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Infection & Immunology Flashcards

1
Q

What is an abscess?

A

Mass of necrotic tissue, with dead and viable neutrophils suspended in tissue breakdown products (pus), surrounded by inflammatory exudate

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2
Q

What causes an abscess?

A

Tissue barrier disrupted by injury/infection/migration of normal flora to sterile areas
Becomes walled off in an attempt to limit further spread of infection
Common bacteria - Staph, Strep, Enteric (E Coli)

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3
Q

What kind of abscesses does TB cause?

A

COLD - no inflammation

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4
Q

What are the risk factors for abscesses?

A

Local: tissue necrosis, under perfusion, foreign body
Systemic: diabetes, immunosuppression

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5
Q

What are the symptoms of an abscess?

A

Local pain, swelling, heat, redness, impaired function of area
Systemic - fever, malaise

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6
Q

What are the signs of an abscess O/E?

A

Acute inflammation
If in organ -> localising signs
Swinging fever (periodic release of microbes/cytokines into systemic circulation) –> initiate search for infected collection

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7
Q

Where is an abscess often found if you can’t find one anywhere?

A

Under diaphragm

Subphrenic abscess

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8
Q

How are abscesses investigated?

A
  1. Bloods - neutrophilia
  2. Imaging - USS, CT, MRI to search for site
  3. Aspiration - pus = low glucose, acidic, culture pus for organisms/AB sensitivity
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9
Q

How are abscesses managed?

A
  1. Prevention - prophylactic ABx (during ops) if given early during infection, not effective once abscess formed
    2/ General - drainage, removal of necrotic tissue, correction of predisposing cause
  2. Surgery - drain by incision w packing/drains
  3. Interventional radiology - US/CT to localise and aspirate
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10
Q

What are the complications of abscesses?

A
  • Spread > cellulitis / bacteraemia w systemic sepsis
  • Chronic abscess
  • Discharging sinus/fistula
  • Destruction of normal underlying tissue
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11
Q

What is the prognosis for an abscess?

A

Good if drained and predisposing factor removed
Untreated - tend to point to nearest epithelial surface and discharge contents
Deep abscesses may become chronic

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12
Q

Which tissues does candida usually invade?

A

Tissues normally resistant to infection

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13
Q

What causes candidiasis most commonly?

A

Candida albicans

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14
Q

What does candidiasis look like?

A

Erythematous
Peeling edges
Moist
Rugged

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15
Q

How is candidiasis investigated?

A

Superficial smear of lesion for microscopy - +ve for Candida

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16
Q

What is cellulitis?

A

Acute, non-purulent spreading infection of the SC tissue, causing overlying skin inflammation

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17
Q

What causes cellulitis?

A
  • Penetrating injury (cannulation)
  • Local lesions (bites, seb cysts surgery)
  • Fissuring (anal, toe web spaces)
    All allow pathogenic bacteria to enter skin
  • Rarely arises spontaneously from blood-borne sources (septicaemia)
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18
Q

What are the risk factors for cellulitis?

A

Skin break
Poor hygiene
Poor vascularisation of tissue - DM

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19
Q

How do cellulitis and erysipelas differ?

A

Both - erythema, oedema, warm, tender

Cellulitis - not raised, indistinct margins

Erysipelas - characteristic raised, indurated border

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20
Q

What are the signs of cellulitis O/E

A

Lesion
No fluid thrill, fluctuation

Periorbital - swollen eyelids, conjunctival infection
Orbital - proptosis, impaired acuity, eye movement

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21
Q

How is cellulitis investigated?

A
  1. Bloods - high WCC
  2. If next to wound/pustular focus - CULTURE and molecular diagnostic procedures - growth of common pathogen, e.g. S. aureus
  3. CT/MRI if abscess suspected/orbital - assess posterior spread of infection
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22
Q

How is cellulitis managed?

A

Medical -

  • Flucloxacillin/co-amoxiclav PO
  • Hospitals - IV vancomycin (MRSA cover) + ceftazidime (Pseudomonas cover for immunocompromised)
  • Penicillin/macrolide prophylaxis if recurrent

Surgical - orbital decompression

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23
Q

What causes HSV?

A

dsDNA
Transmitted via close contact with individual shedding the virus
Kissing
Sexual intercourse

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24
Q

What are the symptoms of HSV?

A

HSV1: primary infection often asymptomatic, but possibly pharyngitis, painful eating, herpetic whitlow (finger abscess)

Recurrent infection/reactivation: prodrome (6h), peri-oral tingling and burning, vesicles appear (48h), ulcerate, crust over, heal in 8-10d

HSV2: very painful blisters and rash in genital, perigenital and anal area, dysuria, fever, malaise

HSV encephalitis - HSV1
HSV keratoconjunctivitis - epiphoria (watering eyes), photophobia

25
What are the signs of HSV1 primary infection?
Tender cervical lymphadenopathy Erythematous/oedematous pharynx Oral ulcers filled with yellow slough (gingivostomatitis) Digital blisters/papules (herpetic whitlow)
26
What are the signs of HSV2 infection?
``` Maculopapular rash Vesicles Ulcers Inguinal lymphadenopathy Pyrexia ```
27
How is HIV transmitted?
1. Sexual transmission 2. Blood (+other bodily fluids) - mother to child (intrauterine, childbirth, breastfeeding), needles (IVDU, healthcare workers), blood product transfusion, organ transplantation
28
What are the symptoms of HIV?
1 - Seroconversion (4-8w post-infection) Self-limiting: fever, night sweats, lymphadenopathy, sore throat, oral ulcers, rash, myalgia, headache, encephalitis, diarrhoea 2. Early/asymptomatic (18m-5y+) Persistent lymphadenopathy (>1cm nodes at 2+ extrainguinal sites for >3m) Progressive minor symptoms - rash, oral thrush, WL, malaise 3. AIDS Syndrome of secondary diseases - severe immunodeficiency/direct effect of HIV infection - CD4<200
29
What are the direct effects of HIV infection?
Neuro: polyneuropathy, myelopathy, dementia Lung: lymphocytic interstitial pneumonia Heart: cardiomegaly, myocarditis Haem: anaemia, thrombocytopaenia GI: anorexia, HIV enteropathy (malabsorption, diarrhoea), severe wasting Eyes: cotton wool spots
30
What are the common secondary infections in AIDS?
``` Bacterial: Mycobacterium TB - lungs, GI, skin Staphylococci - skin Salmonella Strep pneumoniae Haemophilus influenza ``` ``` Viral: CMV - retinitis, colitis, encephalitis HSV - encephalitis VSV - recurrent shingles HPV EBV ``` Fungal: PCP, cryptococcus (meningitis), Candida, aspergillosis
31
What tumours are related to HIV/AIDS?
Kaposi's sarcoma Squamous cell carcinoma Non-Hodgkin's/Hodgkin's lymphoma
32
How is HIV investigated?
1. Serum HIV ELISA followed by Western Blot to confirm (expensive) 2. Serum HIV rapid test 3. Serum p24 antigen - high 4. Serum HIV DNA PCR 5. CD4 count - staging >500 asymp, <350 substantial immunosuppression, <200 AIDS 6. Viral load
33
What causes infectious mononucleosis and how is it transmitted?
- EBV - Transmitted by close contact - Humoral and cellular immune response - IL2 production - Despite IR, EBV is latent in lymphocytes
34
When is infectious mononucleosis most common?
2 peaks 1-6y asymptomatic 14-20y
35
How does infectious mononucleosis present?
- Incubation period of 4-8w with abrupt onset | - Sore throat, fever, fatigue, headache, malaise, anorexia, sweating, abdo pain
36
What are the signs of infectious mononucleosis O/E?
``` Pyrexia Oedema, erythema of pharynx/soft palate White exudate on tonsils - confluent after 1-2d Palatal petechiae Cervical lymphadenopathy Splenomegaly 50% Hepatomegaly 10% Jaundice 5% Maculopapular rash in pts who have received ampicillin ```
37
How is infectious mononucleosis investigated?
1. Bloods: FBC = leucocytosis / LFT = raised aminotransferases 2. Blood film: lymphocytosis (>20% atypical lymphocytes) 3. Paul-Bunnell/Monospot test: presence of heterophile antibodies produced in response to EBV 4. Throat swab to exclude strep tonsils
38
How is infectious mononucleosis managed?
CONSERVATIVE: rest, no contact sports for 2w due to increased risk of splenic rupture MEDICAL: Paracetamol, NSAIDs for fever, throat discomfort, malaise Corticosteroids in severe cases - haemolytic anaemia, tonsillar swelling, obstructive pharyngitis
39
When do patients with mono develop a widespread maculopapular rash?
Amoxicillin | Ampicillin
40
What are the complications of infectious mononucleosis?
- Lethargy for months - Airway obstruction - Haemolytic/aplastic anaemia, thrombocytopaenia - Splenic rupture, fulminant hepatitis, pancreatitis, renal failure - GBS, encephalitis, viral meningitis
41
What is malaria?
Infection with the protozoa Plasmodium (P. falciparum - most serious and potentially fatal, P. vivax, P. ovale, P. malariae)
42
What causes malaria?
Transmitted through bite of female Anopheles mosquito | Protozoa infect RBC and grow intracellularly
43
Which populations have some innate immunity to malaria?
Sickle cell trait G6PD deficiency Pyruvate kinase deficiency Thalassaemia
44
How does malaria usually present?
Non-specific: headache, weakness, myalgia, arthralgia, anorexia, diarrhoea Peak temperatures every 48h Cerebral malaria - headache, disorientation, coma
45
What are the signs of malaria O/E?
Pyrexia Rigors Anaemia Hepatosplenomegaly
46
How is malaria investigated?
1. Giemsa-stained thick and thin blood smears - detection of asexual or sexual forms of the parasites inside erythrocytes 2. Rapid diagnostic tests - show visible band after 15m ``` 3. Bloods: FBC - thrombocytopaenia, mild anaemia U/E LFT - high UC BR, aminotransferases ABG - metabolic/lactic acidosis Glucose - hyper or hypo ``` 4. Clotting profile - prolonged PT 5. Urinanalysis - protein, urobilinogen, BR
47
How is VSV transmitted?
Highly contagious Aerosol inhalation Direct contact with vesicular secretions
48
How does chickenpox present?
Prodromal malaise Mild pyrexia Sudden appearance of intensly itchy spreading rash on face+trunk>extremities, oropharynx, conjunctivae + genitourinary tract As vesicles weep and crust over, new vesicles appear Contagious from 48h before rash and until all vesicles crust over (7-10d)
49
How does shingles present?
May occur after period of stress Tingling/hyperparasthesiae in dermatomal distribution Followed by painful skin lesions Recovery in 10-14 days
50
What are the signs of chickenpox O/E?
Maculopapular rash evolving into crops of vesicles with areas of weeping (exudate) and crusting (vesicles, macules, papules, crusts may all be present at one time) Skin excorations Mild pyrexia
51
What are the signs of shingles O/E?
Vesicular maculopapular rash in dermatomal distribution | Skin excoriation
52
How is chickenpox managed?
Kids - treat symptoms - chamomile lotion, analgesia, antihistamines Adults - consider acyclovir, valaciclovir or famciclovir if within 24h of rash onset, esp in elderly, smoker, immunocompromised or pregnant
53
How is shingles managed?
Consider acyclovir, valaciclovir or famciclovir if within 24h of rash onset, esp in elderly, smoker, immunocompromised or pregnant Low dose amitriptyline Simple analgesia - paracetamol
54
What are the complications of chickenpox?
``` Secondary infection Scarring Pneumonia Encephalitis Cerebellar snydrome Congenital varicella syndrome ```
55
What are the complications of shingles?
Post-herpetic neuralgia Zoster opthalmicus (rash involves ophthalmic division of CNV) Ramsay-Hunt syndrome Sacral zoster --> urinary retention Motor zoster - muscle weakness of myotome at similar level to affected dermatome
56
Which organism most commonly causes orbital cellulitis?
Haem. influenzae
57
Which organisms commonly cause cellulitis?
Strep. pyogenes | Staph. aureus (MRSA not common)
58
What is erysipelas?
A distinct form of superficial cellulitis with a raised, sharply demarcated edge distinguishing it from uninvolved skin
59
When may EBV reactivation occur?
Period of stress | Immunosuppression

Y3 (20 decks)

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