Long-term data show adaptability of pneumococcus, despite medicines, vaccines

During the past seven decades, the epidemiology of invasive pneumococcal disease as well as individual serotypes has changed, with pneumococcal conjugate vaccine serotypes being most dominant, according to study findings.

To better understand why invasive pneumococcal disease is still a major contributor to worldwide morbidity and mortality, researchers in Denmark conducted a retrospective, cohort study based on nationwide laboratory surveillance data of invasive pneumococcal disease from 1938 to 2007.

There were 25,502 registered invasive pneumococcal disease cases. For the first 40 years, the reported median incidence of invasive pneumococcal disease was 2.8 cases per 100,000 population, but this number rose during the 1980s and 1990s to 15.7 cases per 100,000 population. The researchers connected this increase to a rise in bacteremia cases. Additionally, they noted incidence rates remained highest in high-risk groups: children aged younger than 5 years and adults aged 65 years or older.

The researchers said that the increasing prevalence of vaccine serotypes was related to the more recent widespread use of antibiotics and the subsequent selective pressure “that favored an increase in the prevalence of the serogroups represented in PCV7 that often were associated with antibiotic resistance.” However, the emergence of nonvaccine serotypes, such as 19A, was also a concern due to known antibiotic resistance.

The researchers acknowledged that the use of a small, relatively homogenous population in Denmark may have caused the results to be less applicable to other countries. However, they wrote that they hoped “this study will contribute to the understanding of pneumococcal disease and support vaccine developers and policy makers in their evaluation of the epidemiological aspects of pneumococcal disease in the future.” – by Melissa Foster

Harboe ZB. Clin Infect Dis. 2010;50:329-337.

PERSPECTIVE

Denmark has a remarkable resource for the study of pneumococcal infections; the Statens Serum Institut has been serotyping pneumococcal isolates since 1937. National laboratory surveillance was collected uninterruptedly from 1937 for more than 25,000 isolates from cases of invasive pneumococcal disease (IPD).

The pneumococcal conjugate vaccine (PCV7) was introduced in 2007 and this article, published in Clinical Infectious Diseases, provides changes in disease incidence, serotype distribution and antibiotic resistance over the 70 years beginning in 1937 and prior to introduction of PCV7.

Although bacteremia increased during the 1980s and 1990s (likely due to increased number of cultures of blood obtained from patients with pneumonia or fever), the incidence of meningitis remained relatively constant.

The epidemiology of serotype distribution is similar to that described in the United States: types 1, 3 and 5 were dominant during the preantibiotic period followed by a decrease in their incidence over the subsequent years; type 2 almost disappeared; PCV7 serotype/groups 6, 7F, 14 and 23F were important through the surveillance period.

The emergence of serotype 19A as an important pathogen has been noted in the United States and other countries since introduction of PCV7, but 19A was identified as increasing in importance in Denmark in 2003 — prior to the introduction of PCV7. These data support the concept of the plasticity of the pneumococcus and the ability of the organism to adopt to the environment and present as an important pathogen, despite efforts through drugs and vaccines to diminish its importance.

– Jerome Klein, MD

Infectious Diseases in Children Editorial Board