Antibiotic resistance among pneumococcal infections is a recognized problem and one that has generally been increasing worldwide. Resistance has led to changes in empiric therapy for meningitis and otitis media in several countries. Studies from Finland, Russia, and South Africa indicate increasing prevalence of resistance to macrolide and beta-lactam antibiotics (see posters RES-40, 33, 26). Now, researchers are beginning to hone on the molecular mechanisms of resistance and particularly the clones of resistant infections that are driving much of this problem (see posters RES-11, 17, 21, 27, 35, 37, 42, 44).

According to Prof. Keith Klugman, co-chair of the Scientific Session on Antibiotic resistance, “Our understanding of the molecular basis of antibiotic resistance among pneumococci has never been better and is expanding everyday. Further research in this area is critical for improving our approaches to treatment and prevention of pneumococcal infections everywhere.”

Dr. Shabhir Madhi is co-author on poster presentations highlighting both the problem of antibiotic resistant infections and a potential solution. On the one hand, Dr. Madhi is co-author of a poster from South Africa highlighting an increase in beta-lactam resistant infections (see poster RES-26). Between 1999-2002, among children <5 years of age, the proportion of invasive isolates resistant to penicillin increased from 27% to 36%. On the other hand, he also reports from a randomized trial of 9-valent pneumococcal conjugate vaccine that vaccination reduced the risk of penicillin resistant infections by 52% (see poster RES-32). In each case, he stresses that continued vigilance is essential.

“The combined implications of these two studies are that while some factors are driving up antibiotic resistance in pneumococci, we can begin to prevent many of these infections by vaccination.”, says Dr. Scott. “While the vaccine’s efficacy is a big step forward, we can’t let ourselves get overconfident. Continued careful surveillance for invasive pneumococcal disease and routine testing of antibiotic resistance are essential.”

Mathematical models of transmission dynamics represent powerful tools for understanding the potential effects of various interventions. In the Modeling and Herd Immunity session, researchers from UK, Germany, and France present models showing a wide variety of health impacts of pneumococcal disease and vaccination. Using data from a longitudinal study of pneumococcal carriage conducted in UK families, Melegaro and colleagues developed a model to estimate transmission from the community and within the family (see oral presentation MOD-03). According to the authors, differences in serotype-specific transmissibility and carriage duration have important implications for vaccine effectiveness.

In Germany, Claes and colleagues estimated the potential health and economic impact of herd immunity in adults following routine infant immunization with pneumococcal conjugate vaccine (see poster MOD-11). Using a Markov model, they estimated that, through herd immunity, a routine infant immunization could prevent nearly 60,000 invasive pneumococcal infections and 2,700 deaths among German adults and result in a savings of >54 million EURO.

From France, a word of caution. A mathematical model developed by Temime and colleagues predicts that in high antibiotic exposure environments, including France and other southern European countries, vaccination has less of an impact on the risk of penicillin-resistant pneumococcal meningitis than in lower antibiotic use environments such as the USA (see poster MOD-14).

“Mathematical modelling offers a way to integrate and interpret epidemiologic and biological data to understand pneumococcal populations and how they react to interventions like vaccinations and antibiotic treatment,” says co-chair, Dr. Marc Lipsitch of Harvard University.

The genetic diversity of the pneumococcus is one of the most important challenges in terms of developing vaccines. Phylogenetic characterization of a collection of pneumococci from diverse settings and clinical states can provide insights into vaccine development, according to a study from Huot and colleagues at the Boston University Medical Center in the USA. Their study included 1100 pneumococcal isolates from 15 countries and both asymptomatic, colonized individuals and patients with different pneumococcal diseases. According to their study, serotypes included in and not included in the current pneumococcal conjugate vaccines were closely related genetically. This finding implies that any capsule type might become associated with any genetic backbone by horizontal transfer and hence allow for new pathogenic strains to emerge.

In short, genetic diversity makes pneumococci formidable opponents to our prevention efforts.