Bacterial endocarditis is a serious infection that attacks the inner lining of the heart and its valves, caused when harmful bacteria travel through the bloodstream and settle in the heart. While uncommon, this condition can rapidly damage critical heart structures and lead to life-threatening complications if not promptly identified and treated. Understanding the warning signs, who is most at risk, and how the disease develops is essential for early detection and successful outcomes.

Epidemiology

Bacterial endocarditis remains a relatively rare condition, but its impact on those affected can be devastating. In developed countries, the disease occurs at a rate of approximately 2.6 to 7 cases per 100,000 people each year.^[1] Despite advances in medical care and prevention strategies, bacterial endocarditis continues to pose significant health challenges, particularly for certain vulnerable populations.

The typical person affected by bacterial endocarditis is older, with a median age of 58 years at the time of diagnosis.^[1] Men are more likely to develop this condition than women, with studies showing that bacterial endocarditis occurs twice as often in men as in women.^[1][2] This gender difference holds true across various age groups and geographic regions.

Interestingly, the patterns of bacterial endocarditis have shifted over recent decades. While the condition itself is becoming more common due to an aging population and increased use of implanted heart devices, the types of bacteria causing infections have changed. What was once predominantly caused by bacteria from the mouth and throat is now more frequently caused by skin bacteria, particularly in healthcare settings.^[1] This shift reflects changes in medical practices, including more frequent use of intravenous catheters and implanted medical devices.

Healthcare-associated cases of bacterial endocarditis now represent approximately 30% of all infections, a substantial increase from previous decades.^[1] This means that nearly one-third of people who develop bacterial endocarditis acquire the infection through contact with the healthcare system, whether through surgery, medical devices, or hospitalization.

Causes

Bacterial endocarditis develops when harmful bacteria enter the bloodstream and travel to the heart, where they attach to the inner lining or valves and begin to multiply. The body naturally hosts many types of bacteria in various locations including the mouth, respiratory system, skin, and digestive tract. Under normal circumstances, these bacteria cause no problems. However, certain events can allow these microorganisms to escape their usual locations and enter the bloodstream.^[1]

Medical and dental procedures that break the skin or tissue provide an opportunity for bacteria to slip into the bloodstream. This includes professional dental cleanings, tooth extractions, tonsil removal, examination of the airways with special instruments, and various types of surgery.^[1] Even routine activities like brushing teeth can occasionally cause bacteria to enter the blood, although the immune system usually clears these invaders quickly.

Not all bacteria can cause bacterial endocarditis, but many common types are capable of doing so. The two most frequent culprits are staphylococci (often called staph) and streptococci (often called strep).^[1] Among these, Staphylococcus aureus has become the most commonly identified pathogen, responsible for around 30% of cases in developed countries and up to 50% of healthcare-related infections.^[1][2]

Other bacteria that can cause bacterial endocarditis include various streptococcal species, enterococci (which account for approximately 15-18% of cases), and a group of bacteria known as HACEK organisms. This group includes Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella.^[1] Less commonly, fungi such as Candida and Aspergillus can cause endocarditis, particularly in people with weakened immune systems, though fungal cases represent only about 1% of total infections.^[1]

The heart normally has strong defenses against infection. A healthy heart has smooth inner surfaces and properly functioning valves that make it difficult for bacteria to attach and establish an infection. However, when the heart has pre-existing damage or abnormalities, it becomes much easier for bacteria to stick to these rough or damaged areas and begin growing. This is why people with certain heart conditions face much higher risk of developing bacterial endocarditis than those with healthy hearts.^[1]

Risk Factors

Certain groups of people face significantly elevated risk of developing bacterial endocarditis due to underlying health conditions or lifestyle factors. Understanding these risk factors helps identify who needs extra precautions and preventive measures.

Heart-related conditions represent the most significant risk factors for bacterial endocarditis. People with artificial heart valves face particularly high risk, as do those who have had previous valve repair or replacement surgery.^[1][2] The artificial materials used in these valves provide an easier surface for bacteria to attach and grow compared to natural heart tissue. Similarly, individuals with implantable cardiac devices such as pacemakers or defibrillators are at increased risk.

Congenital heart disease—meaning heart problems present from birth—significantly increases susceptibility to bacterial endocarditis. This includes conditions such as ventricular septal defect (a hole between the heart’s lower chambers), patent ductus arteriosus (an abnormal opening between major blood vessels), coarctation of the aorta (narrowing of the main artery), and complex conditions like tetralogy of Fallot or transposition of the great arteries.^[1] Even after surgical repair, many of these conditions continue to pose some risk because of scar tissue or residual defects.

Various types of heart valve disease create risk, including valves that leak, valves that don’t open properly (stenosis), and conditions like mitral valve prolapse when accompanied by valve leakage. People with rheumatic heart disease—heart damage caused by untreated strep infections—also face elevated risk.^[1] Those who have previously had bacterial endocarditis are at particularly high risk of developing it again, even if the first episode was successfully treated.

Beyond heart conditions, several other medical situations increase vulnerability to bacterial endocarditis. People who inject drugs intravenously face substantially elevated risk, with bacteria from needles or contaminated substances easily entering the bloodstream.^[1][2] Those requiring hemodialysis for kidney failure are at increased risk due to frequent vascular access and potential exposure to bacteria during treatment sessions. Individuals with weakened immune systems, whether from disease or medications, have reduced ability to fight off bacterial invasions of the heart.

Poor dental hygiene and gum disease create conditions where bacteria from the mouth can more easily enter the bloodstream, increasing risk of bacterial endocarditis. This connection between oral health and heart infection underscores the importance of regular dental care for at-risk individuals.^[1] Other conditions that elevate risk include having an indwelling intravenous catheter (a tube left in a vein for medication delivery), diabetes, and being over 60 years of age.^[1][2]

Symptoms

Bacterial endocarditis can announce itself in very different ways depending on how quickly the infection develops and which bacteria are involved. In some people, symptoms appear suddenly and become severe within days—this rapid onset is called acute bacterial endocarditis. In others, the disease develops gradually over weeks or even months with milder symptoms—this slower progression is known as subacute bacterial endocarditis.^[1][2]

The most common early symptom is fever, often accompanied by chills and night sweats. The fever typically rises above 100°F (38.4°C) and may persist for two to three days or longer, particularly in people with known heart conditions.^[1][2] Many people describe feeling as though they have the flu, with general fatigue, muscle aches, and joint pain throughout the body.

As the infection affects the heart’s function, additional symptoms may develop. Chest pain can occur, particularly when breathing. Shortness of breath may develop as the damaged heart valves struggle to pump blood effectively. A new or changed heart murmur—an abnormal whooshing sound heard through a stethoscope—often develops as the infection damages valve structures.^[2][3] The heart rate may become abnormally fast (tachycardia) as the heart works harder to compensate for reduced efficiency.

Other symptoms reflect the widespread effects of the infection. Loss of appetite and unintended weight loss are common. Swelling may appear in the feet, legs, or abdomen as fluid accumulates when the heart cannot pump effectively. Blood may appear in the urine (hematuria), signaling that the infection has affected the kidneys or that infected clumps have traveled to these organs.^[2]

Less common but distinctive symptoms can appear on the skin and extremities. Tiny purple, red, or brown spots called petechiae may appear on the skin, in the whites of the eyes, or inside the mouth. Painless red, purple, or brown flat spots called Janeway lesions may develop on the palms of the hands or soles of the feet. Painful red or purple bumps called Osler nodes can appear on the fingertips or toes. The spleen—an organ on the left side of the abdomen—may become enlarged and tender.^[2][3]

Because bacterial endocarditis can be life-threatening, anyone experiencing fever along with other concerning symptoms—particularly those with known heart conditions or risk factors—should seek medical attention immediately. Early recognition and treatment significantly improve outcomes and reduce the risk of serious complications.

Prevention

Prevention strategies for bacterial endocarditis focus on two main approaches: reducing opportunities for bacteria to enter the bloodstream and protecting high-risk individuals when such opportunities cannot be avoided.

Maintaining excellent oral hygiene stands as one of the most important preventive measures. Daily brushing and flossing help prevent gum disease, which can allow mouth bacteria to enter the bloodstream more easily. Regular dental checkups twice yearly enable early detection and treatment of dental problems before they become serious.^[1] For people at high risk, it is crucial to inform the dentist about their heart condition, as they may need preventive antibiotics before certain dental procedures.

For high-risk individuals, taking antibiotics before certain medical, dental, or surgical procedures provides important protection. This preventive antibiotic strategy, called prophylaxis, aims to prevent bacteria released during procedures from establishing an infection in the heart. Procedures where prophylaxis may be recommended include dental cleanings, tooth extractions, tonsil removal, certain surgeries on the respiratory passages or digestive system, gallbladder or prostate surgery, and examination of airways with special instruments.^[1][2]

Not everyone needs preventive antibiotics—current guidelines focus on those at highest risk, including people with artificial heart valves, those with previous bacterial endocarditis, individuals with certain complex congenital heart conditions, and heart transplant recipients who develop valve problems. People in these high-risk groups should carry a card in their wallet stating their need for preventive antibiotics and should never undergo relevant procedures without first consulting with their doctor.^[1]

For people who inject drugs, stopping drug use represents the most effective way to reduce risk of bacterial endocarditis. For those unable to stop, using clean needles and proper injection techniques can reduce but not eliminate risk. Individuals requiring hemodialysis should ensure that treatments occur in facilities that follow strict infection control procedures.

People with heart conditions that increase risk of bacterial endocarditis should maintain overall good health practices. This includes managing chronic conditions like diabetes, which can weaken immune function and increase susceptibility to infections. Avoiding unnecessary intravenous catheters and having existing catheters removed as soon as medically appropriate reduces one avenue for bacteria to enter the bloodstream.

Finally, anyone who has had bacterial endocarditis should remain vigilant for signs of recurrence and maintain close communication with their healthcare team. Regular follow-up appointments allow doctors to monitor heart function and catch any problems early. These individuals should never ignore symptoms like persistent fever, new heart murmurs, or other warning signs that could indicate the infection has returned.

Pathophysiology

Understanding how bacterial endocarditis damages the heart requires looking at the step-by-step process by which bacteria transform from harmless travelers in the bloodstream into destructive invaders of heart tissue.

The process typically begins with damage to the inner lining of the heart (the endocardium) or to the heart valves. This damage can result from turbulent blood flow, congenital abnormalities, previous surgery, or wear and tear on artificial valves. When the smooth endocardial surface becomes rough or damaged, platelets (tiny cell fragments involved in blood clotting) and a protein called fibrin accumulate at these sites, forming small, uninfected clumps called non-bacterial thrombi.^[1]

When bacteria enter the bloodstream—whether from a dental procedure, injection drug use, or another source—they circulate throughout the body. In healthy individuals with normal hearts, the immune system usually eliminates these bacteria quickly, and the smooth heart surfaces resist bacterial attachment. However, in people with damaged heart tissue or abnormal valves, the bacteria encounter the platelet-fibrin clumps that have formed on rough surfaces. These sites become ideal locations for bacteria to settle.^[1][2]

Once bacteria attach to these damaged areas, they begin to multiply rapidly. As bacterial colonies grow, they attract more platelets and fibrin, creating larger masses called vegetations. These vegetations consist of densely packed bacteria interlocked within layers of fibrin and platelets, all stuck to the heart valve or inner lining.^[1][2] The structure of these vegetations is significant—the thick layers of platelets and fibrin create a mechanical barrier that protects bacteria from the immune system and makes it difficult for antibiotics to penetrate.

As bacteria continue to multiply within vegetations, they produce enzymes—special proteins that break down surrounding tissue. These enzymes gradually destroy the heart valve tissue and the endocardial surface, creating holes, tears, or other structural damage.^[1][2] Damaged valves cannot open and close properly, which disrupts normal blood flow through the heart. Valves may become leaky (allowing blood to flow backward) or stiff and narrowed (restricting forward blood flow).

When heart valves don’t work correctly, the heart must work much harder to pump blood throughout the body. The heart muscle may enlarge in an attempt to compensate, but over time, this increased workload can lead to heart failure—a condition where the heart cannot pump enough blood to meet the body’s needs. Symptoms like shortness of breath, fluid accumulation in the legs and abdomen, and fatigue result from this reduced pumping efficiency.^[1]

Pieces of the bacterial vegetations can break off and travel through the bloodstream to other parts of the body. These traveling clumps, called emboli, can block blood vessels wherever they lodge. If an embolus blocks a blood vessel in the brain, it causes a stroke. Emboli lodging in the kidneys can cause kidney damage and blood in the urine. Those traveling to the spleen can cause splenic enlargement and pain. Emboli reaching small blood vessels in the skin cause the characteristic spots and lesions described in the symptoms section.^[1][2]

The infection also triggers widespread inflammation throughout the body as the immune system attempts to fight the bacteria. This systemic inflammation contributes to symptoms like fever, chills, muscle aches, and fatigue. In severe cases, the inflammatory response can damage organs even beyond where emboli have traveled.

In some cases, the infection spreads beyond the valves into deeper heart tissue, creating pockets of pus called abscesses or abnormal connections between heart chambers called fistulas. These complications require surgical intervention to repair and represent some of the most dangerous consequences of bacterial endocarditis.^[2]

The speed at which this pathophysiological process unfolds depends largely on the virulence of the bacteria involved. Highly aggressive bacteria like Staphylococcus aureus can rapidly damage heart tissue and cause acute endocarditis with severe symptoms developing within days. Less aggressive organisms may cause slower, more gradual damage over weeks or months, resulting in subacute endocarditis with milder initial symptoms.^[1][2]