Viruses are the most common cause of a sore throat. However, strep throat is an infection in the throat and tonsils caused by bacteria called group A Streptococcus (group A strep or GAS).Streptococcus pyogenes is the technical name for the genus and species of this bacteria that can tolerate air exposure. The species name is derived from the Greek word streptos meaning a chain of berries (kokkos [coccos in Latin]). The infection itself is pus (pyo) forming (genes).
Strep throat is so common that anyone with a sore throat immediately wonders if they have GAS and whether or not they need an antibiotic. Although most children with a sore throat have a viral infection, only about 25% have Strep throat. In adults, Strep throat occurs about half as much.
How common is Strep?
Each year, there are an estimated 700 million or more Strep infections across the globe. Strep infections typically occur in the throat, but they can also involve the genital mucosa, rectum, and skin.
There are four primary methods of transmitting Strep:
- Inhalation of respiratory droplets
- Skin contact
- Contact with contaminated objects (fomites), surfaces, or dust
- Transmission through food or drink
The mortality from Strep infections is small at about 0.1%. However, there are upwards of one million global cases each year that can be severe and invasive. These cases have a mortality rate of 25%.
It is important to recognize cases of Strep throat and to treat them promptly. Children tend to have a higher incidence of Strep pharyngitis due to their lower immunity and frequent exposure in community settings such as schools, nurseries, and churches. Strep occurs more often in the late winter and early spring.
Early identification of the causative agent of an infection is important. This is particularly true in the case of Strep throat because, aside from streptococcal pharyngitis, potentially more serious diseases can result, including:
- Rheumatic fever
- Rheumatic heart disease
- Scarlet fever
What is Rheumatic Fever?
Acute rheumatic fever (ARF) is less common today because of the advent of antibiotics, particularly penicillin. Acute rheumatic fever is an autoimmune inflammatory disease that develops as a result of a strep infection.
It has extremely variable manifestations.. Most people with acute rheumatic fever are predisposed to repeat Strep infections.
The most significant complication of ARF is rheumatic heart disease, which usually occurs after repeated bouts of acute illness. Rheumatic heart disease can cause problems with the valves of the heart among other things.
Signs and Symptoms of Strep
It’s common for someone with Strep to experience pain and a fever without a cough. Many children complain that the sore throat is the worst they have ever had. This comparison to prior sore throats and the characteristic foul-smelling breath is often enough to identify Strep.
Strep throat is a mild infection, but it can be very painful. The most common symptoms of Strep throat include:
- A sore throat that can start very quickly
- Pain when swallowing (odynophagia)
- Trouble swallowing (dysphagia)
- Red, swollen tonsils that sometimes have white patches or streaks of pus
- Tiny, red spots on the roof of the mouth, soft palate, and hard palate
- Swollen lymph nodes in the front of the neck
- Lethargy or fatigue
- Malaise or general feelings of illness
Other symptoms may include a headache, stomach pain, nausea, or vomiting. Someone with strep throat may also develop a rash. When this happens, it is known as scarlet fever.
The following symptoms suggest a virus is the cause of the illness instead:
- Runny nose
- Hoarseness (changes in your voice that make it sound breathy, raspy, or strained)
- Conjunctivitis (pink eye)
Viral pharyngitis vs. Strep throat
It can be difficult to distinguish between viral pharyngitis and Strep throat. Many healthcare providers use a throat swab or culture to help in the diagnosis.
Laboratory evaluation of pharyngitis falls into two broad categories: rapid antigen detection tests (RADTs) and throat culture.
RADTs offer the advantage of a speedy diagnosis, which allows for swift administration and proper withholding of antibiotics. RADTs are expensive and have a lower sensitivity compared to throat cultures.
Throat cultures are traditionally best for the diagnosis of Strep throat. However, it can take up to two days to produce a result. Throat cultures are technically more difficult and can be variable.
Both RADTs and throat cultures can prompt healthcare providers to over-diagnose and over-prescribe antibiotics. This is because, many times, tests will be positive when they should not be. This is called a false-positive.
When this occurs, the patient may have the Strep organism in their throat without the infection. This means they are just carriers of the bacteria.
No matter what type of test is used in the outpatient setting, providers must judiciously select patients to be screened in order to avoid a large number of false-positive results.
The probability that streptococci is causing pharyngitis can be estimated using a diagnostic scoring system.
The Centor score is a tool that was developed to help distinguish Strep throat from viral pharyngitis, so antibiotics can be appropriately prescribed. It is calculated by assigning one point for each of the following:
- Absence of a cough
- Presence of tonsillar exudates
- Swollen, tender anterior cervical nodes
The Centor score can range from 0 to 4.
The McIsaac score modifies the Centor score by considering the differences in incidence of Strep throat in children versus older adults. The Centor score is used, but providers must add one point if the patient is younger than 15 years and subtract one point if the patient is aged 45 years or older.
A score of 2 or more should prompt the clinician to perform a pharyngeal swab for rapid testing or a bacterial culture to evaluate for Strep throat. If the score is 3 or more, it would be reasonable for the clinician to treat the patient for Strep throat. Routine blood tests for Strep throat are unnecessary.
The Centers for Disease Control and Prevention (CDC) and the American College of Physicians-American Society of Internal Medicine (ACP-ASIM) endorse the Centor score to determine the risk of Strep throat and to guide the management of acute Strep throat in adults.1
A Final Word
Whether the diagnosis is Strep throat or viral pharyngitis, supportive care needs to be the same. It is important to maintain hydration, control fever, and make sure the patient avoids spreading the infection to others.
The debate about whether to prescribe antibiotics is ongoing. On one hand, it is important to avoid complications such as rheumatic heart disease. On the other hand, judicious use of antibiotics is key to the prevention of antibiotic resistance strains.
1Fine AM, Nizet V, Mandl KD. Large-scale validation of the Centor and McIsaac scores to predict group A streptococcal pharyngitis. Arch Intern Med. 2012 Jun 11. 172 (11):847-52.