Microbiology
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Infections
Question 2 of 77
A 28 year old patient, known to be an IV drug user, presents to ED with a one month history of fever, night sweats and malaise, and is noted to have a systolic murmur on examination which was not present four months ago. Echocardiography demonstrates tricuspid regurgitation. Which of the following pathogens is the most likely cause of these clinical findings:
Answer:
This patient is likely to have right-sided infective endocarditis of the tricuspid valve. Staphylococcus aureus is most commonly associated with infective endocarditis in IV drug users. Being a skin commensal, it may be introduced to the venous system in those injecting drugs into their veins and the tricuspid valve is the first of the heart valves to receive blood from the venous system.Infective Endocarditis
Microbiology / Infections
Last Updated: 21st April 2019
Infective Agents
- Bacteria
- Staphylococcus aureus (intravenous drug use, indwelling vascular catheters, prosthetic or native valves)
- Coagulase-negative Staphylococcus spp. (neonates and prosthetic heart valves)
- Alpha-haemolytic streptococci (dental conditions or procedures)
- Streptococcus agalactiae
- Enterococcus spp. (gastric surgery or pathology)
- HACEK organisms:
- Haemophilus spp.
- Actinobacillus actinomycetemcomitans
- Cardiobacterium hominis
- Eikenella corrodens
- Kingella kingae
- Fungi
- Candida spp.
- Aspergillus spp.
- Histoplasma spp.
Pathogenesis
There are two main risk factors for infective endocarditis:
- Bacteraemia
- IVDU
- dental treatment or poor hygiene
- infections e.g. skin, UTI, respiratory
- cardiac surgery e.g. pacemaker insertion
- venous procedures e.g. cannula or central venous line insertion
- Abnormal cardiac epithelium
- Heart valve disease
- Rheumatic heart disease
- Prosthetic heart valves
- Structural defects e.g. VSD, PDA, calcified aortic stenosis, hypertrophic cardiomyopathy
- Previous episode of infective endocarditis
Structurally weakened and damaged endocardium is susceptible to colonisation with an infective organism, especially if a thrombus has already been deposited. This process of infection and deposition of thrombus continues, forming the characteristic vegetation lesion. As the disease progresses, the valve is destroyed and regurgitation or obstruction develops. Thrombi from the vegetation can embolise to distant sites. In addition, infective organisms can enter the circulation and form immune complexes.
Clinical Disease
- Symptoms
- Systemic features: fever and night sweats, malaise, weight loss
- Haematuria
- Arthralgia
- Symptoms of heart failure
- Signs
- Clubbing
- New/changed murmur
- Splenomegaly
- Osler's nodes (painful, red, raised lesions on pulps of fingers)
- Janeway lesions (red painless macules on palm)
- Splinter haemorrhages (small, straight lesions under the nails)
- Roth's spots (red lesions with central pale zone seen on fundoscopy)
- Petechiae on skin
Complications
- Right-hand side (associated with IVDU)
- Pulmonary embolism
- Lung abscess
- Left-hand side
- Renal failure (immune complex deposition or decreased renal blood flow)
- Stroke (thrombotic embolism or cerebral haemorrhage)
- Distal gangrene (embolism or vasculitis)
- Gastrointestinal/splenic embolism
Diagnosis
- Urine dipstick - microscopic haematuria
- Blood tests (FBC, U&Es, CRP/ESR) - anaemia, neutrophil leucocytosis, raised inflammatory markers
- Blood cultures (three separate sets)
- Echocardiography (transesophageal or transthoracic) - vegetations or valve dysfunction
- Chest x-ray - signs of heart failure
Treatment
| Infection | Treatment |
|---|---|
| Initial 'blind' therapy for native-valve endocarditis |
|
| Initial 'blind' therapy for prosthetic-valve endocarditis |
|
| Native-valve endocarditis caused by Staphylococci spp. |
|
| Prosthetic-valve endocarditis caused by Staphylococci spp. |
|
| Endocarditis caused by Streptococcus spp. |
|
| Endocarditis caused by Enterococci spp. |
|
| Endocarditis caused by HACEK microorganisms: |
|
Prevention
Patients at risk of endocarditis should be:
- advised to maintain good oral hygiene;
- told how to recognise signs of infective endocarditis, and advised when to seek expert advice.
Antibacterial prophylaxis and chlorhexidine mouthwash are not recommended for the prevention of endocarditis in patients undergoing dental procedures.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
