Hidden diagnosis behind viral infection: the danger of anchoring bias

Abstract

Anchoring bias is one of the most common diagnostic biases that may lead to closed-minded thinking and could result in unnecessary tests, inappropriate patient management and even misdiagnosis. A 4-year-old boy was brought to the emergency department because of shaking chills. On the basis of bilateral swollen preauricular areas, high level of serum amylase and the prevalence of mumps, he initially received a diagnosis of mumps in spite of the shaking chills. However, blood culture turned out to be positive for two different kinds of bacteria. The patient finally received a diagnosis of polymicrobial bacteraemia resulting from suppurative appendicitis. We must consider and rule out bacteraemia in the differential diagnosis for patients who present with shaking chills, even in the presence of symptoms or information consistent with a more common viral infection such as mumps. In addition, intra-abdominal infection should be ruled out in the presence of polymicrobial enterobacteriaceae bacteraemia.

Background

In the emergency department (ED), anchoring bias is one of the most frequent cognitive biases which could eventually lead to unnecessary tests, inappropriate patient management and even misdiagnosis. As there are many chances to make a cognitive error, physician must be aware of the dangers of cognitive bias, such as anchoring bias. We report a case where a physician was influenced by anchoring bias. Moreover, the patient was found to have a polymicrobial bloodstream infection resulting from suppurative appendicitis.

Case presentation

The patient was a 4-year-old boy who had no medical history, including mumps. Also, he was never vaccinated against mumps. Three days prior to admission, he had a fever of 38°C, sore throat and a swollen preauricular area. Two days prior to admission, he received a diagnosis of mumps by a family physician because bilateral preauricular areas were swollen and mumps was prevalent in the nursery school. He gradually developed nausea, diarrhoea and periumbilical abdominal pain.

The day before admission, he was brought to the ED because of shaking chills that lasted for 20 min and lip cyanosis. He did not have abdominal pain. His general appearance was good. Vital signs on arrival were significant for a heart rate of 172 bpm and an axillary body temperature of 39.9°C. Physical examination revealed that bilateral preauricular areas were swollen and tender. He had no abdominal tenderness or other signs suggesting peritonitis. Laboratory findings were as follows: white cell (WCC) count 1.2×10⁹/L with 43% neutrophils, platelet count 100×10⁹L, amylase 304 U/L, C reactive protein (CRP) 1.93 mg/dL. Blood cultures were also obtained because we considered bacteraemia in the differential diagnosis at this point because of shaking chills and tachycardia. However, at that moment he received a diagnosis of mumps on the basis of clinical manifestations, elevated amylase level and the high prevalence of mumps at his nursery school. Therefore, he was discharged. We assumed that the low levels of WCC and platelets were due to myelosuppression triggered by viral infection.

Twelve hours after obtaining blood cultures, the cultures were positive for gram-negative rods and gram-positive cocci and later identified as Escherichia coli and Streptococcus bovis, respectively.

On the day of admission, we had called him to revisit the hospital because he likely had bacteraemia. Vital signs at this time were as follows: respiratory rate of 22bpm, heart rate of 110 bpm and an axillary body temperature of 37.4°C. Physical examination showed periumbilical abdominal tenderness, but he did not have rebound pain. WCC and CRP were elevated to 23 340/µL and 15.76 mg/dL, respectively. Suspecting intraperitoneal infection according to the results of physical examination and blood culture, we performed a contrast-enhanced abdominal CT scan. The CT scan showed an inflamed appendix distended by fluid with parietal hyperenhancement and an appendicolith within the lumen. Furthermore, defect foci of the wall were seen (figure 1). The final diagnosis was acute perforated appendicitis complicated with parotitis. He underwent a laparoscopic appendectomy and was administered antibiotics intravenously. He was discharged 15 days after the operation with neither abdominal complications nor preauricular swelling. The cultures of ascites fluid and abscess in the appendix revealed the same bacteria as from the blood cultures obtained the day before admission.

Figure 1.

The contrast-enhanced abdominal CT scan shows an inflamed appendix distended by fluid with parietal hyperenhancement and an appendicolith within the lumen (circle).

Outcome and follow-up

He was discharged 15 days after the operation with neither abdominal complications nor preauricular swelling. When he was followed up on 18th days of discharge, his general condition was good and did not have any sequelae.

Discussion

We presented a patient initially receiving a diagnosis of mumps despite the presence of shaking chills, which later turned out to be a polymicrobial bloodstream infection resulting from a perforated appendicitis. This case is instructive in addressing two important issues. One is the danger of anchoring bias in the ED, which can result in unnecessary tests and even lead to misdiagnosis. Another is the need to rule out intra-abdominal infection in the presence of polymicrobial enterobacteriaceae bacteraemia.

First of all, generally, we must consider and rule out bacteraemia in the differential diagnosis for patients who present with shaking chills and tachycardia, even in the presence of symptoms or information consistent with a viral infection, such as mumps. According to previous reports, shaking chills in febrile children significantly increase the likelihood of bacterial infection.^{1 2} It is critical to perform blood cultures so as not to miss bacteraemia when there are suggestive symptoms of bacteraemia such as shaking chills,¹ even in children.² In the present case, although the presence of shaking chills was a critically important sign suggestive of bacteraemia,^{1 2} we were biased in our interpretation due to anchors strongly indicating mumps infection. However, we were able to salvage the case by obtaining blood cultures. Anchoring is the tendency to fixate on specific features of a presentation too early in the diagnostic process.³ There are quite a few case reports suggesting that cognitive biases were associated with diagnostic errors.⁴ Although all physicians can make some cognitive errors, emergency physicians should pay additional attention to diagnostic biases because clinical decision-making in the ED has unique characteristics. That is to say, physicians in the ED must see many patients at the same time, including those who are referred from other hospitals with a prior diagnosis. Therefore, physicians in the ED can easily get into a situation where cognitive errors could occur.³ It is, first of all, critical to be aware of biases and strategies for debiasing.⁵ Symptoms and other clinical information that do not match the diagnosis should raise an index of suspicion for a hidden underlying pathology.

Another issue is that intra-abdominal infection should be ruled out in the presence of polymicrobial enterobacteriaceae bacteraemia. The rate of blood culture positivity in acute appendicitis is actually low. A prospective study revealed that systemic bacteraemia was 0% at 30 min before surgery and 6% during surgery.⁶ Furthermore, blood cultures became positive in only 10% of cases of acute appendicitis with perforation, and an extremely low percentage in appendicitis without perforation.⁷ In general, the cause of acute appendicitis is polymicrobial infection. An average of 10 different organisms were isolated from surgical specimens.⁸ Blood cultures which were obtained from the mesenteric vein during surgery became positive in 38%, and 63% (12/19 cases) of them were polymicrobial infection.⁶ Although systemic polymicrobial bacteraemia was not reported as common in the previous study, there is the theoretical possibility of polymicrobial bacteraemia from acute appendicitis with perforation. Despite the theoretical basis for developing polymicrobial bloodstream infection in patients with appendicitis, this has rarely been reported in previously healthy children. Polymicrobial bloodstream infection is reported to be related to high mortality among children with chronic medical conditions.^{9 10} The mortality and morbidity of polymicrobial bloodstream infection in previously healthy children is still not well understood.

In conclusion, we must recognise that anchoring bias could result in diagnostic delays and critical outcomes. Also, intra-abdominal infection should be ruled out in the presence of polymicrobial enterobacteriaceae bacteraemia. Bacteraemia should be considered in the differential diagnosis of patients with shaking chills and tachycardia, even in the presence of information consistent with viral infection. Further research should be done to find the actual impact of anchoring bias on treatments and outcomes and to understand the epidemiology of polymicrobial bloodstream infections in otherwise healthy paediatric populations.

Learning points.

• Anchoring bias is one of the most important cognitive biases in the emergency department and could eventually cause unnecessary tests, inappropriate patient management and even misdiagnosis.

• Bacteraemia should be considered as a differential diagnosis and ruled out when patients present with shaking chills even in the presence of symptoms and information which consistent with viral infection such as mumps.

• The intra-abdominal infection should be ruled out in the presence of polymicrobial enterobacteriaceae bacteraemia.

• It is crucial for physicians to be aware of dangers of cognitive biases in order to avoid misdiagnosis.