A streptococcal group infection

Introduction to A streptococcal infection Group Astreptococci, also known as streptococcus pyogenes, is one of the most important pathogens in human bacterial infections. The main infections are acute pharyngitis, acute tonsillitis, lung infection, scarlet fever, skin and soft tissue infection, and systemic infection, which is also an indirect cause of allergic diseases, rheumatic fever and acute glomerulonephritis. In recent years, the serious infection caused by group A streptococci, the increase in the incidence of invasive group Astreptococcus infections, has also caused people to pay more attention to this type of bacterial infection. basic knowledge The proportion of illness: the probability of population 9% Susceptible population: most of the sick are children Mode of infection: respiratory tract transmission, contact transmission Complications: rheumatic fever, acute pharyngitis

Cause of infection of streptococcus A

(1) Causes of the disease

A streptococcus group is a type B hemolytic reaction, so it used to be called beta-hemolytic streptococcus. The biochemical taxonomy is S. pyogenes. According to its surface antigen, it can be divided into more than 90. The serotype, the current role of surface antigen R, T, S protein components are still unknown, M protein is an important factor in the pathogenic ability of streptococcus, it can resist the phagocytosis of the body white blood cells, such as no M protein It is non-virulent and can acquire specific immunity against M protein after infection, and it can be kept for several years. Lipoteichoic acid is also an important virulence factor in the cell wall, which can make bacteria attach to the host. On the mucosa and cell membrane, the pathogenicity of the A-streptococcus group also comes from the production of toxins and extracellular proteins. The toxins are:

1 Pyrogenic exotoxin, also known as erythema toxin, is a heat-resistant protein, which is antigenic. In addition to causing scarlet fever-like rash on the skin, it also has purulent, cytotoxic and endotoxin toxicity. It also has a superantigen effect, at least three kinds of A, B, and C (some people think that there are four) different antigenic types, and the strain that does not produce erythema toxin can be transformed into a toxigenic strain after being acted upon by phage which can produce erythema toxin.

2 streptolysin has the effect of dissolving red blood cells to kill white blood cells, platelets and damage the heart. There are two kinds of streptococcal hemolysin, O and S. O-streptolysin is antigenic, and can produce corresponding antibodies after infection. It has been kept for several months, so it can be used as one of the signs of recent infection of streptococcus. S-streptolysin is not antigenic or antigenic, and its antibody has not been detected in the body.

Extracellular proteins produced by streptococcus A

1 hyaluronidase, which dissolves the interstitial hyaluronic acid, making bacteria easy to spread in tissues.

Streptokinase, also known as fibrinolytic enzyme, converts plasminogen in the blood into plasmin, which prevents blood from coagulating or dissolves coagulated blood clots. Enzyme, also known as deoxyribonuclease (DNase), can dissolve highly viscous DNA. This enzyme has four different serotypes, A, B, C, and D. It has antigenicity to produce antibodies, and 4 nicotinamide adenine. Dinucleotide nucleosidase (NADase), which can decompose the corresponding tissue components, thereby destroying some of the body's defense capabilities, such as white blood cells can be killed, 5 opacity factor (OF), is an alpha lipid Protease can make horse serum turbid and inhibit the body's specific and non-specific immune response.

(two) pathogenesis

The bacteria fall on the respiratory mucosa or other tissues and multiply quickly. Because the M protein resists the phagocytosis of the white blood cells of the body, if the body's resistance is low at the time, it is difficult to quickly destroy the bacteria, and the bacteria can produce hemolysin during the process of proliferation. Decomposes the host's blood cells, dies, streptokinase and hyaluronidase can destroy the tissue barrier of the host and spread the infection. The streptodornase can degrade the nucleic acid of the host cell, making it an inflammatory foci that is beneficial to bacteria. Nutrient components, accumulation of inflammatory substances and proliferation of streptococcus, leading to a decrease in local tissue pH, is more conducive to the enhancement of bacterial protease activity, further aggravating tissue destruction, plus the body's inflammatory exudation reaction, forming a local tissue of suppuration changes, and further Can cause bacteremia, sepsis, meningitis, peritonitis and other diseases, streptococcal pyrogenic exotoxin (SPE) can cause fever, suppuration, rash, in recent years, it is believed to have superantigen effect, non-specific Stimulate T cell proliferation, release cytokines such as TNF, IL-1, IL-6, IFN-, and greatly enhance endotoxin Shock effects, while reducing the body's phagocytic cells and B cells to produce antibodies, leading to the clinical emergence of toxic shock-like syndrome (TSLS), also known as streptococcal toxic syndrome Shock syndrome (STSS), experiments have shown that the toxicity of pyrogenic exotoxin A (SPEA) is significantly greater than SPEB and SPEC, playing a more important role in the pathogenesis of TSLS, 2 to 4 weeks of infection of A streptococcal group Patients may have rheumatism and glomerulonephritis, heart may develop myocarditis, pericarditis and endocarditis, and then cause heart valve damage, the pathogenesis of which is still unclear, polyarthritis and glomerulonephritis, It may be related to streptococcal antigen-antibody complexes. Recently, streptococcal M protein and exotoxin are considered superantigens, and superantigen may be one of the causes of autoimmunity after infection.

A streptococcal infection prevention

Source of infection

Patients and carriers of normal people have nasopharyngeal, skin-borne bacteria, and an anal vaginal bacteria caused by outbreaks. The patient should be isolated and treated, isolated to the throat swab and cultured. In the case of a scarlet fever epidemic in a group of children's institutions, children with acute pharyngitis and tonsillitis were treated with scarlet fever isolation. Penicillin prevention is given to susceptible people who are in close contact. Carriers in the children's agency staff should be temporarily removed from work and given penicillin G treatment.

2. Route of transmission

The respiratory tract can be transmitted in direct contact. There have also been reports of outbreaks of angina caused by eating contaminated food. Poor living, poor sanitation, overcrowding, close contact, etc. all contribute to the occurrence of streptococcal infection. The patient's secretions and contaminants should be disinfected, and medical personnel should wear masks. Seek medical attention when there is an unexplained infection.

3. Population susceptibility

With benzathine penicillin, adult monthly intramuscular injection of 1.2 million U, children 600,000 ~ 1.2 million U, treatment for several years, until the condition is stable, allergic to penicillin can be erythromycin 250mg, 2 times a day, long-term use If the patient can not adhere to the long course of treatment, it can be used for regular throat swab culture. When group A streptococcus is found, it is treated with penicillin or erythromycin according to acute streptococcal pharyngitis for a course of treatment. The dose is the same as above.

Patients with scarlet fever should be treated with isolation to control the source of infection. The isolation period is 6 days, the throat swab culture is turned negative, the patients without complications can be discharged, or the family can be isolated, the child care institution or school has a scarlet fever epidemic, acute pharyngitis and Patients with tonsillitis should be treated with scarlet fever isolation, and those who are in close contact with susceptible people should be quarantined for 7 to 12 days. There are also those who advocate penicillin prevention.

The carrier should also be treated with penicillin until the culture is turned negative to control the source of infection, which is especially important for the staff of the child care institution.

Streptococcal respiratory infection should be avoided in crowded public places, reduce the chance of infection caused by droplet spread, improve the environment and pay attention to personal hygiene to avoid wound contamination and reduce the incidence of skin and wound infection.

A streptococcal infection complications Complications Rheumatic fever Acute pharyngitis

Suppurative complications

Infection directly affects adjacent tissues or organs and spreads to the lumen. Such complications are common in children. Commonly, there are suppurative submandibular or cervical lymphadenitis, suppurative otitis media, mastoiditis, sinusitis, tonsil abscess, and posterior pharynx. Wall abscess, etc., streptococcus spread through the sieve plate caused by meningitis, brain abscess and intracranial venous sinus embolism occasionally, caused by group A streptococcus pneumonia, lung abscess, mediastinal inflammation, pericarditis, etc. are currently rare.

2. Migration complications

Blood-borne dissemination of bacteria can produce septic arthritis, endocarditis, meningitis or brain abscess, osteomyelitis and liver abscess, etc. Currently, such complications have been rare since effective antibacterial therapy.

3. Non-suppurative complications

Allergic diseases caused by streptococci, including rheumatic fever and acute glomerulonephritis.

In addition to certain "skin" type strains, group A streptococci can cause rheumatic fever, usually starting 3 weeks after acute tonsillitis or angina, but it is as short as 2 to 3 days, up to 1 The incidence of rheumatic fever in patients with tonsillitis and scarlet fever is about 2.8%. The incidence of rheumatic fever caused by erysipelas is unknown. Rheumatic fever does not occur after impetigo, but it can cause glomerulonephritis.

Acute glomerulonephritis usually starts in the third week after streptococcal infection. Some types of streptococcal infections in group A are associated with the onset of nephritis, such as respiratory type 12 and impetigo. Common strains of nephritis, others are 1, 4, 25, 55, 57, 60 and 61, etc., in the streptococcal infection that can cause glomerulonephritis, the incidence of the disease can reach 10% to 15%.

A streptococcal infection symptoms Common symptoms Responsive dull peritonitis Lung infection erysipelas septicemia high fever hypotension

Streptococcus A can cause purulent diseases throughout the body, the most common of which are the following.

1. Acute pharyngitis, acute tonsillitis: patients with more children, mostly in the winter and spring, patients may have fever, sore throat, headache and other symptoms, examination of pharyngeal and tonsil congestion, edema and purulent exudate It can form a pseudomembrane, and some patients may have rheumatism or nephritis during the recovery period.

2. Erysipelas: When the skin has minor damage (such as athlete's foot) or when it is degraded (aged), it is beneficial to the occurrence of erysipelas. After the bacteria enters the damaged area, it can spread through the lymph. Patients may have systemic symptoms such as fever, headache, general malaise, etc. Within a few hours, local skin appears erythema, the boundary is clear, and the normal skin is higher. In severe cases, bullae and tissue necrosis with purulent fluid may occur, and the nearby lymph nodes may be swollen and tender.

3. Skin and soft tissue infections: neonatal umbilical infection; infants and young children may suffer from impetigo; surgical wound infection, etc., cellulitis often leads to bacteremia, the most serious is necrotizing fasciitis, For the subcutaneous deep fascia and fat progressive necrotic infection process, the infection mostly begins with trauma (inconspicuous trauma) or surgery, local red, swollen, hot, pain, and soon expand outward, 24-48h lesion The color changes from red to purple, then turns blue, forming blister and bullae containing yellow liquid. The purple area begins to necrosis on the 4th to 5th day, the boundary is clear at 7 to 10 days, and the necrotic skin falls off, revealing a wide subcutaneous Necrotic tissue, patients with high fever, weakness, slow response, easily lead to bacteremia, sepsis, in fact, TSLS patients are often accompanied by severe soft tissue infection, there are still patients with myositis, but more with necrotizing fasciitis Single shots are rare.

4. Toxic shock-like syndrome (TSLS): From the late 1980s, the rare serious group A infection was significantly increased. Most of the patients were healthy people aged 20-50 years. Most of the pathogens were group A. And M3 type, as well as M12 and M28 type, can produce exotoxin A and B, the invasion portal is mostly skin and soft tissue, especially important is cellulitis and necrotizing fasciitis (70%), lung Infection is also an important source. Patients with chills, high fever, and severe pain in certain areas, such as limbs, chest, heart (like myocardial infarction), joints, and abdomen (like peritonitis), have low blood pressure and even shock. Drowsiness, confusion, even insanity, hallucinations, etc. Impaired renal function or even acute renal failure; liver function can be abnormal, ALT and blood bilirubin can be increased; acute respiratory distress syndrome can also occur, many patients with serum protein reduction, blood calcium and sodium reduction, etc., although modernized rescue And treatment, the mortality rate is still more than 30%, in short, the clinical manifestations of TSLS and Staphylococcus caused by TSS no difference, have: 1 fever. 2 low blood pressure. 3 scarlet fever or erythematous rash, peeling later. 4 with more than 3 important organs of damage, such as renal failure, adult respiratory distress syndrome, liver function damage and brain dysfunction.

5. Other infections: A streptococcus group can cause endophthalmitis, sinusitis, vaginitis, endometritis, pneumonia, etc., the body's immune deficiency can develop into bacteremia, and then meningitis, endocarditis , peritonitis, arthritis, osteomyelitis, puerperal fever, thrombophlebitis, etc.

Examination of A streptococcal infection

Blood around

The total number of white blood cells and neutrophils increased, and those with suppurative complications were higher. In severe cases, the cell classification of TSS patients may shift to the left, and the sputum acid granules may increase to 5% to 10% after rash. In patients with TSS, the platelet count can be normal at the onset and then decreased.

2. Urine routine

Proteinuria can occur in patients with hyperthermia, and urinary protein increases with nephritis, and red blood cells and casts appear. Uncomplicated urine abnormalities disappear after heat retreat.

3. Bacterial culture

There are group A streptococci in the secretions or exudates of throat swabs or wounds. The recovery serum can detect antibodies such as anti-streptolysin O, and TSS caused by invasive group A streptococci. The positive rate of blood culture can be Up to 60%.

4. Other

Patients with TSS may have decreased lung function, decreased oxygen saturation, liver function, renal dysfunction, and hypoproteinemia.

Patients with TSS may have decreased lung function.

Diagnosis and identification of A streptococcal infection

Mainly based on bacterial culture, in addition to hemolytic reaction, the classification and type should be determined by serum classification, and the anti-streptolysin O antibody in the serum of the patient should be detected. The titer is more than 1:400.

Streptococcal tonsillitis still needs to be differentiated from the following diseases.

1. Pharyngeal diphtheria: slow onset, fever is lower than this disease, pharyngeal congestion, covering gray-white pseudomembrane, and can spread soft palate, uvula and pharyngeal wall, etc., the fake membrane is not easy to wipe off, when peeling The bleeding surface can be left behind, and the throat swab culture and smear examination are helpful for diagnosis.

2. Infectious mononucleosis: The signs of pharynx can be similar to those of streptococcal infection, but the fever lasts for a long time, the antibiotics do not respond, the abnormal lymphocytes in the surrounding blood are significantly increased, and the heterophilic agglutination test is positive.

3. Fan Shang (Fen Sen) angina: bad breath, tonsy gray membrane on the tonsils and soft palate, secondary necrosis, and shallow ulcers formed after necrotic tissue shedding, no obvious congestion or edema around the tissue, lesions Mostly one side, the systemic symptoms are light, the heat is low, the white blood cell count is normal, and the exudate smear can find the spirulina and the fusiform bacterium.

4. Drug rash: It can be a scarlet fever-like rash, a history of medication and a certain incubation period, no angina and "strawberry tongue" change, the symptoms of poisoning are light.

5. Measles: At the beginning of the onset, there are obvious symptoms of catarrh and mucosal plaque of oral measles. The rash occurs 4 days after onset, which is a maculopapular rash, which is widely distributed and the skin between the rashes is normal.

6. Rubella: light red rash, behind the ear, occipital lymph nodes, pharyngeal symptoms, no "strawberry tongue."

7. Staphylococcus aureus infection: Because the bacterium has red rash toxin, it can also be a scarlet fever-like rash, which is mainly determined by bacterial culture.

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