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What Is Streptococcus?
Streptococcal infections are caused by a group of bacteria called streptococci. Several types exist, and the diseases they produce range from mild sore throat to life-threatening bloodstream infections.
Streptococci are broadly divided into two main groups:
- Alpha-hemolytic streptococci.
- Beta-hemolytic streptococci, which are further subdivided into several groups, include most notably Group A and Group B.
Group A Streptococcus (GAS), also known as Streptococcus pyogenes
Group A is responsible for:
- Streptococcal pharyngitis (tonsillitis / strep throat) typically causes a painful, red throat, and the tonsils may appear swollen or covered with white patches.
- Scarlet fever typically follows streptococcal pharyngitis and causes a diffuse skin rash, known as an exanthem.
- Impetigo is a contagious skin infection.
- Toxic shock syndrome, a rare but life-threatening systemic reaction.
- Cellulitis and necrotizing fasciitis (the so-called “flesh-eating bacteria” infection). Endocarditis is an infection of the heart valves.
Group B Streptococcus (GBS) (Streptococcus agalactiae)
Group B streptococcus can cause:
- Bloodstream infections (sepsis), pneumonia, and meningitis are particularly serious in newborns.
- In adults (especially the elderly or immunocompromised): urinary tract infections, skin infections, pneumonia, and bloodstream infections.
A screening test during pregnancy determines whether the mother carries GBS vaginally. If positive, intravenous antibiotics administered during labor can prevent transmission to the newborn and potentially save the baby’s life.
Streptococcal Pharyngitis (Strep Throat)
Streptococcal pharyngitis, commonly known as strep throat or streptococcal tonsillitis when the tonsils are primarily affected, is a highly contagious bacterial infection that can affect both children and adults. It is caused by Streptococcus pyogenes (Group A beta-hemolytic streptococcus) and is characterized by:
- Sore throat.
- Pain when swallowing.
- Fever.
- Red, swollen tonsils, which sometimes have white patches or streaks of pus.
- Swollen lymph nodes in the neck.
In children, less specific symptoms may also appear:
- Headache
- Stomach ache
- Nausea and/or vomiting
Transmission occurs primarily through breathing in infected respiratory droplets expelled by close contacts.
While generally not dangerous, strep throat can lead to serious complications if left untreated or inadequately treated. A rapid test can identify the bacterium in the throat, and if positive, antibiotic therapy enables rapid clinical improvement and prevents transmission to others.
Symptoms typically improve within 3–5 days, even sooner when antibiotics are started promptly. Children can safely return to school after 24 hours on antibiotics. The risk of complications in adults is low, and most streptococcal infections respond well to antibiotics.
Causes
Strep throat is caused by Streptococcus pyogenes, also known as Group A beta-hemolytic streptococcus (GAS). These bacteria are highly contagious and spread primarily through:
- Respiratory droplets, which spread when an infected person coughs or sneezes.
- Shared utensils: drinking from the same glass or eating from the same plate as an infected person.
- Indirect contact: touching a contaminated surface, such as doorknobs, keyboards, or toys, and then touching the mouth, nose, or eyes.
Risk Factors
Group A streptococcus appears in 4–6 out of every 20 children with sore throat. In contrast, it is found in only 1–3 out of every 20 adults, which highlights the significantly higher susceptibility of the pediatric population.
Key risk factors include:
Age
Strep throat occurs most often in children aged 5 to 15 years, which is the peak age for streptococcal pharyngitis. The infection is rare in children under 3. Parents of school-age children and adults who have frequent contact with children face a higher risk than the general adult population.
Close Contact with an Infected Person
The most important single risk factor. Members of the same household as an infected person are frequently exposed and at high risk of secondary infection.
Crowded Environments
Infectious diseases spread efficiently wherever large numbers of people gather. Classrooms, nurseries, daycare centers, military barracks, and sports teams all represent settings where Group A streptococcus transmits easily.
Contagion: How Is It Spread?
Streptococcus pyogenes lives in the nose and throat and spreads particularly easily among children. When an infected person coughs or sneezes, they expel tiny respiratory droplets containing the bacterium, which can infect nearby individuals when inhaled.
Other transmission routes include:
- Sharing food or drinks with an infected person
- Touching contaminated surfaces and then touching the mouth or nose
- Contact with Group A strep skin lesions (e.g., impetigo)
Contagiousness Timeline
- An infected person is most contagious at the peak of symptoms.
- Without treatment: A patient may remain contagious for up to 21 days after symptoms begin, even once the initial symptoms have resolved.
- With appropriate antibiotic treatment: The patient is typically no longer contagious within 24 hours of starting therapy.
Symptoms
Symptoms appear 2–5 days after exposure to the bacterium (incubation period). While generally not a dangerous infection, it can be extremely painful.
Typical Symptoms of Strep Throat
- Sore throat typically begins suddenly; it appears within hours instead of developing gradually.
- Pain when swallowing, often severe.
- Fever typically refers to a temperature above 38°C (100.4°F).
- Red, swollen tonsils often appear with white patches or streaks of pus, a condition known as exudative tonsillitis.
- Petechiae, small red or purple spots on the soft or hard palate, are highly suggestive of a streptococcal infection.
- Swollen, tender lymph nodes in the neck.
Additional Symptoms (Especially in Children)
- Headache
- Stomach pain
- Nausea or vomiting
Scarlet Fever Rash
In some patients, typically only during their first-ever streptococcal infection, a diffuse skin rash (exanthem) may appear. This rash is known as scarlet fever. On subsequent streptococcal infections, the rash typically does not recur (immunity to the erythrogenic toxin develops).
Symptoms That Are NOT Typical of Strep Throat
The following symptoms suggest a viral, rather than bacterial, etiology and should reduce clinical suspicion for streptococcal infection:
- Cough and a runny or congested nose are far more typical of a viral upper respiratory infection.
- Hoarseness typically indicates viral laryngitis.
- Conjunctivitis (red eyes) is characteristic of adenovirus, not streptococcus.
Important: The presence of white patches on the tonsils does NOT automatically indicate a bacterial infection. The same appearance can sometimes occur with viral infections, such as infectious mononucleosis (glandular fever). This is why clinical scoring systems and diagnostic tests are essential.
Other Possible Manifestations
If the bacterium spreads beyond the throat, it may lead to conditions like sinusitis, vaginitis, or impetigo, with the specific infection determined by the anatomical site of secondary colonization.
Duration
With 10 days of antibiotic therapy:
- Fever typically resolves within 24 hours of starting antibiotics
- Other symptoms (sore throat, difficulty swallowing) generally resolve within 2–3 additional days
- Return to school or work is generally safe after 24 hours on antibiotics (once afebrile and feeling well enough)
Without treatment:
- Symptoms may resolve spontaneously within 7–10 days, but the patient remains contagious for up to 21 days and faces a significantly elevated risk of serious complications
Dangers and Complications
Strep throat can be followed by complications if the bacteria spread to other parts of the body or trigger an abnormal immune response.
Local Complications
- Peritonsillar abscess (quinsy) is a collection of pus between the tonsil and the pharyngeal wall. It is a painful surgical emergency.
- Retropharyngeal or parapharyngeal abscess.
- Cervical lymphadenitis: significantly enlarged and infected neck lymph nodes.
- Sinusitis or otitis media.
Serious Systemic Complications (If Untreated or Undertreated)
| Complication | Description |
|---|---|
| Acute rheumatic fever | An autoimmune reaction causing inflammation of the heart, joints, and nervous system; can cause permanent heart valve damage |
| Scarlet fever | A toxin-mediated rash illness following pharyngitis |
| Fourth disease (Filatov-Dukes) | A mild exanthematous illness related to streptococcal infection |
| Bloodstream infection (sepsis) | Bacteria enter the bloodstream |
| Impetigo | Superficial skin infection |
| Post-streptococcal glomerulonephritis | Immune complex deposition in the kidneys → kidney damage |
| Streptococcal toxic shock syndrome | A potentially fatal multiorgan failure syndrome |
| PANDAS syndrome | Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections |
| Mastoiditis | Infection of the mastoid bone behind the ear |
The most feared non-suppurative complication is acute rheumatic fever, which can permanently damage heart valves and is entirely preventable with a complete course of antibiotic therapy. This is the primary reason why strep throat must always be treated with a full 10-day antibiotic course.
Invasive Group A Strep (iGAS)
International health authorities closely monitor invasive Group A Streptococcal (iGAS) infections, which are severe and potentially fatal. These infections occur when GAS bacteria invade normally sterile body compartments, such as the bloodstream, muscles, adipose tissue, lungs, or joints. Examples include:
- Bacteremia and toxic shock syndrome.
- Pneumonia: a streptococcal lung infection.
- Cellulitis is a deep soft tissue infection.
- Osteomyelitis is a bone infection.
- Necrotizing fasciitis is a severe condition involving the rapid destruction of deep fascial tissue and muscle, often referred to as “flesh-eating disease”.
It is uncommon for streptococcal pharyngitis alone to progress to iGAS. However, children with concurrent viral infections, particularly those with chickenpox (varicella) or influenza, face a meaningfully higher risk of developing iGAS. This is because viral infections damage skin and mucosal barriers while also temporarily weakening immune defenses.
Diagnosis and Testing
Accurately identifying the cause of a sore throat is clinically essential: the vast majority of sore throats (approximately 85–90% in adults) are caused by viruses and do not require antibiotics. Group A streptococcal infection requires specific antibiotic treatment. Therefore, the decision to prescribe antibiotics should rely on a structured diagnostic approach, not just visual inspection.
Clinical Assessment and Risk Scores
Before ordering tests, clinicians use validated clinical scoring systems to estimate the pre-test probability of GAS infection:
Centor Score / McIsaac Score
| Criterion | Score |
|---|---|
| Absence of cough | +1 |
| Fever > 38°C | +1 |
| Tonsillar exudate (white patches) | +1 |
| Tender anterior cervical lymphadenopathy | +1 |
| Age 5–15 years | +1 |
| Age > 45 years | −1 |
- Score 0–1: Viral etiology very likely → no testing needed; no antibiotics
- Score 2–3: Intermediate probability → perform rapid test
- Score ≥4: High probability → perform rapid test; strong consideration for empirical antibiotic therapy
Rapid Antigen Detection Test (RADT)
The rapid strep test (RADT) is the primary diagnostic tool in routine clinical practice. A swab is rubbed over the tonsils and posterior pharyngeal wall and tested for Group A streptococcal antigen. Results are available in 10–15 minutes.
- High specificity: a positive result confirms the diagnosis, justifying immediate antibiotic therapy.
- Moderate sensitivity: false negatives can occur in approximately 10–20% of cases. This is especially true if the swab technique is suboptimal or bacterial load is low.
Throat Culture
The throat swab culture remains the gold standard for diagnostic accuracy. The sample is sent to a laboratory where it is plated on selective blood agar medium and incubated for 24–48 hours to allow GAS to grow and be identified.
When is culture recommended after a negative rapid test?
- In children and adolescents: Current US (IDSA) guidelines recommend confirming a negative RADT with throat culture when clinical suspicion remains high. This is because children face a greater risk of rheumatic fever, and the culture can detect the roughly 15% of false negatives.
- In adults: The risk of rheumatic fever is very low; confirmatory culture after a negative RADT is generally not required unless clinical suspicion is very high or the patient has a history of rheumatic fever
Blood Tests (ASO Titer)
The Anti-Streptolysin O (ASO) titer measures the level of antibodies produced against a toxin secreted by Group A streptococcus.
Important: The ASO titer is NOT useful for diagnosing an acute streptococcal infection currently in progress. It indicates past exposure to streptococcus. Antibody levels typically rise one to three weeks after infection and may remain elevated for months. The ASO titer should not be used to decide whether to prescribe antibiotics today.
The ASO titer is used primarily to support the diagnosis of post-streptococcal complications (rheumatic fever, glomerulonephritis) weeks after the original infection.
Treatment
The three objectives of treating streptococcal pharyngitis are:
- Accelerate clinical recovery and reduce symptom severity and duration
- Prevent transmission to close contacts
- Prevent serious complications, including acute rheumatic fever, peritonsillar abscess, and other suppurative and non-suppurative sequelae.
Antibiotic Therapy
Unlike viral sore throats, Group A streptococcal pharyngitis must be treated with targeted antibiotic therapy. Streptococcus pyogenes remains universally sensitive to penicillin, as no clinically significant resistance to penicillin has ever been documented in GAS.
First-Line Antibiotics
| Antibiotic | Notes |
|---|---|
| Amoxicillin | First choice in most guidelines; excellent tolerability and palatability for children; wide availability |
| Penicillin V (phenoxymethylpenicillin) | Narrow-spectrum first choice in IDSA guidelines; taken 2–3 times daily |
Amoxicillin with Clavulanic Acid (Augmentin)
In specific clinical situations, especially when co-infection with beta-lactamase-producing organisms is suspected (such as Staphylococcus aureus or certain anaerobes), the physician may prescribe the combination of amoxicillin with clavulanic acid. This is not routinely required for uncomplicated strep throat.
Treatment Duration
A full 10-day course of antibiotics is essential, even if the patient feels completely well after 24–48 hours. Premature discontinuation:
- Dramatically increases the risk of relapse
- Increases the risk of immunological complications (especially rheumatic fever)
- Promotes selection of resistant bacterial strains
Alternatives for Penicillin-Allergic Patients
| Alternative | Notes |
|---|---|
| Azithromycin (macrolide) | Shorter course (5 days); convenient but increasing macrolide resistance in some regions |
| Clarithromycin (macrolide) | 10-day course |
| First-generation cephalosporins (e.g., cefalexin, cefadroxil) | Highly effective; suitable if the penicillin allergy is not anaphylactic type (cross-reactivity risk is very low) |
Symptom Management
To relieve pain and fever during the first days of illness, supportive medications (always as directed by a physician) include:
- Paracetamol (acetaminophen) is the first choice for treating fever and pain. It is suitable for all ages, including young children.
- Ibuprofen provides an effective anti-inflammatory and analgesic effect. It is particularly useful for reducing severe throat pain and difficulty swallowing.
- Throat sprays or lozenges can provide temporary topical relief of pharyngeal discomfort. However, they do not replace antibiotic therapy.
Lifestyle Measures and Practical Remedies
During the acute phase, the following comfort measures can help:
- Adequate hydration: Drink plenty of fluids, such as water, warm herbal teas, or clear broths, to prevent fever-related dehydration and keep mucous membranes moist.
- Soft, cool foods: Yogurt, ice cream, smoothies, warm (not hot) soups, and mashed potatoes are easier to swallow and soothing; avoid very hot, acidic (citrus), or spicy foods.
- Salt water gargles: Gargling with warm salt water (1/4 to 1/2 teaspoon of salt in 8 oz of warm water) can temporarily reduce pharyngeal swelling and discomfort; safe for children old enough not to swallow the solution.
- Rest: Essential to support immune function and recovery.
Managing the Asymptomatic Carrier
A streptococcal “carrier” is a person who tests positive for GAS on throat swab but has no symptoms of infection. In most cases:
- Carriers do not require antibiotic treatment.
- The risk of complications and of transmitting infection to close contacts is extremely low in true carriers.
- Treatment of carriers is considered only in exceptional circumstances. For example, this may occur during outbreaks of rheumatic fever in closed communities or if a household member has a history of rheumatic fever.
Prevention
Having had strep throat once does not confer protective immunity; reinfection can occur at any time. There is currently no vaccine available to prevent streptococcal pharyngitis.
Isolation Measures
If diagnosed with strep throat:
- Stay home from work, school, or daycare until you have been fever-free AND have been on antibiotics for at least 24 hours
- Avoid sharing eating utensils, glasses, or personal items
Hand Hygiene: The Most Important Preventive Measure
- Wash hands frequently with soap and water for at least 20 seconds, especially after coughing or sneezing, before eating, and before preparing food.
- Use alcohol-based hand sanitizer when soap and water are unavailable.
- Cover your mouth and nose when coughing or sneezing. Use a tissue, then dispose of it immediately. Alternatively, cough into your elbow or sleeve.
- Avoid touching your face (eyes, nose, mouth) with unwashed hands.
Environmental Hygiene
- Wash dishes, glasses, and utensils used by an infected person thoroughly. Once properly washed, they can be safely reused.
- Disinfect frequently touched surfaces (doorknobs, light switches, mobile phones) during illness.
Frequently Asked Questions
What are the symptoms of streptococcus (strep throat)?
The typical symptoms of strep throat include: sudden-onset sore throat, pain when swallowing, fever, red and swollen tonsils (sometimes with white patches or streaks of pus), petechiae (small red spots) on the palate, and swollen tender lymph nodes in the neck.
How long does strep throat last?
With a full 10-day course of antibiotics, fever typically resolves within 24 hours and other symptoms (sore throat, swallowing difficulty) within a further 2–3 days. Return to school or work is safe after 24 hours on antibiotics.
What should I do if I have strep throat?
If strep throat is suspected, consult a doctor promptly to confirm the diagnosis with a throat swab and begin antibiotic therapy if confirmed.
Can someone with strep throat go out?
Not until they have been on appropriate antibiotic therapy for at least 24 hours and are fever-free.
Can strep throat be recognized without a throat swab?
Unfortunately, clinical signs alone are not enough to confirm the diagnosis. A rapid strep test or throat culture is required.
What is the difference between strep throat and scarlet fever?
Streptococcus is the bacterium that causes strep throat. Scarlet fever is a specific complication that occurs when the infecting strain produces erythrogenic toxins, causing a widespread skin rash in addition to the throat infection. Importantly, the rash typically appears only during the first-ever streptococcal infection. After that, subsequent infections do not produce the rash because the patient has developed immunity to the toxin.
Which antibiotic is best for strep throat?
Amoxicillin (or penicillin V) is the first-line treatment of choice. In cases where other organisms are suspected, amoxicillin-clavulanic acid may be prescribed. In patients with penicillin allergy, macrolides (azithromycin) or cephalosporins may be used instead.
Can strep throat resolve naturally without antibiotics?
While strep throat can sometimes resolve without treatment, this is strongly inadvisable. Without antibiotics, serious complications can arise. These include rheumatic fever, which may cause permanent heart damage; kidney inflammation; and toxic shock syndrome.
How long is strep throat contagious?
Without treatment: up to 21 days after symptom onset. With appropriate antibiotic therapy: generally not contagious after 24 hours of treatment.
Why do you get strep throat?
Strep throat is a contagious infection. It spreads through contact with an infected person, primarily via respiratory droplets.
How can you tell if a child has strep throat?
In a child with fever and severe sore throat, a physician should be consulted promptly. A throat swab is the only reliable way to confirm the diagnosis.
What is the incubation period of strep throat?
Symptoms typically appear 2–5 days after exposure to the bacterium.
What happens if strep throat is not treated?
Untreated strep throat exposes the patient to a significant risk of serious complications. These include peritonsillar abscess, acute rheumatic fever (which can cause permanent heart damage), post-streptococcal glomerulonephritis (kidney damage), toxic shock syndrome, PANDAS syndrome, mastoiditis, and spread to the bloodstream.
Can adults get scarlet fever?
Yes, adults can contract scarlet fever. However, it is less common than in children because adults typically have a more mature immune system and may have prior immunity to streptococcal toxins.
Is strep throat contagious?
Yes, strep throat is highly contagious. It spreads primarily through respiratory droplets or contact with contaminated objects.
How many times can you get strep throat?
There is no limit to the number of times a person can contract strep throat. Infection does not confer lasting immunity, so reinfection from new streptococcal exposures is always possible.
What symptoms should prompt a strep test?
A rapid strep test should be considered when a patient presents with fever, an intense sore throat of sudden onset, tonsillar exudate (white patches), tender swollen neck lymph nodes, or systemic symptoms such as vomiting and nausea. This is particularly important if the patient does not have a cough, as its absence suggests a viral etiology may be less likely.
Is it possible to be reinfected with strep, and what treatment is indicated?
Yes, reinfection is entirely possible. This is especially true if you have close, ongoing exposure to infected individuals. Confirmed reinfection is treated with the same antibiotic regimen as a first episode. If recurrent strep throat is a significant problem (≥3–4 documented episodes per year), specialist referral to an otolaryngologist (ENT) to discuss tonsillectomy may be appropriate.
Sources and Bibliography
- CDC – Strep Throat (Group A Streptococcal Pharyngitis)
- Shulman ST, et al. Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis: 2012 Update by the Infectious Diseases Society of America. Clin Infect Dis 2012; 55:e86–e102.
- McIsaac WJ, et al. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ 1998; 158:75–83.
- Carapetis JR, et al. The global burden of group A streptococcal diseases. Lancet Infect Dis 2005; 5:685–694.
- Van Brusselen D, et al. Streptococcal pharyngitis in children: to treat or not to treat? Eur J Pediatr 2014; 173:1275–1283.
