Definition and Overview

Bacterial endocarditis is a condition in which the inner lining of the heart becomes inflamed due to bacterial infection. Known as endocardium, this lining is made up of heart valves. It is a serious condition that, if left untreated, can lead to severe complications such as stroke or even death, especially since the heart valves in the endocardium do not have a dedicated blood supply and therefore does not directly receive white blood cells. When bacteria attach to the endocardium, a lesion surrounded by a platelet layer (vegetation) forms. Bacteria that are enclosed by the vegetation become inaccessible to the body’s bacterial-specific host antibodies. Thus, treatment becomes necessary.

Bacterial endocarditis presents in two forms, namely:

  • Subacute bacterial endocarditis (SBE) - Caused by streptococci bacteria, specifically viridans streptococci. Patients with SBE experience mild to moderate symptoms that progress slowly over a period of weeks or even months.

  • Acute bacterial endocarditis (ABE) - Progresses faster, usually over a period of days to weeks. It is often due to Staphylococcus aureus bacteria and can cause metastatic infection.

These terms are no longer always used nowadays with cases generally classified as either short or long incubation depending on whether they progress within a period of six weeks or longer.

Causes of Condition

The most common organisms that are known causes of bacterial endocarditis are:

  • Staphylococcus aureus

  • Streptococci of the viridians group, or viridians Alpha-hemolytic streptococci

  • Coagulase negative Staphylococci

  • Enterococci

Less common causes are:

  • Propionibacterium

  • Tropheryma whipplei

  • Citrobacter koseri

  • Neisseria bacilliformis

In a healthy individual, when these bacteria enter the bloodstream, the body is able to clear them out without any consequences to the person’s health. However, some individuals are unable to fend off the bacteria, which may eventually reach their endocardium. The risk of this happening is greater in patients who have pre-existing heart problems, such as damaged or artificial heart valves, congenital heart defects, chronic rheumatic heart disease, and degenerative valvular lesions. This is also true for those with an implantable cardioverter-defibrillator and whose immune system is weak or compromised. Patients who suffer from kidney failure that requires haemodialysis, diabetes mellitus, and HIV/AIDS, as well as unrelated medical conditions, such as colorectal cancer and chronic urinary tract infection also face a greater risk of developing infective endocarditis.

Key Symptoms

Common bacterial endocarditis symptoms include:

  • Low-grade but intermittent fevers

  • Heart murmurs

  • Petechiae or round spots caused by bleeding into the skin

  • Subungual haemorrhages or dark red linear lesions of the nail bed

  • Tender subcutaneous nodules on the finger pads

  • Lesions on the palms and soles

  • Retinal haemorrhages with clear centres

  • Splenomegaly or enlargement of the spleen

  • Stiff neck

  • Delirium

  • Conjunctival haemorrhage

  • Cardiac arrhythmia

More severe symptoms of bacterial endocarditis include embolic stroke and intracerebral haemorrhage.

On the other hand, subacute bacterial endocarditis symptoms include:

  • Anorexia

  • Weight loss

  • Flu-like symptoms

  • Pleuritic pain

  • Polymyalgia-like symptoms

  • Rheumatic fever syndrome

  • Headache

  • Abdominal pain, usually in the right upper quadrant

  • Vomiting

  • Appendicitis-like symptoms

Who to See and Types of Treatments Available

Patients who experience at least some of the symptoms above should go to a doctor right away for bacterial endocarditis treatment. A general practitioner or family doctor can diagnose the condition, prescribe the appropriate medication, or refer the patient to a specialist, if needed.

The primary treatment for bacterial endocarditis is antibiotic therapy. Doctors prescribe the appropriate type of antibiotic based on the organisms that caused the condition as well as the patient’s medical history. To minimise bacterial resistance, doctors also usually prescribe combination therapy, in which they use two types of medications, such as penicillin and aminoglycoside.

The goal of treatment is to destroy the infectious agent to relieve and stop all of the patient’s symptoms. This typically requires a high dose of antibiotics delivered intravenously, which helps maximise the delivery of antibiotic molecules into the vegetation that has formed in the heart valves. Antibiotic therapy is usually continued for two to six weeks depending on the specific bacteria involved. The treatment period can be shortened to two weeks if the infection in the bloodstream has cleared earlier than expected or if there are complications, such as heart failure, arrhythmia, or pulmonary embolism.

Patients who are suffering from certain complications due to the infection are provided with additional treatment. In around 15 to 25% of cases, this may require surgical procedures, such as debridement of the infected material. This is usually necessary when the patient has:

  • Congestive heart failure that does not respond to standard medical therapy

  • Fungal endocarditis, which does not respond to antibiotics

  • Sepsis that persists 72 hours after correct antibiotic therapy

  • Septic emboli that recur two weeks after antibiotic therapy

  • Aneurysm rupture

  • Septal abscess

  • Valve stenosis or regurgitation

Infective endocarditis that is not treated promptly and correctly can lead to fatal results. Even with treatment, the prognosis can be quite poor, especially if the patient is old, the infection is caused by resistant strains of bacteria, treatment is delayed, the vegetation is too large, and if there is valve ring abscess or prosthetic valve infection.

Bacterial endocarditis prognosis is also generally better for right-sided endocarditis than left-sided endocarditis as the former tends to respond better to antimicrobial therapy.


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  • Huckell VF. “Infective endocarditis.” Merck Manuals.

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  • Hoen B. “Infective endocarditis.” N Engl J Med 2013; 368:1425-1433.

  • Macdonald JR. “Acute infective endocarditis.” Infect Dis Clin North Am. 2009 Sep; 23(3): 643-644.

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