Antibiotic Resistance Surveillance Indicators

Monitoring antibiotic resistance involves numerous indicators, which vary depending on the bacterial species and the antibiotics being studied. To prioritize this monitoring, relevant bacteria-antibiotic pairs have been defined by microbiologists based on the therapeutic importance of the molecules and the level of resistance to them. Following the same principle, yeast-antifungal pairs are studied. The level of a bacterium’s resistance to an antibiotic is measured using various techniques (inhibition zone diameter, minimum inhibitory concentration, etc.). It is then translated into semi-quantitative classes (susceptible, intermediate, or resistant) for clinicians based on critical values defined in France by the Antibiogram Committee of the French Society of Microbiology (CA-SFM). The indicators produced can target either bacteria with reduced susceptibility (intermediate and resistant) or only resistant bacteria. Multidrug resistance primarily affects bacteria responsible for nosocomial infections, but also those responsible for community-acquired infections. The emergence of multidrug resistance is a step toward a therapeutic dead end. A bacterium is said to be multidrug-resistant to antibiotics when, due to the accumulation of acquired resistance to several families of antibiotics, it is no longer sensitive to more than a small number of molecules usable in therapy. Finally, for tuberculosis in particular, resistance data are stratified based on whether cases have already been treated or have never been treated with the standard antibiotics. Two types of indicators are commonly calculated to quantify bacterial resistance to antibiotics

Proportion within the species

The proportion of resistance within the species is generally the first indicator used. This indicator can be generated directly by laboratories but relies on two prerequisites: the collection of identical information for both resistant and non-resistant strains, and the deduplication of strains identified in the same patient over the study period. This indicator is very meaningful to non-specialists and is used by clinicians to guide their prescribing practices.

Incidence

Incidence is used to reflect the spread of infections caused by antibiotic-resistant bacteria. In hospital or community settings, the denominator for the cumulative incidence is the number of admitted patients (the indicator is then applicable only to short-stay facilities) or the number of residents. During an epidemic and when the denominator is a number of people (admitted patients or residents), the cumulative incidence is called the attack rate.For incidence density (ID), used primarily in hospital settings, the denominator will be the number of hospital days. This indicator is best suited for tracking long-term transmission dynamics and assessing the impact of prevention measures within the program to combat multidrug-resistant bacteria.

Frequency and Level

Currently, the available data are primarily national data updated annually. The emergence and spread of antibiotic-resistant bacteria are phenomena with slow dynamics. Thus, annual surveillance provides sufficient monitoring of the evolution of bacterial resistance in France. This frequency is the standard at the European level and in the vast majority of countries. Some national surveillance networks have sufficient coverage to conduct regional analyses and have identified disparities from one region to another (for example, the BMR-Raisin network regarding the incidence of MRSA or ESBL-producing E. coli). The availability of representative regional data on antibiotic resistance should be encouraged, as it is of interest to prescribers. However, these regional disparities still need to be better understood.