Intro to ID Flashcards
What is the leading cause of death and morbidity worldwide?
Infectious disease (15 million deaths annually)
What % of presentations does infectious disease make up, in GP and ED respectively?
> 70% in GP
~20% in ED
What is the #2 most prescribed agent in Aus?
Antimicrobials (15-20% of all prescriptions)
About 20% of public hospital in-patients receive Abx
What is the major cause of inappropriate antibiotic use?
Poor clinical judgment about the presence of a bacterial infection where there is none
What % of antibiotic use is empirical?
~80%
What is the 3-tier approach to ID?
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)
Give 6 examples of immunological defects which may impact susceptibility to infection
Post-chemotherapy neutropenia Lymphocyte dysfunction (e.g. HIV) Immunoglobulin deficit (e.g. myeloma) Splenectomy Pregnancy Malnutrition (similar effect to HIV)
What kind of infections does post-chemotherapy neutropenia predispose to?
Bacterial sepsis
What kind of infections does lymphocyte dysfunction predispose to?
Intracellular or slow-growing pathogens
What kind of infections does immunoglobulin deficit predispose to?
Encapsulated bacteria
What kind of infections does splenectomy predispose to?
Pneumococcal infection
Describe the diurnal pattern of body temperature
Highest in the evening, lowest in the morning
Therefore fever in the morning is ALWAYS significant!
Give 2 examples of conditions notorious for falsely “masking” signs of infection severity
Diabetes
Corticosteroids
What temperature range suggests bacterial sepsis?
> 38.4C
<36C
What HR is suggestive of bacterial sepsis?
> 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
What RR is suggestive of bacterial sepsis?
> 20/min
List 4 more signs of bacterial sepsis
Altered mental state
Hypoxaemia (PaO2 20mmHg
What are 2 important factors to remember when considering BP in a pt with suspected bacterial sepsis?
Hypotension is often a late sign
A “normal” BP can be low if the pt is ordinarily hypertensive
What is the usual timeline for MCS testing?
24-48h to growth
24hr to identification
24-48hr to Abx susceptibilities
Usually 3-5 days
What do rigors indicate?
Serious illness until proven otherwise (admit!)
How can signs vary according to the pt’s age?
Infants - prominent
Adolescents - confusing
Adults - affected by comorbidities
Elderly - blunted
When should you take blood cultures?
If serious infection is suspected
What is the common infectious disease presentation in general practice?
Respiratory tract infections
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?
Acute CAP, like S. pneumoniae
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?
TB
Lung Ca with secondary infection
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?
Febrile neutropenia with acute Gram-negative or staphylococcal pneumonia (likely to require early ICU admission)
Acute aspiration pneumonia following chemo-related vomiting
What is the emphasis on when managing infections of various organ systems? (I.e. tier 2 of the 3-tier approach to ID)
Clinical Dx
Lab Ix
Choice of Rx
Monitoring Rx
What factors are important to ascertain on Hx in a patient with suspected infection?
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
What might the nature of onset of the illness tell you about possible underlying causes?
Bacterial sepsis usually abrupt onset
Viral infections often (but not always) evolve more gradually
What are the 2 types of symptoms to be considered in an infectious disease Hx? Give examples of each
Systemic (e.g. fever, chills, sweats, myalgia, LOW, lethargy, fatigue; prominence reflects severity)
Localising (e.g. cough diarrhoea, pain; these can be misleading)
Give examples of contexts in which an apparent “localising” symptom may be misleading
Diarrhoea can be a symptom of bacteraemic illness and not a GI infection
Dry cough can be associated with typhoid
List 3 settings which may predispose to illness
Recent operations
Accidents/injuries
New medications (e.g. adverse events, Abx may affect bug’s resistance pattern)
What aspects of epidemiology are important to ascertain in an infectious disease Hx?
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)
List specific signs to look for on physical examination in the infectious disease patient
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!
7 signs of bacterial sepsis
Fever Tachycardia Tachypnoea Altered mental state Hypoxaemia Oliguria Hypotension (late sign)
8 key Abx??
??
What public health issues are important to consider in the assessment of the infectious diseases patient?
Importance of incubation times and periods of infectivity/transmissibility
Notifiable diseases
Outbreak management
Contact tracing
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?
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
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?
DDx: salmonella (from eggs), campylobacter (from ground beef in hamburgers)
Mx: fluid replacement/resusc, generally self-limiting, no Abx needed (unless at)
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?
Dx: diabetic foot ulcer with underlying ostemyelitis
Mx: surgical debridement +/- long-term Abx
Does the absence of fever rule out infection?
NO
What does staph aureus bacteraemia indicate?
Endocarditis or osteomyelitis until proven otherwise (staph aureus bacteraemia is always significant!)
What are some possible reasons a patient may not improve on Abx, other than failure of the Abx?
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!
