ConditionInfections
Streptococcal Infection (Strep)
A streptococcal infection is any illness caused by Streptococcus bacteria. Group A strep causes strep throat, scarlet fever, impetigo and cellulitis, and rarely severe invasive infections such as necrotizing fasciitis and toxic shock. Group B strep can cause serious infections in newborns and older adults. Streptococcus pneumoniae is a leading cause of pneumonia, ear infections and meningitis. Most strep infections are easily treated with antibiotics such as penicillin, which also prevent complications like rheumatic fever.
Also called: Strep infection, Streptococcus infection, group A strep (GAS), group B strep (GBS), pneumococcal infection
At a glance
- Cause
- Streptococcus bacteria; group A, group B and pneumococcus are the most important.
- Common illnesses
- Strep throat, scarlet fever, impetigo, cellulitis, ear and sinus infections, pneumonia.
- Serious illnesses
- Necrotizing fasciitis, streptococcal toxic shock, sepsis, meningitis, newborn GBS disease.
- Spread
- Respiratory droplets, direct contact with sores, and mother to baby at birth (GBS).
- Diagnosis
- Rapid strep test, throat culture, wound or blood cultures.
- Treatment
- Penicillin or amoxicillin for most; alternatives for allergy; hospital care for invasive disease.
When to get help
Call 911 or go to the ER
- Rapidly spreading redness and swelling with pain far worse than the skin looks, fever and feeling very ill (possible necrotizing fasciitis): call 911 or your local emergency number
- Fever with low blood pressure, confusion, fast breathing or a sunburn-like rash (possible toxic shock or sepsis)
- A newborn with fever or low temperature, poor feeding, breathing problems or floppiness
- Severe headache, stiff neck and fever
- Drooling, difficulty breathing or being unable to swallow with a sore throat
See a doctor within a day or two
- Sore throat with fever and no cough, especially in a child aged 5 to 15: get a strep test
- A sandpaper-like rash with sore throat (possible scarlet fever)
- Spreading red, warm, tender skin
- Dark or cola-colored urine, swelling or joint pain weeks after a strep infection
Book a routine appointment
- Repeated episodes of strep throat
- Pregnant at 36 to 37 weeks: group B strep screening
Usually safe to manage at home
- A sore throat with cough, runny nose and hoarseness, which suggests a virus rather than strep
Types of streptococcal bacteria
| Group | Main infections | Who is at risk |
|---|---|---|
| Group A (S. pyogenes) | Strep throat, scarlet fever, impetigo, cellulitis, erysipelas, necrotizing fasciitis, toxic shock | Children aged 5 to 15 for throat; anyone for skin |
| Group B (S. agalactiae) | Newborn sepsis, pneumonia and meningitis; infections in pregnancy and older adults | Newborns, pregnant people, older adults, diabetes |
| S. pneumoniae (pneumococcus) | Pneumonia, ear and sinus infections, meningitis, bloodstream infection | Young children, adults over 65, chronic illness |
| Viridans streptococci | Dental infections, endocarditis | People with damaged heart valves |
Group A strep infections
Strep throat
Strep throat causes a sudden sore throat, pain on swallowing, fever, swollen tender neck glands, red tonsils with white patches, and sometimes headache, stomach pain or vomiting in children. Cough, runny nose and hoarseness point instead to a virus.
Scarlet fever
Scarlet fever is strep throat with a red, sandpaper-feel rash that starts on the neck and chest, a flushed face with pale skin around the mouth, and a "strawberry tongue".
Skin infections
- Impetigo: sores with honey-colored crusts, often around the nose and mouth in children.
- Cellulitis and erysipelas: spreading red, warm, tender, swollen skin, often with fever.
Invasive group A strep
Rare but serious, and rates have increased in recent years:
- Necrotizing fasciitis: rapidly spreading infection of deep tissues with severe pain out of proportion to the appearance; a surgical emergency.
- Streptococcal toxic shock syndrome: sudden fever, low blood pressure and organ failure.
- Bloodstream infection, pneumonia and sepsis.
Post-strep complications
- Rheumatic fever: joint pain, heart inflammation, rash and movement problems 2 to 4 weeks after untreated strep throat. Antibiotic treatment of strep throat prevents it.
- Post-streptococcal glomerulonephritis: kidney inflammation with dark urine, swelling and high blood pressure, after throat or skin infections.
Group B strep
About 1 in 4 pregnant people carry GBS in the vagina or rectum without symptoms. It can pass to the baby during birth and cause early-onset sepsis, pneumonia or meningitis. Screening at 36 to 37 weeks and IV antibiotics during labor for carriers greatly reduce this risk. GBS also causes urinary, skin, bone and bloodstream infections in older adults and people with diabetes.
Pneumococcal infections
Pneumococcus causes pneumonia, sinusitis, middle ear infections, meningitis and bloodstream infections. Pneumococcal vaccines protect against many strains and are recommended for all infants, adults 50 and older, and people with certain health conditions.
Diagnosis
- Rapid antigen detection test for strep throat; a negative result in children and teens is often confirmed with a throat culture.
- Wound swab or culture for skin infections.
- Blood cultures and imaging for invasive infections.
- Urine and blood tests if kidney complications are suspected.
- Vaginal-rectal swab at 36 to 37 weeks for GBS.
Treatment
- Strep throat: penicillin or amoxicillin for 10 days. Cephalexin, azithromycin or clindamycin for penicillin allergy. People are no longer contagious after 12 hours of antibiotics and once fever-free.
- Impetigo: topical mupirocin for limited areas, oral antibiotics if widespread.
- Cellulitis: oral or IV antibiotics depending on severity.
- Invasive infections: hospital care, IV penicillin plus clindamycin, surgery for necrotizing fasciitis, and intensive support.
- Pain and fever: acetaminophen (paracetamol) or ibuprofen; follow the label dose and do not give aspirin to children or teenagers.
Complete the full course of antibiotics for strep throat, even after feeling better, to prevent rheumatic fever.
Prevention
- wash hands often; cover coughs and sneezes
- do not share cups, utensils or towels
- clean and cover wounds; keep sores covered
- stay home until 12 hours after starting antibiotics and fever-free
- pneumococcal vaccination as recommended
- GBS screening and treatment in pregnancy
Frequently asked questions
What are the symptoms of a strep infection?
Symptoms depend on the site. Strep throat causes a sudden sore throat, fever and swollen neck glands without cough. Skin infections cause red, warm, tender or crusted areas. Serious infections cause high fever, severe pain, low blood pressure and confusion.
How is strep spread?
Group A strep spreads through respiratory droplets from coughs and sneezes, sharing drinks or utensils, and touching infected sores. Group B strep can pass from mother to baby during birth.
Is a strep infection serious?
Most strep infections, like strep throat and impetigo, are mild and respond quickly to antibiotics. Rarely, strep causes invasive infections such as necrotizing fasciitis, toxic shock or sepsis, which are emergencies.
Can strep go away without antibiotics?
Strep throat often improves on its own, but antibiotics shorten illness, reduce spread and prevent complications such as rheumatic fever and abscesses. Doctors recommend treating confirmed strep infections with antibiotics.
Sources
This guide was written from current patient and clinical guidance, including:
- CDC: About group A strep infection
- CDC: About group B strep disease
- CDC: Pneumococcal disease
- Infectious Diseases Society of America: Guideline for diagnosis and management of group A streptococcal pharyngitis
- American Academy of Pediatrics: Red Book, group A streptococcal infections
- MedlinePlus: Streptococcal infections