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Infectious diseases Flashcards

1
Q

What is the difference between infection and colonisation?

A

Infection = microorganisms are growing on or in a person making them unwell

Colonisation = microorganisms grow on or in a person but doesn’t make them unwell (commensals in gut)

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2
Q

what are the risk factors for infection?

A
  • immunosuppression
  • medical devices - cannulas, catheters, lines
  • exposure to abx
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3
Q

what is pyrexia of unknown origin?

A

patient has a fever of higher than 38.3’C for more than 3 weeks and the cause of this cannot be determined after one week of study in hospital

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4
Q

what are the causes of PUO?

A

infectious - TB, infective endocarditis

neoplasm - lymphoma

connective tissue disorder - temporal arteritis, sarcoid, SLE

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5
Q

what needs to be elicited in the history of an infected patient?

A
  • focus on recent hospital admissions, recent food eaten, recent travel
  • contact with others - similar sx
  • risk factors - immunosuppression, medical devices/implants, exposure to abx
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6
Q

when examining an infected patient what would you notice?

A
  • sx of infection - localised pain, fatigue, malaise, headache
  • signs of infection - fever, tachycardia, tachypnoea, hypotension (sepsis)
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7
Q

what are the 1st line investigations for a febrile patient?

A

bedside - obs, urine dip, ECG

bloods - inflammatory markers (CRP and WCC), FBC (neutrophils and lymphocytes), blood chemistry (LFTs)

blood cultures - take immediately before starting abx

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8
Q

when would we use imaging in a febrile patient?

A

CXR for penumonia

CT/MRI/US for abscesses

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9
Q

what is the indication for lumbar puncture in a febrile patient?

A

if meningitis or encephalitis is suspected

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10
Q

what would we expect the lumbar puncture to be in an infected patient?

A 
neutrophilia = bacterial
leukocytosis = viral

low glucose, high proteins (inflammation)

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11
Q

what is MC&S?

A

microscopy, cultures and sensitivity

allows for organisms to be viewed under the microscope - look at shape and size

allows for gram staining

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12
Q

what organism commonly causes soft tissue infections and what abx is used to treat it?

A

staph aureus or pyogenes

flucloxacillin

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13
Q

what is the NEWS score?

A

national early warning score

score a maximum of 3 points in the different categories

used to stratify risk - informs the nursing staff how often to check obs

score of 3 = need to tell a dr

score >= 3 in 1 category = see patient urgently

score >= 5 = SEPSIS

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14
Q

what increases your risk of bacterial infections?

A
  • compromised immune system - immunosuppresion, COPD, diabetes, acutely unwell patients
  • increased exposure to bacteria - IV drug users, medical devices, exposure to abx (c.diff)
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15
Q

what organism usually causes UTIs and how do we treat?

A

e.coli

nitrofurantoin

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16
Q

what organism usually causes pneumonia and how do we treat?

A

strep pneumoniae

doxycyline or doxycycline + benzylpenicillin

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17
Q

what causes infective exacerbations of COPD and how do we treat?

A

strep penumoniae

amoxicillin, doxycycline, erythromycin

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18
Q

how would someone with a bacterial infection present?

A
  • fever
  • fatigue
  • malaise
  • specific sx - relating to region affected
  • Tachycardia
  • Tachypnoea
  • Hypotension (if septic)
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19
Q

what is gram staining?

A

staining technique used to differentiate different types of bacteria - gram positive and negative

stains according to composition of cell wall

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20
Q

what colour is gram positive staining?

A

purple due to thick peptidoglycan wall which retain the purple stain

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21
Q

what colour is gram negative staining?

A

pink or red - no peptidoglycan wall so cannot retain the stain

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22
Q

what are the different bacteria shapes?

A

cocci - round (strep pneumonia, pyrigens, staph aureus)

bacilli - rods (salmonella, clost. botulinum, bacillus anthracis)

spirals - vibrio cholerae, H. pylori

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23
Q

what are encapsulated bacteria and list some examples

A

bacteria with thick outer capsule - evades the immune response

some, killers, have, pretty, nice, capsules

step pneumoniae
klebsiella pneu
haemophilius influenza
psuedomonas aerigunosa
neiserria meningitiditis
cryptococcus neoformans
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24
Q

what are the different types of toxins bacteria can release?

A

endotoxin - located on bacteria surface- triggers complement -> inflammation

enterotoxin - targets gut (c.diff)

exotoxin - secreted by bacteria, causes pathology at site distant from growth

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25
Q

what investigations would we order for a patient with a suspected bacterial infection?

A

urine dip - leukocytes and nitrates (UTI)

  • CRP and WCC - raised (infection and inflammation)
  • FBC - raised WCC
  • blood cultures
  • U&Es - degree of dehydration, any renal function
  • LFTs
  • Clotting - risk of DIC or sepsis

CXR - pneumonia

  • LP MC&S - raised neutrophils, low glucose, high protein, cloudy
  • sputum culture - green/yellow
  • echo - suspect endocarditis
  • stool culture - C.diff contains GDH antigens
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26
Q

what antigens would a stool sample for c.diff contain?

A

GDH

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27
Q

how do we usually manage a patient with a bacterial infection?

A

take blood cultures

start patient on broad spec abx

then check blood culture sensitivities

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28
Q

what is the abx treatment for a patient with meningitis?

A

give broad spec abx immediately before cultures

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29
Q

list some common gram negative bacteria

A

Neisseria meningitis, Neisseria gonorrhoea, haemophilia influenza, E.coli, Klebsiella, Pseudomonas aeruginosa, Moraxella catarrhalis, campylobacter

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30
Q

list some common gram positive bacteria?

A

staphylococcus, streptococcus, enterococcus, listeria, mycobacterium. clostridium, bacillus

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31
Q

what is MRSA?

A

staphylococcus aureus that is resistant to beta-lactam antibiotics eg penicillins, cephalosporins, carbapenem

Antibiotic treatment: doxycycline, clindamycin, vancomycin, teicoplanin, linezolid

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32
Q

what are non-microbiological investigations?

A

bloods - WCC, CRP

body fluids - CSF biochem

imaging - XR, US, CT, MRI

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33
Q

what are microbiological investigations?

A

microscopy

culture (MC&S)

serological testing - Ag or Ab detection

molecular test - NA detection

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34
Q

what 3 considerations need to be made when picking an abx?

A
  • patient - hx of allergy, renal and hepatic function, immunocompromied, ability to tolerate drugs PO, severity of illness, complications, age, pregnant
  • known or likely to have the causative organism
  • risk of bacterial resistance with repeated courses
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35
Q

what are the risk factors for abx resistance?

A
  • likely to develop in hospitals due to
    • immunosuppressed patients
    • invasive procedures
    • invasive lines
    • disruption to host defences
36
Q

what are the 4 mechanisms of abx resistance?

A
  • inherent resistance - bacteria doesn’t contain the abx target
  • de novo development of resistance - mutation in bacteria allowing it to avoid abx destruction
  • transmission of resistance within the bacterial species
  • acquisition of colonisation by resistant bacteria - particularly in hospitals
37
Q

what does bactericidal and bacteriostatic mean?

A
  • bactericidal (kill bacteria) - when an infection is severe or life-threatening
  • bacteriostatic (inhibit bacterial growth) - allows for the host’s defence mechanism to kill the bacteria, assumes it is intact
38
Q

which abx inhibit cell wall synthesis?

A
  • beta-lactams (penicillin, cephlasporins, flucoxacillin) - inhibit peptidogylcan synthesis
    • can be combined with augmentin (beta lactamase inhibitor) = co-amoxiclav
  • glycopeptides (vancomycin) - disrupt cross-linking of peptidoglycan
39
Q

which abx inhibit ribosomes?

A
  • aminoglycosides (gentamicin, streptomycin) - irreversibly bind to bacterial ribosomes
  • tetracycline (doxycycline) - stop RNA from binding to ribosome
  • macrolides (erythromycin, clarithromycin) - irreversibly bind to bacterial ribosomes
40
Q

which abx are antimetabolites and antifolates?

A
  • trimethoprim - interferes with folic acid synthesis

- sulphonamides

41
Q

which abx inhibit nucleic acid synthesis?

A
  • quinolones

- nitrimidazoles (metronidazole) - inhibits DNA synthesis by damaging DNA

42
Q

what abx do we give to bacteria resistance to beta lactams?

A

co-amoxiclav (augmentin)

43
Q

what bacteria are metronidazole only effective in?

A

anaerobes

44
Q

what is the stepwise approach for abx coverage?

A
  • begin with amoxicillin to cover streptococcus, listeria and enterococcus
  • switch to co-amox to cover staph, haemophilius and e.coli
  • switch to tazocin to cover pseudomonas
  • switch to meropenem to cover extended spectrum beta lactamase bacteria
  • add teicoplanin or vancomycin to cover MRSA
  • add clarithromycin or doxycycline to cover atypical bacteria
45
Q

what is bacteraemia?

A

This is the presence of bacteria in the blood, this is not necessarily pathological.

46
Q

what is septicaemia/sepsis?

A

replication of bacteria within blood, leading to a blood infection and the propagation of this infection.

This leads to life-threatening organ dysfunction due to a dysregulated host response to the infection

body launches a large immune response to an infection which results in systemic inflammation that affects the function of organs throughout the body

47
Q

what is sepsis syndrome/shock?

A

infection of the blood leads to Systemic Inflammatory Response Syndrome (SIRS) in which the bodies response to systemic infection leads to inflammatory reactions which lead to multi-system organ failure.

This causes persisting hypotension which leads to reduced tissue perfusion and thus causes anaerobic resp to occur.

48
Q

how is septic shock defined?

A

sepsis in combination with:

lactate >2mmol/L despite fluid resuscitation

patient requires vasopressors to keep arterial pressure >65

49
Q

risk factors for sepsis?

A
  • young (<1) and old (>75)
  • immunocompromised - chemo, immunosuppressants, steroids
  • chronic cionditions - COPD, diabetes
  • ITU patients
  • surgery, burns, trauma
  • pregnancy
  • indwelling lines or catheters
  • IV drug users
50
Q

what vital signs does the NEWS include and what would these be in a patient with suspected sepsis?

A
  • temperature (fever)
  • RR (tachypnoea)
  • HR (tachycardia)
  • O2 sats (low)
  • BP (hypotensive)
  • consciousness level (low)
51
Q

what are signs of potential sources of infection for sepsis?

A

Signs of potential sources of infection

Dysuria - UTI

Cough - Pneumonia

Cellulitis - Skin Infection

Discharge from wound

Headache - Meningitis

New Heart Murmur - Infective Endocarditis

D&V - Gastrointestinal Infection

52
Q

what is a sign of meningococcal septicaemia?

A

non blanching rash

53
Q

list some other signs of sepsis

A 
reduced urine output 
long CR
mottled skin
cyanosis 
new onset AF
54
Q

what is often the first sign of sepsis?

A

tachypnoea

55
Q

what are the sepsis red flags?

A 
unresponsive 
systolic BP <90
HR >130
RR >25 
needs O2 to maintain sats above 92%
non blanching rash
mottled
not passed urine in 18 hours 
urine output <0.5ml/kg/hr
lactate >2
recent chemo
56
Q

what happens in sepsis when immune cells detect large amounts of bacteria?

A

macrophages, lymphocytes and mast cells release cytokines, ILs, TNF, NO

all to trigger systemic inflammatory response

57
Q

in sepsis, what does the systemic inflammatory response lead to?

A

vasodilation

  • results in reduced blood pressure and thus decreased tissue perfusion, reducing tissue oxygen delivery.
  • This leads to a rise in blood lactate as tissues are undergoing anaerobic respiration

increased vascular permeability

  • Cytokines cause blood vessels to become more permeable, allowing fluid to leak into the interstitial space and thus leading to oedema, reducing intravascular volume.
  • This reduction in intravascular volume leads to further hypotension and reduced tissue perfusion.

activation of coagulation system

  • release of inflammatory cytokines leads to inappropriate activation of the coagulation cascade, leading to the inappropriate deposition of fibrin.
  • inappropriate activation of clotting -> clotting factors used up -> more prone to haemorrhage (DIC)
58
Q

what is septic shock?

A
  • when arterial BP drops so low -> organ hypo-perfusion

- leads to rise in blood lactate (anaerobic resp), less O2 delivered to tissues

59
Q

what is severe sepsis?

A

sepsis with organ failure/dysfunction

Hypoxia

Oliguria

Acute Kidney Injury

Thrombocytopenia

Coagulation Dysfunction

Hypotension

Hyperlactaemia (<2 mmol/L)

60
Q

what are the investigations for suspected sepsis?

A
  • Bedside
    • obs for NEWS
    • urine dip - UTI
    • ECG - arrhythmia
  • bloods
    • blood cultures
    • serum lactate - blood gas
    • FBC, U&Es, serum glucose, CRP, clotting screen, LFTs
  • hourly urine output
  • imaging - CT or CXR
61
Q

what is the sepsis 6?

A

GIVE 3

  • IV fluids - fluid challenge (500ml bolus crystalloid over 15 mins)
  • abx - broad spectrum IV
  • O2 - maintain at 94-98% unless COPD (88-92%)

TAKE 3

  • blood cultures
  • urine output - hourly measurements
  • lactate
62
Q

what do you do after delivering sepsis 6 and the patient is not improving?

A

refer to ICU immediately

63
Q

what is the difference between healthcare associated infection and community associated infection?

A

healthcare associated is acquired in a healthcare facility - multi-drug resistant strains

community associated is not acquired in a healthcare setting - strains are usually sensitive to abx and tx

64
Q

why are anti-microbial resistant infections more common in HCAI than CAI?

A

• More abx are used in the hospital setting (at much higher doses)
○ Therefore abx pressure on the bacteria for survival
• Concentration of very ill patients who are more susceptible
-Deficiency in hygiene/cleanliness of the hospital

65
Q

compare examples of HCAI and CAI

A

CAI:

  • gastroenteritis (campylobacter, salmonella, shigella)
  • community acquired pneumonia
  • meningitis
  • septic arthritis
  • community acquired MRSA

HCAI:

  • c.diff infection, norovirus
  • hospital acquired pneumonia
  • post-neurosurgical meningitis
  • periprosthetic joint infection
  • catheter related blood stream infections
66
Q

what is classified as hospital acquired pneumonia?

A

pneumonia that develops in a patient after 72 hours

67
Q

what are the risk factors for hospital acquired pnemonia?

A

intubation
stroke - aspiration
immobility

68
Q

what are the causative organisms of hospital acquired pneumonia?

A
  • gram -ve bacteria - e.coli, pseudomonas, legionella

- gram +ve - strep pneumoniae, MRSA

69
Q

1st line investigations for hospital acquired pneumonia?

A
  • sputum culture

- blood cultures - if pyrexial

70
Q

how do we manage someone with hospital acquired pneumonia?

A
  • abx - pipercillin/tazobactam +/- vancomycin if MRSA suspected
  • review previous sputum results
  • check MRSA screen
  • check for prior abx use
71
Q

how would someone with hospital acquired pneumonia present?

A

Productive Cough

Difficulty Breathing

Fever

72
Q

risk factors for MRSA

A
  • Recurrent Healthcare Admissions
  • Residential/Nursing Home
  • Recurrent Antibiotic Use
  • Chronic Skin Conditions
73
Q

what is a common source for MRSA bacteraemia?

A

cannula and catheter

remove immediately

74
Q

how would someone with MRSA present?

A
  • cellulitis or soft tissue infection
  • erythema and oedema around cannula site
  • fever
  • signs of sepsis
75
Q

what organisms can cause cellulitis?

A
  • staph aureus (MRSA)

- streptococcus pyogens (group A strep)

76
Q

how do we investigate MRSA?

A
  • blood cultures
  • swab cannula site
  • send cannula tip for culture
77
Q

how do we manage MRSA?

A
  • source control - remove cannula

- abx - vancomycin or teicoplanin

78
Q

what type of bacteria is c.diff?

A

anaerobic gram positive rod bacteria

it is part of the normal gut flora and exists as a commensal.

79
Q

what is c.diff often associated with?

A

abx associated diarrhoea

80
Q

how to distinguish between c.diff and norovirus?

A

if patient has severe diarrhoea and vomiting suspect norovirus (c.diff does not cause vomiting)

81
Q

how does someone with c.diff abx associated diarrhoea present?

A
  • Severe Watery Diarrhoea
  • Severe Bloody Diarrhoea
  • Abdominal Pain
  • Fever
82
Q

how does someone with severe c.diff present?

A
  • WBC >15
  • rise in serum creatinine (AKI)
  • colitis
83
Q

how do we investigate someone with suspected c.diff?

A
  • FBC (raised WCC)
  • raised CRP
  • U&Es (raised creatinine = AKI due to fluid loss)
  • imaging - abdo XR - toxic megacolon
  • stool sample - presence of GDH antigens
    • then test specifically for c.diff toxin
  • colonoscopy - pseudomembranous colitis
84
Q

what are we looking for in the stool sample of a patient with c.diff?

A

presence of GDH antigens AND c.diff toxins

85
Q

how do we manage c.diff?

A
  • immediately be isolated to a side room with barrier nursing undertaken to prevent the spread to other patients -c.diff spores infectious
  • abx
    • severe - vancomycin
    • non-severe - metronidazole
86
Q

what is a complication of c.diff and how should we manage it?

A

toxic megacolon

  • refer to gastro and surgical opinion (may require colectomy to prevent perforation)

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