Streptococcus pyogenes infection

technician holding plate with bacterial colonies and blood test in the laboratory / doctor with growth of colonies of bacteria in culture medium plateOverview

Streptococcus pyogenes is a common, wide-spread bacteria which cause many acute suppurative infections, including pharyngitis, scarlet fever, soft tissue infections (impetigo, erysipelas, cellulitis), myositis and life-threatening conditions like streptococcal toxic shock syndrome, necrotizing fasciitis, and sepsis. Rheumatic heart disease and acute rheumatic fever are the postinfectious syndromes responsible for about 500,000 deaths per year worldwide. Streptococcus pyogenes belongs to a so-called group A streptococcal infection (GAS) according to Lancefield’s classification and is the one and only bacterium comprising this group.

Bacterium

Streptococci are gram-positive, non-motile bacteria 0.6 to 1.0 µm in diameter with a spherical form and produce capsules of hyaluronic acid. These organisms form pairs or short to a moderate-length curvy chain of bacteria and that is basically the reason why these bacteria are being called streptococci – this name is formed from Latin words “streptos” and “coccus” which mean “twisted” and “grain”, respectively. Streptococci create colonies with a zone of so-called β (complete) hemolysis around themselves when are cultured and hence they are known as β-hemolytic bacteria.

Pharyngitis

Streptococcal throat infection happens in individuals of all ages, although it is most common in children, except those under the age of 3.

The incubation period lasts from 1 to 4 days.

  • Sore throat;
  • Painful swallowing;
  • Fever and chills;
  • General malaise;
  • Abdominal symptoms such as nausea, vomiting and abdominal pain are usually observed in children;

The back wall of the pharynx appears red and swollen with enlarged lymphoid follicles. Tonsils are also enlarged with purulent patches on their surface. Furthermore, the lymph nodes under the lower jaw and on the neck are usually involved – they appear painful and enlarged.

Scarlet fever

Scarlet fever is associated with pharyngeal infection when bacteria start producing erythrogenic toxins (exotoxins). These toxins cause the appearance of diffuse reddish rash on the second day of the disease. The first elements occur on the chest and later spread to the other parts of the trunk, neck, and limbs. The rash is usually described as sandpaper. Additionally, red like a strawberry tongue is characteristic for scarlet fever.

Impetigo (pyoderma)

Impetigo is a skin infection characterized by the vesiculopustular rash. Although it may be caused by any streptococci or Staphylococcus aureus, GAS is the most common pathogen. Poor hygiene seems to be the major risk factor for impetigo. Typically the rash appears on the face (especially the area around the mouth and nose) and the legs, albeit other sites may also be affected. 

The lesion at first appears as red papules which later turn into vesicles and eventually pustules with honey-like crusts.   

Erysipelas

Another type of streptococcal skin infection is known as erysipelas. In most cases, the disorder is caused by GAS infection, although other streptococci may also be involved.  The disease is characterized by the red flame-like area, usually localized on the face or the extremities. The lesion is raised above the surrounding skin with the well-defined margins.   Erysipelas affects the elderly and infants. Frequently face erysipelas is associated with a preceding throat infection, albeit there is no explanation of how the throat infection can eventually spread to the skin.

Necrotizing fasciitis

The deeper tissues, including the fascia – the connective tissues surrounding the muscles – may be infected with streptococci leading to the quickly spreading necrosis of these tissues. 

Diagnosis

  • Increased white blood cells (WBCs) count with neutrophilia (high neutrophils number);
  • A rapid strep test is performed to detect Streptococcus antigens from the pharyngeal swabs;
  • A throat culture is considered the gold standard to diagnose Streptococcal infection, although its disadvantage is that it requires a lot of time before the bacteria grow;
  • C-reactive protein levels typically are increased in streptococcal pharyngitis;

Treatment

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as paracetamol and ibuprofen may be prescribed to relieve pain and fever.

The bacterial infection should be treated with antibiotics. Despite the fact that the symptoms usually resolve within 3-5 days, antibiotics should be given for at least 10 days. Natural penicillins and their forms remain the mainstay treatment for GAS.

Applicable medicines

  • Benzathine penicillin G 1.2 million units or penicillin V 500 mg per orally twice a day for 10 days. Amoxicillin is an alternative;
  • Erythromycin is recommended for individuals allergic to penicillin;

 

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