What Is Group A Streptococci Infection
Group A streptococci is also called streptococcus pyogenes, and group A streptococci has hemolytic reaction type β, so it used to be called β-hemolytic streptococcus, which is one of the most important pathogens in human bacterial infection. The infections mainly include acute pharyngitis and acute tonsillitis, but also can cause lung infection, scarlet fever, skin and soft tissue infection and systemic infection. It is also an indirect cause of allergic diseases such as rheumatic fever and acute glomerulonephritis. In recent years, the serious infection caused by group A streptococci and the increasing incidence of invasive group A streptococci infections have caused people to pay more attention to this kind of bacterial infection.
What Is The Cause Of Group A Streptococci Infection
Group A Streptococcus showed hemolytic reaction type β, so it was called β-hemolytic streptococcus in the past. According to biochemical classification, this bacterium is Streptococcus pyogenes. According to their surface antigens, they can be divided into more than 90 serotypes. At present, the function of surface antigen R, T, S protein components is not known, while M protein is an important factor for Streptococcus to have pathogenic ability. It can resist the phagocytosis of white blood cells, and it is non-toxic without M protein. Specific immunity to M protein can be obtained after infection, and can be maintained for several years.
Lipoteichoic acid in cell wall is also an important virulence factor, which can make bacteria adhere to host mucosa and cell membrane.
The pathogenicity of Group A Streptococcus also comes from the toxin and extracellular protein produced.
There are two kinds of toxins in group a streptococcus:
1. pyrogenic exotoxin, also known as erythema toxin, is a heat-resistant protein with antigenicity. Besides causing scarlet fever rash on skin, it also has the functions of suppuration, cytotoxicity, enhancement of endotoxin toxicity, etc. It also has the function of superantigen. There are at least three different antigen types, A, B and C, and some scholars believe that there are four different antigen types. Strains that do not produce erythema toxin can become toxigenic strains after interacting with bacteriophages that can produce erythema toxin.
2. Streptolysin can dissolve red blood cells, kill white blood cells and platelets, and damage the heart. There are two kinds of streptolysin, O and S. O Streptococcus hemolysin has antigenicity, and can produce corresponding antibodies after infection, which can be maintained for several months, so it can be used as one of the signs of streptococcus newly infected. S streptococcal hemolysin has no antigenicity or weak antigenicity, and its antibody has not been found in human body.
There are five kinds of extracellular proteins produced by Group A Streptococcus.
1. Hyaluronidase, which can dissolve hyaluronic acid in interstitial tissues, makes bacteria easy to spread in tissues.
2. Chain channel enzyme, also known as deoxyribonuclease (DNase), can dissolve highly viscous DNA. The enzyme has four different serotypes: A，B，C and D. Antigenicity can produce antibodies.
3. Streptokinase, also known as fibrinolytic enzyme, can transform plasminogen in blood into plasmin, thus preventing blood coagulation or dissolving coagulated blood clots.
4. Serum opacity factor (OF) is an alpha lipoprotein enzyme. It can make horse serum turbid. It can inhibit specific and non-specific immune responses.
5. Nicotinamide adenine dinucleotide nucleosidase (NADase) can decompose the corresponding tissue components, thus destroying some defense capabilities of the body, for example, white blood cells can be killed.
Bacteria multiply rapidly on respiratory mucosa or other tissues. Because M protein can resist the phagocytosis of white blood cells, if the body's resistance is low at that time, it is difficult to eliminate bacteria quickly. During the proliferation of bacteria, hemolysin can be produced, causing the host's blood cells to decompose and die. Streptococcus pyrogenic exotoxin (SPE) not only can cause fever, suppuration and rash, but also has the function of superantigen in recent years, which can stimulate the proliferation of T cells nonspecifically, release cytokines such as TNF, IL-1, IL-6 and IFN-γ, greatly enhance the endotoxic shock effect, and at the same time reduce the antibody-producing function of phagocytes and B cells. It leads to toxic shock-like syndrome (TSLS), which can also be called streptococcal toxic shock syndrome (STSS).
Streptodornase can degrade the nucleic acid of host cells, and make it a nutrient component beneficial to bacteria in inflammatory foci. Streptokinase and hyaluronidase can destroy the tissue barrier of the host and spread the infection. The accumulation of inflammatory substances and the proliferation of streptococci lead to the decrease of pH in local tissues, which is more conducive to the enhancement of bacterial protease activity and further aggravates tissue destruction. Combined with the inflammatory exudation reaction of the body, the suppurative changes of local tissues are formed. Then it can cause bacteremia, septicemia, meningitis, peritonitis and other diseases. Experiments have proved that the toxicity of pyrogenic exotoxin A(SPEA) is obviously greater than that of SPEB and SPEC. It plays a more important role in the pathogenesis of TSLS. Rheumatism and glomerulonephritis may occur in some patients infected by Group A Streptococcus for 2-4 weeks. Myocarditis, pericarditis and endocarditis may occur in the heart, and then cause damage to the heart valve. Its pathogenesis is still unclear. The occurrence of polyarthritis and glomerulonephritis may be related to streptococcus antigen-antibody complex. Recently, it is considered that Streptococcus M protein and exotoxin are superantigens, and superantigens may be one of the causes of autoimmune after infection.
What Are The Symptoms Of Group A Streptococci Infection
Group A Streptococcus can cause purulent diseases all over the body, the most common of which are as follows.
1. Acute pharyngolaryngitis and acute tonsillitis. The majority of patients are children. Most of them occur in winter and spring. Patients may have fever, sore throat, headache and other symptoms. Examination showed congestion, edema and purulent exudate in pharynx and tonsil, which could form pseudomembrane. Rheumatism or nephritis may occur in some patients during recovery period.
2. Infection of skin and soft tissue. When skin is slightly damaged or degenerated, it is beneficial to erysipelas. Bacteria can spread through lymph after entering the damaged part. Patients may have general symptoms such as fever, headache and general discomfort. Within a few hours, erythema appeared on local skin with clear boundary and higher than normal skin. In severe cases, bullae containing purulent fluid and tissue necrosis may occur, and nearby lymph nodes may be enlarged and tender. For example, neonatal umbilical infection, infant may suffer from pustulosis, surgical wound infection and so on. Cellulitis often leads to bacteremia. The most serious is necrotizing fasciitis, which is a process of progressive necrotizing infection of deep subcutaneous fascia and fat. Infection usually starts with inconspicuous trauma or surgery. Red, swelling, heat and pain appeared locally, and quickly spread outward. The color of the lesion changed from red to purple and then turned blue within 24-48 hours, forming blisters and bullae containing yellow liquid. On the 4th to 5th day of disease, the purple area began to necrosis, and on the 7th to 10th day, the boundary was clear, and the necrotic skin fell off, showing extensive necrotic tissue under the skin. Patients suffer from high fever, weakness and unresponsiveness, which easily lead to bacteremia and septicemia. In fact, TSLS patients are often accompanied by severe soft tissue infection. There are still patients with myositis, but most of them coexist with necrotizing fasciitis, and the single occurrence is relatively rare.
3. Toxic shock-like syndrome (TSLS). From the late 1980s, the rare serious group A bacteria infection increased obviously. Most patients are healthy people aged 20-50. Most of the pathogenic bacteria are M1 and M3, M12 and M28, which can produce exotoxin A and B. Most of the invasion portals are skin and soft tissue, especially cellulitis and necrotizing fasciitis, accounting for 70%. Lung infection is also an important source. Patients suffer from chills and high fever, accompanied by severe pain in certain parts, such as limbs, chest, heart, joints and abdomen. There are hypotension and even shock, lethargy, confusion and even insanity, hallucinations, impaired renal function and even acute renal failure, abnormal liver function, elevated ALT and blood bilirubin, and acute respiratory distress syndrome. Many patients have decreased serum protein and blood calcium and sodium. Despite modern rescue and treatment, the mortality rate is still above 30%. In a word, the clinical manifestations of TSLS are no different from TSS caused by staphylococcus, including:
- Scarlet fever or erythema rash with late desquamation
- More than three important organs were damaged, such as renal failure, adult respiratory distress syndrome, impaired liver function and abnormal brain function.
4. Other infections. Group A Streptococcus can cause endophthalmitis, sinusitis, vaginitis, endometritis, pneumonia and so on. People with insufficient immunity can develop bacteremia, and then meningitis, endocarditis, peritonitis, arthritis, osteomyelitis, puerperal fever, thrombophlebitis, etc.
How To Check For Group A Streptococcus Infection
Mainly based on bacterial culture. Besides hemolysis reaction, the group and type should be determined by serum classification. Detection of anti-streptolysin O antibody in patients' serum with titer above 1∶400 has diagnostic significance.
In addition, when toxic shock syndrome (TSS) occurs, the following diagnostic tests can also be performed
1. Bacterial culture. Group A streptococci grow in secretions or exudates of throat swab or wound. Anti-streptolysin O antibodies can be detected in serum during recovery period. The positive rate of TSS caused by invasive group A streptococci in blood culture can be as high as 60%.
2. Urine routine. Proteinuria may occur in patients with high fever, and urine protein increases with nephritis, and red blood cells and tubules appear. Urine abnormality disappears after fever.
3. Peripheral hemogram. The total number of white blood cells and neutrophils increased, especially in patients with suppurative complications. In patients with severe infection, such as TSS, the cell classification could shift to the left. In patients with scarlet fever, the eosinophils could increase to 5%-10% after eruption. The platelet count of TSS patients can be normal at the beginning of the disease, and then decrease.
4. Others. TSS patients may show hypofunction of lung, hypoxemia of blood oxygen, hypofunction of liver and kidney, hypoproteinemia and so on.
How To Prevent Group A Streptococcus Infection
1. The source of infection. The nasopharynx and skin of patients and carriers can carry bacteria, and there are reports of outbreak and epidemic caused by anus and vagina carrying bacteria. Patients should be treated in isolation until the swabbing culture turns negative. When scarlet fever is prevalent in collective children's institutions, patients with acute pharyngitis and tonsillitis are treated according to scarlet fever isolation. Penicillin prevention was given to susceptible people in close contact. Carriers in the staff of children's institutions should temporarily adjust their posts and give penicillin G treatment.
2. Ways of transmission. Respiratory tract and direct contact can spread. There are also reports that eating contaminated food has caused angina outbreak. Living in poverty, poor sanitation, crowded living and close contact all contribute to the occurrence of streptococcal infection. Patients' secretions and pollutants should be disinfected, and medical personnel should wear masks. When infection of unknown origin occurs, seek medical advice promptly.
3. People's susceptibility. Group A Streptococcus can invade people of any age, but most of the patients are children. During the epidemic period, people should avoid crowded public places, pay attention to personal hygiene and avoid wound infection.
How To Treat Group A Streptococcus Infection
Penicillin is the first choice for the treatment, but considering that there may be drug-resistant strains, the dosage should be increased or other drugs should be used, such as erythromycin, clindamycin, first-generation and second-generation cephalosporin antibiotics, etc. It is best to refer to the local drug sensitivity results.
Because of the close relationship between group A streptococcal infection and rheumatic fever, patients with rheumatic heart disease or rheumatic fever are suitable for prevention. Antibiotics are used to prevent the occurrence of streptococcal respiratory infection, while penicillin is the first choice for prevention. Benzathine penicillin can be used. Adults are given 1.2 million U intramuscular injection every month, and children are given 600,000 ~ 1.2 million U intramuscular injection every month. The course of treatment is more than several years until the condition is stable. People who are allergic to penicillin can be given erythromycin 250mg twice a day for a long time. If patients can't insist on a long course of treatment, they can be swabbed regularly. When group A streptococci are found, penicillin or erythromycin is used as acute streptococcal pharyngitis.
Patients with scarlet fever should be treated in isolation to control the isolation period of infection source for 6 days. Those who turn negative in throat swab culture can be discharged from hospital without complications, or they can be isolated at home. When scarlet fever is prevalent in nursery institutions or schools, those with acute pharyngitis and tonsillitis should be treated in isolation according to scarlet fever, and those with close contacts in susceptible population should be quarantined for 7-12 days. Some people also advocate giving penicillin preventive medication.
Carriers should also be treated with penicillin until the culture turns negative, so as to control the source of infection, which is especially important for the staff of nursery institutions.
Prognosis: Except for invasive group A streptococcal infection, the prognosis was good after early treatment with penicillin, and the incidence of rheumatic fever and glomerulonephritis also decreased. Invasive group A streptococcal infection has a high mortality at present. If it can be diagnosed as early as possible and antitoxin or cytokine is used in treatment, its prognosis may be improved.
How To Identify Group A Streptococcus Infection
1. Streptococcal tonsillitis needs to be differentiated from the following diseases.
- Pharyngeal diphtheria: the onset is slow, fever is lower than that of this disease, pharyngeal congestion is absent, and it is covered with gray false membrane, which can spread to soft palate, uvula and pharynx wall, etc. The false membrane is not easy to wipe away, and bleeding surface can be left when peeling off. Swallow swab culture and smear examination are helpful for diagnosis.
- Infectious mononucleosis: throat signs can be similar to streptococcus infection, but fever lasts for a long time, antibiotics do not react, abnormal lymphocytes in peripheral blood picture increase significantly, and heterophile agglutination test is positive.
- Fensen angina: dirty gray pseudomembrane and secondary necrosis on tonsil and soft palate. There are superficial ulcers formed after necrotic tissue shedding, and there is no obvious congestion or edema in surrounding tissues. Most of the lesions were unilateral, with mild systemic symptoms, low fever and normal white blood cell count. Exudate smear can be used to find Helicoverpa Vincent and Fusobacterium.
2. Erysipelas: With characteristic skin lesions, it can be diagnosed that there are few bacteria in the skin lesions and it is difficult to obtain positive results. In a word, it is difficult to distinguish group A streptococcus infection from other pyogenic infections, and the differential diagnosis is mainly based on the results of bacterial culture. In addition, the titer of anti-streptolysin O antibody in patients' serum is helpful to judge whether it is active infection.
3. Scarlet fever: It is characterized by typical rash, pale mouth, "strawberry tongue" or "raspberry tongue", increased white blood cells and neutrophils, increased eosinophils after rash, etc., and group A streptococcus can be diagnosed by throat swab culture. It can also be identified by skin whitening test.
4. Drug rash: It may be scarlet fever rash, with a history of taking medicine and a certain latent period, without angina and "strawberry tongue" change, with mild poisoning symptoms.
5. Measles: There are obvious catarrhal symptoms and oral measles mucosal spots at the beginning of the disease, and rash occurs 4 days after the onset, which is a maculopapule with wide distribution and normal skin between rashes.
6. Rubella: Light red rash, swollen lymph nodes behind ears and occipital, mild throat symptoms, no "strawberry tongue".
7. Staphylococcus aureus infection: Because the bacterium has rash toxin, it can also show scarlet fever rash, and the identification mainly depends on bacterial culture.
What Are The Complications Of Group A Streptococcus Infection
1. Suppurative complications: Infection directly invades adjacent tissues and organs or spreads to lumens. Such complications are more common in children, such as suppurative submandibular or cervical lymphadenitis, suppurative otitis media, mastoiditis, sinusitis, peritonsillar abscess, posterior pharyngeal abscess, etc. Meningitis, brain abscess and intracranial venous sinus embolism caused by streptococcus spreading through sieve plate are rare. Pneumonia, lung abscess, mediastinitis and pericarditis caused by group A streptococci are rare at present.
2. Non-suppurative complications: allergic diseases caused by streptococcus, including rheumatic fever and acute glomerulonephritis.
Except for some "skin" strains, group A streptococci can cause rheumatic fever, which usually starts 3 weeks after acute tonsillitis or angina, but it also happens as short as 2-3 days and as long as 1 month or so. The incidence of rheumatic fever in tonsillitis and scarlet fever is about 2.8%. The incidence of rheumatic fever after erysipelas is unknown, and rheumatic fever does not occur after impetigo, but it can cause glomerulonephritis.
Acute glomerulonephritis usually occurs in the third week after streptococcal infection. Some types of group A streptococcal infections are related to the onset of nephritis. For example, respiratory infection type 12 and impetigo-causing type 49 are common strains causing nephritis, while others are types 1, 4, 25, 55, 57, 60 and 61. Among streptococcal infections that can cause glomerulonephritis, 10%-15% of them are complicated with the disease.
3. Migratory complications: purulent arthritis, endocarditis, meningitis or brain abscess, osteomyelitis, liver abscess and so on can be produced by blood-borne spread of bacteria. At present, such complications have been rare since effective antimicrobial treatment.