Table 1 Supporting quotations for Molecular Diagnostic Necessity theme

Positive results facilitate choosing targeted antibiotics

1. [Molecular diagnostics] would provide something more diagnostic than just a non-specific CRP or white cells that could guide specific antibiotic choice if we wanted to start them. Because, of course, in most cases, we just have to choose the most appropriate antibiotic based on what we think is the cause, which, depending on how concerned we are about the patient, it would be… the more concerned you are about them, or the more unwell they look, the broader-spectrum antibiotic you might choose. So, it could be helpful to perhaps not just start them on meropenem or Tazocin [Piperacillin/Tazobactam]. –P15, middle-grade trainee, Hospital 3

2. […] if you had something [i.e., molecular diagnostics] that could give you quicker results you could give someone more appropriate antibiotics from the start. –P20, early-career trainee, Hospital 4

3. [Molecular diagnostics] would mean your rationalisation of your antibiotic regime would be much faster. You’d be able to switch to one with the correct sensitivities within six hours rather than 12 to 24, which would be much better. –P21, middle-grade trainee, Hospital 3

Positive results lower threshold for starting antibiotics

4. […] if I had proof that there was a bacteria [sic] in someone who was spiking a temperature, then I think I would be more likely to start antibiotics. […] In the same way if I had a positive urine dip or a consolidation on a chest X-ray. –P44, middle-grade trainee, Hospital 1

5. […] even if there is a positive result in the test I would still think about starting it [antibiotics]. I wouldn’t start it automatically. –P8, consultant, Hospital 4

6. [Molecular diagnostics] might change what [antibiotic] I give but it wouldn’t decide whether I give anything. –P29, consultant, Hospital 4

7. For starting antibiotics, it would probably not be helpful to know the microbiology [i.e., molecular diagnostic results] as such. Because for starting antibiotics, or for a decision of which antibiotics, you need to have a context. Once you know that the patient is deteriorating in some way, and the context is triggering the confirmation that this is not inflammation, it is actually infection, obviously, to know what is going on in the body, with a name with a species, can make a huge difference, definitely. –P1, consultant, Hospital 3

Negative results indicate absence of respiratory infection

8. […] if that [molecular test result] was negative, I wouldn’t give her [vignette patient] any antibiotics. –P35, senior trainee, Hospital 2

9. If that [molecular test] comes up negative and I’ve got a patient who, yes, at the moment doesn’t look particularly infected, probably just still sit, watch and wait and see. […] But, a clear negative in a patient who’s otherwise now looking to be frankly septic, more septic than this does, then it might change the spectrum antibiotics I want to consider. So, say that [central] line was relatively new, so maybe I’m more suspicious of the line than I would have been otherwise. […] where it’s clearly negative, then it would change my thinking around other likely sources of infection. –P48, consultant, Hospital 1

Molecular diagnostic results increase confidence in prescribing decisions

10. [Having molecular test results] would mean that you can be confident that you’ve identified a pathogen that is sensitive, and that you could use a more narrow-spectrum antibiotic to focus that pathogen that you think is responsible for the sepsis, rather than having a bit of a panic using a broad-spectrum antibiotic. […] [Molecular results will] help a lot in terms of keeping the more powerful antibiotics for the situations in which you really need them. And that, in turn, will help to reduce the antibiotic resistance in the future. –P53, middle-grade trainee, Hospital 3

11. […] [If the molecular test] comes back positive, I come out of this state of diagnostic uncertainty, I feel much happier now. Because while I’m in the waiting zone I’m in a state of angst, have I made the right decision, have I made the wrong decision? […] And so great, if I’ve made a diagnosis more quickly, it’s lovely that we remove the diagnostic angst. And I can be happy that I’m now making a good decision for the patient and by proxy a good decision for the population. I don’t have to feel bad about needlessly increasing antibiotic resistance. –P43, consultant, Hospital 1