Table of Contents
Overview – Bacteraemia and Septicaemia
Bacteraemia and septicaemia are clinically significant conditions representing the presence and systemic spread of bacteria within the bloodstream. While bacteraemia simply refers to viable bacteria in the blood, septicaemia (an outdated term) involves the spread of microbes from a local site to the bloodstream via the lymphatics. Modern clinical focus has shifted to sepsis, which describes the host’s dysregulated inflammatory response to infection, often leading to systemic complications like hypotension, tachycardia, and multi-organ dysfunction. Understanding these processes is vital in recognising at-risk patients and intervening early to prevent morbidity and mortality.
Definition
- Bacteraemia: Presence of viable bacteria in the bloodstream
- Septicaemia: Historical term; spread of microbes from a wound via lymphatics to the bloodstream
- Sepsis: A clinical syndrome where bacteraemia triggers a systemic inflammatory response (fever/hypothermia, tachypnoea, tachycardia, hypotension)
The Human Eco-System
- Commensal flora exist in:
- Skin (e.g. Staphylococcus)
- Pharynx and bronchial tree (e.g. Streptococcus)
- Gut (e.g. Escherichia coli)
- Vagina (e.g. Lactobacilli)
- Sterile sites include:
- Lungs
- Uterus and fallopian tubes
- Urinary tract (above the urethra)
- Peritoneal cavity
- Solid organs
- Blood
- Cerebrospinal fluid (CSF)
Pathophysiology
The bloodstream as a microbial environment
- Favourable conditions for microbes:
- Rich in oxygen, water, nutrients
- Neutral pH and 37°C temperature
- Unfavourable conditions:
- Constant blood flow → inhibits microbial adherence
- Host defences: phagocytes, antibodies, complement, interferon
- Filtering via spleen and liver
Sources of Bloodstream Infections
- Endogenous (commensal flora):
- Skin, nasopharynx, gastrointestinal tract
- Exogenous (environmental or invasive):
- Medical procedures, trauma, infections
Causes of Bacteraemia
- Dental work or even brushing teeth
- Minor skin injuries
- Gastrointestinal procedures (e.g. colonoscopy, polypectomy)
- Urinary catheterisation
- Ruptured abscesses (skin, visceral, bone)
- Major infections: pneumonia, urinary tract infections, wound infections
- Contaminated intravenous devices
Conditions Required for Infection
- Large bacterial load
- Anatomical defect
- Faulty heart valves
- Disrupted epithelium
- Microbial virulence factors
- Capsules → resist phagocytosis
- Secreted enzymes (e.g. proteinases)
- Compromised host immunity
At-Risk Patients
- Disrupted physical barriers (e.g. wounds, IV lines)
- Devitalised tissue (e.g. necrosis)
- Granulocyte dysfunction (e.g. chemotherapy, diabetes)
- Complement deficiencies
- Asplenia or splenic dysfunction
- ↑Risk from encapsulated organisms
Bacterial Safe Havens
- Damaged endocardium and valves
- Foreign materials (e.g. catheters, prosthetics)
- Promote biofilm formation
- Avoid immune surveillance
Diagnosis of Bacteraemia
- Blood cultures (best obtained before antibiotic initiation)
- Imaging for locating primary/secondary foci
- Histopathology and culture of lesions or abscesses
Summary – Bacteraemia and Septicaemia
Bacteraemia and septicaemia represent microbial invasion of the bloodstream, with sepsis describing the resulting inflammatory host response. Recognition of common sources, host risk factors, and prompt diagnostic steps (such as blood cultures and imaging) is crucial. These conditions underscore the importance of sterile technique and vigilance in vulnerable patients. For a broader context, see our Microbiology & Public Health Overview page.