Intro to ID

Question 1

What is the leading cause of death and morbidity worldwide?

Answer 1

Infectious disease (15 million deaths annually)

Question 2

What % of presentations does infectious disease make up, in GP and ED respectively?

Answer 2

> 70% in GP

~20% in ED

Question 3

What is the #2 most prescribed agent in Aus?

Answer 3

Antimicrobials (15-20% of all prescriptions)

About 20% of public hospital in-patients receive Abx

Question 4

What is the major cause of inappropriate antibiotic use?

Answer 4

Poor clinical judgment about the presence of a bacterial infection where there is none

Question 5

What % of antibiotic use is empirical?

Answer 5

~80%

Question 6

What is the 3-tier approach to ID?

Answer 6

Tier 1: problem-solving of clinical syndromes, taking into account symptoms (e.g. fever, cough, diarrhoea, rash, sore throat, etc) and pt groups (e.g. overseas-born, returned traveller, immunosuppressed, post-op, etc)
Tier 2: management of infections of various organ systems (e.g. meningitis, endocarditis, pneumonia, osteomyelitis, gastroenteritis, UTIs)
Tier 3: specific infections and pathogens (e.g. S. aureus, N. meningitidis, Salmonella, Campylobacter, HIV/AIDS, influenza, hepatitis A/B/C, STIs, malaria, TB, etc)

Question 7

Give 6 examples of immunological defects which may impact susceptibility to infection

Answer 7

Post-chemotherapy neutropenia
Lymphocyte dysfunction (e.g. HIV)
Immunoglobulin deficit (e.g. myeloma)
Splenectomy
Pregnancy
Malnutrition (similar effect to HIV)

Question 8

What kind of infections does post-chemotherapy neutropenia predispose to?

Answer 8

Bacterial sepsis

Question 9

What kind of infections does lymphocyte dysfunction predispose to?

Answer 9

Intracellular or slow-growing pathogens

Question 10

What kind of infections does immunoglobulin deficit predispose to?

Answer 10

Encapsulated bacteria

Question 11

What kind of infections does splenectomy predispose to?

Answer 11

Pneumococcal infection

Question 12

Describe the diurnal pattern of body temperature

Answer 12

Highest in the evening, lowest in the morning

Therefore fever in the morning is ALWAYS significant!

Question 13

Give 2 examples of conditions notorious for falsely “masking” signs of infection severity

Answer 13

Diabetes

Corticosteroids

Question 14

What temperature range suggests bacterial sepsis?

Answer 14

> 38.4C

<36C

Question 15

What HR is suggestive of bacterial sepsis?

Answer 15

> 90/min, but beware of relative bradycardia in certain situations (for each 0.5-0.6C increase in temperature, HR should increase by ~10/min)
BEWARE B-BLOCKERS AND PATIENTS WITH HEART BLOCK

Question 16

What RR is suggestive of bacterial sepsis?

Answer 16

> 20/min

Question 17

List 4 more signs of bacterial sepsis

Answer 17

Altered mental state

Hypoxaemia (PaO2 20mmHg

Question 18

What are 2 important factors to remember when considering BP in a pt with suspected bacterial sepsis?

Answer 18

Hypotension is often a late sign

A “normal” BP can be low if the pt is ordinarily hypertensive

Question 19

What is the usual timeline for MCS testing?

Answer 19

24-48h to growth
24hr to identification
24-48hr to Abx susceptibilities
Usually 3-5 days

Question 20

What do rigors indicate?

Answer 20

Serious illness until proven otherwise (admit!)

Question 21

How can signs vary according to the pt’s age?

Answer 21

Infants - prominent
Adolescents - confusing
Adults - affected by comorbidities
Elderly - blunted

Question 22

When should you take blood cultures?

Answer 22

If serious infection is suspected

Question 23

What is the common infectious disease presentation in general practice?

Answer 23

Respiratory tract infections

Question 24

45 year old male presents with 3/7 fever, sweats, cough, SOB and 2kg LOW
Previously well
CXR shows right upper lobe consolidation
Likely Dx? Likely pathogen?

Answer 24

Acute CAP, like S. pneumoniae

Question 25

45 year old male presents with fever, sweats, cough, SOB and 2kg LOW Ex-smoker with insulin-dependent DM 2/12 Hx increasing blood-stained, purulent sputum after 1/12 trip to India DDx?

Answer 25

TB | Lung Ca with secondary infection

Question 26

45 year old male presents with fever, sweats, non-productive cough, 1/7 rapidly increasing SOB and 2kg LOW PHx: Hodgkin's lymphoma (just completed 3rd cycle of "CHOP" chemotherapy 2/52 earlier), severely neutropenic O/E: BP 75/50 DDx? Likely pathogen?

Answer 26

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

Question 27

What is the emphasis on when managing infections of various organ systems? (I.e. tier 2 of the 3-tier approach to ID)

Answer 27

Clinical Dx Lab Ix Choice of Rx Monitoring Rx

Question 28

What factors are important to ascertain on Hx in a patient with suspected infection?

Answer 28

The illness: onset and duration ("when were you last well"), the order, severity and progression of various symptoms, response to therapy received during illness The setting: previous state of health (co-morbidities), ?immunosuppression (e.g. pregnancy, malnutrition), predisposing events, epidemiology, contact with similar illness or known infectious disease, vaccination Hx

Question 29

What might the nature of onset of the illness tell you about possible underlying causes?

Answer 29

Bacterial sepsis usually abrupt onset | Viral infections often (but not always) evolve more gradually

Question 30

What are the 2 types of symptoms to be considered in an infectious disease Hx? Give examples of each

Answer 30

Systemic (e.g. fever, chills, sweats, myalgia, LOW, lethargy, fatigue; prominence reflects severity) Localising (e.g. cough diarrhoea, pain; these can be misleading)

Question 31

Give examples of contexts in which an apparent "localising" symptom may be misleading

Answer 31

Diarrhoea can be a symptom of bacteraemic illness and not a GI infection Dry cough can be associated with typhoid

Question 32

List 3 settings which may predispose to illness

Answer 32

Recent operations Accidents/injuries New medications (e.g. adverse events, Abx may affect bug's resistance pattern)

Question 33

What aspects of epidemiology are important to ascertain in an infectious disease Hx?

Answer 33

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

Question 34

List specific signs to look for on physical examination in the infectious disease patient

Answer 34

Eyes: conjunctival haemorrhages (e.g. staph endocarditis), scleral jaundice Skin: rashes (esp petechial), cellulitis (esp on legs), evidence of IVDU Muscles: marked tenderness (sepsis) LNs: esp posterior cervical nodes, tenderness of jugulo-digastric nodes (early bacterial tonsilitis), axillary and inguinal nodes (CMV, HIV) Throat: signs may precede symptoms in streptococcal tonsilitis, oedema of the uvula (useful sign of bacterial infection) Neck: neck stiffness (meningitis) Heart: murmurs (endocarditis), pericardial rub Lungs: subtle crackles (pneumonia), pleural rub Abdomen: tenderness, enlargement without pain NB don't forget about covered areas!

Question 35

7 signs of bacterial sepsis

Answer 35

``` Fever Tachycardia Tachypnoea Altered mental state Hypoxaemia Oliguria Hypotension (late sign) ```

Question 36

8 key Abx??

Answer 36

??

Question 37

What public health issues are important to consider in the assessment of the infectious diseases patient?

Answer 37

Importance of incubation times and periods of infectivity/transmissibility Notifiable diseases Outbreak management Contact tracing

Question 38

55 year old female presents with 4/52 of fever, sweats and LOW PHx: RHD with "leaky valve" 2/52 before illness onset she had a tooth abscess drained by dentist O/E: temp 38.2C, AR murmur, red "peticheal" rash on fingertips and under toenails, no retinal haemorrhages Likely Dx? Likely pathogen? Mx?

Answer 38

Dx: RHD with subsequent aortic valve endocarditis Pathogen: Likely viridans streptococci Mx: depends on pathogen and degree of valve damage, options include prolonged IV Abx (2-4/52) and surgical valve resection with prosthetic valve replacement

Question 39

20 year old female medical student, previously well, attended Aus Day BBQ and consumed "undercooked egg rolls", hamburgers and potato salad, as well as 5 beers Next day developed severe watery diarrhoea, low grade fevers, severe lethargy and lost 4kg over 24hrs (moderate dehydration) DDx and likely source of pathogen? Mx?

Answer 39

DDx: salmonella (from eggs), campylobacter (from ground beef in hamburgers) Mx: fluid replacement/resusc, generally self-limiting, no Abx needed (unless at)

Question 40

35 year old diabetic male with painless, purulent foot ulcer 3/52 of increasingly unstable diabetic control Occasional low-grade fevers Offensive odour from ulcer O/E: grossly deformed foot, marked sensory neuropathy, ulcer that probes to bone Dx? Mx?

Answer 40

Dx: diabetic foot ulcer with underlying ostemyelitis Mx: surgical debridement +/- long-term Abx

Question 41

Does the absence of fever rule out infection?

Answer 41

NO

Question 42

What does staph aureus bacteraemia indicate?

Answer 42

Endocarditis or osteomyelitis until proven otherwise (staph aureus bacteraemia is always significant!)

Question 43

What are some possible reasons a patient may not improve on Abx, other than failure of the Abx?

Answer 43

Too short a period to observe an improvement Undrained focus of infection Infection is not bacterial I.e. a second course of Abx is rarely needed!