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This article introduces what antibiograms are, their purpose, and a brief overview of how to develop them.

In the next two steps, we will be discussing surveillance. Setting up a local AMR surveillance system requires the collection of local data, and this needs to be based on local needs and resources. Antibiograms can inform guidelines for treating specific infections such as pneumonia or UTIs.

An antibiogram is a collection of data developed and maintained by a healthcare facility to show which organisms isolated from patient samples are susceptible to which antibiotics. Antibiograms can also describe and monitor antimicrobial resistance trends over time. The results are often presented as a table which could, for example, have separate lists for Gram positive and Gram negative bacteria. The information from local antibiograms helps inform the recommendations for the choice of antibiotics in a policy or guideline.

Microbiological support is needed from either a microbiologist or lab technician to process patient samples and conduct susceptibility testing, communicate with prescribers, and keep the antibiogram updated over time. These can be shared with another site where a small facility does not have laboratory facilities and staff. Microbiologists may be able to train clinical staff about effective sampling methods and help to develop antimicrobial use guidelines and policies from local resistance data. Clinicians can provide microbiologists with clinical and demographic data to help with analysis.

Developing an antibiogram

When considering how to develop an antibiogram, it is useful to consider:

  • What resources will you need?
  • What data do you want to collect?
  • How will you interpret your antibiogram?
  • How often will the antibiogram be used in your facility?
  • How often will the antibiogram be updated?

The diagram below shows the key steps in developing and communicating an antibiogram.

How to develop an antibiogram. For patient samples, include only one isolate per patient during the analysis period. For microbe isolates, include only diagnostic isolates, not surveillance isolates. When conducting antimicrobial susceptibility testing, calculate the percentage susceptibility and include only susceptible isolates, not those with intermediate susceptibility. For data quality checks include only final verified results and species with over 30 isolates tested, or else combine results over time or area. Communication of data should be done regularly and at least annually.

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This infographic is also available as a screen-reader compatible PDF.

When developing an antibiogram, consider the following tips:

  • Analyse/present data regularly, at least annually.
  • Include only final, verified results.
  • Include only species with ≥ 30 isolates tested (in certain circumstances, > 30 isolates may not be available – in this case combine two consecutive years’ isolates into the calculation).
  • Include diagnostic (not routine surveillance/screening) isolates.
  • Information only on antimicrobials routinely tested in the laboratory.
  • Include the first isolate per patient in the period analysed, irrespective of the body site from which the specimen was obtained or the antimicrobial susceptibility pattern.
  • Calculate the percentage susceptibility because clinicians would generally avoid prescribing an antimicrobial if a test result indicates intermediate susceptibility.
  • Isolates with intermediate susceptibility should not be included in the calculation of the percentage of isolates that are susceptible.

An aggregate antibiogram can be developed from cumulative records of antibiotic use against isolated organisms in a local area and can include data from multiple healthcare facilities. As well as summarising data about local antimicrobial resistance patterns, an aggregated antibiogram can help to compare susceptibility rates between facilities, to identify prescribing challenges and to monitor trends over time.

Below is an example of an aggregated or cumulative antibiogram, taken from the WHO toolkit (page 85).

Example section of percentage susceptibilities in a cumulative antibiogram. There is a table with a list of Gram negative bacteria on the left and some example antibiotics along the top of the table. The numbers in the table represent the example percentage susceptibilities of each organism tested against each antibiotic.

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Update and Use

Computer support is ideally needed to extract data and update antibiograms. In the absence of dedicated IT support, software such as the free WHONET software can help with the analysis. The antibiogram should be rapidly accessible by all clinicians, perhaps via the facility’s intranet. An antibiogram that is regularly used by prescribers and updated in communication with laboratory staff can be used to inform clinical guidelines (as shown below) and is a vital part of a facility’s ASP.

Flowchart of how cumulative antibiograms help define local antibiotic prescribing guidelines.

Now it’s your turn! Does your facility have the resources and expertise to prepare and use antibiograms? How have you used Antibiograms in your practice? Share your answers in the comments below.

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How to set up an Antimicrobial Stewardship Programme

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