, characteristics of the infected person, and the use of antibiotics and vaccines.
Changes in the prevalence of a particular S. pneumoniae strain within a population were also noted to have occurred throughout its history and it was determined that S. pneumoniae could frequently transform through a process known as recombination, or capsular switching. In this process, the bacterial cell incorporates DNA from other closely related bacteria into its own genome which enables it to adapt and allow it to become resistant to antibiotics or evade vaccine-acquired immunity.
