Endocarditis: what are the causes
and who is at greater risk

Article written and reviewed by Dr Luca Moretti

Infective endocarditis develops when microorganisms, mainly bacteria and more rarely fungi, enter the bloodstream and are able to adhere to the endocardium, heart valves or prosthetic material present in the heart. It is therefore not enough for a bacterium to reach the bloodstream temporarily: whether the disease develops depends on the type of microorganism, the magnitude and duration of bacteremia, and the presence of cardiac surfaces on which the infection can become established.
People at greatest risk are those who have already had endocarditis, certain prosthetic valves or valve repairs, specific congenital heart diseases or other important predisposing factors. There are also conditions that are not strictly cardiac, such as hemodialysis, venous catheters, recent hospitalization and injection drug use, that can increase risk.

The main factors that can promote endocarditis include:

• previous infective endocarditis;
• prosthetic valves and material used for certain valve repairs;
• certain congenital heart diseases;
• valvular heart disease and other structural abnormalities of the heart;
• implantable cardiac devices, particularly when they become infected;
• vascular catheters, hemodialysis and frequent exposure to invasive healthcare procedures;
• injection of drugs or other substances;
• bacterial infections that reach the bloodstream.

The presence of a risk factor does not mean that endocarditis is inevitable and, conversely, the disease can also occur in people without known heart disease. Knowing one’s level of risk is useful above all for recognizing suspicious signs earlier and applying preventive measures correctly. The monograph on infective endocarditis discusses pathophysiology, diagnosis and treatment in detail; here the aim is to understand how the infection arises and which conditions make it more likely.

How endocarditis develops: from the bloodstream to the heart valves

Most cases of infective endocarditis require a phase of bacteremia, meaning the presence of bacteria in the bloodstream. Microorganisms may originate from the mouth, skin, gastrointestinal or genitourinary tract, from an infection at another site, or from vascular access or a healthcare procedure. Bacteremia can also occur transiently during everyday activities, especially when the gums or oral tissues are inflamed.
In most people, the immune system rapidly eliminates these microorganisms. The problem arises when a microorganism with a particular ability to adhere encounters a favorable surface, for example a damaged valve or a prosthesis. Aggregates of fibrin, platelets and microorganisms called vegetations may then form, sustaining the infection and potentially damaging the valve or releasing emboli.

Among the most important microorganisms in contemporary endocarditis are Staphylococcus aureus, streptococci and Enterococcus faecalis. Their distribution varies according to age, type of valve, healthcare exposure and portal of entry. Fungal forms are much less common, but can be particularly difficult to treat.
The fact that some cases are linked to microorganisms from the oral cavity does not mean that dental treatment causes most cases of endocarditis. Cumulative exposure to bacteremia from everyday activities and oral health play an important role, which is why guidelines emphasize continuous dental prevention and not only antibiotics before certain procedures.

Who is considered at high risk

ESC guidelines distinguish people at particularly high risk, for whom specific preventive measures are recommended. This category includes those who have had previous infective endocarditis, because the likelihood of recurrence and complications is higher than in the general population.
High-risk conditions also include prosthetic valves implanted surgically and the transcatheter prosthetic valves specified in the guidelines, as well as prosthetic material used for certain valve repairs. Prosthetic valve endocarditis has specific diagnostic and therapeutic features and may be associated with a greater risk of complications than many forms involving native valves.

Certain congenital heart diseases are also high-risk conditions, particularly unrepaired cyanotic forms and some situations in which shunts, conduits or other prosthetic material are present. After surgical repair without residual defects or a prosthetic valve, preventive indications may change over time and must be defined according to the type of procedure.
The ESC also includes ventricular assist devices among high-risk conditions. Other transcatheter procedures, such as certain mitral or tricuspid repairs, require specific risk assessment.

Valvular heart disease, pacemakers, dialysis and other factors that increase risk

There is also an intermediate-risk category. According to the ESC, it includes, among other conditions, rheumatic heart disease, degenerative valvular disease, congenital valve abnormalities such as a bicuspid aortic valve, hypertrophic cardiomyopathy and cardiac implantable electronic devices. In these people, oral hygiene, skin care, appropriate treatment of infections and attention to suspicious signs are particularly important, but the risk category does not automatically coincide with an indication for antibiotics before dental treatment.
A pacemaker or defibrillator can in fact be involved in an infection of the system, especially at the pocket or leads. This condition is discussed in detail in the monograph on cardiac device-related endocarditis. The mere presence of the device, however, does not in itself justify dental antibiotic prophylaxis.

Non-cardiac factors recognized by the guidelines include central venous catheters, hemodialysis, immunosuppression, recent hospitalization, recent dental or surgical procedures, and injection drug use. These conditions can increase exposure to bacteremia or to particularly aggressive microorganisms.
With injection drug use, endocarditis often involves the right side of the heart, especially the tricuspid valve, although other structures may also be affected. Right-sided endocarditis can also present with septic pulmonary emboli and requires specialist management.

Endocarditis and dental health: why oral hygiene matters more than prophylaxis alone

The mouth normally contains numerous bacteria. If the gums are inflamed or bleed easily, everyday activities such as chewing and brushing the teeth can promote small transient bacteremias. For this reason, prevention of endocarditis does not consist of taking antibiotics every time one goes to the dentist: the main goal is to reduce oral inflammation and infection over time.
The ESC recommends that people at high or intermediate risk brush their teeth twice a day and undergo regular dental check-ups; for those at high risk, professional follow-up is recommended at least twice a year, whereas for other at-risk patients it is recommended at least annually. Bacterial foci should also be treated promptly, good skin hygiene maintained, wounds disinfected and antibiotic self-medication avoided.

Antibiotic prophylaxis before invasive dental procedures is reserved for selected categories at high risk and is addressed separately, because not all heart diseases require antibiotics. This distinction is important both to avoid unnecessary prophylaxis and to ensure that people with a genuine indication are protected.

Is endocarditis contagious?

Endocarditis is not a contagious disease in the usual sense of the term. It is not normally contracted by being near, touching, kissing or sharing spaces with a person who has it. It is a complication that develops when certain microorganisms reach the bloodstream and are able to colonize the heart in a susceptible host.
This does not mean that all the responsible microorganisms are always non-transmissible: some infections that cause bacteremia may have their own modes of transmission. What does not pass directly from one person to another is the endocarditis process itself.

For people in an at-risk category, the most useful approach is to know their condition, inform physicians and dentists about it, maintain good oral and skin hygiene and not ignore persistent fever without an obvious cause. In these cases, it is important to seek assessment before starting antibiotics independently, because any blood cultures are more informative when obtained before antimicrobial therapy.

Frequently asked questions about the causes of endocarditis

What causes endocarditis?
In most cases, bacteria reach the bloodstream and colonize valves, the endocardium or intracardiac material. More rarely, the cause is fungal.

Are people with a prosthetic valve at greater risk?
Yes. Prosthetic valves are among the conditions associated with the highest risk and are included in specific recommendations for prevention of endocarditis.

Does a pacemaker increase the risk?
A pacemaker or defibrillator can be involved in cardiac infections, but the mere presence of the device does not mean that antibiotic prophylaxis is required before dental treatment.

Can you get endocarditis from the dentist?
An invasive dental procedure can cause transient bacteremia and represent a risk especially in predisposed people, but it is not correct to attribute most cases of endocarditis to dental treatment. Everyday activities can also produce bacteremia, and good oral health is a central part of prevention.