Clinical Subject Page

Streptococcal Infection

Streptococcal Infection refers to infections caused by bacteria belonging to the genus Streptococcus. These Gram-positive bacteria can cause localized infections such as pharyngitis and skin infections, as well as serious invasive diseases including pneumonia, bacteremia, meningitis, necrotizing fasciitis, and sepsis

Also called

Strep infection

ICD-10

A49.1

Specialty

Infectious

Onset

Acute

Reviewed

August 2026

On This Page

Overview

Overview
Etiology & Risk Factors

Etiology & Risk Factors
Pathophysiology

Pathophysiology
Clinical Presentation

Clinical Presentation
Bacterial Classification

Bacterial Classification
History Taking

History Taking
Physical Examination

Physical Examination
Investigations

Investigations
Diagnosis

Diagnosis
Management

Management
Complications

Complications
Prognosis

Prognosis
Key Points / Clinical Pearls

Key Points / Clinical Pearls

Overview

-Streptococcal Infection can affect almost any body system. Clinical manifestations depend on the species and site of infection.

Important examples include:

Pharyngitis
Tonsillitis
Scarlet fever
Impetigo
Cellulitis
Erysipelas
Pneumonia
Meningitis
Bacteremia
Endocarditis
Necrotizing fasciitis
Sepsis

-Some infections can also cause immune-mediated complications after the initial infection, particularly acute rheumatic fever and post-streptococcal glomerulonephritis.

Teaching point Group A Streptococcal pharyngitis should be recognized and treated appropriately because it can cause both invasive disease and immune-mediated complications such as acute rheumatic fever.

Etiology & Risk Factors

-Etiology

–Streptococcal Infection is caused by Gram-positive cocci that typically occur in chains or pairs.

Important species include:

Streptococcus pyogenes — Group A Streptococcus (GAS)
Streptococcus agalactiae — Group B Streptococcus (GBS)
Streptococcus pneumoniae — pneumococcus
Viridans group streptococci
Streptococcus gallolyticus

Transmission varies according to the organism and infection, including respiratory droplets, direct contact, and endogenous colonization.

-Risk Factors

Close contact with infected individuals
Crowded living conditions
Skin breaks or wounds
Diabetes mellitus
Immunosuppression

Pathophysiology

Streptococcal exposure or colonization → bacterial adherence and multiplication → local tissue invasion and inflammation → clinical infection → possible bloodstream invasion → sepsis or metastatic infection

Certain strains can also produce toxins or trigger immune-mediated disease.

Clinical Presentation

-Symptoms:

Presentation depends on the site of infection.

Pharyngitis

Sudden sore throat
Fever
Painful swallowing
Headache
Tender cervical lymph nodes

Skin Infection

Redness
Pain
Swelling
Warmth
Fever

Invasive Infection

High fever
Severe pain
Chills
Weakness
Hypotension
Altered mental status

-Signs:

Tonsillar erythema or exudates
Tender anterior cervical lymphadenopathy
Erythematous skin
Cellulitis or erysipelas
Fever
Tachycardia
Hypotension in severe infection

Important Note Severe pain that appears disproportionate to the visible skin findings, particularly with rapidly progressive swelling or systemic toxicity, should raise suspicion for necrotizing fasciitis.

Bacterial Classification

Streptococci · Classification

Classification by Hemolysis

Alpha-Hemolytic

• S. pneumoniae — optochin sensitive, bile soluble

• Viridans streptococci — optochin resistant

Beta / Gamma

• S. pyogenes — β, Group A

• S. agalactiae — β, Group B

• Enterococcus — usually γ, Group D

Major Streptococci — Exam Comparison

Organism	Hemolysis / group	Key test / clue	Classic association
S. pyogenes	β Group A	PYR +; bacitracin sensitive	Pharyngitis, scarlet fever, rheumatic fever, PSGN
S. agalactiae	β Group B	CAMP +	Neonatal sepsis, meningitis
S. pneumoniae	α No Lancefield group	Optochin sensitive + bile soluble	CAP, otitis media, sinusitis, meningitis
Viridans streptococci	α No Lancefield group	Optochin resistant; bile insoluble	Dental caries + subacute endocarditis
Enterococcus spp.	Usually γ Group D	Bile-esculin +; 6.5% NaCl growth	UTI, endocarditis
S. gallolyticus	Usually α/γ · Group D	Bile-esculin +	Colorectal neoplasia
S. anginosus group	α / β / γ	Abscess-forming	Deep abscesses

Most tested: Group A = S. pyogenes · Group B = S. agalactiae · Group D = Enterococcus/S. gallolyticus.

High-Yield Exam Associations

Classic tests

• S. pyogenes → PYR +, Group A

• S. agalactiae → CAMP +, Group B

• S. pneumoniae → optochin sensitive + bile soluble

• Viridans → optochin resistant

• Enterococcus → bile-esculin +

Classic disease links

• S. pyogenes → rheumatic fever / PSGN

• S. agalactiae → neonatal sepsis/meningitis

• S. pneumoniae → meningitis / pneumonia

• Viridans → dental caries / endocarditis

• S. gallolyticus → colorectal neoplasia

Memory hook: A = pyogenes · B = agalactiae · D = Enterococcus/gallolyticus.

History Taking

-Ask about:

Fever and duration
Sore throat or painful swallowing
Skin wounds or infections
Rapid progression of pain or swelling
Recent respiratory infection
Recent close contact with infected individuals
Recent surgery or trauma
Diabetes or immunosuppression
Previous streptococcal infection
Joint or muscle pain
Dark urine or edema after recent pharyngitis or skin infection

Physical Examination

-General Examination

Temperature
Heart rate and blood pressure
General appearance
Signs of sepsis or shock

-System-Specific Examination:

Examine the throat and tonsils
Palpate cervical lymph nodes
Inspect the skin for cellulitis, erysipelas, or wounds
Assess rapidly progressive soft-tissue lesions
Examine joints when septic arthritis is suspected
Perform neurological examination when meningitis is suspected

Investigations

-Complete Blood Count

Useful when systemic or invasive infection is suspected.

-Biochemistry / Specific Tests

Depending on the presentation:

Throat swab or rapid antigen detection test for suspected GAS pharyngitis
Blood cultures for suspected bacteremia or sepsis
Wound or tissue culture from purulent or deep infections
Antistreptolysin O (ASO) antibodies in selected patients when investigating a recent streptococcal infection and its immune-mediated complications

-Imaging

Imaging depends on the suspected infection:

Chest X-ray for suspected pneumonia
Ultrasound for selected soft-tissue collections
CT or MRI when deep infection or necrotizing fasciitis is suspected

-Special / Confirmatory Tests

Microbiological Culture

Culture identifies the organism and provides antimicrobial susceptibility information when appropriate.

For suspected necrotizing fasciitis, surgical exploration and tissue sampling are more important than delaying treatment for imaging.

Diagnosis

Streptococcal Infection is diagnosed according to the clinical syndrome and confirmed with appropriate microbiological testing.

Clinical presentation → site-specific specimen → rapid testing or culture → identification of Streptococcus species → susceptibility testing when appropriate.

For GAS pharyngitis, clinical assessment combined with rapid antigen testing or throat culture is used when indicated.

Home Home Clinical Cases Infectious System Clinical Cases Streptococcal infection

Management

Streptococcal Infections · Treatment by Condition

S. pyogenes (Group A Strep) — GAS Infections

Condition	1st Line	Alternative (Penicillin allergy)	Duration
Pharyngitis / Tonsillitis	Phenoxymethylpenicillin (Pen V) 500 mg QDS PO or Amoxicillin 500 mg TDS PO	Azithromycin 500 mg OD PO Cefalexin 500 mg QDS PO	10 days (5 days azithromycin)
Scarlet fever	Amoxicillin 500 mg TDS PO or Pen V 500 mg QDS PO	Azithromycin PO	10 days
Impetigo Non-bullous (GAS or Staph)	Topical mupirocin — localised Flucloxacillin PO — extensive (covers both GAS + Staph)	Cefalexin PO	5–7 days
Erysipelas Superficial dermis, raised border	Benzylpenicillin IV (severe) Pen V / Amoxicillin PO (mild)	Clindamycin IV/PO Cefalexin PO	5–10 days
Cellulitis Deeper dermis — GAS ± Staph	Flucloxacillin PO/IV — covers both Mild: Cefalexin PO	Clindamycin PO/IV Co-amoxiclav PO	5–7 days (mild) 10–14 days (severe)
Necrotising fasciitis Surgical emergency	Benzylpenicillin 2.4g IV q4h + Clindamycin 900 mg IV q8h — anti-toxin + Meropenem — if mixed/polymicrobial suspected	IVIG — adjunct for toxin neutralisation Surgical debridement — essential, not optional	Until clinically clear post-debridement
Streptococcal TSS	Benzylpenicillin IV + Clindamycin IV (anti-toxin — inhibits SPE production)	IVIG 1–2g/kg — adjunct; neutralises superantigen ICU + vasopressors if shock	10–14 days
Rheumatic fever — prophylaxis To prevent ARF recurrence	Benzathine penicillin G 1.2 MU IM every 4 weeks — gold standard secondary prophylaxis	Pen V 250 mg BD PO Azithromycin — if penicillin allergy	5–10 years (no carditis) 10 years or to age 40 (carditis)
Bacteraemia / Endocarditis	Benzylpenicillin 2.4g IV q4h ± Gentamicin — synergy for endocarditis	Ceftriaxone 2g IV OD Vancomycin — if penicillin allergy	4 weeks (native valve) 6 weeks (prosthetic)

S. pyogenes is NEVER resistant to penicillin — if failing penicillin, think: wrong diagnosis, re-infection, or tolerance (not resistance). Clindamycin always added in toxin-mediated disease (TSS, necrotising fasciitis) — inhibits protein synthesis → stops toxin production.

S. agalactiae (Group B Strep) — GBS Infections

Condition	1st Line	Alternative	Duration
Neonatal sepsis / meningitis	Benzylpenicillin IV + Gentamicin — synergistic; start empirically De-escalate to penicillin alone once confirmed GBS	Ampicillin + Gentamicin — equivalent	Sepsis: 10 days Meningitis: 14–21 days
Intrapartum prophylaxis GBS+ on vaginal swab at 35–37 wks	Benzylpenicillin 3g IV loading → 1.5g IV q4h during labour	Ampicillin 2g IV → 1g IV q4h Allergy (low risk): Cefalexin Allergy (high risk): Clindamycin or Vancomycin	Until delivery
Maternal bacteraemia / chorioamnionitis	Benzylpenicillin IV + Gentamicin	Ampicillin + Gentamicin	7–14 days
Adult invasive disease Bacteraemia, pneumonia, endocarditis (elderly / DM)	Benzylpenicillin IV or Ampicillin IV	Ceftriaxone 2g IV OD Vancomycin — penicillin allergy	10–14 days (bacteraemia) 4 weeks (endocarditis)

S. pneumoniae (Pneumococcus) — Infections

Condition	1st Line	Alternative / Resistant	Duration
CAP (mild — outpatient)	Amoxicillin 500 mg–1g TDS PO	Doxycycline 200 mg OD PO Clarithromycin 500 mg BD PO	5–7 days
CAP (moderate — hospitalised)	Amoxicillin 1g TDS IV/PO ± Clarithromycin (atypical cover)	Ceftriaxone 2g IV OD + Clarithromycin	7 days
CAP (severe — ICU)	Ceftriaxone 2g IV OD + Clarithromycin IV or + Levofloxacin 500 mg IV OD	Moxifloxacin IV — if beta-lactam allergy	7–10 days
Meningitis	Ceftriaxone 2g IV q12h — empirical first line + Dexamethasone 0.15 mg/kg q6h × 4 days — reduces hearing loss + mortality	PRSP (penicillin-resistant): Ceftriaxone + Vancomycin Pen-sensitive: Benzylpenicillin IV	10–14 days
Otitis media Children — watchful waiting first if mild	Amoxicillin 80–90 mg/kg/day (high dose) — overcomes intermediate resistance	Co-amoxiclav — amoxicillin failure or β-lactamase producers Cefuroxime	5–10 days
Sinusitis (bacterial)	Amoxicillin 500 mg TDS PO or Co-amoxiclav — if no improvement in 48h	Doxycycline or Levofloxacin — penicillin allergy	5–7 days
Endocarditis	Benzylpenicillin 1.2g IV q4h — penicillin-sensitive Ceftriaxone 2g IV OD — alternative	PRSP: Ceftriaxone + Vancomycin	4 weeks

PRSP (Penicillin-Resistant S. pneumoniae): Resistance is relative — high-dose amoxicillin overcomes intermediate resistance in lung/ear (high antibiotic levels). For meningitis — always use ceftriaxone ± vancomycin (CSF levels critical). Dexamethasone before or with 1st antibiotic dose for pneumococcal meningitis.

Enterococcus faecalis / faecium — Infections

Condition	1st Line	Alternative / VRE	Duration
UTI (uncomplicated)	Amoxicillin 500 mg TDS PO or Nitrofurantoin 100 mg BD PO	Fosfomycin 3g single dose Co-amoxiclav PO	5–7 days
UTI (complicated / catheter-associated)	Amoxicillin IV/PO Remove catheter if possible	Vancomycin IV — if VRE suspected or amoxicillin resistant	7–14 days
Endocarditis Most serious enterococcal infection	Ampicillin 2g IV q4h + Ceftriaxone 2g IV q12h — preferred combination (no nephrotoxicity) or Ampicillin + Gentamicin — classic synergistic combination	VRE endocarditis: Linezolid or Daptomycin high dose	6 weeks
Bacteraemia	Ampicillin IV — E. faecalis Vancomycin IV — E. faecium (often ampicillin resistant)	VRE: Linezolid or Daptomycin	14 days
VRE (Vancomycin-Resistant Enterococcus)	Linezolid 600 mg BD IV/PO Daptomycin 8–12 mg/kg IV OD	Tedizolid — linezolid alternative Tigecycline — salvage (high failure rate in bacteraemia)	Per site (14–42 days)

Enterococcus key rules: Intrinsically resistant to cephalosporins + clindamycin — never use these alone. Ampicillin + ceftriaxone (double β-lactam) now preferred over ampicillin + gentamicin for endocarditis — equal efficacy, less nephrotoxicity. E. faecium more resistant than E. faecalis. S. bovis bacteraemia → always colonoscopy to rule out colorectal cancer.

Viridans Streptococci — Subacute Bacterial Endocarditis (SBE)

Condition	1st Line	Alternative	Duration
Native valve endocarditis Penicillin-sensitive (MIC ≤0.125)	Benzylpenicillin 1.2g IV q4h or Ceftriaxone 2g IV OD — once-daily; outpatient option	Vancomycin IV — penicillin allergy	4 weeks
Native valve endocarditis Penicillin-tolerant (MIC 0.125–2)	Benzylpenicillin IV + Gentamicin × 2 weeks synergy	Ceftriaxone + Gentamicin	4 weeks
Prosthetic valve endocarditis	Benzylpenicillin IV + Gentamicin — 6 weeks total	Vancomycin IV ± Gentamicin	6 weeks
Dental prophylaxis High-risk cardiac conditions	Amoxicillin 3g PO single dose 1h before procedure	Clindamycin 600 mg PO — penicillin allergy Azithromycin 500 mg PO	Single dose

Viridans strep = oral flora → SBE after dental procedures. Dental prophylaxis only for high-risk cardiac conditions: prosthetic valves, previous IE, congenital heart disease, cardiac transplant with valvulopathy. No longer recommended for all valvular disease (NICE 2023).

Complications

Abscess formation
Bacteremia
Sepsis
Septic shock
Necrotizing fasciitis
Toxic shock syndrome
Pneumonia
Meningitis
Endocarditis
Osteomyelitis
Septic arthritis
Acute rheumatic fever
Post-streptococcal glomerulonephritis

Prognosis

The prognosis varies according to the organism, infection site, and severity. Localized infections such as uncomplicated pharyngitis generally have an excellent outcome with appropriate treatment. Invasive infections such as bacteremia, necrotizing fasciitis, meningitis, and septic shock can cause substantial morbidity and mortality, particularly when treatment is delayed.

Key Points / Clinical Pearls

Streptococcal Infection is caused by Gram-positive Streptococcus species.
Streptococcus pyogenes is Group A Streptococcus.
Streptococcus agalactiae is Group B Streptococcus.
Streptococcus pneumoniae commonly causes respiratory and invasive infections.
Pharyngitis and skin infections are common presentations.
Invasive disease can cause bacteremia and sepsis.
Severe pain out of proportion to skin findings suggests necrotizing fasciitis.
Appropriate microbiological testing helps identify the causative organism.
Blood cultures are important in suspected bacteremia or sepsis.
Penicillin or amoxicillin is commonly used for susceptible GAS pharyngitis.
Severe invasive disease requires intravenous antibiotics.
Necrotizing fasciitis requires urgent surgical debridement.

Centers for Disease Control and Prevention (CDC). Group A Streptococcal (GAS) Disease .
Centers for Disease Control and Prevention (CDC). Clinical Guidance for Group A Streptococcal Pharyngitis .
Carapetis JR, Steer AC, Mulholland EK, Weber M. The Global Burden of Group A Streptococcal Diseases. Lancet Infect Dis. 2005;5(11):685-694. PubMed .
Stevens DL, Bryant AE. Severe Group A Streptococcal Infections. In: Streptococcus pyogenes: Basic Biology to Clinical Manifestations. NCBI Bookshelf .
Stevens DL, Bisno AL, Chambers HF, et al. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections. Clin Infect Dis. 2014;59(2):e10-e52. Clinical Infectious Diseases .
Shulman ST, Bisno AL, Clegg HW, et al. Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis. Clin Infect Dis. 2012;55(10):e86-e102. PubMed .
National Library of Medicine (NIH). Streptococcal Infections . StatPearls.