Streptococcal infections are caused by a common group of bacteria that can lead to illnesses ranging from a mild sore throat to serious, life-threatening conditions. These infections spread easily from person to person and affect millions of people worldwide every year, making them one of the most frequently encountered bacterial infections in medical practice.

Epidemiology

Streptococcal infections represent a significant global health burden, with hundreds of millions of cases occurring annually. Healthcare providers around the world see more than 616 million new cases of strep throat alone each year, making it the most common cause of bacterial sore throat in both adults and children.^[11]

The distribution of these infections varies considerably by age. Strep throat is most common in school-aged children between the ages of 5 and 15 years, with a particularly high incidence among children aged 3 to 9 years.^[9] Among adults, the condition accounts for 5% to 15% of new cases of sore throat in the United States, while in children it represents 15% to 35% of new sore throat cases.^[11] The incidence of streptococcal throat infections declines dramatically from its peak among school-age children, with adults experiencing far lower rates.^[9]

More severe forms of streptococcal disease, known as invasive group A streptococcal disease (when the bacteria invade deeper parts of the body), occur less frequently but carry more serious consequences. Approximately 9,000 to 11,500 cases of invasive disease occur in the United States each year, resulting in 1,000 to 1,800 deaths.^[10] The Centers for Disease Control and Prevention estimates that less than 10% of these cases are the most severe forms, such as necrotizing fasciitis (sometimes called “flesh-eating bacteria”) and streptococcal toxic shock syndrome.^[10]

Seasonal patterns play a clear role in the spread of streptococcal infections. The condition is more common during winter and early spring months, coinciding with periods when people spend more time indoors in close contact with others.^[9] Geographic and demographic factors also influence infection rates, with certain populations showing increased vulnerability to severe disease.

Causes

Streptococcal infections are caused by bacteria from the genus Streptococcus. The most common culprit is Streptococcus pyogenes, also known as group A Streptococcus or group A strep. This is a facultative anaerobic gram-positive coccus that appears in fine chains when examined under a microscope after staining.^[9] There are more than 120 different strains of group A Streptococcus bacteria, and different strains may cause different types of illness or varying degrees of severity.^[4]

Another important type is group B Streptococcus, which can cause blood infections, pneumonia, and meningitis in newborns. Pregnant women can carry this bacteria and pass it to their babies during birth, though screening tests during pregnancy and antibiotics given during labor can help prevent newborn infections.^[2] Group B strep can also cause infections in adults, especially those aged 65 or older or those with existing health problems, leading to urinary tract infections, blood infections, skin infections, and pneumonia.^[2]

The bacteria that cause streptococcal infections are highly contagious and spread easily between people. The primary routes of transmission include respiratory droplets and direct contact. When an infected person talks, coughs, or sneezes, they release tiny droplets containing the bacteria into the air. Other people can breathe in these droplets or touch surfaces where the droplets have landed and then touch their mouth or nose, introducing the bacteria into their own bodies.^[5]

Direct contact transmission occurs when someone touches infected skin sores or comes into contact with fluid from those sores. Sharing personal items like drinking glasses, utensils, or plates with an infected person can also facilitate transmission before these items are properly washed.^[3] Rarely, group A strep bacteria can spread through food that isn’t handled properly.^[5]

It’s important to understand that some people can carry group A streptococci in their throat or on their skin without showing any symptoms of disease. These individuals, called carriers, can still pass the bacteria to others, though they are much less contagious than people who are actively ill.^[10] As many as 1 in 5 children are strep carriers.^[19]

Risk Factors

While anyone can develop a streptococcal infection, certain groups of people face higher risks. Age is one of the most significant factors. Children, particularly those between 3 and 15 years old, are at the highest risk for strep throat infections. Infants under 3 years of age rarely develop typical strep throat, though they can develop other manifestations of streptococcal infection.^[9]

Close contact with infected individuals dramatically increases the risk of transmission. Parents of school-aged children and adults who frequently interact with children, such as teachers and childcare providers, face increased exposure.^[11] Living in the same household with someone who has a strep infection represents particularly high-risk contact, as does having a kissing relationship with an infected person.^[25]

Environmental and social factors also contribute to infection risk. People in crowded settings have higher chances of contracting streptococcal infections. These settings include households with multiple family members, daycares, schools (including colleges), military barracks, and detention or correctional facilities.^[4][13] The concentration of people in confined spaces facilitates the spread of respiratory droplets containing the bacteria.

For serious invasive group A streptococcal infections, additional risk factors come into play. Certain medical conditions increase vulnerability, including cancer, chronic heart, kidney, liver, or lung disease, diabetes, immunocompromising conditions (having a weakened immune system), and obesity.^[5] Viral infections such as flu or chickenpox can also increase the risk of developing severe streptococcal disease.^[5]

People aged 65 years or older face elevated risks for both contracting infections and developing severe complications. Other high-risk groups include American Indian, Alaska Native, Native Hawaiian, and Pacific Island populations, people who inject drugs or are experiencing homelessness, and residents of long-term care facilities.^[5] Physical factors such as having open sores or wounds, or breaks in the skin can allow bacteria to penetrate deeper tissues and cause more serious infections.^[10]

Symptoms

The symptoms of streptococcal infections vary considerably depending on where in the body the infection occurs. The presentation can range from relatively mild discomfort to severe, life-threatening illness.

When streptococcal bacteria infect the throat and tonsils, the condition known as strep throat develops. This typically begins with a sore throat that comes on quickly and suddenly. The pain can range from mild to severe and is often accompanied by difficulty or pain when swallowing.^[1] Fever is common, often developing rapidly, with the highest temperature typically occurring on the second day of infection.^[11] Many people experience fever higher than 101°F (38.3°C).^[19]

Upon examination, the throat and tonsils appear red, sore, and swollen. White patches, spots, or streaks of pus may be visible on the throat and tonsils. Tiny red spots called petechiae (small areas of bleeding under the skin) can appear on the roof of the mouth.^[1][4] The lymph nodes in the neck typically become swollen and tender to the touch.^[1]

Additional symptoms that may accompany strep throat include headache, body aches, chills, loss of appetite, nausea or vomiting (especially in younger children), and stomach pain.^[1][11] One notable feature that helps distinguish strep throat from viral infections is the absence of a cough. If someone has a cough along with other cold symptoms like a runny nose or hoarseness, they more likely have a viral infection rather than strep throat.^[11]

Some people with strep throat may develop an additional complication called scarlet fever. This occurs when certain strains of streptococcal bacteria produce toxins. Scarlet fever causes a distinctive rash that feels rough like sandpaper. The rash typically starts on the face and neck, then spreads to the arms, legs, and body, becoming more noticeable around skin folds such as the armpits, groin, elbows, and knees.^[3] People with scarlet fever may have a flushed face with paleness around the mouth and a bright red, bumpy tongue that looks like a strawberry.^[3]

When streptococcal bacteria infect the skin, they cause different symptoms. Impetigo produces small, red to purple sores on the nose, mouth, arms, and legs. These sores leak a clear to yellow fluid or pus and eventually develop crusty yellow scabs.^[4] The affected areas may be itchy.

Cellulitis, another skin infection, causes pain, swelling, redness, and warmth in the affected area. The skin may appear puffy and feel tender to the touch.^[2]

Invasive group A streptococcal infections produce severe symptoms that indicate a medical emergency. These include severe muscle aches, nausea and vomiting, diarrhea, dizziness, fever, large wounds or blisters with black spots forming on the skin, severe pain that spreads beyond a wound, skin that changes color from red to purple, and swelling that is warm to the touch.^[4] Early signs of necrotizing fasciitis include fever, severe pain and swelling, and redness at a wound site.^[10] Symptoms of streptococcal toxic shock syndrome may include fever, dizziness, confusion, low blood pressure, rash, and abdominal pain.^[10]

It’s crucial to note that some people infected with group A strep bacteria show no symptoms at all. These asymptomatic carriers may not feel unwell but can still transmit the bacteria to others, though they are less contagious than people with active symptoms.^[3]

Prevention

Preventing streptococcal infections focuses on three main goals: limiting exposure to and spread of bacteria, treating infections promptly when they occur, and using preventive antibiotics in appropriate situations.^[22]

Good hygiene practices form the foundation of prevention. Washing hands frequently with soap and water is one of the most effective ways to prevent the spread of infections. This is especially important after coughing, sneezing, or touching shared objects in public places.^[3] When soap and water aren’t available, using an alcohol-based hand sanitizer provides an alternative.^[22]

Respiratory etiquette helps reduce transmission through airborne droplets. Covering your mouth and nose with a tissue when coughing or sneezing prevents bacteria from entering the air. If a tissue isn’t available, coughing or sneezing into your elbow or sleeve rather than your hands is recommended.^[3] Used tissues should be disposed of quickly.^[7]

Avoiding close contact with people who are known to be infected reduces exposure risk. If someone in your household has strep throat, encourage them to stay home until they’re no longer contagious—usually 24 hours after beginning antibiotic treatment.^[3][7] Don’t share utensils, cups, plates, or other personal items with infected individuals. After these items have been washed with hot, soapy water, they’re safe for others to use.^[10][14]

Maintaining overall health strengthens your body’s natural defenses against infection. Getting adequate sleep, eating a balanced diet rich in fruits and vegetables, and staying physically active all support immune system function.^[24] Staying well-hydrated helps keep throat tissues moist and healthy, reducing susceptibility to irritation and infection.^[24]

Proper wound care is essential for preventing skin infections. All minor cuts, scrapes, and injuries that break the skin should be cleaned thoroughly with soap and water. After cleaning, cover draining or open wounds with clean, dry bandages until they heal.^[22] For deep or serious wounds, seek care from a healthcare provider. People with open wounds or skin infections should avoid spending time in hot tubs, swimming pools, or natural bodies of water like lakes, rivers, or oceans until the wounds have healed.^[22]

Taking care of other health conditions can reduce infection risk. Treating fungal infections promptly is important, as is maintaining good dental hygiene. Poor dental care can lead to throat irritation and increase vulnerability to infection.^[24] For people with diabetes, checking feet daily for injuries or signs of infection is particularly important.^[22]

When someone does develop a strep infection, seeking prompt medical attention and following treatment recommendations helps prevent spread to others and reduces the risk of complications. Children with confirmed strep infections should not attend school, kindergarten, or childcare centers until they have received at least 24 hours of antibiotic treatment and feel well.^[3]

Preventive antibiotics are typically not given to close contacts of someone with a strep infection. However, there are important exceptions. People who have had rheumatic fever may need preventive antibiotics over many years to prevent recurrence. For patients with serious invasive infections, healthcare providers may give antibiotics to close contacts who are 65 years or older or have other risk factors for severe disease.^[22]

Currently, there is no vaccine available to prevent group A strep infections.^[5] This makes behavioral prevention measures even more critical.

Pathophysiology

Understanding how streptococcal infections affect the body helps explain why these bacteria can cause such varied illness, from mild throat infections to life-threatening conditions. The process begins when group A Streptococcus bacteria enter the body and encounter the immune system.

In a typical strep throat infection, bacteria colonize the throat and tonsils, adhering to the surface of these tissues. The bacteria multiply rapidly, and the body’s immune system responds by sending white blood cells to fight the infection. This immune response causes inflammation (the body’s reaction to fight infection or heal injury, characterized by redness, warmth, swelling, and pain). The inflammation makes the throat and tonsils red, swollen, and painful. Small blood vessels in the area may leak fluid, contributing to the swelling, and may even produce the tiny red spots (petechiae) seen on the roof of the mouth.^[1]

The lymph nodes in the neck, which are part of the immune system’s filtering network, become swollen and tender as they trap bacteria and produce more immune cells to fight the infection. The fever that develops is part of the body’s defense mechanism—higher temperatures can help inhibit bacterial growth and enhance immune system function.^[11]

In cases of scarlet fever, specific strains of group A strep bacteria produce toxins called erythrogenic toxins. These toxins spread through the bloodstream and cause the characteristic rash by dilating small blood vessels in the skin. The toxins also affect the tongue, causing it to become swollen and bumpy with an intense red color.^[8]

When streptococcal bacteria infect the skin, they penetrate through breaks in the skin barrier—cuts, scrapes, insect bites, or other wounds. Once inside, they trigger inflammation in the skin layers. In impetigo, bacteria multiply in the superficial layers of skin, causing blisters that rupture and form the characteristic honey-colored crusts. In cellulitis, bacteria penetrate deeper layers, causing more extensive inflammation, warmth, redness, and swelling.^[2]

Invasive group A streptococcal disease occurs when bacteria breach the body’s primary defenses and enter normally sterile areas such as the bloodstream, deep muscle and fat tissue, or the lungs. This can happen when someone has breaks in the skin or when their immune system is weakened and unable to contain the bacteria at the initial site of infection.^[10]

In necrotizing fasciitis, streptococcal bacteria produce enzymes that break down tissue. These enzymes allow the infection to spread rapidly along the planes between muscles, destroying tissue as it progresses. The bacteria also produce toxins that cause blood vessels to become blocked, cutting off blood supply to the affected tissues. Without blood flow, the tissue dies (becomes necrotic), turning black. This process can advance extremely quickly, sometimes over the course of hours.^[10]

Streptococcal toxic shock syndrome occurs when bacteria produce massive amounts of toxins that enter the bloodstream. These toxins trigger an overwhelming immune response throughout the entire body. Blood vessels dilate widely, causing blood pressure to drop dangerously low. Organs such as the kidneys, liver, and lungs can be damaged by the toxins and by inadequate blood flow. This multi-organ dysfunction can be fatal if not treated aggressively.^[14]

Some complications of streptococcal infection result from the immune system’s response rather than direct bacterial damage. In rheumatic fever, which can develop several weeks after a strep throat infection, the body’s immune system mistakenly attacks its own tissues. Antibodies produced to fight the bacteria cross-react with proteins in the heart, joints, and other tissues. This can cause painful, swollen joints and, more seriously, can damage heart valves, leading to long-term heart problems.^[1][3] Similarly, some kidney damage following strep infections occurs because immune complexes (combinations of antibodies and bacterial proteins) become trapped in the kidney’s filtering units, causing inflammation and impaired kidney function.^[3]

The incubation period for streptococcal pharyngitis—the time between exposure to the bacteria and the development of symptoms—is approximately 2 to 5 days.^[13] During this time, bacteria are multiplying and triggering immune responses, but symptoms haven’t yet appeared. Understanding this timeline helps explain why someone might not immediately feel sick after exposure to an infected person.