Mathematical models as tools for evaluating the effectiveness of interventions: a comment on Levin

An individual-based network model to evaluate interventions for controlling pneumococcal transmission

Background

Streptococcus pneumoniae is a major cause of morbidity and mortality worldwide, but also a common colonizer of the upper respiratory tract. The emergence and spread of antibiotic resistant pneumococcal strains has threatened effective therapy. The long-term effects of measures aiming to limit pneumococcal spread are poorly understood. Computational modeling makes it possible to conduct virtual experiments that are impractical to perform in real life and thereby allows a more full understanding of pneumococcal epidemiology and control efforts.

Methods

We have developed a contact network model to evaluate the efficacy of interventions aiming to control pneumococcal transmission. Demographic data from Sweden during the mid-2000s were employed. Analyses of the model's parameters were conducted to elucidate key determinants of pneumococcal spread. Also, scenario simulations were performed to assess candidate control measures.

Results

The model made good predictions of previous findings where a correlation has been found between age and pneumococcal carriage. Of the parameters tested, group size in day-care centers was shown to be one of the most important factors for pneumococcal transmission. Consistent results were generated from the scenario simulations.

Conclusion

We recommend, based on the model predictions, that strategies to control pneumococcal disease and organism transmission should include reducing the group size in day-care centers.

Evolving Concepts of Pharmaceutical Company–Sponsored Surveillance Studies

As a result of increasing bacterial resistance to antimicrobial agents, there is a need to conduct studies that monitor changes in susceptibility. In addition to studying the emergence and dissemination of antibacterial resistance, pharmaceutical companies perform surveillance studies for a number of reasons. As an example, the Alexander Project was conducted to study community-acquired respiratory infections internationally over 10 years. The project's findings have been valuable in the study of antimicrobial resistance. The Alexander Project has also been instrumental in the study of the evolution of resistance genes and in predictions of future rates of resistance, as well as in establishing the importance of high-quality data, the complexity of the evolution of resistance, and the need to disseminate the results in a variety of formats. Although there has been a reduction in pharmaceutical company studies, consolidated efforts between industry, government, and private groups have increased. Future surveillance efforts by pharmaceutical companies will likely be more targeted and disease directed.

The use and resistance to antibiotics in the community

The frequency of resistance to antibiotics among common community-acquired pathogens, and the number of drugs to which they are resistant have been increasing worldwide. The relationship between antibiotic usage and resistance is strongly supported by data from several studies. Countries with the highest per capita antibiotic consumption have the highest resistance. The emergence of penicillin-resistant Streptococcus pneumoniae is related to high consumption of antibiotics in general, as well as to increased use of aminopenicillins and/or probably to wider use of oral cephalosporins. Increased consumption of macrolides, especially the long-acting ones, correlates significantly with the level of macrolide resistance of group A streptococci and S. pneumoniae while increased use of oral cephalosporins might be associated with the increase of beta-lactamase-producing strains of Moraxella catarrhalis. Trimethoprim/sulphamethoxazole resistance is strongly associated with resistance to penicillin. A rise in consumption of fluoroquinolones is consonant with a higher rate of resistance to quinolones of S. pneumoniae, Escherichia coli and other Gram-negative bacteria. Paediatric bacterial isolates are more often resistant to various antimicrobial agents than isolates from adult patients; this higher resistance rate may be due to more frequent antimicrobial treatments in children, and extensive child to child transmission. Reliable data on antimicrobial consumption and resistance should form a basis for national policies devised to reduce the resistance of microorganisms to antibiotics.

Antibiotic policies and control of resistance

PURPOSE OF THE REVIEW

The current worldwide pandemic of antibiotic resistance shows no signs of abating. It is clear that it is driven mainly by heavy and often inappropriate antibiotic use. Although control measures are widely practised, it is important that we assess their efficacy critically in order to concentrate expensive control efforts where they will be most effective. The past year has seen much activity in this area, with evidence-based assessments of the literature according to strict guidelines, as well as progress in basic science studies of mechanisms of resistance, and their causes and relations to pathogenicity and adaptability.

RECENT FINDINGS

The present review summarizes current developments in the causes of antibiotic resistance, the classification of antibiotic stewardship and control measures, the evidence base for their efficacy, current problems in hospital practice, the adaptability of bacteria, the content of antibiotic policies and anticipated activities.

SUMMARY

The conclusions from the published literature are that much of it that pertains to changing prescribing practices does not stand up to modern evidence-based analysis concepts. Nevertheless, we can learn from experience in changing other areas of medical practice. We must be pragmatic and must not expect to change the world, but rather take it step by step, recognizing barriers and measuring outcomes and quality indicators. Studies into the molecular basis of resistance confirm the superb genetic adaptability of micro-organisms. They will always be several steps ahead of us. Nevertheless, we are learning how to modify our prescribing habits to minimize resistance, not only by using antibiotics less frequently but also by altering dosing schedules in various ways.