Humans

Resistance data can be used to support decisions on antibiotic therapy and may facilitate development or revision of treatment guidelines. Data can further be used to inform key stakeholders of the scale of the problem. Here you find guidance, methods and tools to measure antibiotic resistance patterns in bacteria isolated from humans, and can access selected databases and reports on the topic.

Data can be generated on a small or large scale. Conducting point prevalence studies or surveys is a good way to get started and can be useful to quickly assess the current situation. It is usually also possible to find some evidence of the resistance situation from for example scientific studies or initiatives within countries. Over time efforts can be scaled up and eventually act as inputs to national surveillance.

Point prevalence studies

Point prevalence studies (PPS) can be used for measuring a variety of components related to antibiotic resistance. Several parameters are usually measured during a limited period of time, for example one day. It can hence provide comprehensive results with relatively little effort. The studies can be repeated and thereby also provide useful data on trends and outcomes of interventions. Data from point prevalence studies can be used and analyzed independently or can be an input to larger surveillance efforts.

National surveillance systems

Broad-scale surveillance of antibiotic resistant bacteria of public health importance allows tracking of resistance trends and identification of new resistant strains. The WHO Global Antimicrobial Resistance Surveillance System (GLASS) was launched by WHO in 2015 in an effort to standardize surveillance across the world. Resources and information for setting up national surveillance can be found in POLICY: Implement the national action plan – Surveillance of antibiotic resistance.

Selecting pathogens and antibiotics

Selection of key pathogens and which antibiotics that should be tested on each isolate should be made prior to collecting antibiotic resistance data. It is also important to monitor which types of infections are prevalent within different settings to be able to choose relevant pathogens to monitor for resistance, see MEASURE – Infections for more information.

Susceptibility testing of bacteria

The most frequently used tests to determine if bacteria are susceptible or resistant to antibiotics are disc diffusion tests and minimum inhibitory concentration (MIC) tests. The MIC is the lowest concentration of an antibiotic that inhibits the growth of a bacterium. In order to determine if a bacterial strain is resistant to a specific antibiotic, clinical MIC break point values are used as guidelines. For example, the European Committee on Antimicrobial Susceptibility testing (EUCAST) provides break point values used in the European countries and are free of charge. The Clinical and Laboratory and Standards Institute (CLSI) also provides break point values, however, there is a fee for use. All results should be reported, whether bacteria are susceptible or resistant.

Please note that it is very important that all products used in susceptibility testing are of good quality. EUCAST issues warnings about known quality issues on their website.  

The microbiology laboratory

The clinical microbiology laboratory is an essential component of work to measure and monitor resistance in bacteria and for correct treatment of infectious diseases. For accurate results, the collection of patient samples should be standardized and follow good laboratory practice. Samples should be handled according to the methods described in manuals for basic laboratory procedures. It is important to take into consideration if the samples need to be transported to other laboratories for analysis, and make suitable preparations. Also, for monitoring bacterial resistance rates, an adequate number of samples is needed.

External quality assessment tools

Hospitals and laboratories undertaking surveillance activities should also participate in an external quality assessment (EQA) program. EQA is used for comparing the results from individual laboratories in the network with reference results. The WHO/NICD Microbiology EQAs program in Africa developed a manual that contains summaries of surveys and technical documents for setting up EQA programs.

Selected Resources