Infection and Immunity Flashcards
The febrile child
Management
- Children who are significantly unwell, particularly if there is no focus of infection, will require investigations and observation or treatment in a paediatric assessment unit or A&E
- A septic screen will be required
- Parenteral antibiotics are given immediately to seriously unwell children, e.g. a third-generation cephalosporin such as cefotaxime or ceftriaxone if >3 months old. In infants 1–3 months old, cefotaxime (in case of septicaemia or meningitis) and ampicillin (in case of Listeria infection) are usually given
The febrile child
Septic screen
- Blood culture
- Full blood count including differential white cell count
- Acute phase reactant, e.g. C-reactive protein (CRP)
- Urine sample
Consider if indicated
- Chest X-ray
- Lumbar puncture (unless contraindicated)
- Rapid antigen screen on blood/CSF/urine
- Meningococcal and pneumococcal PCR on blood/CSF
- PCR for viruses in CSF (especially HSV and enterovirus)
The febrile child
- Upper respiratory tract infection (URTI) is an extremely common cause
- Check for otitis media
- Serious bacterial infection must be considered if there is no focus of infection, especially urinary tract infection or septicaemia, or there are Red Flag features of life-threatening illness
- The younger the child, the lower the threshold for performing a septic screen and starting antibiotics
Serious life-threatening infections
Bacterial meningitis
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- Bacterial infection of the meninges usually follows bacteraemia. Much of the damage caused by meningeal infection results from the host response to infection and not from the organism itself
- release of inflammatory mediators and activated leucocytes, together with endothelial damage, leads to cerebral oedema, raised intracranial pressure and decreased cerebral blood flow.
Organisms causing bacterial meningitis according to age:
Neonatal - 3 months: Group B strep. ecoli and other coliforms, Listeria monocytogenes
1 month - 6 years: Neisseria meningitis, strep pneumonia. Haemophilus influenza
>6 years: Nessria meingitis, strep pneumonia
Serious life-threatening infections
Bacterial meningitis
Assessment & investigation of meningitis/encephalitis
Management
- The choice of antibiotics will depend on the likely pathogen.
- A third-generation cephalosporin, e.g. cefotaxime or ceftriaxone, is the preferred choice to cover the most common bacterial causes
- Beyond the neonatal period, dexamethasone administered with the antibiotics reduces the risk of long-term complications such as deafness
Serious life-threatening infections
Bacterial meningitis
Cerebral complications
- Hearing loss. Inflammatory damage to the cochlear hair cells may lead to deafness. All children who have had meningitis should have an audiological assessment promptly, as children who become deaf may benefit from hearing amplification or a cochlear implant.
- Local vasculitis. This may lead to cranial nerve palsies or other focal lesions.
- Local cerebral infarction. This may result in focal or multifocal seizures, which may subsequently lead to epilepsy.
- Subdural effusion. Particularly associated with Haemophilus influenzae and pneumococcal meningitis. This is confirmed by CT scan. Most resolve spontaneously but may require prolonged antibiotic treatment.
- Hydrocephalus. May result from impaired resorption of CSF (communicating hydrocephalus) or blockage of the ventricular outlets by fibrin (non-communicating hydrocephalus). A ventricular shunt may be required.
- Cerebral abscess. The child’s clinical condition deteriorates with the emergence of signs of a space-occupying lesion. The temperature will continue to fluctuate. It is confirmed on CT scan. Drainage of the abscess is required.
Serious life-threatening infections
Bacterial meningitis
Prophylaxis
Prophylactic treatment with rifampicin to eradicate nasopharyngeal carriage is given to all household contacts for meningococcal meningitis and Haemophilus influenzae infection. It is not required for the patient if given a third-generation cephalosporin, as this will eradicate nasopharyngeal carriage. Household contacts of patients who have had group C meningococcal meningitis should be vaccinated with the meningococcal group C vaccine.
Serious life-threatening infections
Viral Meningitis
Two-thirds of CNS infections are viral. Causes include enteroviruses, Epstein–Barr virus, adenoviruses and mumps. Mumps meningitis is now rare in the UK due to the MMR vaccine. Viral meningitis is usually much less severe than bacterial meningitis and a full recovery can be anticipated. Diagnosis of viral meningitis can be confirmed by culture or PCR of CSF; culture of stool, urine, nasopharyngeal aspirate, throat swabs; and serology.
Serious life-threatening infections
Encephalitis/encephalopathy
Encephalitis
- Onset can be insidious and includes behavioural change
- Consider if HSV (herpes simplex virus) could be the cause
- Treat potential HSV with parenteral high-dose aciclovir until diagnosis is excluded.
in encephalitis there is inflammation of the brain substance, although the meninges are often also affected. Encephalitis may be caused by:
- Direct invasion of the cerebrum by a neurotoxic virus (such as herpes simplex virus, HSV)
- Delayed brain swelling following a disordered neuroimmunological response to an antigen, usually a virus (post-infectious encephalopathy), e.g. following chickenpox
- A slow virus infection, such as HIV infection or subacute sclerosing panencephalitis (SSPE) following measles.
Serious life threatening infections
Toxic shock syndrome
Toxin-producing Staphylococcus aureus and group A streptococci can cause this syndrome, which is characterised by:
- Fever >39°C
- Hypotension
- Diffuse erythematous, macular rash.
Toxin released from infection at any site, ie small abrasions or burns,acts as a superantigen, in addition to the above, causes organ dysfunction, including:
- conjunctivae, oral mucosa, genital mucosaMucositis
- Gastrointestinal: vomiting/diarrhoea
- Renal impairment
- Liver impairment
- Clotting abnormalities and thrombocytopenia
- Central nervous system: altered consciousness
Serious life threatening infections
Necrotising fasciitis/cellulitis
- Severe subcutaneous infection, often involving tissue planes from the skin down to fascia and muscle.
- The area involved may enlarge rapidly, leaving poorly perfused necrotic areas of tissue, usually at the centre
Invading organism may be Staphylococcus aureus or a group A streptococcus, with or without another synergistic anaerobic organism. Intravenous antibiotic therapy alone is not sufficient to treat this condition. Without surgical intervention, the infection will continue to spread. Clinical suspicion of necrotising fasciitis warrants urgent surgical consultation and intervention. Intravenous immunoglobulin (IVIG) may also be given.
Specific bacterial infections
Pneumococcal infections
Pneumococcal infection
- Causes not only minor infections such as otitis media but also invasive disease
- Susceptibility is increased in hyposplenism (e.g. sickle cell disease and nephrotic syndrome)
- Vaccination is included in the standard immunisation schedule.
- Streptococcus pneumoniae is often carried in the nasopharynx of healthy children.
- organism may cause pharyngitis, otitis media, conjunctivitis, sinusitis as well as ‘invasive’ disease (pneumonia, bacterial sepsis and meningitis)
- organism may cause pharyngitis, otitis media, conjunctivitis, sinusitis as well as ‘invasive’ disease (pneumonia, bacterial sepsis and meningitis)
- With the inclusion of the 13-valent pneumococcal vaccine into the standard immunisation schedule in the UK, the incidence of invasive disease has declined.
Specific bacterial infections
Haemophilus infection
H. influenzae type b was an important cause of systemic illness in children, including otitis media, pneumonia, epiglottitis, cellulitis, osteomyelitis and septic arthritis and was the second most common cause of meningitis in the UK. Immunisation has been highly effective and it now rarely causes systemic disease.
Staphylococcal and group A streptococcal infections
- Staphylococcal and streptococcal infections are usually caused by direct invasion of the organisms.
- They may also cause disease by releasing toxins which act as superantigens.
- Whereas conventional antigens stimulate only a small subset of T cells which have a specific receptor, superantigens bind to a part of the T-cell receptor which is shared by many T cells and therefore stimulates massive T-cell proliferation and cytokine release.
- Other diseases following staphylococcal and streptococcal infections are immune-mediated.
Staphylococcal and group A streptococcal infections
Impetigo
- localised, highly contagious, staphylococcal and/or streptococcal skin infection, most common in infants and young children
- more common where there is pre-existing skin disease, e.g. atopic eczema
- Rupture of the vesicles with exudation of fluid leads to the characteristic confluent honey-coloured crusted lesions
- Narrow-spectrum systemic antibiotics (e.g. flucloxacillin) are needed for more severe infections, although more broad-spectrum antibiotics such as co-amoxiclav or cefaclor have simpler oral administration regimens, taste better and therefore have better adherence
Staphylococcal and group A streptococcal infections
Periorbital cellulitis
Staphylococcal and streptococcal infections
Symptoms are caused by direct invasion of bacteria or by release of toxins
Impetigo is highly contagious
Periorbital cellulitis should be treated aggressively to prevent spread to the orbit or brain
Scalded skin syndrome is rare but serious.
- In periorbital cellulitis there is fever with erythema, tenderness and oedema of the eyelid
- In young, unimmunised children it may also be caused by Haemophilus influenzae type b which may also be accompanied by infection at other sites, e.g. meningitis
- In older children, it may spread from a paranasal sinus infection or dental abscess.
- Periorbital cellulitis should be treated promptly with intravenous antibiotics to prevent posterior spread of the infection to become an orbital cellulitis.
- It may be complicated by abscess formation, meningitis or cavernous sinus thrombosis.
