Infection and Immunology Flashcards
What is the incidence of meningococcaemia?
2/3 are viral
80% of bacterial cases are in patients younger than 16yo
- 10% mortality
- 10% neurological deficit
What is the pathophysiology of meningococcaemia?
N. meningitides causes it
A+C occur in Asia and Africa
B+C occur in Europe, North and South America
Infection is preceded by nasopharyngeal colonisation
What are the virulence factors of N. meningtitides?
Polysaccharide capsule
Lipo-oligosacchardie endotoxin (mediates invasion and is protein body responds to)
Immunoglobulin A1 protease (cleaves membranes and helps virus survive intracellularly)
What are other causative organisms of meningitis?
Neonates to 3 months - Group B strep, E. coli, Listeria
1 month - 6 years - N. meningitidis, Strep. pneumoniae, H. influenzae
> 6 years - N. meningitidis, Strep. pneumoniae
How does meningitis present in the first 3 months?
In neonate period, associated with maternal infection or pyrexia on delivery
Hyper/hypothermia Irritability Lethargy Bulging fontanelle Quiet at rest but cries when moved
How does meningitis present >3 months?
Features more associated with bacterial infection - fever, vomiting, irritability, lethargy
Petechial rash common
Postive Kernig and Brudzinski
What is septicaemia?
Activation and stimulation of immune system by cytokines
Capillary leak
Coagulopathy
Metabolic derangement
Myocardial failure
How does capillary leak occur in sepsis?
Presentation until day 4
Vascular permeability increases causing protein to enter intravascular space and urine -> severe hypovolaemia
Initial vasoconstriction to compensate but eventually decreased venous return and cardiac output
How does coagulopathy occur in sepsis?
Cytokines activate procoagulation factors in blood vessel wall -> endothelial damage
Damaged wall inhibits anticoagulation properties -> intravascular clotting and multiple organ failure
How does metabolic derangement occur in sepsis?
Acidosis with severe abnormalities Hypokalaemia Hypocalcaemia Hypomagnesaemia Hypophosphataemia
How does myocardial failure occur in sepsis?
Function remains impaired after circulating volume is restored
Gallop rhythm with elevated central venous pressure and hepatomegaly
What are differentials of meningococcal septicaemia?
Sepsis Febrile seizures Measles Mumps HSP ITP Reye's syndrome
What is the initial treatment of meningitis?
Ceftriaxone or cefotaxime
Dexamethasone reduces risk of long term complications
Rifampicin to eradicate nasopharyngeal carriage in household contacts
What are complications of meningococcal disease?
DIC Thrombocytopenia Septic arthritis Pericarditis Bacterial endocarditis Gangrene
What are causative agents of early onset neonatal sepsis?
Ascending infection from the birth canal into amniotic fluid –> pneumonia and septicaemia
Group B strep
E. coli
H. influenzae
Listeria
What are causative agents of late-onset neonatal sepsis?
Staph. epidermidis Staph. aureus E. coli Klebsiella Pseudomonas Enterobacter Candida
What are the causes of infant sepsis?
H. influenze B
Strep. pneumoniae
N. meningitides
Salmonella
What is the pathophysiology of shock?
Inadequate delivery of substrates and oxygen to meet metabolic needs of the tissue
Anaerobic respiration leads to lactic acid accumulation until energy cannot be produced any more
Disruption of cell membrane pumps -> accumulation of intracellular sodium and efflux of potassium
What antibiotics are used for septicaemia?
6-8 weeks AMPICILLIN + gent, cefotacime or ceftriaxone
Older infants have cefs
What is the pathophysiology of an allergic reaction?
Type 1 hypersensitivity
Involves IgE and mast cells which bind together via antigens
Release of inflammatory mediators -> vasodilation, smooth muscle contraction, increased small vessel permeabilty, secretion of mucus
How is HIV passed to children?
Pregnancy, delivery or breast feeding
What are risks of HIV?
Opportunistic infections - TB, PCP (give co-trimoxazole), VZV, HSV, candida
Blood problems - thrombocytopenia, anaemia, neutropenia
Kaposi’s sarcoma, non-Hodgkin’s lymphoma
DON’T GIVE BCG VACCINE -> DIC
How does infectious mononucleosis present?
1-2 weeks of fatigue and malaise Sore throat Headache - retro-orbital LUQ pain - spleen enlargement (?rupture) Fever
What are complications of mono?
Hepatitis
Jaundice
Thrombocytopenia
What is the diagnostic criteria for Kawasaki disease?
Fever >30 for >5 days Conjunctival injection in both eyes Change to mouth or throat Chnage to skin on arms or legs Rash Swollen lymph nodes of neck
What are the three phases of Kawasaki disease?
Phase 1 (acute) - weeks 1+2 Symptoms appear suddenly and severely
Phase 2 (sub-acute) - weeks 3+4
Symptoms are less severe but irritability and pain persist
Complications arise
Phase 3 (convalescent) - weeks 4-6 Child begins to recover but may still lack energy
What is the treatment of Kawasaki disease?
IV immunoglobulins reduce risk of aneurysm
Aspirin reduces risk of thrombosis
Warfarin and antiplatelets
What are complications of Kawasaki disease?
Aneurysm
Heart problems
What are causes of immunosuppression?
Deliberate - bone marrow or organ transplant, treated of autoimmune disease
Non-deliberate - malnutrition, ageing, leukaemia, lymphoma, multiple myeloma
What are causes of immunodeficiency?
Primary - intrinsic defect of immune defect present from birth, genetic, mainly boys
Secondary (more common) - caused by another disease or treatment such as infection, malignancy, malnutrition, HIV, splenectomy or nephrotic syndrome
How do T-cell defects present?
Severe and/or unusual viral and fungal infections and failure to thrive in first months of life
Severe combined immunodeficiency (SCID) - defective cellular immunity altering T and B cell lymphocytes
Treated by bone marrow transplant
HIV infection - causes a progressive T cell deficiency
How do B-cell defects present?
Infants has passive immunity from mother but afterwards up to 2 years, there are severe bacterial infections esp. ear, sinuses, skin and pulmonary
Can lead to failure to thrive, bronchiectasis and impaired hearing
X-linked agammaglobulinaemia - B-cells can’t mature
Common variable immunodeficiency (CVID) - later onset but high risk of autoimmune disorders and malignancies
How do neutrophil defects present?
Recurrent bacterial infections - abscesses, poor wound healing, perianal disease, peridontal infectiond, aspergillosis, granulomas
Chronic granulomatous disease - X-linked recessive, defect in phagocytosis
How do leucocyte function defects present?
Delayed separation of umbilical cord
Delyaed wound healing
Chronic skin ulcers
Deep seating infection
Leucocyte adhesion deficiency (LAD) - neutrophils can’t migrate to sites of infection
How do complement defects present?
Recurrent bacterial infections, SLE like illness, recurrent meningococcal infection
How are immunodeficiencies treated?
Co-trimoxazole to prevent pneumocystis jiroveci
Antibiotic prophylaxis - azithromycin
How does typhoid fever present?
Infection with salmonella typhi or paratyphi
Worsening fever Headache Cough Abdo pain Myalgia GI symptoms may not appear til second week
May have splenomegaly, bradycardia and rose coloured spots
What are complications of typhoid fever?
GI perforation
Myocarditis
Hepatitis
Nephritis
Needs cephalosporin or ampicillin
How does malaria present?
Worst in children 6 months to 5 years
Typical onset 7-10 days after innoculation
Fever, diarrhoea, vomiting, jaundice, anaemia, thrombocytopenia
What are complications of malaria?
Severe anaemia
Cerebral malaria - rapidly developing encephalopathy becuase of parasite adhering to microvasculature causing blockage
How is malaria treated?
Quinine
Bed nets
What is the immunisation schedule?
Newborn - BCG if high risk
2,3 and 4 months - 5 in 1 (diptheria, tetanus, pertussis, Hib, polio)
2, 4 and 12 months - pneumococcal and meningitis B
2 and 3 months - rotavirus
3 months and 1 year - meningitis C
1 year - Hib/men C booster, MMR
pre-school - MMR and 4 in 1 pre-school booster (diptheria, tetanus, pertussis, polio)
13 years - HPV
14 years - 3 in 1 (diptheria, tetanus, polio), men ACWY
What is pseudomembranous colitis?
Antibiotics wipe out colonising bacteria leaving only C. diff
Watery diarrhoea +/- blood, abdo cramps, fever
What presents with a heliotrope rash around the eyes and knuckles?
Juvenile dermatomyositis
Elevated CK
What is chronic fatigue syndrome?
Infection like onset >6 months and causes reduction in activity levels Impaired memory/concentration Myalgia and arthralgia Headaches Sore throat Tender lymph nodes
What investigations are done for CFS?
FBC - rule out anaemia, iron deficiency and leukaemia ESR/CRP - shouldn't be raised Blood glucose U+E TFT LFT Urine dip
What is the diagnostic criteria for SLE?
4 need to be present
Malar/discoid rash Photo sensitivity Oral ulcers Arthritis Pleuritis/pericarditis Renal disorder Seizures/psychosis Haemolytic anaemia/leukopenia/thrombocytopenia Antinuclear antibody positive Antiphospholipid positive
