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Chapter: Medicine Study Notes : Infectious Diseases

Streptococcus - Bacterial Disease

Streptococcus Pyogenes (Group A, b Haemolytic), Viridians Streptococci (plus also Enterococcus faecalis), Streptococcus Lancefield Group B.

Bacterial Disease




Streptococcus Pyogenes (Group A, b Haemolytic)


·        NB: Lancefield Groups only apply to b Haemolytic Streps

·        Causes:

o   Commonly: acute pharyngitis, cellulitis, impetigo (also caused by group C) 

o   Uncommonly: necrotising fasciitis (haemolytic strep gangrene), strep toxic shock syndrome, scarlet fever, erysipelas (= contagious skin infection with strep pyogenes), acute otitis media

o   Rarely: pneumonia, infective endocarditis

·        Has remained sensitive to penicillin

·        Identical strep can lead to a variety of infections:

o   Sore throat

o   Impetigo/Cellulitis.

o   Toxic Shock Syndrome

o   Myositis

o   Necrotising Fasciitis

·        Infection via throat (mainly) or via skin (impetigo/wound infection):

o   Suppurative: tissue invasion

o   Non-suppurative (after 2 – 8 weeks):

§  Rheumatic Fever

§  Glomerulonephritis

o   Super antigens: pyogenic exotoxins – ability to avoid classical antigen processing by APCs

·        Scarlet Fever:

o   Direct response to Streptococcal toxins (cf virus rash which is autoimmune and therefore delayed) 

o   Presentation: fever, exudative pharyngitis, scarlatina rash (fine punctate rash with perioral sparing), desquamation

o   Skin feels like sandpaper then desquamates.  May get purpura in flexures

o   Tongue affected – white then strawberry red

·        Streptococcus Toxic Shock Syndrome:

o   First described in children.  Now associated with Tampon use

o   Early (1 – 7 days): vague, viral like illness: fever, chills, myalgia, diarrhoea 

o   Later: abrupt onset of pain (not necessarily associated with findings), redness, hypotension, renal failure, ARDS, coagulopathy. May lead to necrotising fasciitis. Also skin diffusely erythematous like sunburn, conjunctivitis

o  Desquamation a week later characteristic

o  Age group: 2- 50 year olds, no predisposing or underlying disease

o  Bacteriology:

§  Blood culture +ive in 60%

§  Swab or aspirate in 95%

§  M protein types 1 & 3: impedes phagocytosis by leucocytes, expressed on cell wall 

o  Lab tests: Haematuria, ­Cr, ¯albumin and ¯Ca, serum CK for deep tissue infections

o  Treatment: Ceftriaxone

·        Necrotising fasciitis: 

o  Diffuse swelling and mild erythema, followed by bullae filled with clear fluid. Spreads along facial planes 

o  Infection of subcutaneous tissue ® progressive destruction of fascia and fat but may spare the skin itself. 

o  25 cases per year in NZ

o  Requires aggressive surgical debridement

o  Causative bacteria:

§  Group A strep most common

§  Staph Aureus

§  C. Perfringens

§  C. Sceptica

o  Predisposing factors:

§  Diabetes

§  Peripheral vascular disease

§  Chicken pox

§  Minor trauma/surgical procedures

o  Use of NSAIDs masks inflammation and delays diagnosis


Streptococcus Lancefield Group B


·        b Haemolytic Streps

·        Eg Strep agalactiae: differential in neonatal meningitis.  Normal vaginal commensal


Streptococcus Pneumoniae


·        Is a haemolytic but not classified as a Viridians

·        Causes: 

o  Commonly: acute otitis media, acute sinusitis, febrile convulsion in infants, community acquired pneumonia, infectious exacerbations of chronic bronchitis, meningitis (nasty type) 

o  Uncommonly: peritonitis (2ndary to chronic hepatic/renal disease of to infected IUCD)

o  Rarely: infective endocarditis

·        Antibiotic sensitivity:

o  Parenteral: 

§  Penicillin resistance in 1% blood isolates in adults and 11% in kids Þ Strep pneumonia penicillin resistance is not an issue in adults but is in kids 

§  Ceftriaxone

§  Vancomycin (for penicillin resistant strains and MRSA)

o  Oral: amoxycillin, erythromycin, cefaclor, tetracycline (not kids or pregnant)

·        Vaccination:

o  Pneumovax 

o  Polysaccharide-based subunit vaccine containing 23 serotypes covering 90% of strains causing invasive pneumococcal disease 

o  Contains T-cell independent antigens Þ non-immunogenic if < 2 years (and poor response for some serogroups up to age 6). Predominant IgM response without induction of memory. 5 yearly boosters recommended 

o  Recommended for:

§  > 65 years

§  > 2 with asplenia, immunocompromised (including nephrotic syndrome) and chronic illness

o  Conjugate vaccines generating IgG response being worked on….


Viridians Streptococci (plus also Enterococcus faecalis)


·        Causes UTI, abdominal wound sepsis, infective endocarditis (uncommon)

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