Currently in the UK, patients with acute suspected gastroenteritis persisting for more than several days undergo routine faecal microbiology tests to investigate the cause of acute diarrhoea with or without vomiting. A decision tree model was constructed to see if the use of integrated multiplex PCR tests (xTAG, FilmArray and Faecal Pathogens B) is cost-effective compared with conventional care (the PHE pathway) for rapidly identifying gastrointestinal pathogens in people with suspected infectious gastroenteritis. In this section, the structure of the model is described. Conventional testing was chosen pragmatically as the benchmark for comparison within the model as it represents current practice.
Models developed
To assess the cost-effectiveness of integrated multiplex PCR tests compared with conventional care, a de novo decision tree model was developed in Microsoft Excel®(version 16, Microsoft Corporation, Redmond,
WA, USA). A decision tree model was the most appropriate choice as gastroenteritis is a self-limiting illness and usually stops within 2 weeks (i.e. diarrhoea lasts for 5–7 days and stops within 2 weeks and vomiting lasts for 1–2 days and stops within 3 days).58
The base economic model (model 1) includes hospitalised adult patients with suspected gastroenteritis (acute hospital admissions). The following subgroups of people with suspected gastroenteritis are explored in subsequent models: model 2, young children; model 3, people in the community; model 4, people who are immunocompromised; and model 5, people with a history of recent foreign travel (to areas other than Western Europe, North America, Australia or New Zealand).
Model 1: hospitalised adult patients with suspected gastroenteritis
The economic model was developed by determining the different clinical pathways for patients with suspected gastroenteritis. We have used information from the systematic review of clinical effectiveness, published literature and expert opinion to develop the different clinical pathways. The model structure is the same for both the GPP and conventional care arms (the main differences between the two arms are when test results are received and whether or not patients move from isolated to non-isolated care earlier, are treated earlier or are discharged earlier).Figure 10shows the overall structure comparing the different treatment arms,Figure 11shows the different pathways for patients who are isolated andFigure 12shows the different pathways for patients who are not isolated.
The pathway assumes that an adult patient is admitted to (or already in) hospital with suspected
gastroenteritis (diarrhoea and/or vomiting). A decision is made by the medical staff regarding whether the patient goes to a side room (isolated) or stays on an open bay/ward (not isolated). This decision may depend on the availability of isolation rooms.
The patient provides a stool sample to test for suspected gastroenteritis. The stool sample is then sent to the laboratory (or transported in some instances when the laboratory is not on site) for testing. The model
evaluates the consequences of using a multiplex integrated PCR test (xTAG, FilmArray or Faecal Pathogens B) or conventional testing. When results are returned, care is determined according to whether a pathogen(s) has or has not been detected. The presence of a pathogen is determined by conventional testing, as the benchmark test.
Isolated patients
In the following pathways,‘treatment’refers to pathogen-specific treatment over and above general care, hydration and hygiene management received by all patients. In the case of isolated patients in whom a pathogen has been detected, there are four options:
1. discharge the patient because symptoms have resolved 2. continue to isolate the patient and provide treatment
3. continue to isolate the patient and do not provide any treatment 4. deisolate the patient and do not provide any treatment.
With the final three options, symptoms can either resolve naturally, or can persist; in both cases, the patient is subsequently discharged when appropriate.
Isolate Conventional Not isolate Isolate x-TAG Not isolate Patient admitted to hospital Isolate FilmArray Not isolate Isolate Faecal Pathogens B Not isolate Go to faecal pathogen arm Go to faecal pathogen arm Go to conventional arm Go to conventional arm Go to xTAG GPP arm Go to xTAG GPP arm Go to FilmArray arm Go to FilmArray arm
FIGURE 10 Overall model structure for patients with suspected gastroenteritis comparing the different treatment arms.
No treatment – discharge
Symptoms resolve – discharge Isolate and treat
Symptoms persist – discharge Pathogen
Symptoms resolve – discharge Isolate and not treat
Isolate Symptoms persist – discharge Symptoms resolve – discharge Deisolate and not treat Symptoms persist – discharge Symptoms resolve – discharge No treatment – discharge Symptoms resolve – discharge Isolate and treat
No pathogen Symptoms persist – discharge Pathogen Symptoms resolve – discharge Isolate and not treat
Symptoms persist – discharge
Symptoms resolve – discharge Deisolate and not treat
Symptoms persist – retest Symptoms persist – discharge No treatment – discharge No pathogen Symptoms resolve – discharge Isolate and not treat
Symptoms persist – discharge Symptoms resolve –
discharge Deisolate – not treat
Symptoms persist – discharge
Stool sample received and test
conducted
Test results back
No treatment – discharge
Symptoms resolve – discharge
Isolate and treat
Symptoms persist – discharge
Pathogen
Symptoms resolve – discharge
Isolate and not treat
Not isolate Symptoms persist – discharge Symptoms resolve – discharge Not treat Symptoms persist – discharge Symptoms resolve – discharge No treatment – discharge Symptoms resolve – discharge
Isolate and treat No pathogen Symptoms persist – discharge Pathogen Symptoms resolve – discharge
Isolate and not treat
Symptoms persist – discharge Symptoms resolve – discharge Not treat Symptoms persist – retest Symptoms persist – discharge No treatment – discharge No pathogen Symptoms resolve – discharge Not treat Symptoms persist – discharge
In the case of isolated patients in whom no pathogen has been detected, there are three options: 1. discharge the patient because symptoms have resolved naturally
2. keep the patient in isolation because symptoms persist 3. deisolate the patient and do not provide any treatment.
Patients in whom symptoms persist undergo retesting. (These patients remain in isolation.) The second test results either will or will not detect a pathogen. Patients in whom a pathogen is detected follow the same care pathway as isolated patients in whom a pathogen has been detected. In the case of patients in whom no pathogen is detected there are two options:
1. discharge the patient because symptoms have resolved
2. continue to isolate the patient and do not provide any treatment.
In the latter case, symptoms can either resolve naturally or persist; in both cases, the patient is subsequently discharged. Among patients who have been deisolated and who have received no treatment, symptoms can either resolve naturally or can persist; in both cases, the patient is subsequently discharged.
Non-isolated patients
For non-isolated patients in whom a pathogen has been detected, there are four options: 1. discharge the patient because symptoms have resolved
2. isolate the patient and provide treatment
3. isolate the patient and do not provide any treatment 4. do not provide any treatment.
With the final three options, symptoms can either resolve naturally, or can persist; in both cases, the patient is subsequently discharged when appropriate.
Among non-isolated patients in whom no pathogen has been detected, symptoms can resolve naturally or persist. Patients whose symptoms have resolved are discharged. Patients with persistent symptoms are retested. Those patients in whom a pathogen is detected follow the same care pathway as non-isolated patients in whom a pathogen has been detected. For patients in whom no pathogen is detected, there are two options:
1. discharge the patient because symptoms have resolved 2. do not provide any treatment.
In the case of the latter option, symptoms can either resolve naturally or persist; in both cases, the patient is subsequently discharged when appropriate.