Paeds Immunology and Infectious Disease

Question 1

When does post vaccination fever start and end?

Answer 1

Begins within 24hrs of shot
Lasts 2-3 days
Usually mild fevers

Question 2

How high is too high for a fever related to teething?

Answer 2

Fevers related to teething should not exceed 38.5C
If higher than this suspect another source

Question 3

What is the most common cause of serious bacterial infection (SBI) without an obvious cause?

Answer 3

Urinary tract infections (UTI)
Peaks in 2nd yr of life for girls (8.1%)
Uncircumcised boys much higher rate than circumcised in 1st year of life, then both drop off

Question 4

What is the rate of occult bacteraemia and what are the usual causes?

Answer 4

Used to be 10% but now <0.5%, largely due to HiB and pneumococcal vaccines
Thus unvaccinated and pre-vaccinated children have much higher rates
Other causes although rare include Salmonella species, E.coli and Meningococcus

Question 5

What is the most common cause of occult bacteraemia (OB) in age group 3months to 5yrs?

Answer 5

Strep pneumoniae
Although with the advent of vaccines it rarely causes serious invasive infections (<5%)

Question 6

Independent of vaccination status, which risk factors increase the rate of OB becoming an SBI?

Answer 6

Indigenous status
Nephrotic syndrome
Asplenia
Active cancer (+/- on chemo)
Intracranial shunt
Cochlear implant
Immunosuppresive therapy
HIV/AIDS/congenital immune deficiency

Question 7

Which is the highest risk age groups for bacterial meningitis?

Answer 7

90% of bacterial meningitis occurs in children <5yo
Neonates have the highest mortality rate of 20%
1/3rd of children will have ongoing neurological sequelae post infection

Question 8

What are the most common organisms causing meningitis in children <3mo?

Answer 8

Listeria monocytogenes
E.coli/Klebsiella/enterobacter
Group B strep

Usually acquired by vertical transmission from the mother

Question 9

What are the most common organisms causing meningitis in children >3mo?

Answer 9

Neisseria meningitides
Strep pneumoniae
Previously H. influenzae prior to vaccination (much higher risk in unvaccinated)

Usually acquired by encapsulated strains entering the bloodstream and crossing the BBB, thus asplenia is a significant risk factor

Question 10

What are the most common causes of viral meningitis?

Answer 10

Coxsackie virus
Enterovirus
Paraechovirus

HSV meningitis is uncommon and usually recovers well, but if becomes HSV encephalitis has very poor outcomes

Question 11

What are the risk factors for meningitis in a febrile child?

Answer 11

Recent neurosurgical procedure
VP shunt or cochlear implant
Immunocompromised (consider cryptococci and mycobacteria)
Maternal GBS in <3mo
Contact with patients with enterovirus, HSV cold sore or meningitis
Overseas travel

Question 12

How does giving antibiotics first alter the findings of an LP in meningitis?

Answer 12

Does not alter the cell count, protein levels or glucose levels
PCR for pneumo/meningococcus still highly sensitive and specific
Much lower likelihood of culturing the bacteria (although only 70-80% chance in those without antibiotics)

Question 13

What are the normal values for paediatric CSF?

Answer 13

In a traumatic tap the RBC’s should be disregarded and the WCC’s treated as normal, if they are high then treat

Question 14

When should dexamethasone be considered in meningitis and what is the evidence?

Answer 14

0.15mg/kg QID IV for any cases in children over 3mo
No evidence for or against <3mo
Older than 3mo shown to reduce rates of hearing loss
Poor evidence if partially treated (ie on amoxicillin for URTI)

Question 15

What are the TORCH infections?

Answer 15

Toxoplasmosis
Other (Syphilis, VZV)
Rubella
CMV
Herpes Simplex Virus

In utero infections leading to severe downstream complications

Question 16

Who gets idiopathic facial cellulitis?

Answer 16

Usually in children aged 0-5yrs
It can be caused by bacteraemia and blood cultures are often indicated

Question 17

What are the indications for antibiotics in otitis media?

Answer 17

• Systemically unwell
• <6months old
• ATSI
• Immunocompromised
• Affecting the only hearing ear
• Cochlear implant on that side
• Likely suppurative complication (ie mastoiditis etc)

Question 18

What are the signs of mastoiditis?

Answer 18

Protruding auricle
Posterior auricular swelling and erythema
External auditory canal oedema

Question 19

What is the treatment for mastoiditis?

Answer 19

Urgent paeds ENT referral
Fast
analgesia
50mg/kg of Flucloxacillin + 50mkg/kg of ceftriaxone/cefotaxime

Question 20

What are the Major Jones criteria for Acute Rheumatic Fever?

Answer 20

Arthritis
- Poly low risk, mono high risk

Carditis/Valvulitis

Sydenhams Chorea
- CNS involvement

Subcutaneous nodules

Erythema marginatum

Question 21

What are the minor Jones criteria for Acute Rheumatic Fever

Answer 21

Arthralgia
- Poly low risk, mono high risk
- Only used if arthritis absent

Fever >38.5C

Prolonged PR interval
- Only used if Carditis absent
- prolongation varies with age from 110 neonate to 200 in late teens

Elevated inflammatory markers
- CRP >30
- ESR >60 low risk and >30 high risk

Question 22

How is the diagnosis of acute rheumatic fever made

Answer 22

Must have recent suspected GAS infection
+

Child meets 2 major criteria
Or
1 Major and 2 minor criteria

Question 23

What is a mnemonic for the major jones criteria?

Answer 23

JONES

J- Joints ie arthritis
O- pericardial effusion makes heart shaped like an O
N- subcutaneous Nodules
E- erythema marginatum
S- Sydenhams chorea

Question 24

What are the antibiotics given for suspected meningoencephalitis in different age groups?

Answer 24

<2 months
- Cefotaxime 50mg/kg and Benzylpenicillin 60m/kg

> 2months
- Ceftriaxone 50mg/kg +/- Vancomycin 15mg/kg if MRSA suspected/confirmed

Consider Aciclovir 20mg/kg if suspected viral cause (ie HSV)

Question 25

What is the cause of retropharyngeal abscesses in children and who are most affected?

Answer 25

S. Aureus and GAS (sometimes HiB) are the most common causes, usually post URTI with primary or secondary bacterial invasion

Most common in 2 - 4yr age range

Also associated with throat trauma ie swallowing something sharp

Question 26

What are the Lateral neck xray findings in Retropharyngeal abscesses?

Answer 26

• Widening of the pre-vertebral/retropharygeal soft tissue, considered wide if wider than the accompanying full vertebral body
• Has the advantage of being able to be done sitting (as opposed to a CT)
• Cannot distinguish a retropharyngeal abscess from a prevertebral abscess

Question 27

What is the antibiotics of choice for retropharyngeal abscess?

Answer 27

Amoxicillin/Clavulanate 25mg/kg IV

Question 28

What are the potential complications of a retropharyngeal abscess?

Answer 28

Sepsis
Airway obtruction
Aspiration
IJ thrombosis
Jugular vein thrombophlebitis (Lemierre syndrome)
Severe dehydration
Mediastinitis
Carotid artery injury
Atlantoaxial dislocation
Death

Question 29

What is the classic triad of haemolytic uraemic syndrome?

Answer 29

AKI
Anaemia (microangiopathic)
Thrombocytopaenia

Often see “schistocytes” on peripheral smear of the blood

Can be Coombs test -ve

HUS only rarely presents with fever (5-20%) but if present this is a poor prognostic sign

Question 30

What is the most common cause of HUS?

Answer 30

STEC, shiga toxin producing E. coli

Most often occurs post E. coli gastroenteritis

Question 31

How long should children with Pertussis be excluded from childcare for?

Answer 31

Until 5 days of treatment is completed