4.3.2 Rapid testing

At the heart of diagnostic stewardship is timeliness – specifically, the need to deliver timely laboratory results to guide efficient and effective treatments.

Microbiology laboratories typically take 4–5 days to provide phenotypic antimicrobial susceptibility testing (AST) results. It takes around 48–96 hours for isolation and identification and 48–72 hours for AST to be completed using traditional methods. It takes longer for test results for food animals because of the transport time for samples to reach the laboratory.

In contrast to conventional culture methods, rapid testing aims to provide results in minutes to hours.

A key concern of traditional testing is that antimicrobial treatment often commences before laboratory results are available. This is referred to as empirical therapy, and it is when decisions are based on clinical judgment alone. Empirical therapy contributes to AMR because it can lead to unnecessary antimicrobial use (e.g. if the pathogen ends up being a virus) and inappropriate antimicrobial selection (e.g. use of broad-spectrum antibiotics). Empirical therapy is common in food animal medicine because of the challenges of accessing laboratory services and the high costs associated with testing.

Common technologies used for rapid testing include:

• antigen-lateral flow devices (LFD)
• SNAP tests (enzyme immunoassays for a range of diseases and chemicals)
• real-time polymerase chain reaction (qPCR).

You can find out more about what these technologies involve here [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] , as well as in the module E2 Isolating and Identifying bacteria (animal or human), at some time in the future.

There are many challenges in developing rapid tests that can perform as accurately and reliably as traditional methods. Many rapid tests are still in the development phase because of these issues and commercialisation costs.

In food animals, many of the rapid tests available or in development are designed to detect viruses (e.g. foot-and-mouth disease, rinderpest, high-pathogenic avian influenza). There are some laboratory-based rapid tests available for bacteria that can perform fast identification of bacteria and resistance genes or markers (e.g. PCR – see module E2) but they are usually only available in reference (and/or research) laboratories, access to which may pose transport and economic problems. However, ‘pen-side’ rapid tests for bacteria cannot yet replace the need for culture-based methods, and the equipment necessary to carry out the techniques listed above is relatively expensive, meaning it may have limited application in the animal health laboratories of many LMICs.

In practical terms, rapid test technologies that can be used in the field have the most potential in food animal medicine. These tests can be used as an initial screening test and assist with diagnostic decisions. For example, if the test confirms a viral pathogen, a decision may be made that antibacterials are unnecessary.

Rapid tests for use in the field for animal health should:

• be cheap to buy
• require minimal equipment
• be robust in field conditions (withstand dust, water)
• not require a power source
• be easy to use, with minimal instructions so farmers and farm workers can use them if needed
• need minimal sample preparation
• work at stable temperature (i.e. do not need refrigeration)
• produce rapid (