Streptococcus: characteristics, associated diseases and treatments

Published on

in collaboration with

Gaëlle Bourgeois (infectiologist)

Streptococci are a large family of bacteria. Streptococci A (GAS) and B (GBS) are the most common species. They are commonly found in the body, without being pathogenic. But they can sometimes be the cause of more or less serious infections. The explanations of Dr. Gaëlle Bourgeois, infectiologist.

Streptococci are a type of Gram-positive bacteria (which appear purple under the microscope after using the Gram stain technique in research). Their name refers to their shape: these bacteria have a spherical shape and are grouped in small chains.

There are many species of streptococci present in the human body, the most common being species A (Streptococcus pyogenes) and B (Streptococcus agalactiae). “The different species of streptococci are distinguished by their habitat, their sensitivity to antibiotics and the pathologies they cause.”, says Dr. Bourgeois.

Regarding health, streptococci A (GAS) and B (GBS) can cause mild infections and others more serious.

Streptococci A and B: where are they found?

Streptococci A (GAS) and B (GBS) are present in our body, without being pathogenic. Strep A is present in the throat and on the skin. Streptococcus B is present in the female genitalia. “It can also be found in the throat and in the digestive tract”, specifies the infectiologist.

Streptococci A and B are commensal bacteria in our body: they are present but do not necessarily cause infection or disease. Healthy carriers can, however, transmit these bacteria to other individuals who may develop symptoms. The transmission of the bacterium (present in a sick person or without symptoms) can occur:

  • Through the air, when coughing or sneezing;
  • Through physical contact;
  • Or by contact with objects themselves contaminated by secretions from the nose or throat (telephone, cutlery, toys, etc.).

What are the diseases caused by streptococcus A?

There are two main types of infections caused by streptococcus A: ENT infections and skin infections.

ENT infections

strep throat

The most common strep A infection is strep throat. “ThisThis disease most often affects children from the age of 3 and is generally not serious”, let the specialist know. About 20% of those affected suffer from sore throat, fever, intense redness of the pharynx with tonsillar exudate (white spots on the tonsils). The rest of the patients present symptoms, less important, similar to those of a viral angina. Lymph nodes in the neck may swell and be painful on palpation.

Note that most angina is linked to a virus. In children, 60 to 75% of sore throats are viral. In adults, a virus is responsible for 75 to 90% of angina.

Scarlet fever

Strep A can also cause scarlet fever, a disease that occurs at the same time as strep throat. “Scarlet fever develops when strep A produces a specific toxin. Symptoms are vomiting, angina, redness of the skin which begins at the level of the thorax and then reaches the limbs, except for the palms of the hands and the feet”, explains Dr. Bourgeois.

Streptococcus A can also sometimes cause ear infections, especially in children.

skin infections


Impetigo often follows chickenpox in children. Impetigo lesions form on pre-existing skin lesions that become infected by scratching. We speak of impetiginization of the lesions. Impetigo first develops around the orifices (nostrils, mouth, anus) but can quickly spread to the scalp and the rest of the body through self-contamination when scratching. Pimples contain pus. They break easily to give way to seeping erosion or dry out and take on a crusty appearance.

Non-necrotizing bacterial dermohypodermatitis

This infection is manifested by fever, a sore leg that turns red due to the rapid proliferation of bacteria under the skin. The entry point for the bacteria is usually a skin wound, most often athlete’s foot.

Invasive infections

In 20% of cases, streptococcus A is the cause of invasive infections. These infections develop more readily in frail people such as the elderly, those affected by cancer, kidney failure, unbalanced diabetes and immunocompromised patients.”, observes the infectiologist.

Streptococcal toxic shock

Streptococcal toxic shock occurs when certain strains of strep A produce a toxin. Patients present with fever, chills, redness of the skin linked to circulatory failure and difficulty breathing. It is a serious disease, fatal in 40% of cases.

Necrotizing bacterial dermohypodermatitis

It is a serious skin infection since it causes fever and infection of the limbs that can go as far as gangrene.

Other serious infections

Streptococcus can develop in the lungs and cause pneumonia. In some cases, it can affect the heart (endocarditis) and the bones.

More than three quarters of infections caused by streptococcus A are non-invasive”, reassures Dr. Bourgeois.

What diseases are caused by Streptococcus B?


Strep B can cause maternal infections such as postpartum endometritis, an infection of the uterine lining after childbirth. Endometritis is manifested by fever, abdominal pain, and smelly, dirty vaginal discharge.

newborn infections

Streptococcus B is potentially pathogenic in newborns. The child can become infected in utero. In this case, the infection occurs within the first 5 days and results in meningitis or pulmonary involvement. The newborn can also be contaminated when passing through the vagina during delivery. The infection appears between 6 days and three months after birth. Infection can result in meningeal or bone involvement.

Serious infections in frail people

Strep B infection can also be dangerous in the elderly and those who are severely debilitated by cancer, chronic disease (diabetes) or immunosuppression. In adults, infection may result in pulmonary infectionangina, arthritis, endocarditis or meningitis.

Streptococcal infections can be detected through clinical examination. This may be sufficient for diagnosis in some cases. However, the symptoms identified by the doctor during the clinical examination sometimes lead to other diagnostic examinations. In case of angina, the diagnosis can be confirmed by culturing a sample taken from the throat. There are also rapid tests that can be performed in the doctor’s office or in a pharmacy: a swab is passed to the level of the throat. If the test is positive for strep A, the diagnosis is confirmed. If the test is negative, culture should be done to confirm the diagnosis in children and adolescents. Culture is not necessary in adults as they are less affected by streptococcal infections.

There is no vaccine against infections with streptococci A and B. Research on candidate vaccines is in progress, indicates the Institut Pasteur on its site.

The treatment of a streptococcal infection is always based on antibiotic therapy.

Streptococcus A

ENT and skin infections related to streptococcus A are treated with amoxicillin. This antibiotic belongs to the family of broad-spectrum penicillins, ie active on a greater number of germs than simple penicillin.

The doses of medication will be adapted according to the infection in question. Since angina is most often viral, the prescription of amoxicillin is therefore not systematic. It is decided by a doctor after a rapid diagnostic orientation test for angina (TROD angina) positive for streptococcus. For people allergic to amoxicillin, the alternative is clindamycin. If strep throat is left untreated, it can lead to rheumatic fever. It is an inflammation of the joints, heart, skin and nervous system. Acute rheumatic fever can occur at any age, but most often appears between the ages of 5 and 15. Most people who suffer from rheumatic fever recover from it, but cardiac damage can be permanent in rare cases.

In case of impetigo, antibiotic therapy with drugs should not be systematic. It depends on the extent of the lesions but most of the time local care (cleaning and disinfection) is sufficient.

For serious infections, antibiotic therapy (amoxicillin) is given intravenously. “In the case of streptococcal toxic shock, another antibiotic is added, in addition to amoxicillin, to combat the toxin produced by the bacteria. Resuscitation measures are also put in place”, points out Dr. Bourgeois.

The treatment of necrotizing bacterial dermohypodermatitis requires surgery during which the necrotic tissue is removed.

Streptococcus B

Streptococcal B infections are also treated with amoxicillin or clindamycin in the presence of amoxicillin allergy. In case of meningitis, the antibiotic given immediately in extreme emergency is 3rd generation cephalosporin, intravenously.

Fortunately, the risk of maternal and infantile streptococcal B infections is low today thanks to systematic screening for streptococcal B in pregnant women (vaginal swab) between the 34th and 38th week of amenorrhea. If the mother-to-be is a carrier of the bacteria, intravenous antibiotic treatment is put in place as soon as labor begins. This considerably reduces the risk of transmission to the newborn. “The establishment of intravenous antibiotic treatment is also decided if more than 12 hours elapse between the rupture of the water bag and the birth of the baby, if there is a history of neonatal infection with Streptococcus B if delivery occurs before 37 weeks of amenorrhea”says the infectiologist.

What about streptococcal resistance to antibiotics?

Antibiotic resistances have been described in all species of streptococci and no family of antibiotics is free from resistance, the research indicates. The incidence of this resistance varies from one species to another and depending on the country and represents a real health problem. However, in France, even if we observe an increase in the resistance of streptococci to antibiotics, the latter remain overall very effective in treating streptococcal infections.

Streptococcus: characteristics, associated diseases and treatments