Infectious diseases Flashcards
What is the difference between infection and colonisation?
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)
what are the risk factors for infection?
- immunosuppression
- medical devices - cannulas, catheters, lines
- exposure to abx
what is pyrexia of unknown origin?
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
what are the causes of PUO?
infectious - TB, infective endocarditis
neoplasm - lymphoma
connective tissue disorder - temporal arteritis, sarcoid, SLE
what needs to be elicited in the history of an infected patient?
- focus on recent hospital admissions, recent food eaten, recent travel
- contact with others - similar sx
- risk factors - immunosuppression, medical devices/implants, exposure to abx
when examining an infected patient what would you notice?
- sx of infection - localised pain, fatigue, malaise, headache
- signs of infection - fever, tachycardia, tachypnoea, hypotension (sepsis)
what are the 1st line investigations for a febrile patient?
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
when would we use imaging in a febrile patient?
CXR for penumonia
CT/MRI/US for abscesses
what is the indication for lumbar puncture in a febrile patient?
if meningitis or encephalitis is suspected
what would we expect the lumbar puncture to be in an infected patient?
neutrophilia = bacterial leukocytosis = viral
low glucose, high proteins (inflammation)
what is MC&S?
microscopy, cultures and sensitivity
allows for organisms to be viewed under the microscope - look at shape and size
allows for gram staining
what organism commonly causes soft tissue infections and what abx is used to treat it?
staph aureus or pyogenes
flucloxacillin
what is the NEWS score?
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
what increases your risk of bacterial infections?
- compromised immune system - immunosuppresion, COPD, diabetes, acutely unwell patients
- increased exposure to bacteria - IV drug users, medical devices, exposure to abx (c.diff)
what organism usually causes UTIs and how do we treat?
e.coli
nitrofurantoin
what organism usually causes pneumonia and how do we treat?
strep pneumoniae
doxycyline or doxycycline + benzylpenicillin
what causes infective exacerbations of COPD and how do we treat?
strep penumoniae
amoxicillin, doxycycline, erythromycin
how would someone with a bacterial infection present?
- fever
- fatigue
- malaise
- specific sx - relating to region affected
- Tachycardia
- Tachypnoea
- Hypotension (if septic)
what is gram staining?
staining technique used to differentiate different types of bacteria - gram positive and negative
stains according to composition of cell wall
what colour is gram positive staining?
purple due to thick peptidoglycan wall which retain the purple stain
what colour is gram negative staining?
pink or red - no peptidoglycan wall so cannot retain the stain
what are the different bacteria shapes?
cocci - round (strep pneumonia, pyrigens, staph aureus)
bacilli - rods (salmonella, clost. botulinum, bacillus anthracis)
spirals - vibrio cholerae, H. pylori
what are encapsulated bacteria and list some examples
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
what are the different types of toxins bacteria can release?
endotoxin - located on bacteria surface- triggers complement -> inflammation
enterotoxin - targets gut (c.diff)
exotoxin - secreted by bacteria, causes pathology at site distant from growth
what investigations would we order for a patient with a suspected bacterial infection?
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
what antigens would a stool sample for c.diff contain?
GDH
how do we usually manage a patient with a bacterial infection?
take blood cultures
start patient on broad spec abx
then check blood culture sensitivities
what is the abx treatment for a patient with meningitis?
give broad spec abx immediately before cultures
list some common gram negative bacteria
Neisseria meningitis, Neisseria gonorrhoea, haemophilia influenza, E.coli, Klebsiella, Pseudomonas aeruginosa, Moraxella catarrhalis, campylobacter
list some common gram positive bacteria?
staphylococcus, streptococcus, enterococcus, listeria, mycobacterium. clostridium, bacillus
what is MRSA?
staphylococcus aureus that is resistant to beta-lactam antibiotics eg penicillins, cephalosporins, carbapenem
Antibiotic treatment: doxycycline, clindamycin, vancomycin, teicoplanin, linezolid
what are non-microbiological investigations?
bloods - WCC, CRP
body fluids - CSF biochem
imaging - XR, US, CT, MRI
what are microbiological investigations?
microscopy
culture (MC&S)
serological testing - Ag or Ab detection
molecular test - NA detection
what 3 considerations need to be made when picking an abx?
- 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
what are the risk factors for abx resistance?
- likely to develop in hospitals due to
- immunosuppressed patients
- invasive procedures
- invasive lines
- disruption to host defences
what are the 4 mechanisms of abx resistance?
- 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
what does bactericidal and bacteriostatic mean?
- 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
which abx inhibit cell wall synthesis?
- 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
which abx inhibit ribosomes?
- aminoglycosides (gentamicin, streptomycin) - irreversibly bind to bacterial ribosomes
- tetracycline (doxycycline) - stop RNA from binding to ribosome
- macrolides (erythromycin, clarithromycin) - irreversibly bind to bacterial ribosomes
which abx are antimetabolites and antifolates?
- trimethoprim - interferes with folic acid synthesis
- sulphonamides
which abx inhibit nucleic acid synthesis?
- quinolones
- nitrimidazoles (metronidazole) - inhibits DNA synthesis by damaging DNA
what abx do we give to bacteria resistance to beta lactams?
co-amoxiclav (augmentin)
what bacteria are metronidazole only effective in?
anaerobes
what is the stepwise approach for abx coverage?
- 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
what is bacteraemia?
This is the presence of bacteria in the blood, this is not necessarily pathological.
what is septicaemia/sepsis?
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
what is sepsis syndrome/shock?
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.
how is septic shock defined?
sepsis in combination with:
lactate >2mmol/L despite fluid resuscitation
patient requires vasopressors to keep arterial pressure >65
risk factors for sepsis?
- 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
what vital signs does the NEWS include and what would these be in a patient with suspected sepsis?
- temperature (fever)
- RR (tachypnoea)
- HR (tachycardia)
- O2 sats (low)
- BP (hypotensive)
- consciousness level (low)
what are signs of potential sources of infection for sepsis?
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
what is a sign of meningococcal septicaemia?
non blanching rash
list some other signs of sepsis
reduced urine output long CR mottled skin cyanosis new onset AF
what is often the first sign of sepsis?
tachypnoea
what are the sepsis red flags?
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
what happens in sepsis when immune cells detect large amounts of bacteria?
macrophages, lymphocytes and mast cells release cytokines, ILs, TNF, NO
all to trigger systemic inflammatory response
in sepsis, what does the systemic inflammatory response lead to?
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)
what is septic shock?
- when arterial BP drops so low -> organ hypo-perfusion
- leads to rise in blood lactate (anaerobic resp), less O2 delivered to tissues
what is severe sepsis?
sepsis with organ failure/dysfunction
Hypoxia
Oliguria
Acute Kidney Injury
Thrombocytopenia
Coagulation Dysfunction
Hypotension
Hyperlactaemia (<2 mmol/L)
what are the investigations for suspected sepsis?
- 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
what is the sepsis 6?
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
what do you do after delivering sepsis 6 and the patient is not improving?
refer to ICU immediately
what is the difference between healthcare associated infection and community associated infection?
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
why are anti-microbial resistant infections more common in HCAI than CAI?
• 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
compare examples of HCAI and CAI
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
what is classified as hospital acquired pneumonia?
pneumonia that develops in a patient after 72 hours
what are the risk factors for hospital acquired pnemonia?
intubation
stroke - aspiration
immobility
what are the causative organisms of hospital acquired pneumonia?
- gram -ve bacteria - e.coli, pseudomonas, legionella
- gram +ve - strep pneumoniae, MRSA
1st line investigations for hospital acquired pneumonia?
- sputum culture
- blood cultures - if pyrexial
how do we manage someone with hospital acquired pneumonia?
- abx - pipercillin/tazobactam +/- vancomycin if MRSA suspected
- review previous sputum results
- check MRSA screen
- check for prior abx use
how would someone with hospital acquired pneumonia present?
Productive Cough
Difficulty Breathing
Fever
risk factors for MRSA
- Recurrent Healthcare Admissions
- Residential/Nursing Home
- Recurrent Antibiotic Use
- Chronic Skin Conditions
what is a common source for MRSA bacteraemia?
cannula and catheter
remove immediately
how would someone with MRSA present?
- cellulitis or soft tissue infection
- erythema and oedema around cannula site
- fever
- signs of sepsis
what organisms can cause cellulitis?
- staph aureus (MRSA)
- streptococcus pyogens (group A strep)
how do we investigate MRSA?
- blood cultures
- swab cannula site
- send cannula tip for culture
how do we manage MRSA?
- source control - remove cannula
- abx - vancomycin or teicoplanin
what type of bacteria is c.diff?
anaerobic gram positive rod bacteria
it is part of the normal gut flora and exists as a commensal.
what is c.diff often associated with?
abx associated diarrhoea
how to distinguish between c.diff and norovirus?
if patient has severe diarrhoea and vomiting suspect norovirus (c.diff does not cause vomiting)
how does someone with c.diff abx associated diarrhoea present?
- Severe Watery Diarrhoea
- Severe Bloody Diarrhoea
- Abdominal Pain
- Fever
how does someone with severe c.diff present?
- WBC >15
- rise in serum creatinine (AKI)
- colitis
how do we investigate someone with suspected c.diff?
- 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
what are we looking for in the stool sample of a patient with c.diff?
presence of GDH antigens AND c.diff toxins
how do we manage c.diff?
- 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
what is a complication of c.diff and how should we manage it?
toxic megacolon
- refer to gastro and surgical opinion (may require colectomy to prevent perforation)
