What happens if a positive blood culture is left untreated?

Consequences of Untreated Positive Blood Culture

Untreated positive blood cultures are associated with significantly increased mortality, with patients having a 2.44 times higher likelihood of in-hospital death compared to those with negative blood cultures. 1

Mortality Risk

• Patients with true-positive blood cultures have a weighted in-hospital mortality rate of 15.9%, compared to 3.8% in the general population with suspected infection 1
• Positive blood cultures identify a patient population at high risk of death, with affected patients being 12 times more likely to die during hospitalization than patients without positive blood cultures 2
• The 30-day mortality rate for patients with positive blood cultures collected in emergency departments is approximately 11.5% 1
• In patients with infective endocarditis (a serious complication of bacteremia), the in-hospital mortality rate remains high at 15-20%, with 1-year mortality approaching 40% 1

Disease Progression

• Untreated bacteremia can lead to seeding of infection to various organs and tissues, resulting in metastatic infections 1
• Without appropriate antimicrobial therapy, bacteremia can progress to sepsis and septic shock, which are associated with hemodynamic instability and organ dysfunction 1
• For every hour delay in initiating antibiotics in patients with septic shock, mortality increases by approximately 10% 1
• Continuous bacteremia and persistently positive cultures after starting therapy are poor prognostic signs 1

Specific Complications

• Infective endocarditis: Bacteria in the bloodstream can attach to heart valves, leading to vegetation formation, valve destruction, and heart failure 1
• Metastatic infections: Untreated bacteremia can spread to joints, bones, brain (meningitis), lungs, and other organs 1
• Septic emboli: Fragments of vegetations can break off and cause vascular occlusion and infarction in distant organs 1
• Immunologically mediated events: Bacteremia can trigger immune complex formation, leading to glomerulonephritis and other immune-mediated complications 1

Risk Factors for Poor Outcomes

• Certain pathogens carry higher mortality risk, particularly Staphylococcus aureus bacteremia 1
• Healthcare-associated and hospital-acquired bacteremia have worse outcomes than community-acquired infections 3
• Patients with comorbidities and immunosuppression are at higher risk for complications 1
• Persistent bacteremia (positive blood cultures after 3-4 days of appropriate therapy) indicates treatment failure and significantly worse prognosis 1

Management Implications

• Blood cultures should be obtained before initiating antimicrobial therapy to maximize yield 4
• Empiric antibiotic therapy should be initiated as soon as blood cultures are collected in patients with suspected sepsis 1
• Appropriate antibiotic recommendations by infectious disease specialists improve outcomes, with appropriate treatment rates of 92% when recommendations are given versus 79% without 5
• Source control (removal of infected devices, drainage of abscesses) is essential for successful treatment 1
• Follow-up blood cultures are necessary to document clearance of bacteremia 1

Monitoring and Follow-up

• Patients with positive blood cultures require close monitoring in the emergency and inpatient settings 6
• Echocardiography is reasonable before or at completion of antimicrobial therapy to establish a baseline for subsequent comparison in patients with bacteremia 1
• Patients should be educated about signs of recurrent infection and instructed to seek immediate medical attention for persistent fever 1
• Long-term follow-up is necessary to monitor for relapse and delayed complications 1

In conclusion, untreated positive blood cultures represent a medical emergency with significant mortality risk. Prompt identification of the causative organism, initiation of appropriate antimicrobial therapy, and source control are essential to improve outcomes and prevent the development of life-threatening complications.