About 33 million people are affected by rheumatic heart disease with an additional 47 million having asymptomatic damage to their heart valves. As of 2010 globally it resulted in 345,000 deaths, down from 463,000 in 1990.

In Western countries, rheumatic fever has become fairly rare since the 1960s, probably due to the widespread use of antibiotics to treat streptococcus infections. While it has been far less common in the United States since the beginning of the 20th century, there have been a few outbreaks since the 1980s. Although the disease seldom occurs, it is serious and has a case-fatality rate of 2–5%.

Rheumatic fever primarily affects children between ages 5 and 17 years and occurs approximately 20 days after strep throat. In up to a third of cases, the underlying strep infection may not have caused any symptoms.

The rate of development of rheumatic fever in individuals with untreated strep infection is estimated to be 3%. The incidence of recurrence with a subsequent untreated infection is substantially greater (about 50%). The rate of development is far lower in individuals who have received antibiotic treatment. Persons who have suffered a case of rheumatic fever have a tendency to develop flare-ups with repeated strep infections.

The recurrence of rheumatic fever is relatively common in the absence of maintenance of low dose antibiotics, especially during the first three to five years after the first episode. Recurrent bouts of rheumatic fever can lead to valvular heart disease. Heart complications may be long-term and severe, particularly if valves are involved. In countries in Southeast-Asia, sub-saharan Africa, and Oceania, the percentage of people with rheumatic heart disease detected by listening to the heart was 2.9 per 1000 children and by echocardiography it was 12.9 per 1000 children.

No vaccines are currently available to protect against "S. pyogenes" infection, although research is underway to develop one. Difficulties in developing a vaccine include the wide variety of strains of "S. pyogenes" present in the environment and the large amount of time and people that will be needed for appropriate trials for safety and efficacy of the vaccine.

A drug-resistant strain of scarlet fever, resistant to macrolide antibiotics such as erythromycin, but retaining drug-sensitivity to beta-lactam antibiotics such as penicillin, emerged in Hong Kong in 2011, accounting for at least two deaths in that city—the first such in over a decade. About 60% of circulating strains of the group A "Streptococcus" which cause scarlet fever in Hong Kong are resistant to macrolide antibiotics, says Professor Kwok-yung Yuen, head of Hong Kong University's microbiology department. Previously, observed resistance rates had been 10–30%; the increase is likely the result of overuse of macrolide antibiotics in recent years.

Scarlet fever occurs equally in both males and females. Children are most commonly infected, typically between 5–15 years old. Although streptococcal infections can happen at any time of year, infection rates peak in the winter and spring months, typically in colder climates.

The morbidity and mortality of scarlet fever has declined since the 18th and 19th century when there were epidemics caused by this disease. Around 1900 the mortality rate in multiple places reached 25%. In The improvement in prognosis can be attributed to the use of penicillin in the treatment of this disease. The frequency of scarlet fever cases has also been declining over the past century however, there have been several reported outbreaks of the disease in various countries in the past decade. The reason for these recent increases remains unclear in the medical community.

A large number of causes of myocarditis have been identified, but often a cause cannot be found. In Europe and North America, viruses are common culprits. Worldwide, however, the most common cause is Chagas' disease, an illness endemic to Central and South America that is due to infection by the protozoan "Trypanosoma cruzi". Many of the causes listed below, particularly those involving protozoa, fungi, parasites, allergy, autoimmune disorders, and drugs are also causes of eosinophilic myocarditis.

Bacterial myocarditis is rare in patients without immunodeficiency.

Another form of endocarditis is healthcare-associated endocarditis when the infecting organism is believed to be transmitted in a health care setting like hospital, dialysis unit or a residential nursing home. Nosocomial endocarditis is a form of healthcare associated endocarditis in which the infective organism is acquired during stay in a hospital and it is usually secondary to presence of intravenous catheters, total parenteral nutrition lines, pacemakers, etc.

Finally, the distinction between "native-valve endocarditis" and "prosthetic-valve endocarditis" is clinically important. Prosthetic valve endocarditis can be early ( 1 year following valvular surgery).

- Early prosthetic valve endocarditis is usually due to intraoperative contamination or a postoperative bacterial contamination which is usually nosocomial in nature.

- Late prosthetic valve endocarditis is usually due to community acquired microorganisms.

Prosthetic valve endocarditis is commonly caused by "Staphylococcus epidermidis" as it is capable of growing as a biofilm on plastic surfaces.

Infective endocarditis is an infection of the inner surface of the heart, usually the valves. Symptoms may include fever, small areas of bleeding into the skin, heart murmur, feeling tired, and low red blood cells. Complications may include valvular insufficiency, heart failure, stroke, and kidney failure.

The cause is typically a bacterial infection and less commonly a fungal infection. Risk factors include valvular heart disease including rheumatic disease, congenital heart disease, artificial valves, hemodialysis, intravenous drug use, and electronic pacemakers. The bacterial most commonly involved are streptococci or staphylococci. Diagnosis is suspected based on symptoms and supported by blood cultures or ultrasound.

The usefulness of antibiotics following dental procedures for prevention is unclear. Some recommend them in those at high risk. Treatment is generally with intravenous antibiotics. The choice of antibiotics is based on the blood cultures. Occasionally heart surgery is required.

The number of people affected is about 5 per 100,000 per year. Rates, however, vary between regions of the world. Males are affected more often than females. The risk of death among those infected is about 25%. Without treatment it is almost universally fatal.

Nonbacterial thrombotic endocarditis (NBTE) is most commonly found on previously undamaged valves. As opposed to infective endocarditis, the vegetations in NBTE are small, sterile, and tend to aggregate along the edges of the valve or the cusps. Also unlike infective endocarditis, NBTE does not cause an inflammation response from the body. NBTE usually occurs during a hypercoagulable state such as system-wide bacterial infection, or pregnancy, though it is also sometimes seen in patients with venous catheters. NBTE may also occur in patients with cancers, particularly mucinous adenocarcinoma where Trousseau syndrome can be encountered. Typically NBTE does not cause many problems on its own, but parts of the vegetations may break off and embolize to the heart or brain, or they may serve as a focus where bacteria can lodge, thus causing infective endocarditis.

Another form of sterile endocarditis is termed Libman–Sacks endocarditis; this form occurs more often in patients with lupus erythematosus and is thought to be due to the deposition of immune complexes. Like NBTE, Libman-Sacks endocarditis involves small vegetations, while infective endocarditis is composed of large vegetations. These immune complexes precipitate an inflammation reaction, which helps to differentiate it from NBTE. Also unlike NBTE, Libman-Sacks endocarditis does not seem to have a preferred location of deposition and may form on the undersurfaces of the valves or even on the endocardium.

Some strains of group A streptococci (GAS) cause severe infection. Severe infections are usually invasive, meaning that the bacteria has entered parts of the body where bacteria are not usually found, such as the blood, lungs, deep muscle or fat tissue. Those at greatest risk include children with chickenpox; persons with suppressed immune systems; burn victims; elderly persons with cellulitis, diabetes, vascular disease, or cancer; and persons taking steroid treatments or chemotherapy. Intravenous drug users also are at high risk. GAS is an important cause of puerperal fever worldwide, causing serious infection and, if not promptly diagnosed and treated, death in newly delivered mothers. Severe GAS disease may also occur in healthy persons with no known risk factors.

All severe GAS infections may lead to shock, multisystem organ failure, and death. Early recognition and treatment are critical. Diagnostic tests include blood counts and urinalysis as well as cultures of blood or fluid from a wound site.

Severe Group A streptococcal infections often occur sporadically but can be spread by person-to-person contact.

Public Health policies internationally reflect differing views of how the close contacts of people affected by severe Group A streptococcal infections should be treated. Health Canada and the US CDC recommend close contacts see their doctor for full evaluation and may require antibiotics; current UK Health Protection Agency guidance is that, for a number of reasons, close contacts should not receive antibiotics unless they are symptomatic but that they should receive information and advice to seek immediate medical attention if they develop symptoms. However, guidance is clearer in the case of mother-baby pairs: both mother and baby should be treated if either develops an invasive GAS infection within the first 28 days following birth (though some evidence suggests that this guidance is not routinely followed in the UK).

Intensive cardiac care and immunosuppressives including corticosteroids are helpful in the acute stage of the disease. Chronic phase has, mainly debility control and supportive care options.

The symptoms of strep throat usually improve within three to five days, irrespective of treatment. Treatment with antibiotics reduces the risk of complications and transmission; children may return to school 24 hours after antibiotics are administered. The risk of complications in adults is low. In children, acute rheumatic fever is rare in most of the developed world. It is, however, the leading cause of acquired heart disease in India, sub-Saharan Africa and some parts of Australia.

Complications arising from streptococcal throat infections include:

- Acute rheumatic fever

- Scarlet fever

- Streptococcal toxic shock syndrome

- Glomerulonephritis

- PANDAS syndrome

- Peritonsillar abscess

- Cervical lymphadenitis

- Mastoiditis

The economic cost of the disease in the United States in children is approximately $350 million annually.

Autoimmune heart diseases are the effects of the body's own immune defense system mistaking cardiac antigens as foreign and attacking them leading to inflammation of the heart as a whole, or in parts. The commonest form of autoimmune heart disease is rheumatic heart disease or rheumatic fever.

There are several causes of acute pericarditis. In developed nations, the cause of most (80–90%) cases of acute pericarditis is unknown but a viral cause is suspected in the majority of such cases. The other 10–20% of acute pericarditis cases have various causes including connective tissue diseases (e.g., systemic lupus erythematosus), cancer, or involve an inflammatory reaction of the pericardium following trauma to the heart such as after a heart attack such as Dressler's syndrome. Familial mediterranean fever and TNF receptor associated periodic syndrome are rare inherited autoimmune diseases capable of causing recurring episodes of acute pericarditis.

Acute rheumatic fever (ARF) is a complication of respiratory infections caused by GAS. The M-protein generates antibodies that cross-react with autoantigens on interstitial connective tissue, in particular of the endocardium and synovium, that can lead to significant clinical illness.

Although common in developing countries, ARF is rare in the United States, possibly secondary to improved antibiotic treatment, with small isolated outbreaks reported only occasionally. It is most common among children between 5 and 15 years old and occurs 1–3 weeks after an untreated GAS pharyngitis.

ARF is often clinically diagnosed based on Jones Criteria, which include: pancarditis, migratory polyarthritis of large joints, subcutaneous nodules, erythema marginatum, and sydenham chorea (involuntary, purposeless movement). The most common clinical finding is a migratory arthritis involving multiple joints.

Other indicators of GAS infection such as a DNAase or ASO serology test must confirm the GAS infection. Other minor Jones Criteria are fever, elevated ESR and arthralgia. One of the most serious complications is pancarditis, or inflammation of all three heart tissues. A fibrinous pericarditis can develop with a classic friction rub that can be auscultated. This will give increasing pain upon reclining.

Further endocarditis can develop with aseptic vegetations along the valve closure lines, in particular the mitral valve. Chronic rheumatic heart disease mostly affects the mitral valve, which can become thickened with calcification of the leaflets, often causing fusion of the commissures and chordae tendineae.

Other findings of ARF include erythema marginatum (usually over the spine or other bony areas) and a red expanding rash on the trunk and extremities that recurs over weeks to months. Because of the different ways ARF presents itself, the disease may be difficult to diagnose.

A neurological disorder, Sydenham chorea, can occur months after an initial attack, causing jerky involuntary movements, muscle weakness, slurred speech, and personality changes. Initial episodes of ARF as well as recurrences can be prevented by treatment with appropriate antibiotics.

It is important to distinguish ARF from rheumatic heart disease. ARF is an acute inflammatory reaction with pathognomonic Aschoff bodies histologically and RHD is a non-inflammatory sequela of ARF.

Strep throat is caused by group A beta-hemolytic streptococcus (GAS or S. pyogenes). Other bacteria such as non–group A beta-hemolytic streptococci and fusobacterium may also cause pharyngitis. It is spread by direct, close contact with an infected person; thus crowding, as may be found in the military and schools, increases the rate of transmission. Dried bacteria in dust are not infectious, although moist bacteria on toothbrushes or similar items can persist for up to fifteen days. Contaminated food can result in outbreaks, but this is rare. Of children with no signs or symptoms, 12% carry GAS in their pharynx, and, after treatment, approximately 15% of those remain positive, and are true "carriers".

The most common cause is viral infection and includes adenovirus, rhinovirus, influenza, coronavirus, and respiratory syncytial virus. It can also be caused by Epstein-Barr virus, herpes simplex virus, cytomegalovirus, or HIV. The second most common cause is bacterial infection of which the predominant is Group A β-hemolytic streptococcus (GABHS), which causes strep throat. Less common bacterial causes include: "Staphylococcus aureus" (including methicillin resistant Staphylococcus aureus or MRSA ),"Streptococcus pneumoniae", "Mycoplasma pneumoniae", "Chlamydia pneumoniae", "Bordetella pertussis", "Fusobacterium" sp., "Corynebacterium diphtheriae", "Treponema pallidum", and "Neisseria gonorrhoeae".

Anaerobic bacteria have been implicated in tonsillitis and a possible role in the acute inflammatory process is supported by several clinical and scientific observations.

Under normal circumstances, as viruses and bacteria enter the body through the nose and mouth, they are filtered in the tonsils. Within the tonsils, white blood cells of the immune system destroy the viruses or bacteria by producing inflammatory cytokines like phospholipase A2, which also lead to fever. The infection may also be present in the throat and surrounding areas, causing inflammation of the pharynx.

Sometimes, tonsillitis is caused by an infection of spirochaeta and treponema, in this case called Vincent's angina or Plaut-Vincent angina.

One of the most feared complications of acute pericarditis is cardiac tamponade. Cardiac tamponade is accumulation of enough fluid in the pericardial space --- pericardial effusion --- to cause serious obstruction to the inflow of blood to the heart. Signs of cardiac tamponade include distended neck veins, muffled heart sounds when listening with a stethoscope, and low blood pressure (together known as Beck's triad). This condition can be fatal if not immediately treated.

Another longer term complication of pericarditis, if it recurs over a longer period of time (normally more than 3 months), is progression to constrictive pericarditis. Recent studies have shown this to be an uncommon complication. The definitive treatment for constrictive pericarditis is pericardial stripping, which is a surgical procedure where the entire pericardium is peeled away from the heart.

Pontiac fever is known to have a short incubation period of 1 to 3 days. No fatalities have been reported and cases resolve spontaneously without treatment. It is often not reported. Age, gender, and smoking do not seem to be risk factors. Pontiac fever seems to affect young people in the age medians of 29, 30, and 32. Pathogenesis of the Pontiac fever is poorly known.

Pontiac fever does not spread from person to person. It is acquired through aersolization of water droplets and/or potting soil containing "Legionella" bacteria.

Since the advent of penicillin in the 1940s, a major preoccupation in the treatment of streptococcal tonsillitis has been the prevention of rheumatic fever, and its major effects on the nervous system (Sydenham's chorea) and heart. Recent evidence would suggest that the rheumatogenic strains of group A beta hemolytic strep have become markedly less prevalent and are now only present in small pockets such as in Salt Lake City, USA. This brings into question the rationale for treating tonsillitis as a means of preventing rheumatic fever.

Complications may rarely include dehydration and kidney failure due to difficulty swallowing, blocked airways due to inflammation, and pharyngitis due to the spread of infection.

An abscess may develop lateral to the tonsil during an infection, typically several days after the onset of tonsillitis. This is termed a peritonsillar abscess (or quinsy).

Rarely, the infection may spread beyond the tonsil resulting in inflammation and infection of the internal jugular vein giving rise to a spreading septicaemia infection (Lemierre's syndrome).

In chronic/recurrent cases (generally defined as seven episodes of tonsillitis in the preceding year, five episodes in each of the preceding two years or three episodes in each of the preceding three years), or in acute cases where the palatine tonsils become so swollen that swallowing is impaired, a tonsillectomy can be performed to remove the tonsils. Patients whose tonsils have been removed are still protected from infection by the rest of their immune system.

In strep throat, very rarely diseases like rheumatic fever or glomerulonephritis can occur. These complications are extremely rare in developed nations but remain a significant problem in poorer nations. Tonsillitis associated with strep throat, if untreated, is hypothesized to lead to pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS).

There has long been said to be a link between "rheumatic" pain and the weather. There appears to be no firm evidence in favour or against; a 1995 questionnaire given to 557 people by A. Naser and others at the Brigham and Women's Hospital's Pain Management Center concludes that "changes in barometric pressure are the main link between weather and pain. Low pressure is generally associated with cold, wet weather and an increase in pain. Clear, dry conditions signal high pressure and a decrease in pain."

Carrión's disease, or Oroya fever, or Peruvian wart is a rare infectious disease found only in Peru, Ecuador, and Colombia. It is endemic in some areas of Peru, is caused by infection with the bacterium "Bartonella bacilliformis", and transmitted by sandflies of genus "Lutzomyia".

Cat scratch disease occurs worldwide. Cats are the main reservoir of "Bartonella henselae", and the bacterium is transmitted to cats by the cat flea "Ctenocephalides felis". Infection in cats is very common with a prevalence estimated between 40-60%, younger cats being more commonly infective. Cats usually become immune to the infection, while dogs may be very symptomatic. Humans may also acquire it through flea or tick bites from infected dogs, cats, coyotes, and foxes.

Trench fever, produced by "Bartonella quintana" infection, is transmitted by the human body louse "Pediculus humanus corporis". Humans are the only known reservoir. Thorough washing of clothing may help to interrupt the transmission of infection.

A possible role for ticks in transmission of "Bartonella" species remains to be elucidated; in November 2011, "Bartonella rochalimae", "B. quintana", and "B. elizabethae" DNA was first reported in "Rhipicephalus sanguineus" and "Dermacentor nitens" ticks in Peru.

Many rheumatic disorders of chronic, intermittent joint pain have historically been caused by infectious diseases. Their etiology was unknown until the 20th century and not treatable, like Lyme disease (in the Northern and Northeastern US), coccidiomycosis or Valley fever (in the Western US), and Chikungunya in India and a myriad of causes for postinfectious arthritis also known as reactive arthritis like, for example, the once very common rheumatic fever after Group A Streptococcus infection up to the rare Whipple's disease.

Major rheumatic disorders currently recognized include

- Back pain

- Bursitis/Tendinitis of the shoulder, wrist, biceps, leg, knee cap (patella), ankle, hip, and Achilles tendon

- Capsulitis

- Neck pain

- Osteoarthritis

- Palindromic rheumatism has been theorized to be a form of rheumatoid arthritis.

Although these disorders probably have little in common in terms of their epidemiology, they do share three characteristics: they cause chronic, often intermittent pain, they are difficult to treat and are collectively very common.

Rheumatic diseases caused by autoimmunity include:

- Ankylosing spondylitis

- relapsing polychondritis

- systemic lupus erythematosus

- rheumatoid arthritis

- gout, inflammatory arthritis, pseudogout

- juvenile arthritis

- Sjögren syndrome

- scleroderma

- Polymyositis

- Dermatomyositis

- Behçet's disease

- Psoriatic arthritis