The group A β-hemolytic streptococcus (GAS) (a single species, Streptococcus pyogenes, constituting Lancefield group A) is a form of β-hemolytic Streptococcus bacteria. It is a gram-positive bacterium responsible for a wide range of both invasive and non-invasive infections. The name derives from the Greek word 'streptos,' meaning 'twisted chain,' due to the fact that the bacterium resembles a string of small pearls when viewed under the microscope.
Infection of GAS may spread through direct contact with mucus or sores on the skin. GAS infections can cause >500,000 deaths per year. Despite the emergence of antibiotics as a treatment for Group A β-hemolytic streptococcus, infection of GAS is an increasing problem, particularly in the continent of Africa.
There are many other types of streptococci (species of Streptococcus), including group B Streptococcus and Streptococcus pneumoniae, which cause other types of infections and should not be confused with group A strep. Several virulence factors contribute to the pathogenesis of GAS, such as M protein, hemolysins, and extracellular enzymes.
Types of infection
Group A β-hemolytic streptococcus may cause an infection to the throat and skin. These may vary from very mild conditions to severe, life-threatening diseases. Although it is not completely clear what causes different people to develop different diseases as a result of the same pathogenic bacteria, it is suspected that certain people have certain genes turned on and certain genes turned off, resulting in various diseases. These switches can be controlled by the many virulence factors of GAS. Also, persons with suppressed or compromised immune systems may be more susceptible to certain diseases caused by GAS than other persons with stronger immune systems.
People may also carry the GAS either on the skin or in the throat and show no symptoms. These carriers are less contagious than symptomatic carriers of the bacteria.
The non-invasive infections caused by GAS tend to be less severe and more common. They occur when the bacteria colonizes in the throat area, where it recognizes epithelial cells. The two most prominent infections of GAS are both non-invasive: strep throat (pharyngitis) where it causes 15- 30% of the childhood cases and 10% of adult cases, and impetigo. These may be effectively treated with antibiotics. Scarlet fever is also a non-invasive infection caused by GAS, although much less common.
The invasive infections caused by Group A β-hemolytic streptococcus tend to be more severe and less common. This occurs when the bacterium is able to infect areas where bacteria are not usually found, such as blood and organs. The diseases that may be caused as a result of this include streptococcal toxic shock syndrome (STSS), necrotizing fasciitis (NF), pneumonia, and bacteremia.
In addition, infection of GAS may lead to further complications and health conditions, namely acute rheumatic fever and poststreptococcal glomerulonephritis.
Most Common:
- impetigo, cellulitis, and erysipelas â€" infections of the skin which can be complicated by necrotizing fasciitis â€" skin, fascia and muscle
- strep throat AKA strep pharyngitis â€" pharynx
Less Common:
- Bacteremia can be associated with these infections, but is not typical.
- septic arthritis â€" joints
- osteomyelitis â€" bones
- vaginitis â€" vagina (more common in pre-pubescent girls)
- meningitis* â€" meninges
- sinusitis* â€" sinuses
- pneumonia* â€" pulmonary alveolus
(*Note that meningitis, sinusitis and pneumonia can all be caused by Group A Strep, but are much more commonly associated with Streptococcus pneumoniae and should not be confused.)
Complications of Group A Strep:
- toxic shock syndrome
- scarlet fever
- Rheumatic fever
- Post-streptococcal glomerulonephritis
- PANDAS
Complications
Acute rheumatic fever
Acute rheumatic fever (ARF) is a complication of respiratory infections caused by GAS. The M-protein generates antibodies that cross-react with autoantigens on interstitial connective tissue, in particular of the endocardium and synovium, that can lead to significant clinical illness.
Although common in developing countries, ARF is rare in the United States, possibly secondary to improved antibiotic treatment, with small isolated outbreaks reported only occasionally. It is most common among children between 5 and 15 years old and occurs 1â€"3 weeks after an untreated GAS pharyngitis.
ARF is often clinically diagnosed based on Jones Criteria, which include: pancarditis, migratory polyarthritis of large joints, subcutaneous nodules, erythema marginatum, and sydenham chorea (involuntary, purposeless movement). The most common clinical finding is a migratory arthritis involving multiple joints.
Other indicators of GAS infection such as a DNAase or ASO serology test must confirm the GAS infection. Other minor Jones Criteria are fever, elevated ESR and arthralgia. Of the most serious complications is pancarditis, or inflammation of all three heart tissues. A fibrinous pericarditis can develop with a classic friction rub that can be auscultated. This will give increasing pain upon reclining.
Further endocarditis can develop with aseptic vegetations along the valve closure lines, in particular the mitral valve. Chronic rheumatic heart disease mostly affects the mitral valve, which can become thickened with calcification of the leaflets, often causing fusion of the commissures and chordae tendineae.
Other findings of ARF include erythema marginatum (usually over the spine or other bony areas) and a red expanding rash on the trunk and extremities that recurs over weeks to months. Because of the different ways ARF presents itself, the disease may be difficult to diagnose.
A neurological disorder, Sydenham chorea, can occur months after an initial attack, causing jerky involuntary movements, muscle weakness, slurred speech, and personality changes. Initial episodes of ARF as well as recurrences can be prevented by treatment with appropriate antibiotics.
It is important to distinguish ARF from rheumatic heart disease. ARF is an acute inflammatory reaction with pathognomonic Aschoff bodies histologically and RHD is a non-inflammatory sequelae of ARF.
Post-streptococcal glomerulonephritis
Post-streptococcal glomerulonephritis (PSGN) is an uncommon complication of either a strep throat or a streptococcal skin infection. It is classified as a type III hypersensitivity reaction. Symptoms of PSGN develop within 10 days following a strep throat or 3 weeks following a GAS skin infection. PSGN involves inflammation of the kidney. Symptoms include pale skin, lethargy, loss of appetite, headache, and dull back pain. Clinical findings may include dark-colored urine, swelling of different parts of the body (edema), and high blood pressure. Treatment of PSGN consists of supportive care.
Severe streptococcal infections
Some strains of group A streptococci (GAS) cause severe infection. Severe infections are usually invasive, meaning that the bacteria has entered parts of the body where bacteria are not usually found, such as the blood, lungs, or deep muscle or fat tissue. Those at greatest risk include children with chickenpox; persons with suppressed immune systems; burn victims; elderly persons with cellulitis, diabetes, blood vessel disease, or cancer; and persons taking steroid treatments or chemotherapy. Intravenous drug users also are at high risk. GAS is an important cause of puerperal fever worldwide, causing serious infection and, if not promptly diagnosed and treated, death in newly delivered mothers. Severe GAS disease may also occur in healthy persons with no known risk factors.
All severe GAS infections may lead to shock, multisystem organ failure, and death. Early recognition and treatment are critical. Diagnostic tests include blood counts and urinalysis as well as cultures of blood or fluid from a wound site.
Severe Group A streptococcal infections often occur sporadically but can be spread by person-to-person contact. Close contacts of people affected by severe Group A streptococcal infections, defined as those having had prolonged household contact in the week before the onset of illness, may be at increased risk of infection. This increased risk may be due to a combination of shared genetic susceptibility within the family, close contact with carriers, and the virulence of the Group A streptococcal strain that is involved.
Public Health policies internationally reflect differing views of how the close contacts of people affected by severe Group A streptococcal infections should be treated. Health Canada and the US CDC recommend close contacts see their doctor for full evaluation and may require antibiotics; current UK Health Protection Agency guidance is that, for a number of reasons, close contacts should not receive antibiotics unless they are symptomatic but that they should receive information and advice to seek immediate medical attention if they develop symptoms.
Treatment
Once group A streptococcus is documented as the cause of infection, treatment with penicillin should be started. Antibiotic therapy (using injected penicillin) has been shown to reduce the risk of acute rheumatic fever. Erythromycin or another macrolide can be used in patients allergic to penicillin. Most patients with allergies to pencillins can tolerate oral extended-spectrum (2nd/3rd generation) cephpalosporins, although cefixime may be suboptimal. Treatment with [ampicillin/sulbactam], [Amoxicillin/clavulanic_acid], or [clindamycin] is appropriate if deep oropharyngeal abscesses are present, in conjunction with aspiration or drainage. In cases of streptococcal toxic shock syndrome, treatment consists of penicillin and clindamycin, given with intravenous immunoglobulin.
Relation with tics and obsessive compulsive disorder
In recent years, subsets of children with acute, rapid-onset of tic disorders and obsessive compulsive disorder (OCD) hypothesized to be due to an autoimmune response to group A beta-hemolytic streptococcal infection (PANDAS) have been identified.
Notable cases
- Lana Coc-Kroft (suffered Toxic shock syndrome from the infection, fully recovered)
- Jim Henson, (d.1990, death resulting from Toxic shock syndrome as a complication)
- Sharat Sardana, comedy writer, (d.2009)
References
Note: Elements of the original text of this article are taken from the NIH Fact Sheet "Group A Streptococcal Infections", dated March 1999. As a work of the U.S. Federal Government without any other copyright notice, this is assumed to be a public domain resource.
External links
- Group A streptococcal infection at National Institutes of Health
- Group A streptococcal infections - Frequently Asked Questions at UK Health Protection Agency
