REACHLINE Strep A Rapid Test
Group A Streptococcus (GAS), also known as Streptococcus pyogenes, is one of the most important pathogens in human bacterial infections. GAS can invade any part of the human body, but upper respiratory tract infections are the most common, followed by skin and soft tissue infections. GAS can cause both suppurative diseases and non-suppurative complications. It is also an indirect cause of allergic diseases such as rheumatic fever and acute glomerulonephritis. In recent years, the increase in the incidence of severe infections caused by GAS, invasive Group A streptococcal infections, and their serious consequences have drawn greater attention to such bacterial infections.
Etiology
The pathogen is Group A Streptococcus. The bacteria can reside in the oral cavity and survive for several weeks in sputum, exudates, and other materials. The pathogenicity of streptococci is related to both bacterial components and the toxins and enzymes they produce. Streptococcal infections can also be transmitted through skin wounds. Infection of skin wounds with virulent streptococci from the nasopharynx or wounds is an important cause of skin infections. Dry secretion particles or skin flakes can spread through the air or be indirectly transmitted via hands or handkerchiefs. Streptococci dispersed in the air or contaminating the environment and utensils can also spread such bacterial infections. Puerperal infections can be transmitted by midwives carrying the bacteria in their throats or by infected infants in nurseries. Currently, transmission of streptococcal infections through contaminated food such as milk or dairy products is rare. Invasive Group A streptococcal infections manifest as toxic shock syndrome (TSS), which is often life-threatening. Infections often occur in healthy adults, predominantly those aged 20–50, but cases in children have also been reported. The disease can be transmitted from person to person.
Clinical Manifestations
Respiratory Infections
(1) Acute Pharyngitis and Acute Tonsillitis: The incubation period is generally 2–4 days. The onset is abrupt, with chills or rigors accompanied by high fever of around 39°C, significant sore throat that worsens when swallowing, as well as general aching, fatigue, and headache. Symptoms such as nausea, vomiting, and diarrhea are more common in children.
(2) Scarlet Fever: In addition to the clinical manifestations of acute tonsillitis, scarlet fever presents with special features such as a rash. The rash generally appears within 24 hours of onset. The typical rash consists of widespread, densely distributed, pinpoint-sized, uniformly scattered, slightly raised scarlet red papules on a background of diffusely red skin. Pressing on the rash causes blanching, and it has a fine sandpaper-like texture. In severe cases, it may appear as a hemorrhagic rash.
Skin and Soft Tissue Infections
(1) Erysipelas: Clinical manifestations include local skin inflammation accompanied by chills, fever, and significant toxic symptoms.
(2) Streptococcal Pyoderma: Presents as impetigo, a superficial skin infection, commonly seen in children aged 2–5 with poor hygiene or in military soldiers, and is more prevalent in summer.
(3) Other Infections: Streptococcal cellulitis can occur in burns or wound infections; recurrent cellulitis often occurs in cases with impaired lymphatic circulation, such as filariasis or after axillary lymph node dissection for breast cancer surgery.
(4) Invasive Group A Streptococcal Infections: Clinical manifestations include toxic shock syndrome, necrotizing fasciitis and myositis, cellulitis, and are often accompanied by multiple organ failure.
Examinations
Peripheral Blood Picture:
The total white blood cell count and neutrophil count are elevated, higher in those with suppurative complications. In severe infections, such as TSS, the cell differential may show a left shift. In scarlet fever, eosinophils may increase to 5%–10% after the rash appears. In TSS patients, platelet counts may be normal at onset but subsequently decrease.
Urinalysis:
High fever patients may exhibit proteinuria. With concurrent nephritis, urinary protein increases, and red blood cells and casts appear. In uncomplicated cases, urinary abnormalities resolve after fever subsides.
Etiological Examinations:
For patients with acute pharyngitis and tonsillitis, etiological examination should first involve a throat swab culture. If sampling, culturing, and methods are timely and correct, most patients will yield positive results, with only about 10% showing false negatives.
Other Examinations:
TSS patients may exhibit reduced pulmonary function, decreased blood oxygen saturation, impaired liver and kidney function, hypoproteinemia, and other manifestations.
Diagnosis
A positive throat swab culture remains the "gold standard" for diagnosing Group A streptococcal pharyngitis or tonsillitis. In recent years, rapid antigen detection test (RADT) kits have been developed as auxiliary diagnostic methods to throat swab cultures. When RADT results are negative, throat swab culture results are awaited for definitive diagnosis.
The REACHLINE Strep A Rapid Test Cassette is a qualitative membrane strip based immunoassay for the detection of group A streptococcal antigen. In this test procedure, anti-Strep A antibody is immobilized in the test line region of the cassette. After a specimen is placed in the specimen well, it reacts with anti-Strep A antibody coated particles that have been applied to the specimen pad. This mixture migrates chromatographically along the length of the test strip and interacts with the immobilized anti-Strep A
antibody. If the specimen contains group A streptococcal antigen, a colored line will appear in the test line region indicating a positive result. If the specimen does not contain group A streptococcal antigen, a colored line will not appear in this region indicating a negative result. To serve as a procedural control, a colored line will always appear at the control line region indicating that proper volume of specimen has been added and membrane wicking has occurred.