Which infectious organism is most likely to cause relative bradycardia during a febrile event?

Salmonella typhi Is Most Likely to Cause Relative Bradycardia During a Febrile Event

Salmonella typhi (typhoid fever) is the infectious organism most likely to cause relative bradycardia during a febrile event. 1

Understanding Relative Bradycardia

Relative bradycardia refers to a paradoxical clinical sign where the pulse rate is lower than expected for a given body temperature. This pulse-temperature dissociation is a distinctive feature of certain infections and can provide valuable diagnostic clues.

Evidence for Salmonella typhi

The Centers for Disease Control and Prevention specifically identifies relative bradycardia as a characteristic clinical feature of typhoid fever in their case definitions for infectious conditions 1. According to these guidelines, typhoid fever is "an illness caused by Salmonella typhi that is often characterized by insidious onset of sustained fever, headache, malaise, anorexia, relative bradycardia, constipation or diarrhea, and nonproductive cough."

Multiple clinical studies have confirmed this association:

• Relative bradycardia has been demonstrated as a characteristic feature of typhoid fever with statistical significance (P = 0.003) 2
• In a retrospective review of confirmed typhoid fever cases, high fever associated with bradycardia was noted in 57% of patients 3
• A study from Taiwan found relative bradycardia in 25% of patients with confirmed typhoid fever 4

Why Salmonella typhi Causes Relative Bradycardia

The mechanism appears to be related to Salmonella typhi being both Gram-negative and an intracellular pathogen 2. This combination of characteristics seems to trigger a unique host response that results in the pulse-temperature dissociation.

Comparison with Other Options

Let's examine why the other organisms listed are less likely to cause relative bradycardia:

• P. aeruginosa: As an extracellular Gram-negative bacterium, it typically causes a normal febrile response with corresponding tachycardia 2

• Staphylococcus aureus: As a Gram-positive extracellular organism, it typically causes fever with appropriate tachycardia rather than relative bradycardia 2

• S. pneumoniae: This Gram-positive organism generally produces a normal febrile response with tachycardia 2

• Streptococcus pyogenes: Similar to other Gram-positive pathogens, it typically causes fever with corresponding tachycardia 2

Clinical Significance

Recognizing relative bradycardia in a febrile patient should prompt consideration of specific infections, particularly typhoid fever. This is especially important when evaluating:

• Patients with recent travel to endemic areas
• Patients presenting with prolonged fever of unknown origin
• Cases with gastrointestinal symptoms accompanying fever

Diagnostic Implications

When relative bradycardia is observed in a febrile patient, clinicians should:

1. Consider typhoid fever in the differential diagnosis
2. Obtain appropriate cultures (blood, stool)
3. Evaluate for other causes of relative bradycardia including Legionnaire's disease and Chlamydia pneumonia, which have also been associated with this finding 2

In conclusion, while relative bradycardia can occur in various infectious and non-infectious conditions, Salmonella typhi has the strongest and most well-established association with this clinical finding among the organisms listed.