What is a strep throat?

Strep throat is a bacterial infection of the throat which is also known as streptococcal pharyngitis. Unlike other common infectious causes of a sore throat, a strep throat is highly contagious and if left untreated, it can cause serious and even life-threatening complications.

Causes of Strep Throat

A strep throat is caused by an infection of the throat (pharynx) with with the bacteria known as Streptococcus pyogenes or group A streptococcus (GAS). It is a highly contagious airborne disease which is easily spread by :

  • Mucus droplets when sneezing
  • Saliva droplets when coughing
  • Touching or sharing common objects, especially personal items

Most sore throats are not serious and usually resolve within two or three days to a week, but in case of chronic sore throat beyond this period a consultation with a doctor would be advisable. Untreated strep throat may lead to other complications such as rheumatic fever and glomerulonephritis.

Signs and Symptoms of Strep Sore Throat

Strep sore throat is a common bacterial throat infection occurring both in adults and children, but is most commonly seen between the ages of 5 and 15 years. Some people may be asymptomatic carriers who are capable of spreading the infection although they may have no symptoms of the infection.

Apart from a sore throat, some of the other common signs and symptoms of a strep throat include :

  • Raw, scratchy feeling or irritation of the throat
  • Enlarged, painful tonsils
  • Small red spots (petechiae) on the roof of the mouth (palate)
  • Difficulty in swallowing (dysphagia) and pain upon swallowing (odynophagia)
  • Children often complain of stomach pain and present with nausea and vomiting as well
  • Drooling is more often seen in young children
  • Swollen and painful lymph nodes of the neck
  • Fever
  • Skin rash

Usually, symptoms such as coughing, sneezing or runny nose are absent unless there is a viral upper respiratory tract infection.

However, it is necessary to differentiate between strep throat and other causes of sore throat because some of the symptoms may overlap. Strep sore throat needs early treatment with antibiotics so that other complications do not develop, while a viral sore throat may need no treatment at all and will resolve spontaneously.

Strep Throat Pictures

Pictures from Wikimedia Commons

Picture 1 – Strep throat with tonsillar exudate

Picture 2 – Strep throat with red spots on roof of the mouth

Diagnosis of Strep Throat

Physical examination and a careful history taking is necessary and if characteristic signs like small red spots on the roof of the mouth are present, treatment may be commenced even without further investigation. A number of laboratory tests, including a blood test, throat culture, rapid antigen test, and rapid DNA test, should be considered to identify a strep throat at the earliest possible stage.

  • Complete blood cell count (CBC) to determine the presence and severity of infection may be done. This may be useful to differentiate between non-infectious causes of a sore throat.
  • Anti-streptolysin O (ASO) titer measures the antibodies produced by the body against the streptococcus bacteria. The antibodies may not be present in the blood till a few weeks after the infection hence ASO titer is not helpful in diagnosing a strep throat. However, its importance lies in the fact that it can help to evaluate the complications of strep throat such as rheumatic fever and glomerulonephritis.
  • Throat culture is where a sample taken from the back of the throat by means of a sterile swab and sent for culture in the laboratory to detect the streptococcus bacteria. Culture reports may take two to three days to be ready.
  • Rapid antigen test is a faster procedure to confirm the diagnosis of strep throat but false negative results may occur. Results may be available within a few minutes. The test identifies streptococcal antigens on a sample taken from the throat.
  • Rapid DNA test is used to confirm the diagnosis of strep throat using a swab sample. The advantage over a throat culture is that accurate results are available within a day.

Incubation and Contagious Period of Strep Throat

The incubation period (the time from exposure to the disease till the development of symptoms) for strep throat may vary from 3 to 5 days. Some people are carriers and do not have any symptoms but they may be capable of passing on the disease to others.

The contagious period (the period when a person may be capable of infecting others with the disease) for a person suffering from strep throat will continue from his start of illness till 24 hours of starting antibiotics. The symptoms, however, usually takes longer to disappear. In an infected person who is not on antibiotics the contagious period may be up to 3 weeks, even though no symptoms are present.

Treatment of Strep Throat

Once strep throat is diagnosed, antibiotics are usually prescribed for oral administration. Sometimes penicillin injections may be necessary in a young child where vomiting or difficulty swallowing may affect oral administration. Timely antibiotic administration can help to reduce the duration and severity of symptoms. Antibiotics also help to contain the spread of infection to others as well as reduce chances of complications. The oral antibiotics which are normally given for strep throat are penicillin, amoxicillin, cephalosporin, or azithromycin. Clarithromycin or clindamycin may also be used.

Pain relievers such as ibuprofen or acetaminophen may help to relieve throat pain, headache and fever. Aspirin should not be given to children and young people under the age of 18 because of the risk of developing Reye’s syndrome, which is a potentially life-threatening condition.

In addition, general measures such as adequate rest, plenty of fluids, salt water gargles, throat lozenges, and avoiding foods which irritate the throat may be useful. Often, adding moisture to the air by means of a humidifier or using saline nasal sprays helps to keep the mucus membrane of the throat moist.

Tonsillectomy (surgical removal of the tonsils) may be considered in cases of recurrent episodes of strep throat or tonsillitis, or in cases of persistent peri-tonsillar abscess in spite of drainage.

Complications of Strep Throat

If a strep throat is not treated timeously or adequately, certain complications may develop, the most important of which are rheumatic fever and glomerulonephritis.

  • Rheumatic fever is a serious complication of untreated or inadequately treated strep throat since it may lead to permanent damage to the heart and the heart valves.
  • Post-streptococcal glomerulonephritis is inflammation of the kidneys which may occur as a complication of strep throat especially in children under 7 years of age. However, it usually resolves on its own in a few weeks without causing any permanent kidney damage.
  • Tonsillitis is inflammation of the tonsillar tissue.
  • Peritonsillar abscess is an abscess behind or around the tonsils.
  • Retro-pharyngeal abscess is the formation of abscess behind the throat.
  • Sinusitis is an infection of the paranasal sinuses.
  • Ear infection, usually a middle ear infection (otitis media).

Article reviewed by Dr. Greg. Last updated on November 20, 2010