Strep Infections – Causes, Signs and symptoms

Strep Infections

Also called: Streptococcus Infections, Streptococcal Infections

Reviewed By:
Timothy Yarboro, M.D.


Strep infections are caused by Streptococcus (strep) bacteria and can result in a variety of conditions. Strep bacteria are commonly found on the skin of the human body and in the throat, intestines and other organs without causing an infection. Disease may result when the bacteria invade parts of the body where they usually are not present, or as a result of immunosuppression.

The majority of strep infections are minor, but they can also cause serious disease. Some conditions caused by strep bacteria include:

  • Strep throat
  • Scarlet fever
  • Impetigo
  • Cellulitis
  • Pneumonia
  • Meningitis
  • Necrotizing fasciitis

Strep bacteria may be transmitted through the air and from person to person. Group B streptococcal disease may also be transmitted from a woman to her baby during birth. It is one of the most common causes of infection in newborns and may lead to bacteremia (infection of the blood) or meningitis (infection of the lining of the brain).

Most strep infections are treated with antibiotics. When patients follow the recommendations of their physician, symptoms typically pass quickly. Some strep bacteria have developed antibiotic resistance but certain infections (e.g., streptococcus pneumoniae) may be prevented with a vaccine. Hand washing is also helpful in preventing strep infections.

About strep infections

Strep infections are diseases that result from bacteria of the genus Streptococcus invading the body. The bacteria often live on and in the body without causing disease. Bacteria may often be found on the skin and in the throat, intestines, bladder and genitalia.

A healthy immune system typically prevents strep bacteria from causing infection. However, these bacteria can cause infection in people with immunosuppression (a weakened immune system), that may be due to a medical condition (e.g., HIV/AIDS) or treatment (e.g., steroid medications). Bacteria usually enter the body through a break in the skin (e.g., from a cut or scrape) or tear of the mucous membranes, the moist tissue lining cavities and passageways of the body, such as inside the nose or mouth. Bacteria can also enter through surgical procedures.

There are many types of strep infections and the number of cases of each varies greatly. According to the U.S. Centers for Disease Control and Prevention (CDC), millions of people are infected with strep throat and impetigo each year in the United States. Other types of strep infections are less frequent. According to estimates by the CDC, they occur at the following rates:

  • Streptococcus pneumoniae. In 2002, 37,000 cases were reported. Of these, 34 percent showed antibiotic resistance to at least one medication.

  • Group B streptococcus disease. Approximately 19,000 cases occur each year in the United States. Of these, 1,700 are early-onset disease, which occurs in the first week of a newborn’s life.

  • Invasive group A streptococcal infections. There were 9,400 cases of this severe form of infection reported in 1999. Of these, 600 were necrotizing fasciitis and 300 were streptococcal toxic shock syndrome. About 10 to 15 percent of all invasive group A streptococcal infections are fatal.

Types and differences of strep infections

There are many possible types of strep infections that may develop in a person. They are divided into groups based on which species of bacteria cause the disease.

Group A streptococcal disease results from infection by Streptococcus pyogenes bacteria. Conditions they cause include:

  • Strep throat. Strep throat is a contagious bacterial infection that causes painful inflammation within the throat. It may also be accompanied by scarlet fever, which can produce a rash over much of the body. Left untreated, strep throat can damage the heart valves (rheumatic fever) and kidneys (glomerulonephritis). This is a common infection of children.

  • Impetigo. This highly contagious skin condition is common and usually occurs in children between two and six years old. In addition to strep bacteria, it may also be caused by staphylococcal bacteria (staph infections). Bacteria enter the outer layer of skin and form pus-filled lesions that ooze. The pus may spread the infection to other parts of the body or to other people, which can lead to outbreaks of the disease in group settings such as daycare centers. Impetigo is seldom serious and lesions typically clear up without treatment within a few weeks.

  • Cellulitis. While impetigo affects the top layer of skin, cellulitis is a strep or staph infection of the two deepest layers (dermis and subcutaneous tissue). This disease can affect any area of skin, causing it to become red, hot and painful. In children, symptoms are usually seen in the face and neck, and in adults they often occur in the extremities. Without treatment, the infection can spread to other parts of the body and may cause severe complications. Cellulitis is less common than impetigo and is not as contagious.

  • Necrotizing fasciitis. This severe type of group A strep infection is rare. It may also be referred to as a “flesh-eating” bacteria infection. It results from strep bacteria blocking small blood vessels and preventing the immune system from responding to the infected area. This leads to the decay of muscle, fat and skin tissues as the bacteria reproduce. The mortality rate of necrotizing fasciitis is about 25 percent, according to the U.S. Centers for Disease Control and Prevention (CDC).

  • Streptococcal toxic shock syndrome (STTS). Like necrotizing fasciitis, this is also a severe but rare group A strep infection. Toxins produced by the bacteria can cause a sudden drop in a patient’s blood pressure followed by shock and organ failure. It causes death in nearly half of those infected, according to the CDC.

Group B streptococcal disease is caused by infection with Streptococcus agalactiae bacteria. This group of diseases is most likely to occur in newborns, pregnant women, elderly people and in people with other illnesses. Types of group B strep include:

  • Early-onset group B strep disease. This is the most common cause of infection of the blood (bacteremia) and the lining of the brain (meningitis) in newborns. Infants may also develop pneumonia if the infection moves to the lungs. Cases develop in the first week of life and many start within hours of birth.

  • Late-onset group B strep disease. This form of the disease occurs one week to several months after the child is born. It also causes meningitis.

  • Invasive group B strep infection. Group B strep bacteria are often present in certain parts of the body (e.g., intestines, vagina) without causing disease. When the bacteria develop in an area where they usually are not present, they may cause severe disease. Infection may occur in the bloodstream, lungs, skin, soft tissue, bones, joints or lining of brain. The disease is more severe with increased age. It has a mortality rate of up to 10 percent for adults to age 64, but increases to between 15 and 25 percent for those who are 65 or older, according to the CDC.

Streptococcus pneumoniae is another species of strep bacteria that can infect people. It is a common cause of pneumonia, middle ear infections (otitis media) and invasive diseases like meningitis. The infection can be severe. It has a mortality rate of 14 percent when adults are hospitalized due to illness. In recent years, drug resistant Streptococcus pneumoniae disease (DRSP) has become widespread.

Group C and G streptococcal diseases may also develop in people. They are similar to group A bacteria in appearance and the conditions they cause. Both C and G are found in the environment and in other animals, such as cattle, sheep and chickens. These infections occur most frequently in people with compromised immune systems.

Risk factors and causes of strep infections

Strep infections are caused by several species of bacteria of the genus Streptococcus. The means of transmission and risk factors for infection vary by which species is responsible for disease.

Group A streptococcal diseases are transmitted in bodily fluids. The bacteria are found in saliva and may be spread by drinking or eating after an infected person. They may also be in infected wounds and sores, and contact with them can lead to disease.

While various types of group A strep bacteria can infect anyone and cause a range of disease (e.g., strep throat, impetigo), some people are at greater risk of severe infection. These people include those with chronic illnesses, such as cancer or diabetes mellitus, and patients who use immunosuppressive medications.

Early-onset group B streptococcal diseases are spread during birth. The bacteria live in the vaginal canal of some women, allowing the infant to be infected when exiting the womb. Risk factors for this type of disease include:

  • Premature birth
  • A long period between the mother’s water breaking and the start of labor
  • A mother who tested positive for the bacteria, has had a recent urinary tract infection, or previously had a child born with group B infection

The mode of transmission of other types of group B strep is largely unknown. Some infections have followed trauma or surgery. Others occur with no discernible means of transmission. Certain patients are more at risk for group B strep infections. They include patients who:

  • Have a chronic illness such as cancer or liver failure
  • Are 60 years of age or older
  • Have a history of stroke

Streptococcus pneumoniae bacteria infect people through airborne transmission. The bacteria become aerosolized from coughs and sneezes. They may then be inhaled and start an active infection. Those at greatest risk for infection include:

  • Elderly people
  • Children under age 2
  • Children in daycare centers
  • Patients with other conditions, such as HIV or sickle-cell anemia

Signs and symptoms of strep infections

The signs and symptoms of strep infections vary due to the type of bacteria, the condition caused and its severity.

Strep infections of the skin (e.g., impetigo, cellulitis) may involve symptoms such as pain, rash, blisters, boils and sores that deepen and become ulcers.  

Most strep infections, both of the skin and other systems may also involve a fever. Other common symptoms of infection include sore throat, chills, shaking, fatigue, weakness, nausea and vomiting. Each body system produces characteristic symptoms, such as coughing for pneumonia.

Some of the most serious symptoms may occur when strep infects the bloodstream (bacteremia). There, it may produce a sudden decrease in blood pressure and organ failure.

Diagnosis and treatment of strep infections

To diagnose a strep infection, a physician will usually perform a physical examination and compile the patient’s medical history. The physical examination will check for symptoms and signs of disease, such as fever, lung congestion and throat inflammation. The medical history may include questions about the duration and severity of symptoms.

A suspected strep infection is confirmed by culturing, or growing, the bacteria. To do this, a tissue sample is required. A swab may be taken of the back of the throat or from skin lesions. Blood or spinal fluid samples (spinal tap) may also be taken. The samples are then processed and any bacteria present are grown and identified. This process typically takes one or more days, and allows a strep infection to be confirmed and treatment to be initiated.

A rapid strep test is typically the first test performed in cases of strep throat. This test can generate results in minutes, allowing a physician to make an informed decision about prescribing antibiotics for a patient. The physician uses a swab to gather samples from the throat, and results can be confirmed with a throat culture if necessary. If a culture is obtained, a determination can be made regarding the bacteria’s susceptibility to various antibiotics that may be prescribed.

All strep infections are typically treated with antibiotics. For some infections, the antibiotics may be given intravenously (into a vein), while others are administered orally (by mouth). The medication must be taken according to the physician’s recommendations for complete treatment and to avoid contributing to antibiotic resistance.

In addition to medication, supportive care can ease the symptoms of strep infections. This may include the patient drinking plenty of clear fluids and use of an unheated humidifier. Cold foods and warm liquids may also help ease a sore throat and similar symptoms.

Severe internal strep infections may require surgery as part of treatment. When soft tissue or bone is infected (e.g., necrotizing fasciitis), these tissues need to be surgically removed to prevent spread of the bacteria. In cases of extensive infection, large amounts of tissue may require removal, up to and including amputation of an affected limb.

Prevention methods for strep infections

People can take certain steps to help prevent strep infections. In situations when a person has a contagious strep infection, such as strep throat and impetigo, staying home from school or work helps prevent spreading the infection to others. In addition, proper personal hygiene, especially hand washing with soap and water or alcohol-based lotions, helps kill the bacteria before they can enter the body. Proper care of wounds, including cleansing with soap and water and covering them with sterile bandages helps reduce the risk of spreading an infection. Over-the-counter antibiotic ointment may also be used.

Many types of strep bacteria have developed some degree of antibiotic resistance. Bacterial resistance to medications limits treatment options and makes prevention methods even more important.

Many cases of early-onset group B streptococcal disease can be prevented. Pregnant women are tested for the bacteria between weeks 35 and 37 of the pregnancy. If the vaginal or rectal swabs tests positive, the woman is typically given intravenous antibiotics during labor. According to the U.S. Centers for Disease Control and Prevention (CDC), administering antibiotics during labor makes the woman 20 times less likely to pass group B strep bacteria to the baby.

Vaccines have been developed to help prevent infection by Streptococcus pneumoniae. It is effective against nearly 90 percent of the types of S. pneumoniae bacteria that cause disease in people. Vaccination requires multiple doses and children may receive the first one at two months old. There is also a vaccine against pneumococcal pneumonia that is recommended for individuals age 65 and older and for individuals with high risk of developing pneumococcal pneumonia.

Questions for your doctor on strep infections

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to strep infections:

  1. What are the different types of strep infections?
  2. Are strep infections common?
  3. How can strep infections be prevented?
  4. If one person in my family develops a strep infection, will others in the household also get sick?
  5. Is there a vaccine to prevent strep infections?
  6. How can I tell if I have a strep infection?
  7. How are strep infections treated?
  8. Will treatment require hospitalization?
  9. How are newborns infected with strep bacteria?
  10. Are there any risk factors that make me more susceptible to strep infections?
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