Definition and epidemiology
Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. The Sepsis-3 consensus definitions (2016) require evidence of infection plus an acute increase in the Sequential Organ Failure Assessment (SOFA) score of 2 or more points, representing organ dysfunction. Septic shock is a subset of sepsis with profound circulatory, cellular, and metabolic abnormalities, clinically identified by requiring vasopressors to maintain mean arterial pressure ≥65 mmHg and having serum lactate >2 mmol/L despite adequate fluid resuscitation.
Sepsis affects approximately 49 million people worldwide annually, causing an estimated 11 million deaths. In the United States, there are approximately 1.7 million cases per year, with sepsis being the leading cause of death in hospitalized patients. The incidence is increasing due to aging populations, more immunocompromised patients, and increased recognition. Mortality ranges from 10% in sepsis to 40% or higher in septic shock. Risk is highest in the very young (<1 year), elderly (>65 years), and immunocompromised individuals.
- Sepsis is defined as infection plus SOFA score increase ≥2 points (organ dysfunction)
- Septic shock requires vasopressors to maintain MAP ≥65 mmHg and lactate >2 mmol/L despite fluids
- Hour-1 bundle: lactate, blood cultures, antibiotics within 1 hour, 30 mL/kg fluid bolus, vasopressors if needed
- Norepinephrine is the first-line vasopressor for septic shock
- Quick SOFA (qSOFA): respiratory rate ≥22, altered mentation, systolic BP ≤100 mmHg (2+ suggests sepsis)
- Each hour delay in antibiotic administration increases mortality
- Most common sources: respiratory (50%), intra-abdominal (25%), urinary (15%)
- Elevated lactate (>2 mmol/L) indicates tissue hypoperfusion and predicts mortality
Etiology and risk factors
Sepsis can result from any type of infection—bacterial, viral, fungal, or parasitic. The most common sources are:
- Respiratory tract infections (pneumonia) — most common source (approximately 50%)
- Intra-abdominal infections (peritonitis, cholangitis, appendicitis) — 20-25%
- Urinary tract infections (pyelonephritis, complicated UTI) — 10-15%
- Skin and soft tissue infections (cellulitis, necrotizing fasciitis)
- Bloodstream infections (catheter-related, endocarditis)
- Central nervous system infections (meningitis, encephalitis)
Common causative organisms include Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Candida species. Gram-positive and gram-negative bacteria are approximately equally represented.
Risk factors
- Age extremes (very young, elderly >65 years)
- Immunosuppression (HIV/AIDS, chemotherapy, corticosteroids, transplant recipients)
- Chronic diseases (diabetes mellitus, chronic kidney disease, liver cirrhosis, heart failure)
- Recent surgery or invasive procedures
- Indwelling medical devices (catheters, prosthetic valves)
- Malignancy
- Malnutrition
- Prolonged hospitalization
- Recent antibiotic use (increases risk of resistant organisms)
Pathophysiology
Sepsis results from a complex interaction between the infecting organism and the host immune response. The process involves:
Initial immune activation
Pathogen-associated molecular patterns (PAMPs) from microorganisms bind to pattern recognition receptors (PRRs) such as Toll-like receptors on immune cells. This triggers release of pro-inflammatory mediators including tumor necrosis factor-alpha (TNF-α), interleukin-1 (IL-1), and interleukin-6 (IL-6). These cytokines recruit neutrophils and monocytes to the infection site and activate the complement and coagulation cascades.
Dysregulated immune response
In sepsis, the inflammatory response becomes systemic and dysregulated, with both excessive pro-inflammatory and compensatory anti-inflammatory responses occurring simultaneously. This leads to widespread endothelial injury, increased vascular permeability, and microcirculatory dysfunction.
Coagulation abnormalities
Tissue factor expression increases, activating the extrinsic coagulation pathway. Simultaneously, natural anticoagulants (protein C, protein S, antithrombin) are consumed or downregulated, and fibrinolysis is impaired. This results in widespread microvascular thrombosis and potential disseminated intravascular coagulation (DIC).
Organ dysfunction
Multiple mechanisms contribute to organ failure: microcirculatory dysfunction reduces oxygen delivery, mitochondrial dysfunction impairs cellular oxygen utilization, and direct cytotoxic effects from inflammatory mediators damage tissues. This manifests as acute kidney injury, acute respiratory distress syndrome (ARDS), hepatic dysfunction, myocardial depression, and encephalopathy.
Clinical features
Sepsis presentations vary depending on the infection source and host factors. Clinical features reflect both the underlying infection and the systemic inflammatory response with organ dysfunction.
General signs of infection
- Fever (temperature >38.3°C or 101°F) or hypothermia (<36°C or 96.8°F)
- Tachycardia (heart rate >90 bpm)
- Tachypnea (respiratory rate >20 breaths/min)
- Altered mental status (confusion, disorientation, decreased consciousness)
Signs of organ dysfunction
- Cardiovascular: Hypotension (systolic BP <90 mmHg or MAP <65 mmHg), poor capillary refill, cool extremities, mottled skin
- Respiratory: Hypoxemia, increased work of breathing, requiring supplemental oxygen or mechanical ventilation
- Renal: Oliguria (urine output <0.5 mL/kg/hr), elevated creatinine
- Hepatic: Jaundice, elevated bilirubin and transaminases
- Hematologic: Thrombocytopenia, coagulopathy, petechiae
- Metabolic: Hyperglycemia (in non-diabetics), lactic acidosis
- Neurologic: Delirium, decreased Glasgow Coma Scale score
Quick SOFA (qSOFA) criteria
A bedside tool to identify patients at higher risk of poor outcomes (2 or more criteria suggest sepsis):
- Respiratory rate ≥22 breaths/min
- Altered mentation
- Systolic blood pressure ≤100 mmHg
The source of infection may be clinically apparent (productive cough in pneumonia, flank pain in pyelonephritis) or occult, requiring systematic investigation.
Diagnosis
Sepsis diagnosis requires documented or suspected infection plus evidence of organ dysfunction (SOFA score increase ≥2). There is no single definitive test; diagnosis is clinical, supported by laboratory and microbiological findings.
Laboratory investigations
Complete blood count: Leukocytosis (WBC >12,000/μL), leukopenia (WBC <4,000/μL), or bandemia (>10% immature forms)
Metabolic panel: Elevated creatinine (acute kidney injury), hyperglycemia, electrolyte abnormalities
Lactate level: Elevated lactate (>2 mmol/L) indicates tissue hypoperfusion and correlates with mortality
Coagulation studies: Prolonged PT/INR, low platelets, low fibrinogen (if DIC present)
Liver function tests: Elevated bilirubin, transaminases in hepatic dysfunction
Arterial blood gas: Metabolic acidosis, increased anion gap, hypoxemia
Inflammatory markers: Elevated C-reactive protein (CRP) and procalcitonin (procalcitonin >0.5 ng/mL suggests bacterial infection)
Microbiological investigations
Blood cultures: Obtain at least two sets (aerobic and anaerobic) from different sites before starting antibiotics. Positive in 30-50% of sepsis cases.
Site-specific cultures: Sputum, urine, wound, cerebrospinal fluid, or other body fluids as clinically indicated
Imaging
Guided by suspected source: chest X-ray for pneumonia, abdominal ultrasound or CT for intra-abdominal infection, echocardiography if endocarditis suspected.
SOFA score
Assesses six organ systems (respiration, coagulation, liver, cardiovascular, central nervous system, renal) with scores 0-4 for each. An acute increase of ≥2 points indicates sepsis-related organ dysfunction.
Differential diagnosis
Several conditions can present with systemic inflammation, hemodynamic instability, or multi-organ dysfunction mimicking sepsis:
- Systemic inflammatory response syndrome (SIRS) from non-infectious causes: pancreatitis, severe trauma, burns, major surgery
- Cardiogenic shock: Can present with hypotension, altered mental status, elevated lactate; distinguished by cardiac history, elevated troponin, echocardiographic findings
- Anaphylaxis: Acute onset after allergen exposure, urticaria, angioedema, bronchospasm
- Hypovolemic shock: History of blood loss, dehydration, or fluid losses without infection
- Adrenal crisis: Hypotension refractory to fluids, hyponatremia, hyperkalemia; history of steroid use or adrenal insufficiency
- Toxic shock syndrome: High fever, diffuse erythematous rash, multi-organ involvement; associated with tampon use or Staphylococcus aureus infection
- Acute mesenteric ischemia: Severe abdominal pain out of proportion to exam, metabolic acidosis
- Drug-induced reactions: Neuroleptic malignant syndrome, serotonin syndrome, malignant hyperthermia
- Hematologic emergencies: Thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS)
Careful history, physical examination, and appropriate investigations help distinguish these conditions from sepsis.
Management
Sepsis management follows the Surviving Sepsis Campaign guidelines, emphasizing early recognition and time-sensitive interventions. Management should begin immediately upon recognition.
Initial resuscitation (first hour)
"Hour-1 bundle" includes:
- Measure lactate level: Remeasure if initial lactate is elevated (>2 mmol/L)
- Obtain blood cultures before administering antibiotics
- Administer broad-spectrum antibiotics within 1 hour of recognition
- Begin rapid IV fluid administration: 30 mL/kg crystalloid for hypotension or lactate ≥4 mmol/L
- Apply vasopressors if hypotension persists after fluid resuscitation to maintain MAP ≥65 mmHg
Antimicrobial therapy
Start empiric broad-spectrum antibiotics within 1 hour, covering likely pathogens based on suspected source and local resistance patterns. Examples include:
- Community-acquired pneumonia: Ceftriaxone plus azithromycin, or fluoroquinolone
- Hospital-acquired/ventilator-associated pneumonia: Anti-pseudomonal beta-lactam (piperacillin-tazobactam, cefepime, meropenem) plus anti-MRSA agent (vancomycin or linezolid)
- Intra-abdominal infection: Piperacillin-tazobactam or carbapenem
- Urinary source: Fluoroquinolone or ceftriaxone; consider carbapenem if resistant organisms suspected
De-escalate to narrower-spectrum agents once culture results and sensitivities are available. Typical duration is 7-10 days, adjusted based on clinical response.
Hemodynamic support
Fluid resuscitation: Initial 30 mL/kg crystalloid bolus (normal saline or lactated Ringer's). Reassess volume status frequently; additional fluids guided by dynamic measures (pulse pressure variation, passive leg raise).
Vasopressors: Norepinephrine is first-line for septic shock when fluid resuscitation is insufficient. Target MAP ≥65 mmHg. Vasopressin or epinephrine may be added as second-line agents. Avoid dopamine except in highly selected patients.
Source control
Identify and control the source of infection as soon as possible: drainage of abscesses, debridement of infected tissue, removal of infected devices (catheters, prosthetics), definitive intervention for perforated viscus.
Supportive care
- Mechanical ventilation: Low tidal volume strategy (6 mL/kg ideal body weight) if ARDS develops
- Glucose control: Target <180 mg/dL
- Renal replacement therapy: For severe acute kidney injury with refractory fluid overload, electrolyte abnormalities, or uremia
- Stress ulcer prophylaxis: Proton pump inhibitor or H2-receptor antagonist in high-risk patients
- Venous thromboembolism prophylaxis: Pharmacologic prophylaxis unless contraindicated
Adjunctive therapies
Corticosteroids: Hydrocortisone may be considered in patients with septic shock refractory to fluid and vasopressor therapy. Routine use is not recommended for all sepsis cases.
Monitor closely in an intensive care unit setting with continuous hemodynamic monitoring and frequent reassessment.
Complications and prognosis
Acute complications
- Septic shock: Profound hypotension requiring vasopressors, mortality 40% or higher
- Acute respiratory distress syndrome (ARDS): Bilateral pulmonary infiltrates, severe hypoxemia, high mortality
- Acute kidney injury (AKI): May require renal replacement therapy; risk of chronic kidney disease
- Disseminated intravascular coagulation (DIC): Consumptive coagulopathy with bleeding and thrombosis
- Multi-organ dysfunction syndrome (MODS): Failure of two or more organ systems
- Cardiac dysfunction: Sepsis-induced cardiomyopathy with reduced ejection fraction
- Ischemic injury: Limb or digit ischemia from microvascular thrombosis or vasopressor use
Long-term complications
Post-sepsis syndrome: Survivors often experience persistent physical, psychological, and cognitive impairments including:
- Cognitive dysfunction (memory problems, decreased concentration)
- Physical weakness and fatigue
- Depression, anxiety, post-traumatic stress disorder
- Increased risk of recurrent infections
- Increased long-term mortality compared to general population
Chronic organ damage: Chronic kidney disease, restrictive or obstructive lung disease, cardiac dysfunction
Prognosis
Mortality varies by severity:
- Sepsis: 10-20% mortality
- Septic shock: 40-50% mortality
- MODS: >50% mortality
Prognostic factors associated with worse outcomes include:
- Advanced age
- Delayed antibiotic administration (each hour of delay increases mortality)
- Higher SOFA score
- Persistent hyperlactatemia despite resuscitation
- Immunosuppression
- Comorbid conditions
- Infection with resistant organisms
Early recognition, prompt antibiotic administration, appropriate source control, and protocolized resuscitation improve survival. Long-term follow-up and rehabilitation are important for sepsis survivors.
SEPSIS mnemonic for recognition: Source of infection, Elevated heart rate, Pyrexia or hypothermia, Systolic BP low, Increased respiratory rate, Sick (altered mental status)
Practice questions
1. A 72-year-old man with type 2 diabetes presents to the emergency department with fever, productive cough, and confusion for 2 days. Vital signs: temperature 39.2°C, heart rate 118 bpm, respiratory rate 28 breaths/min, blood pressure 88/52 mmHg, oxygen saturation 88% on room air. Physical exam reveals crackles in the right lower lung field and altered mental status. Chest X-ray shows right lower lobe consolidation. Laboratory results: WBC 18,500/μL, lactate 4.2 mmol/L, creatinine 2.1 mg/dL (baseline 1.0 mg/dL). What is the most appropriate initial management?
2. A 45-year-old woman with a history of alcoholism presents with fever, abdominal pain, and hypotension. Vital signs: temperature 38.8°C, heart rate 125 bpm, respiratory rate 24 breaths/min, blood pressure 85/50 mmHg. After receiving 3 liters of IV normal saline, her blood pressure remains 88/54 mmHg. Laboratory results show lactate 3.8 mmol/L and total bilirubin 4.2 mg/dL. Blood cultures are obtained and broad-spectrum antibiotics started. Which vasopressor should be initiated first?
3. A 68-year-old man is admitted to the ICU with septic shock secondary to pyelonephritis. He received appropriate antibiotics and fluid resuscitation. Blood cultures from admission grow Escherichia coli sensitive to ciprofloxacin, ceftriaxone, and meropenem, but resistant to ampicillin. He was empirically started on meropenem. His clinical condition has improved significantly over 48 hours, with normalized blood pressure off vasopressors and lactate 1.2 mmol/L. What is the most appropriate next step in antibiotic management?
Frequently asked questions
What causes sepsis?
Sepsis is caused by a dysregulated immune response to infection. It can result from bacterial, viral, fungal, or parasitic infections, most commonly originating from the lungs (pneumonia), abdomen (peritonitis), urinary tract (pyelonephritis), or bloodstream. Common bacteria include Staphylococcus aureus, E. coli, Klebsiella, and Pseudomonas. Risk factors include advanced age, immunosuppression, chronic diseases like diabetes, recent surgery, and indwelling medical devices.
What are the first symptoms of sepsis?
Early symptoms include fever or abnormally low body temperature, rapid heart rate (tachycardia), rapid breathing (tachypnea), and confusion or altered mental status. Patients may also experience chills, extreme fatigue, and symptoms related to the infection source (cough in pneumonia, abdominal pain in peritonitis, burning urination in UTI). As sepsis progresses, signs of organ dysfunction appear, including low blood pressure, decreased urine output, difficulty breathing, and skin mottling.
How is sepsis diagnosed?
Sepsis is diagnosed clinically when there is documented or suspected infection plus evidence of organ dysfunction, defined as an acute increase in the SOFA score of 2 or more points. Laboratory tests support diagnosis: elevated or low white blood cell count, elevated lactate (>2 mmol/L), abnormal creatinine, and positive blood cultures. Additional tests include metabolic panels, coagulation studies, and imaging to identify the infection source. No single test confirms sepsis; it requires clinical judgment integrating multiple findings.
Is sepsis curable?
Sepsis is treatable and potentially reversible with prompt medical intervention, but it is not always curable and can be fatal. Mortality ranges from 10-20% in sepsis to 40-50% in septic shock. Survival depends on early recognition, immediate antibiotic therapy within the first hour, adequate fluid resuscitation, source control, and supportive care. Even survivors may experience long-term complications including cognitive impairment, physical weakness, and increased risk of future infections. Early treatment dramatically improves outcomes.
What is the difference between sepsis and septic shock?
Sepsis is infection plus organ dysfunction (SOFA score increase ≥2), while septic shock is a severe subset of sepsis with profound circulatory and metabolic abnormalities. Septic shock is diagnosed when a patient with sepsis requires vasopressor therapy to maintain mean arterial pressure ≥65 mmHg and has serum lactate >2 mmol/L despite adequate fluid resuscitation. Septic shock has much higher mortality (40-50%) compared to sepsis without shock (10-20%) and requires intensive care with vasopressor support.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: R65.20
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.