A culture positive case of streptococcal pharyngitis with typical tonsillar exudate in a 16 year old.
|Classification and external resources|
Streptococcal pharyngitis, streptococcal tonsillitis, or streptococcal sore throat (known colloquially as strep throat) is a type of pharyngitis caused by a group A streptococcal infection. It affects the pharynx including the tonsils and possibly the larynx. Common symptoms include fever, sore throat, and enlarged lymph nodes. It is the cause of 15–40% of sore throats among children and 5–15% in adults.
Strep throat is a contagious infection, spread through close contact with an infected individual. A definitive diagnosis is made based on the results of a throat culture. However, this is not always needed as treatment may be decided based on symptoms. In highly likely or confirmed cases, antibiotics are useful to both prevent complications and speed recovery. Potential complications include rheumatic fever.
Signs and symptoms
Other symptoms include: headache, nausea and vomiting, abdominal pain, muscle pain, or a scarlatiniform rash or palatal petechiae, the latter being an uncommon but highly specific finding. The incubation period and thus the start of symptoms for strep throat is between one to three days post contact. Strep throat is unlikely when any of the symptoms of red eyes, hoarseness, runny nose, or mouth ulcers are present. It is also unlikely when there is no fever.
Mouth wide open showing the throat
A throat infection which on culture tested positive for group A streptococcus. Note the large tonsils with white exudate.
Strep throat is caused by group A beta-hemolytic streptococcus (GAS or S. pyogenes). Other bacteria such as non–group A beta-hemolytic streptococci and fusobacterium may also cause pharyngitis. It is spread by direct, close contact with an infected person and thus crowding as may be found in the military and schools increases the rate of transmission. It has been found that dried bacteria in dust are not infectious, although moist bacteria on toothbrushes or similar items can persist for up to fifteen days. Rarely, contaminated food can result in outbreaks. Of children with no signs or symptoms, 12% carry GAS in their pharynx, and, after treatment, approximately 15% remain carriers.
|Points||Probability of Strep||Management|
|1 or fewer||<10%||No antibiotic or culture needed|
|2||11–17%||Antibiotic based on culture or RADT|
|4 or 5||52%||Empiric antibiotics|
A number of scoring systems exist to help with diagnosis; however, their use is controversial due to insufficient accuracy. The modified Centor criteria is based on 5 criteria and indicates the probability of a streptococcal infection.
One point is given for each of the criteria:
- Absence of a cough
- Swollen and tender cervical lymph nodes
- Temperature >38.0 °C (100.4 °F)
- Tonsillar exudate or swelling
- Age less than 15 (a point is subtracted if age >44)
A score of one may indicated no treatment or culture is needed or it may indicate the need to perform further testing if other high risk factors such as a family member has the disease. The Infectious Disease Society of America recommends against empirical treatment and considers antibiotics only appropriate following positive testing. Testing is not needed in children under three as both group A strep and rheumatic fever are rare, except if they have a sibling with the disease.
A throat culture is the gold standard for the diagnosis of streptococcal pharyngitis with a sensitivity of 90–95%. A rapid strep test (also called rapid antigen detection testing or RADT) may also be used. While the rapid strep test is quicker, it has a lower sensitivity (70%) and statistically equal specificity (98%) as throat culture. In areas of the world were rheumatic fever is uncommon, a negative rapid strep test is sufficient to rule out the disease.
A positive throat culture or RADT in association with symptoms establishes a positive diagnosis in those in which the diagnosis is in doubt. In adults, a negative RADT is sufficient to rule out the diagnosis. However, in children a throat culture is recommended to confirm the result. Asymptomatic individuals should not be routinely tested with a throat culture or RADT because a certain percentage of the population persistently "carries" the streptococcal bacteria in their throat without any harmful results.
As the symptoms of streptococcal pharyngitis overlap with other conditions, it can be difficult to make the diagnosis clinically. Coughing, nasal discharge, diarrhea, and red, irritated eyes in addition to fever and sore throat are more indicative of a viral sore throat than of strep throat. The presence of marked lymph node enlargement along with sore throat, fever and tonsillar enlargement may also occur in infectious mononucleosis.
Tonsillectomy may be a reasonable preventive measure in those with frequent throat infections (more than three a year). The benefits are, however, small and episodes typically lessen in time regardless of measures taken. Recurrent episodes of pharyngitis which test positive for GAS may also represent a person who is a chronic carrier of GAS who is getting recurrent viral infections. Treating people who have been exposed but who are without symptoms is not recommended. Treating people who are carriers of GAS is not recommended as the risk of spread and complications is low.
Untreated streptococcal pharyngitis usually resolves within a few days. Treatment with antibiotics shortens the duration of the acute illness by about 16 hours. The primary reason for treatment with antibiotics is to reduce the risk of complications such as rheumatic fever and retropharyngeal abscesses and they are effective if given within 9 days of the onset of symptoms.
Analgesics such as non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol (acetaminophen) help significantly in the management of pain associated with strep throat. Viscous lidocaine may also be useful. While steroids may help with the pain they are not routinely recommended. Aspirin may be used in adults but is not recommended in children due to the risk of Reye's syndrome.
The antibiotic of choice in the United States for streptococcal pharyngitis is penicillin V due to safety, cost, and effectiveness. Amoxicillin is preferred in Europe. In India, where the risk of rheumatic fever is higher, intramuscular benzathine penicillin G is the first choice for treatment. Appropriate antibiotics decrease the average 3–5 day duration of symptoms by about one day, and also reduce contagiousness. They are primarily prescribed out of a motivation to reduce rare complications such as rheumatic fever and peritonsillar abscess. The arguments in favour of antibiotic treatment should be balanced by the consideration of possible side effects, and it is reasonable to suggest that no antimicrobial treatment be given to healthy adults who have adverse reactions to medication. Antibiotics are prescribed for strep throat at a higher rate than would be expected from its prevalence. Erythromycin and other macrolides or clindamycin are recommended for people with severe penicillin allergies. First generation cephalosporins may be used in those with less severe allergies and some evidence supports cephalosporins as superior to penicillin. Streptococcal infections may also lead to acute glomerulonephritis; however, the incidence of this side effect is not reduced by the use of antibiotics.
The symptoms of strep throat usually improve irrespective of treatment within three to five days. Treatment with antibiotics reduces the risk of complications and transmission; children may return to school 24 hours after antibiotics are administered. The risk of complications in adults is low. In children, acute rheumatic fever is rare in most of the developed world. It is, however, the leading cause of acquired heart disease in India, sub-Saharan Africa and some parts of Australia.
Complications arising from streptococcal throat infections include:
The economic cost of the disease in the United States in children is ~$350 million.
Pharyngitis, the broader category into which Streptococcal pharyngitis falls, is diagnosed in 11 million people annually in the United States. It is the cause of 15–40% of sore throats among children and 5–15% in adults. Cases usually occur in late winter and early spring.
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