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Flashcards in MISC - Infectious disease Deck (19)
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45 yo male presents with:
•Fevers, sweats, cough and SOB
•2kg weight loss
•Previously well, with acute 3 day history


–Acute community-acquired pneumonia
–Most likely pathogen = Steptococcus pneumoniae


45 yo male presents with:
•Fevers, sweats, cough and SOB
•2kg weight loss
•Hodgkin’s Lymphoma - just completed 3rd cycle of “CHOP” chemotherapy 2 weeks earlier
•Severely neutropenic
•24h history of rapidly increasing SOB, no sputum
•Now shocked – BP 75/50


–Febrile neutropenia with acute Gram-negative or staphylococcal pneumonia, likely to require early ICU admission
–Acute aspiration pneumonia following chemo-related vomiting


45 yo male presents with:
•Fevers, sweats, cough and SOB
•2kg weight loss
•Ex-smoker with insulin-dependent diabetes
•2mth Hx increasing blood-stained, purulent sputum after a 1mth trip to India


–Lung CA with secondary infection


What is the 3-tier approach to infectious disease?

Tier 1: Problem-solving of clinical syndromes
A clinical approach based on:
•Symptoms: fever, cough, diarrhoea, rash, sore throat etc
•Patient groups: Overseas-born, returned traveller, immunosuppressed, post-operative patient

Tier 2: Management of infections of various organ systems
•Emphasis is on clinical diagnosis, lab investigations, choice of Rx, monitoring Rx of these organ infections
–e.g. meningitis, endocarditis, pneumonia, osteomyelitis, gastroenteritis, UTIs

Tier 3: Specific infections and pathogens
•These need to be learned individually because of their importance and specific epidemiology, prevention, treatment and control
–e.g. S. aureus, N. meningitidis, Salmonella & Campylobacter, HIV/AIDS, influenza, hepatitis A/B/C, STDs, malaria, TB etc.


Which of Bacteria or virus evolves more gradually?


•Bacterial sepsis – generally has an abrupt onset
•Viral infections – often (but not always) evolve more gradually


Describe systemic symptoms of infection

Fever, chills, sweats, myalgia, weight loss, lethargy, fatigue = presence of an infection (their prominence reflects its severity)


Describe localised symptoms of infection

•Indicate possible sites of infection - e.g. cough, diarrhoea, pain
•However, these can be misleading
–e.g. diarrhoea may be a symptom of bacteraemic illness and not GI infection; a dry cough can be associated with typhoid


List (6) immunological defects possible in patients that you must take a Hx in a possibly infected pt

– Post-chemotherapy neutropenia = neutrophil dysfunction = bacterial sepsis
– Lymphocyte dysfunction (e.g. HIV) = intracellular or slow-growing pathogens
– Immunoglobulin deficit (e.g. myeloma) = encapsulated bacteria
– Splenectomy = pneumococcal infection
– Pregnancy – think of it like a huge malignancy that is curable after 9mths!
– Malnutrition – results in similar immunological defect as HIV infection


What should you ask to develop a good idea of the patient's epidemiology in an infection case?

–Country of birth
–Sexual history
–Occupation/exposure to animals and other vectors
•e.g. mosquitos, ticks, fleas etc.
–Food history
•e.g. unpasteurized milk products, uncooked meat, fast-food take-away meals etc
–Travel history
•where (?overseas) , how long, urban vs rural
•pre-travel vaccination, anti-malarial prophylaxis
–Travel to rural areas – zoonotic contact


What (2) can falsely mask signs of severity of infection?

diabetes, corticosteroids/ immunosuppressants


What should you check in physical examination to elicit any localised infection signs?

•Eyes – conjunctival hemorrhages (e.g. staph. endocarditis); scleral jaundice
•Skin – rashes (esp. petechial); cellulitis (esp. legs); evidence of IVDU
•Heart – murmurs (endocarditis); pericardial rub
•Lungs – subtle crackles = pneumonia; pleural rubs
•Abdominal organs – tenderness and enlargement without pain can be an important clue; splenomegaly can be subtle (always roll the patient)
•Lymph nodes – esp. posterior cervical nodes; tenderness of jugulo-digastric nodes = ?early bacterial tonsillitis; axillary and inguinal nodes – c/w CMV, HIV
•Throat – signs may precede symptoms in streptococcal tonsillitis; oedema of the uvula = a useful sign of bacterial infection
•Muscles – marked tenderness is a good sign of sepsis
•Neck – neck stiffness is important sign of meningitis (esp. in confused patient)
•Covered areas – important if bandaged, plaster casts; ?religious issues


What signs may suggest bacterial sepsis?

•Temperature >38.40C or less than 36.0C

•Tachycardia >90/min
–Beware of relative bradycardia in certain situations
•Physiologically, for each 0.5-0.60C increase in temperature, the HR should increase by ~10 beats/min (relevant if temp is >38.90C)
•Associated with certain diseases – e.g. typhoid
•NB. - not relevant if the patient is taking a beta-blocker or has heart-block!!

•Tachypnoea >20/min
•Altered mental status
•Hypoxaemia (PaO2 less than 72 mmHg or low O2 saturation)
•Oliguria less than 0.5mL/kg/hr
•Hypotension (often a late sign) or a postural drop of >20mmHg
–Beware in hypertensive patients since a “normal” BP may be low for this patient


What is the usual timing of results for growth, identification & ABx susceptibilities?

- 24-48h to growth;
- further 24h to identification (2 days)
- further 24h to ABx susceptibilities (3 days)


•55yo female with past history of rheumatic fever as a child
•Known to have a “leaky heart valve”
•4 week Hx - fevers, sweats, LOW
•Close questioning reveals that about 2 weeks before illness onset she had a tooth abscess drained by dentist
–Temp: 38.20C
–Aortic regurgitation murmur
–Red “peticheal” rash on finger tips and under toe nails
–No. retinal hemorrhages

Likely pathogen?

–Rheumatic heart disease with subsequent aortic valve endocarditis

–Need to clearly identify the exact pathogen(s)
•Likely pathogen – Viridans streptococci

–Mx – Depends on pathogen & degree of valve damage
•Prolonged IV antibiotics – 2-4 weeks
•Surgical valve resection with prosthetic valve replacement


•20yo female medical student
•Previously well
•Attended Australia Day BBQ
–Ate “undercooked egg rolls”, hamburgers and potato salad
–5 beers
•Next day developed:
–Severe watery diarrhoea
–Low grade fevers
–Severe lethargy
–Lost 4kg over 24hrs – moderate dehydration

Likely pathogen?

–Salmonella – esp. from eggs
–Campylobacter – from ground beef in hamburgers

•Fluid replacement/resuscitation
•Generally self-limiting
•NO ANTIBIOTICS NEEDED - unless immunocompromised


•35yo diabetic male with painless, purulent foot ulcer
•3 wks increasing unstable diabetic control
•Occasional low-grade fevers
•Offensive odour from ulcer
–Grossly deformed foot
–Marked sensory neuropathy
–Ulcer - “Probes to bone”

Likely pathogen?

–Diabetic foot ulcer with underlying osteomyelitis

–Need to identify pathogens

–Mx – surgical debridement +/- long-term antibiotics


What must be excluded on presentation of a febrile traveller returning from a malaria-endemic region?



How do presence of clinical signs vary with the patient’s age and co-morbidities?

–Infants – signs often excessively prominent
–Adolescents – signs often confusing
–Adults – signs affected by co-morbidities (e.g. diabetes, HIV)
–Elderly – signs often blunted (e.g. no fever, yet septic)


What do you suspect in Staphylococcus aureus bacteraemia until proven otherwise?

endocarditis or osteomyelitis until proven otherwise

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