What is strep throat and how is it transmitted?

What is strep throat and how is it transmitted?

Publication date: 31-05-2024

Updated on: 31-05-2024

Topic: Immunology, Rheumatology, Allergology and Rare Diseases

Estimated reading time: 1 min

Streptococcus is a bacterium that normally lives on our body. The main bacterial infections are caused by a subgroup of the family of the bacteria called Group A streptococcus. 

We talked more about this with Professor Lorenzo Dagna, head of the Unit of Immunology, Rheumatology, Allergology and Rare Diseases at Ospedale San Raffaele and Associate Professor of Internal Medicine at Vita-Salute San Raffaele University, who explains specifically what streptococcus is, the main symptoms, diagnosis and treatment of the disease.

What is streptococcus

"Streptococci are bacteria that normally live inside our throat," Prof. Dagna explains. "Those that are potentially associated with complications belong to a specific subgroup called group A streptococcus. 

It is not particularly necessary to look for a cause for the presence of streptococcus, as it is quite normal for it to live in our bodies."

Streptococcal pharyngitis

"The main disease caused by strep is pharyngitis, an inflammation of the throat. Some features help to make a diagnosis of streptococcal pharyngitis, such as:

  • very high fever;
  • chills;
  • severe sore throat with a very violent onset. 

Pharyngitis is relevant at all ages, typically in children and adolescents, but it can also develop in adults," the specialist explains. 

Scarlet fever

"In children, especially at the first streptococcal infection, scarlet fever can develop," explains Prof. Dagna. “It is a cutaneous manifestation where a skin rash appears, giving the skin a “sandpaper-like” appearance. It is typically recognized because it starts in the folds of the armpit and spreads throughout the body sparing the mouth where a very pale area can be seen.

It usually appears in those people who have developed streptococcal pharyngitis in the preceding weeks. It is a form of hypersensitivity response to a toxin that streptococcus produces."

Rheumatic disease

The other manifestation for which streptococcus A is known is rheumatic disease. Its development can be caused by the the presence of certain streptococcal proteins that remarkably resemble certain structures in our body. The immune system mounts a response against these streptococcal proteins, and by mistakenly attacking them, it also attacks our body. 

"It would appear that our immune system is tricked and responds by attacking both the streptococcal proteins and certain structures in our body, inflaming them and causing damage," the expert continues. 

This is true in the presence of some genetic-type factors, which are only partially understood, but it is not certain that a child who gets strep will later also develop rheumatic disease. It is currently not understandable who might develop it. So if a person has had recurrent episodes of these infections, they should be treated.


"Rheumatic disease, from a clinical point of view," the specialist continues, "can develop through arthritis, an inflammation of the joints, which is the initial symptom to be considered as a trigger for this disease.


"Rheumatic disease can also involve the heart especially by damaging the heart valves, which can become inflamed as a result of this disease and damaged.” – the doctor specifies. –  There could be a direct problem with the valve if a diagnosis is not made and treatment is not instituted in a timely manner, leading to its early degeneration. 

In patients with rheumatic disease and cardiac valvular involvement, we observe early in life, at a young age, those valvular changes that we more typically observe in elderly individuals over 80-90 years of age. Repair or replacement of diseased valves is often necessary. 

Streptococcal rheumatic disease can also affect other structures of the heart:

  • the heart, as heart muscle, causing myocarditis;
  • the sac that surrounds the heart, the pericardium, and allows it to move freely in the chest, causing rheumatic-based pericarditis."

Sydenham's Chorea or “St. Vitus' dance”

The specialist continues and adds: "Another manifestation may be Sydenham's chorea (named after the author who described it), a neurological manifestation characterized by involuntary movements. It is slangily called “St. Vitus’ dance."

Skin manifestations

Streptococcal rheumatic disease can, in addition, develop skin manifestations through the formation of:

  • spots on the skin;
  • marginal erythema;
  • subcutaneous nodules.


"Finally," the doctor adds, "due to an over-response of the immune system, there can also be inflammation of the kidneys."

Swab diagnosis

To check for the presence of this germ, a rapid pharyngeal swab is taken through which Group A hemolytic Streptococcus Beta hemolyticus proteins are detected.

"Another possibility for diagnosis," he continues, "is to go to a testing laboratory where the exact same swab is taken or a sample obtained by touching the patient's pharynx can be cultured to possibly highlight the presence of Group A Beta Hemolytic Streptococcus and possibly test the efficacy of some antibiotics on it. 

Many people rely on TAS (antistreptolysin titer), a blood test, for diagnosis, but this is not a reliable parameter. TAS makes it possible to state whether a person goes from negative to positive due to contact. However, since contact with streptococcus occurs in almost all cases in the first years of life, it is almost impossible never to have encountered this germ. Having a high or low TAS does not mean anything, but only indicates that contact occurred in the previous months/years."

How to treat streptococcus

When these manifestations occur, it is important to act on the streptococcal trigger and also on the inflammation that has developed in an uncontrolled manner.

"Drugs will be used that go to treat the streptococcal infection through antibiotics and, if there are signs that indicate the presence of rheumatic disease, adopt immuno-suppressive and inflammatory therapy to mitigate the manifestations of the immune system that is attacking the body," the professor says.

If a child or adolescent has strep throat it is preferred to treat it. Group A Beta Hemolytic Streptococcus pharyngitis is the only form of bacterial tonsillitis for which there is a consensus to do treatment. Taking the antibiotic reduces the duration of the disease, but there is no clear evidence that giving the antibiotic to everyone results in improved prognosis for people with the disease. Treating everyone systematically is not necessarily the right solution because of antibiotic side effects. 

If pharyngitis is caused by group A streptococcus it should be treated, especially in children and young adults, through the use of penicillin or similar drugs, such as amoxicillin. Treatment must last at least 10 days, otherwise the infection is not completely eradicated and the risk of creating resistance increases.
Another solution is the injection of penicillin into muscle, which gives at least 15 days' coverage through a single administration and more adequate action."

People with frequent Streptococcus tonsillitis may develop, as explained above, signs related to the disease (such as arthritis or joint pain). This represents a warning sign that it could be the first sign of a rheumatic disease. One must then treat the arthritis with anti-inflammatory or immune-suppressing drugs, which are necessary to extinguish it. At the same time, streptococcal remediation treatment is started by monthly injections of penicillin to eradicate streptococcus.

"In people living with people with Streptococcus, the same care may be needed since they may attach the bacteria to a child who is at greater risk of developing complications," Prof. Dagna concludes. 

An adult with Streptococcus in the throat who has never developed any complications, such as rheumatic disease, is unlikely to develop it. Like all tonsillitis, streptococcus can give local complications such as abscess formation, but its peculiarity is that it also causes other immune-mediated complications."

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