By Mr Kaushalendra Rathore, Cardiothoracic Surgeon, Nedlands, and Dr Manju Rathore GP, East Victoria Park
Infective endocarditis (IE) is an uncommon but fatal infection that targets the endocardium, especially around the inlet-outlet cardiac valves.
In 90-95% of patients aetiology is bacterial and the rest can be a fungal organism. Often severe IE is seen in high-risk patients with a history of various systemic co-morbidities. These cases are managed with the highest suspicion and often get early referral for further evaluation.
However, there is a sizable subset of the patient population at low risk who may get inappropriately delayed diagnosis.
Case study
A 21-year-old male patient presents with night sweats, weight loss – 15kg in the last couple of months – and low grade fever.
Patient was non-alcoholic, non-smoker with no history of recreational drug use. Initial working diagnosis was haematological malignancy and he was admitted under medicine ward.
Trans-thoracic echocardiogram (TTE) showed large aortic root abscess with fistula from aortic valve leaflet to anterior mitral leaflet with severe aortic regurgitation (Figure 1).
Blood cultures were positive for Streptococcus Paragenisus and intra-venous antibiotics were started as per culture sensitivity. Although there was no clinical feature of stroke, multi slice computed tomography (MSCT) angiogram revealed multiple mycotic cerebral aneurysms (5mm) with embolic manifestation in right middle cerebral artery and left parieto-occipital artery.
Abdominal scans showed renal and splenic infarcts. Mycotic aneurysms were managed with endovascular coiling and the patient was taken for an early high-risk cardiac surgery.
Present epidemiology and incidence
With improving healthcare and overall social awareness, nosocomial microbe (Staphylococcus and Streptococcus) associated infections are down trending, but healthcare associated infections from prosthetic implants, cardiology interventions, haemodialysis, chemotherapy ports, for example, and intra venous drug user-related IE is on the rise (Figure 2).
What are the red flags?
Even asymptomatic patients undergoing dental procedure (7.9%), gastrointestinal intervention (3.4%), colonoscopy (3.3%), and urogenital intervention (2.8%) in the last six months are at risk of bacterial colonisation and IE.
The most common site of infection is the aortic valve (49.5%) followed by the mitral (42.0%), tricuspid (11.4%), and pulmonary (2.4%).
A white cell count of >10535/mm3, CRP of >85mg/dl and procalcitonin of ≥ 0.4ng/mL should be considered red flags.
There is a 27-fold higher risk of in-hospital mortality in undiagnosed patients with high biomarkers. Thus, keep a high clinical suspicion when a low-risk patient presents.
How to investigate these patients?
Serology: 10-20% of patients have negative blood culture and reported long-term mortality is higher compared to culture positive patients.
Two thirds of the culture negative cases can be diagnosed with steadfast refining serology – indirect immunofluorescence assays, indirect fluorescent antibody tests [IFAT], enzyme-linked immunosorbent assays [ELISA], complement fixation tests and molecular techniques (PCR).
The first step is ruling out zoonotic organisms, such as Q fever, Bartonella species, Mycoplasma species, Legionella species, using serological testing, followed by running a PCR test to find a specific microbe.
If all these tests are negative then focus can be placed on autoimmune diseases – marantic endocarditis – and antinuclear antibodies or rheumatoid factor should be assessed.
Newer procedures like molecular techniques such as fluorescence in situ hybridisation (FISH), Quorum sensing detection, 16S rRNA PCR and metagenomic sequencing can be useful.
Echocardiography: TTE have very high sensitivity and specificity to diagnose IE and should be used as the first line. Echocardiogram not only shows mechanical complications such as large vegetations, destructive lesions, valve aneurysm, prolapse, chordae rupture, abscess, pseudoaneurysm, and/or fistula formation, but can also assess cardiac functions.
However, it is not so specific in slow growing infections and may require further investigations.
Radiology and nuclear imaging: MSCT and nuclear imaging – 18F-fluorodeoxyglucose positron emission tomography/computed tomography [FDG-PET/CT] – and leucocyte scintigraphy with single-photon emission computed tomography/low-dose CT are other modalities to assist in decision making.
FDG-PET/CT is good for the patients with prosthetic valve endocarditis and patients with extra cardiac infectious complications. A positive signal at the site of prosthetic valve, if implanted less than 3 months back, is highly suspicious of IE.
When to involve a specialist?
Multi-disciplinary consensus should be made by involving a cardiologist, infectious disease physician and surgical team in any patient with persistent signs and symptoms of IE.
Key messages
- Even low-risk cases can present with IE, which can contribute to significant morbidity and mortality if undiagnosed
- The cascade of IE pathogenesis can be impeded by prompt diagnosis and early treatment
- IE should be managed with a multi-disciplinary approach.
Author competing interests – nil
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