Discussion
The WHO guidelines on triage recommend that all patients with suspected or confirmed COVID-19 are clinically triaged.19 In many countries, this proves challenging due to national policy, healthcare accessibility, healthcare resources and the level of community transmission of SARS-CoV-2. Most patients with COVID-19 do not develop complicated illness and will resolve the infection without clinical intervention. Successful clinical pathways are able to pick out the COVID-19 pneumonia reliably and, crucially, early enough for basic medical care to prevent progression of disease.
There have been noticeable improvements in the symptom checkers that were first analysed in April 2020. Notably, the overall referral rate onward to healthcare contact has increased in the USA, UK and Singapore. Other features of the symptom checkers have also been improved. Singapore has included a question on immunosuppression, although it still does not confer such patients to more urgent care. The CDC coronavirus symptom checker has now included age as a defining risk factor. Most symptom checkers have expanded the list of comorbidities affecting triage decisions. And while the seriousness of breathlessness is given variable attention by each national symptom checker, all seem to now give it more weight in triage decisions. While these changes move towards re-establishing the usual standards of care for patients with COVID-19, our results indicate that COVID-19 symptom checkers are too unreliable in discriminating mild from severe COVID-19, and, as such, are likely to confer too great a risk to public, and, if used in place of clinical triage, will only weaken the healthcare response to the pandemic.20
Specifics
Whether the CDC coronavirus symptom checker has in fact worsened outcomes for the USA or not remains unknown. It has not been formally integrated into the US healthcare system or COVID-19 clinical pathways. The fact it functions as a stand-alone patient-led triage service and is freely accessible to the public is concerning. While not formally or preferentially directed to the symptom checker, the US public can seek clinical advice from the automated service, and thereby, potentially—in the patient’s mind—negate the need to undertake actual clinical triage. Given it cannot reliably differentiate between mild and severe COVID-19, any reassurance provided is neither dependable nor evidence based. For example, the CDC coronavirus symptom checker still advises the 63 years old with a 7-day history of persistent fever and worsening cough to remain at home without contacting their healthcare service provider. In the absence of any discoverable quality and safety studies supporting its use, it would seem prudent to discontinue the use of the CDC coronavirus symptom checker until the CDC can prove its efficacy and safety, as would be the case for any diagnostic test.
Singapore remains consistent in its approach to the clinical management of COVID-19.21 All suspected cases of COVID-19 are clinically assessed by a physician and followed-up by primary care.22 This is consistent with the WHO technical guidelines and clinical recommendations for triage and management of COVID-19.19 During our previous analysis in April 2020, Singapore was suffering a surge of COVID-19 infections. The symptom checker was then set to advise the young, non-breathless patient with no comorbidities and a short duration of illness to self-isolate and contact the public health clinic if symptoms worsened or had not improved by day 4.2 This remains a compromise to normal clinical care but may have achieved a low-risk reduction in healthcare burden. Now, with SARS-CoV-2 prevalence less than in April 2020, all suspected cases are clinically assessed.
Unlike the CDC and Singapore COVID-19 symptom checkers, the NHS ‘111’ symptom checkers have a clear and critical role in the national clinical response to COVID-19.8–11 Current advice in the UK to the public (including from contact tracers) is to self-isolate if COVID-19 is suspected or confirmed and if concerned about symptoms to use NHS 111 online services or call ‘111’.23 Altogether this has generated—even during the low SARS-CoV-2 prevalence period of this analysis—around 30 000 online triages per month in England, including around 900 online triages in those 70 years old and over.24 The NHS 111 COVID-19 symptom checkers act as a gatekeeper for further clinical contact. As such, the reliability of the UK’s symptom checkers and the triage criteria set by NHS 111 is critical to COVID-19 patient outcomes and associated healthcare usage.
The NHS England symptom checker has increased the rate of onward referral since April 2020 and now refers patients with self-rated mild or moderate breathing difficulties to call ‘111’. From both a patient safety and healthcare burden perspective, this is a welcomed improvement. However, the NHS England symptom checker (and to some degree the NHS Wales symptom checker) continues to attempt to quantify disease severity with subjective questions and qualifiers likely to cause under-reporting of true disease severity, as it did previously.2 It fails to reliably identify severe COVID-19 or other time-critical COVID mimickers.
Only the NHS Wales symptom checker accounted for age in the triage decision of the cases simulated. The reason for NHS Scotland, England and Northern Ireland not accounting for age—the most reliable predictor of disease severity—remains unclear.
None of the NHS symptom checkers account for ‘silent hypoxia’ (case scenario 1, online supplemental data). Silent hypoxia is the presence of hypoxia (low blood oxygen levels) without any sensation of breathlessness. It indicates severe or critical COVID-19 pneumonia and requires immediate inpatient care. Silent hypoxia affects up to one-third of patients presenting to hospital and carries a poorer prognosis.25 26 The inability of the NHS 111 symptom checkers to identify cases suffering silent hypoxia is likely a terminal limitation to the success of such severity-based symptom checkers as viable triage tools for COVID-19.
The attempt of the NHS 111 COVID-19 symptom checker to determine if COVID-19 is present, then to assign a severity level (ie, non-severe), constitutes a diagnostic process.27 Given the NHS England symptom checker (and all UK national symptom checkers) then provide the clinical advice to ‘self-isolate’ and detailed advice on how to manage symptoms such as cough and breathlessness at home,28 it breaches the boundary between simple signposting (simply deciding who is the most appropriate next healthcare contact) and ventures into the area of diagnosis and clinical management (deciding what treatment is appropriate based on an assessment). The NHS 111 COVID-19 symptom checker should then, at the very minimum, be subject to the same quality standards as any other diagnostic test, including national regulation.
As the UK clinical COVID-19 pathway is heavily reliant on such symptom checkers, together with the subsequent diversion of patients away from actual clinical triage, the NHS 111 symptom checkers are likely to be contributing to the UK’s poor pandemic response, including the high morbidity and mortality. Also of growing concern is the impact the NHS 111 symptom checkers are likely to have on the resilience of society to tolerate background levels of SARS-CoV-2 and post-pneumonia complications (eg, long COVID-19) by delaying presentation of COVID-19 pneumonia to timely, appropriate medical care.
Given the NHS ‘111’ symptom checkers have ventured into diagnosis and, arguably, clinical management, are currently gatekeepers to further healthcare access, fail to reliably triage severe COVID-19 on to further care, fail to account for age as a risk factor (except NHS Wales) and are likely to miss COVID-19 mimickers such as bacterial pneumonia, considerable improvements are needed to render the current NHS 111 COVID-19 symptom checkers fit for purpose.
Future Direction
The use of symptom checkers as part of the national clinical care pathway for COVID-19 (and future pandemics) requires considerably more research and validation.29 Currently, none of the symptom checkers pose a viable option in replacing clinical triage, and as such, effort should focus on resourcing clinical triage services.
Data relating to the use of symptom checkers and the effects these have on future healthcare burden have not yet been analysed. At an operational level, the possibility of severity-based symptom checkers leading to an increase in healthcare burden, including an increase in high-dependency admissions, should sponsor caution and an urgent review of any care pathways depending on such forms of patient-led triage. Our analysis suggests, severity-based COVID-19 symptom checkers (such as the NHS 111 or CDC versions) are likely to increase the healthcare burden associated with the pandemic (in comparison to clinically led, remote triage).
There is the equally challenging obstacle of national versus local triage to overcome. The current NHS 111 symptom checker triages nationally using the same referral thresholds. This may have contributed to the disproportionate healthcare activity across the UK.27 Where a national symptom checker is ‘set’ to respond to critical demand in, for example, London, those using the symptom checker in an area of low demand, for example, the Lake District, will also be held to the same, compromised and rationed access to healthcare. This goes against the principles of triage, in that triage decisions must be responsive to resource availability. It is not justifiable—or logistically savvy—to ration access to healthcare preemptively or without a definitive need to.
In the short term—pending further safety studies—a ‘risk-based symptom checker’ may provide a possible low-risk solution to signposting potential COVID-19 cases, under pandemic conditions. The usual standard remains an actual clinical assessment, but where healthcare resources are insufficient for such a standard of care, an untested symptom checker that can be adjusted in response to risk and demand would be preferable to an untested symptom checker attempting to determine clinical severity from an automated algorithm. A national symptom checker may still have a role in risk stratifying, and with the benefit of postcode localisation, there may be an ability to adjust the ‘risk necessary to take’ more accurately and based on local demands. Such a national service providing local risk stratification must be dynamic and responsive to demands, be under constant data collection and review, and be viewed as a considerable compromise to usual standards of care.
Whatever future version of COVID-19 symptom checkers manifest, they must be designed with the intention of detecting progressive COVID-19 or those at risk of severe disease, not designed with the intention of preventing healthcare contact. Triage itself is not resource saving. But the effort invested in the triage process yields high returns when cases of progressive COVID-19 pneumonia are detected early enough to avoid costly, protracted and complicated admissions. Triage systems must be viewed for what they are: an opportunity to maximise the use of available resources to prevent death, avoid disability and improve healthcare resilience.