Diagnosing streptococcal infections is a critical step in ensuring that patients receive appropriate treatment. Physicians typically combine clinical observations, laboratory tests, and special examinations to differentiate bacterial infections from other diseases with similar symptoms. Early diagnosis can effectively prevent complications and avoid issues related to antibiotic misuse.
The diagnostic process must consider the patient's symptom presentation, epidemiological history, and laboratory evidence. For example, patients with pharyngitis may present with fever and lymphadenopathy, but symptoms alone cannot confirm the diagnosis. Therefore, medical tests such as rapid antigen tests and cultures are necessary means to confirm the infection.
Physicians begin with a detailed history taking, including the duration of symptoms, contact history prior to onset, and vaccination status. Common symptoms such as throat redness, pain during swallowing, fever above 38°C, and the presence of white or yellow exudate on the tonsils are indicators of suspected streptococcal infection.
During the physical examination, physicians will look for skin rashes, cervical lymphadenopathy, or hepatosplenomegaly. For instance, patients with scarlet fever may present with a "sandpaper-like rash," which aids in clinical judgment. Additionally, it is necessary to differentiate from simple viral pharyngitis, which is usually accompanied by rhinorrhea or conjunctivitis.
The rapid antigen test is the most common initial test, capable of detecting bacterial antigens in throat swabs within 5-10 minutes. Although this test is quick, its sensitivity is about 85-90%, which may miss some cases; therefore, negative results require further confirmation through throat culture.
Throat culture is the gold standard, where swab samples are cultured on special media for 24-48 hours, accurately identifying Group A streptococci. This method has an accuracy rate of up to 95%, but it takes longer and is typically used to confirm cases that are clinically suspected despite negative rapid tests.
The Centor criteria and the McIsaac modification are widely used for risk assessment in patients with pharyngitis. The Centor criteria include five indicators: temperature >38°C, absence of cough, tender cervical lymphadenopathy, purulent tonsils, and age-related factors. The higher the score, the greater the likelihood of a bacterial infection.
Screening tools must be combined with laboratory evidence. For patients meeting more than three Centor criteria, if the rapid antigen test is negative, a throat culture should be performed to avoid misdiagnosis. Digital diagnostic tools such as AI image analysis systems have also been developed in recent years to assist in interpreting pharyngoscopic images.
Common symptoms of viral pharyngitis include rhinorrhea, conjunctivitis, and mild fever, while bacterial infections are often accompanied by high fever and severe difficulty swallowing. Distinction is needed from infectious mononucleosis, herpes simplex virus infections, and rheumatic fever.
Skin infections such as cellulitis or impetigo also require differentiation. For example, impetigo caused by streptococci forms yellow crusts, while staphylococcal infections may present with expanding areas of redness. White blood cell counts and classifications in blood tests can aid in differentiation, but ultimately, laboratory evidence is necessary.
Particular attention should be paid to the diagnosis of scarlet fever in pediatric patients, whose typical symptoms include "strawberry tongue" and "Pastia's lines rash." In adult patients, if myocarditis or glomerulonephritis occurs, the possibility of secondary infections should be considered, and anti-nuclear perinuclear factor (APF) tests should be conducted.
Untreated streptococcal infections can lead to serious complications such as nephritis and endocarditis. Early use of antibiotics can shorten the duration of illness, reduce contagiousness, and prevent rheumatic inflammatory sequelae. For example, if treatment is delayed beyond 9 days, the risk of acute glomerulonephritis doubles.
Early diagnosis can avoid unnecessary antibiotic use. Misdiagnosing viral pharyngitis as a bacterial infection can lead to antibiotic misuse. Conversely, if diagnosis is delayed, it may result in acute conditions such as sepsis. Therefore, a rigorous diagnostic process is key to balancing treatment and prevention.
For high-risk groups such as immunocompromised patients, even mild symptoms require proactive laboratory testing. The diagnostic process for pregnant women or patients with chronic diseases must be more cautious, possibly requiring additional PCR testing to ensure accuracy.
The rapid antigen test can determine streptococcal infection within minutes, but its accuracy is about 85-90%, which may result in false-negative results (especially in the early stages of symptoms). If clinical suspicion is high but the test is negative, physicians may proceed with throat culture to improve diagnostic accuracy.
How long does it usually take for symptoms to improve after starting antibiotic treatment?If diagnosed with a streptococcal infection and appropriate treatment is initiated, fever and throat redness typically improve significantly within 24 to 48 hours after medication. However, the full course of antibiotics must be completed, and medication should not be stopped prematurely, even if symptoms disappear, to avoid the risk of bacterial resistance or complications.
How can cross-infection among family members be effectively prevented?Patients should wear masks, use separate utensils, and wash hands frequently. After contact with the patient's secretions, hands should be cleaned immediately. If contacts have a history of exposure and develop similar symptoms, testing should be conducted within 24-48 hours of symptom onset to avoid delayed diagnosis.
If throat pain symptoms are significant but the rapid test is negative, should a re-examination be conducted?Yes. If symptoms are consistent with streptococcal infection (such as purulent throat, fever without cough), but the initial test is negative, the physician may recommend repeating the test or conducting a throat culture 24-48 hours later to rule out false-negative results.
Does not completing the antibiotic regimen on time increase the risk of complications such as rheumatic fever?Yes. Not completing the full course of antibiotics may leave bacteria inadequately cleared, increasing the risk of invasive infections or abnormal immune responses (such as rheumatic fever or nephritis). Adhering to medical advice to complete the medication is key to preventing complications.
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