Diagnostic Bias in the COVID-19 Pandemic
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During the COVID-19 pandemic, healthcare systems have faced unprecedented pressures. One challenge has been to promptly recognize non-COVID-19 conditions. Cognitive bias due to the availability heuristic may cause difficulties in reaching the correct diagnosis. Confirmation bias may also affect imaging interpretation.

A 46-year-old man presented with dyspnoea at rest, dry cough, and malaise. He reported living with a family member with confirmed COVID-19. On examination, he was febrile with a 2 l/min oxygen requirement, and there were inspiratory crackles throughout both lungs. Chest x-ray (CXR) showed extensive bilateral air space shadowing and blood test results supported a provisional diagnosis of viral pneumonitis. Triaged to the COVID-19 admissions area, treatments were commenced accordingly. Pulmonary embolism was excluded on computed tomography pulmonary angiogram (CTPA) which showed widespread diffuse pulmonary changes, but notably also reported mediastinal lymphadenopathy and splenomegaly. Subsequently, the patient described a weight loss of 5 kg over 2 months.

Examination revealed a slim build with a body mass index of 19, oral leucoplakia, and small raised violaceous cutaneous lesions over the trunk. Given these findings, HIV infection was strongly suspected. The patient was moved out of the open ward area into a side room. Despite the patient reporting no risk factors for retroviral infection, the result of HIV serology was positive. Intravenous co-trimoxazole was given for suspected Pneumocystis jirovecii pneumonia (PCP), later confirmed on sputum polymerase chain reaction (PCR) testing. Under specialist HIV services, with an initial low CD4 count of 70 cells/mm3, the patient has responded well to antiretroviral therapy. His COVID-19 swab tests remained negative despite exposure to other ward patients and the risks of hospital-acquired cross-infection. On review of the CXR, it is noteworthy that the changes were predominantly perihilar and in keeping with PCP, unlike the patchy distribution seen in COVID-19 pneumonitis where changes may be more peripheral.

The availability heuristic during the recent pandemic may lead to cognitive bias in favor of COVID-19 diagnosis and delayed recognition of other conditions, especially in patients presenting with similar non-specific features.

Confirmation bias towards COVID-19 can also affect the interpretation of pulmonary imaging which is central to the investigation of cases with suspected pneumonitis.

Diagnostic bias can be mitigated by recognition and allowing time for a thorough clinical history and methodical examination of the patients.