general features of strep
G(+) chains catalase (-) split into groups: -GAS - b-hemolytic, S. pyogenes -GBS - a-hemolytic, perinatal sepsis/newborns, UTIs -viridans - a-hemolytic, endocarditis -mutans - major cause of dental caries
why do you not usually get Ab’s to simple strep with GAS?
too late for Ab’s - they take 7-10d to make, and simple strep infections are usually resolved by that time
potential complications of severe strep throat w/ GAS
- erythrotoxin -> Scarlet fever
- Ag + Ab -> glomerulonephritis (2 weeks)
- cross-reacting Ab’s w/ heart valves -> rheumatic fever
sx of strep throat
- beefy red appearance
- dysphagia
- pus on tonsils
- fever/ chills
- punctate abscess in tonsillar crypts
- peritonsillar, retropharyngeal abscesses
what is strep infection characterized by, histologically?
- neutrophils!!
- more spread: cellulitis -> red, warm (as opposed to staph, which has localized collections of neutrophils)
strep virulence factors
- cell wall polysaccharides/ capsules (M proteins) - prevent phagocytosis
- enzymes: streptokinase, streptolysin O, S - spread through tissues (cellulitis)
- erythrogenic toxins - skin rash (very red lesions)
describe scarlet fever
- febrile exanthematous disorder, age 3-15
- erythrogenic toxin -> violaceous red rash on trunks (blotches over body, not raised)
- strawberry tongue
- later desquamation of skin
- associated with post-strep sequelae
describe PSGN
- 1-2w after strep throat infection
- 4-5w after strep skin infection (impetigo)
- self-limited
- immune complex mediated
- may see signs of acute renal failure - oliguria, hematuria, HTN
describe rheumatic fever
-weeks to months past strep infection
-worse with repeated infections
-acute: fever, joint disease, myocardial and valvular disease
-autoimmune rxn that cross-reacts w/ M Ag’s
-no bacteria present
-corresponds to streptolysin O levels in blood as a
measure of severity of infection
-chronic: long-standing damage to mitral and aortic valves
-thickening of leaflets
describe strep skin infections
- cellulitis, pyoderma - extensive spreading redness, swelling, pain
- common infection of wounds or breaks in skin
- less localized than staph
- can involve subcutaneous tissues
- rare abscesses, some pustules
- rare - necrotizing fasciitis
impetigo
- tends to crust on skin
- contagious skin infection in kids
- involves horny (superficial) layers of skin
erysipelas (GAS, GCS)
- middle-aged persons
- warm climate (tropics)
- orange peel skin
- erythematous skin involvement without supporation (no crusting)
- raised, bright red lesion
- need to be careful if on face -> can lead to meningitis
necrotizing fasciitis
- uncommon deep-seated soft tissue infection
- if scrotal/perianal form: Fournier’s gangrene
- pre-existing immunodeficiency, diabetes
- subcutaneous strep infection with necrosis that is taken over by anaerobes (gas formation on x-ray)
- mortality 50-70%
- tx: surgical debridement to prevent spread
subacute bacterial endocarditis
- associated with S. viridans
- transient bacteremia following dental work
- left sided valvular endocarditis
- greatest risk in patients w/ previously damaged heart valves
- take prophylactic abx for dental work
which group of strep causes puerperal sepsis?
GBS
diagnosis of GAS: strep throat
- rapid strep test: GAS carb Ag
- confirmatory culture 12-48h always!
- cat (-), tells you abx specificity
diagnosis of GAS: rheumatic fever
anti-streptolysin O Ab titer (even though cross-reacting Ab’s are specific for M proteins)
