1.3 Finding the ‘sweet spot’

Although reducing the number of unnecessary tests has many potential benefits for the patient and hospital, underuse of tests could result in serious infections going undiagnosed and untreated. One of the major objectives for diagnostic stewardship for AMR is to identify the ‘sweet spot’: reducing over-diagnosis and false positive results while benefitting from appropriately indicated testing and true positive results. Where this spot lies is infection- and population-specific: that is, related to disease prevalence.

For example, the use of urinalysis dipstick tests and urine culture in elderly female patients without signs and symptoms of a urinary tract infection (UTI) is debatable. These tests are often performed in patients with non-specific presentations (such as a fall or dizziness), and the symptoms are attributed to a UTI, with antimicrobials being prescribed. However, it is known that in this age group, patients often have low-level bacteriuria (bacteria in the urine) that, while not sufficient to cause a UTI, will result in a positive test. The patient will then receive unnecessary antimicrobials and the actual cause of their symptoms might not be properly investigated.

Another example comes with testing for Clostridioides difficile (C. difficile). Although C. difficile is an important infection (associated with AMU), a small proportion of patients carry C. difficile in their gastrointestinal tract without having active infection. Testing may therefore identify patients with colonisation or with resolving infections. There is a fine balance between colonisation and invasion by microorganisms; clinical assessment is required to determine whether the colonisingC. difficile has become dominant in the intestinal microbial population to such an extent that it causes harm to the patient.

A patient benefits from clinicians and microbiologists liaising with each other. If the patient has had a recent infection with C. difficile, there is no benefit to testing: we would still expect the test to be positive, and so it would be a waste of resources. Similarly, a patient with a positive test needs to be assessed to see if they have signs and symptoms of infection rather than colonisation, to prevent unnecessary treatment.

All of this must be balanced with the knowledge that C. difficile infection can be very severe, and is readily transmitted to other patients. Restricting testing too much might result in unrecognised and untreated C. difficile infection, which would result in harm to individual patients and a greater risk of cross-infection. This example demonstrates that providing a test also requires an appreciation of its appropriate use: this is the rationale for improving diagnostic stewardship (Baron et al., 2013).