Bacterial Pathogens Flashcards
S aureus
Virulence factors
Slime layer- interferes with osonophagocytosis Coagulase : plasma clotting Protein A : absorbs serum IgG Catalase: inactivates hydrogen peroxide Beta-lactamase : inactivates penicillin
Panton-Valentine leukocidin : increased cell permeability
Exfoliatins A & B : splits desmosome : skin separation
TSST-1 : induces production of IL-1 & TNF
S. Aureus food poisoning
Caused by
Ingestion of enterotoxin
Most common causes of osteomyelitis & suppurative arthritis in children
Ddx
S aureus
GAS
Kingella kingae
Dx criterion for Staph TSS
Major: Temp >38.8
Hypotension
Erythroderma with convalescent desquamation
Minor: Mucous membranes involved Vomiting, diarrhoea Liver enzymes Renal function Muscle: CK, myalgia CNS Thrombocytopenia
Ddx Staph TSS
Strep TSS
Kawasaki
Scarlet fever
Toxic epidermal necrolysis
Leptospirosis
Measles
Rocky Mountain spotted fever
CONS
Examples
Who affected
S epi
S hominis
S haemolyticus
On skin
Nosocomial infection in neonates, immunocompromised, in dwelling medical devices
S saprophyticus
UTI
CONS
Virulence
Low virulence- need another factor
Biofilm, adhesion to foreign body
Indolent in older children
Most common cause of nosocomial Bacteraemia
CoNS
Usually in association with CVL
CoNS
Rx
Most resistent to methicillin
Rx Vancomycin
S saprophyticus usually sensitive to 1st gen cephalosporin
Strep pneumoniae
Gram stain
Most frequent cause of
Colonisation rates
Children at increased risk
Gram + encapsulated diplococcus
Bacterial Meningitis, Bacteraemia, pneumonia, OM
90% 6mo to 5y colonised at some point
SCD, asplenia, deficiency in humoral immunity, deficiency in complement mediated immunity, HIV, CHD, nephrotic syn, leukaemia & lymphoma
* Influenza
Indication for Amoxicillin in pneumonia
Previously healthy Fully immunised Infants & preschool children Uncomplicated CAP
Consider mycoplasma pneumoniae in
School age child Insidious onset of Sx Wheeze Headache Myalgia
Scarlet fever
Cause
Features
URTI
pyrogenic exotoxin
Rash onset 24-48h after urti
Begins around neck
Diffuse, finely papular erythematous eruption
Goose pimp
Desquamation of face moving downwards (mild sunburn)
GAS
Rx
Exquisitely sensitive to penicillin
Resistent strains not documented
PANDAS
Unproven
GAS & Tics, OCD
No evidence for testing, anti-strep prophylaxis, immunomodulatory Rx
Chorea
Frequency
Features
Exacerbating & relieving factors
Specific signs
In 10-15%
Usually isolated & subtle
Emotional lability, in coordination, poor school performance, uncontrollable movements, facial grimacing
Exacerbated by stress; resolves in sleep
Unilateral
Milk maids grip
Spooning & pronation of extended arms
Wormian darting movement of protruded tongue
Ddx arthritis ARF
Septic
JIA Reactive (Shigella, salmonella, yersinia) Serum sickness SCD Malignancy SLE Post-strep reactive arthritis
Ddx chorea
Huntington Wilson SLE CP Tic Hyperactivity
Neonatal GBS
Intrapartum chemoprophylaxis effect
Rx Neonatal GBS disease
Decreased incidence of early onset sepsis
No effect on late onset disease
Penicillin G
Late onset disease neonatal GBS
Age Increased risk after obstetric complications Clinical manifestations Common serotype Case fatality
7 - 90 days
No effect from obstetric complications
Serotype 3
Bacteraemia, meningitis, OME, septic arthritis
2.8% case fatality
When is risk of TB disease highest
Proportion who get disease <1 y
1-2y
When are the ‘safe’ years
First 2 years post infection
<1y 50% get disease, 10-20% meningitis, dissemination
1-2y 15-29% get disease
5-10y ‘safe school years’
> 10, 19-20% get disease
TB
Proportion children symptomatic with disease
Typical presentation
Infants more or less likely to be symptomatic?
50% children
Cough, fever, malaise, weight loss, decreased appetite, night sweats
Infants 80% symptomatic
TB testing
Which cells release interferon gamma
Sensitivity of TST and IGRA
Antigen specific T cells
Both poorly sensitive
IGRA highly specific
TB meningitis
Symptoms
Typically diagnosed how long after infection
Spread from where via where
Most common in which age group
6-12 mo after initial infection
Headache behaviour change
Convulsions cranial nerve palsies
Hemiplegia
Coma
Lung
Lymphohaematogenous
Miliary
CNS
