Infectious Diseases Flashcards
how many sets of blood cultures should be taken in suspected bacteraemia
standard is to take 3 sets/6 bottles (separate times or separate sites)
how is antibiotic susceptibility classified
susceptible/intermediate/resistance based on minimum inhibitory concentration
what is B-D glucan
a fungal cell wall component which is released into the blood during invasive fungal infection
very sensitive but not specific
NAAT testing
nucleic acid amplification testing
used especially for respiratory viruses e.g. flu
very quick and highly specific
what are the serological things measured for hepatitis B
HBsAg
anti-HBs
anti-HBc
IgM-anti-HBc
which HBV marker shows active infection
HBsAg
what serology shows natural immunity to HBV
anti-HBs positive
anti-HBc positive
what serology shows artificial immunity (vaccination) to HBV
anti-HBs psoitive
rest negative
possible serology explanations if only anti-HBc positive
- resolved infection (most common)
- false positive test
- low level chronic infection
- resolving acute infection
acute vs chronic HBV infection serology results
both:
- HBsAg +ve
- anti-HBc +ve
- anti-HBs -ve
acute has IgM antiHBc whereas chronic doesn’t
steps of diagnosing infection
- could this be infection?
- what organ system?
- what type of microorganism could it be in this patient?
- what specimens need collecting?
- what tests do you want to request?
how is infection diagnosed?
detailed history including travel history, sexual history and occupation history
examination and observations
lab tests; micro, haem, biochemistry
radiology
histopathology
considerations for selecting an antibiotic
- which are effective against the probable pathogen(s)
- which reach the infected site?
- any allergies?
- any pt problems with excretion or metabolism?
- pregnancy?
tetracyclines specific side effect
teeth discolouration especially in children - avoid in under 12s
aminoglycosides specific side effect
ototoxicity and nephrotoxicity
when is therapeutic drug monitoring required
antimicrobials with variable absorption and/or metabolism and/or excretion
e.g.
gentamicin
teicoplanin, vancomycin
‘azole’ antifungals eg. itraconazole
more may need TDM in a critically unwell patient
why is TDM needed
prevent toxicity and ensure therapeutic doses are given
examples of organisms commonly associated with hospital acquired infections
Norovirus
MRSA
Clostridium Difficile
Carbapenem resistant E Coli
how may bacteria be classified
gram staining
morphology; rods, cocci etc
growth requirements; an/aerobic
gram staining
gram negative bacteria stain pink/red
gram positive bacteria stay purple with iodine - thick peptidoglycan wall
what are obligate aerobes and obligate anaerobes
obligate aerobes are bacteria that can only grow in the presence of oxygen
obligate anaerobes can only grow in the absence
what are facultative aerobes/facultative anaerobes
grow well in the presence and absence of oxygen
most human pathogens fall into this criteria
what is Ziehl-Neelson staining
different type of staining used for mycobacterium
bacteria which hold the stain are called acid-fast bacilli
what is done when bacteria are difficult to stain
some bacteria that live inside human cells such as chlamydia and mycoplasma are better identified using PCR or antibodies against them
morphology of bacteria
how they appear under the microscope
cocci- spherical in chains, clusters or pairs
rods- elongated
coccobacilli - in between cocci and rods
spiral - e.g. treponema pallidium/syphilis and Borrelia burgdorferi/lyme disease
how do staphylococci appear compared to streptococci
staph more in clusters
strep in chains
gram negative rods
Escherichia coli, Klebsiella pneumoniae or Proteus mirabilis
what is usually the first choice Abx for anaerobic infections
metronidazole
diarrhoea organisms
salmonella spp.
shigella spp.
yersinia spp.
E coli
campylobacter spp.
samples in a pt with diarrhoea
stool culture/ova/parasites
blood culture, urine culture, HIV, FBC, CRP, U+E, LFT
shigella infection management
common cause of travellers diarrhoea
if stable can be managed at home with hydration - usually resolves after 5-7 days
Antibiotics would only be indicated if there was evidence of Shigella bacteraemia with positive blood cultures
needs follow up - post-infection arthritis can occur
post infectious complications travellers diarrhoea
reactive arthritis
uveitis
urethritis
IBS
what does Candida albicans in a sputum sample represent
colonisation of the respiratory tract or contamination from oral candida
does not cause pneumonia
candida in a blood culture
significant - a medical emergency
high mortality
needs IV antifungals for 2 weeks from when blood cultures start to be negative
most common source of candidaemia
gut flora - can get into blood stream if epithelium becomes damaged for example in sepsis
how can fungal infections be classified
superficial, subcutaneous or deep mycoses
superficial fungal infections
who gets them
examples
common, can happen in anyone but more at risk/severe in immunocompromised e.g. HIV or diabetes
examples
- oral and vaginal thrush
- tinea (ring worm)
- fungal nail infection
- pityriasis versicolour
subcutaneous fungal infections
not common in UK - more in tropical countries
affect the dermis, subcutaneous tissue and adjacent bones and there is often some degree of immunocompromise
deep fungal infections
who gets them
examples
occur in immunocompromised; e.g. from chemotherapy or advanced HIV
invasive candida
invasive aspergillus
PCP
Cryptococcal meningitis
how does candida appear on blood culture
appear as gram positive cocci but much larger
how is candidaemia treated
micafungin
if central line associated remove the line
what infection is chickenpox
important complication requiring admission
primary varicella zoster infection
can cause pneumonitis
risk factors for severe presentation of chicken pox
immuncompromise - diabetes, HIV, medications
systemic inflammatory conditions
smoking, pregnancy and chronic lung disease are also risk factors
chicken pox vaccine
live vaccine so cannot be used in those severely immunocompromised or pregnant women
vaccine is for non-immune healthcare workers and non-immune close contacts of immunocompromised patients
vaccine can be used at prevention and treatment
what is the treatment of varicella zoster in an immunocompromised pt
aciclovir
presentation of chicken pox
usually mild in children
prodrome of fever and lethargy followed by an itchy vesicular rash
spreads from face and trunk to limbs
complications of chicken pox if presentation more severe
pneumonitis
bacterial infection of lesions
encephalitis
keratitis
hepatitis
myocarditis
what type of virus are EBV, cytomegalovirus, karposis sarcoma and HSV1&2
herpes viruses
who does CMV cause disease in
immunocompromised
e.g. can cause retinitis in HIV patients and transplant rejection
how does shingles occur
VZV lies dormant in single nerves or dorsal root ganglion and on reactivation causes symptoms in a dermatome
pain usually precedes the rash
can transmit chicken pox from shingles to non-immune people
action in pregnancy if no recorded hx of chicken pox
test for VZV IgG; if positive no action needed
if negative consider for post exposure prophylaxis with antivirals
risk to mother and foetus of VZV infection
The risk of severe disease in the mother is highest during the second or early third trimester, when she is relatively immunocompromised and more likely to develop pneumonitis
The risk to the foetus is greatest in the first 20 weeks. VZV is one of the “TORCH” infections and can lead to foetal varicella syndrome.
what are the common characteristics of herpes viruses
have a latent period where they reside in neurons; reactivation can be triggered by stress, menstruation, fever, sunlight, cell-mediated immune dysfunction, and HIV
migrate to skin/nerve endings and cause symptoms
opposed by cell mediated immune response
what does
HSV1 cause
HSV2 cause
HSV1 oral ulcers
HSV2 genital ulcers
but both viruses can cause disease in either part of the body
lie dormant in nerves then reactivates in relapses
HSV in pregnancy
Neonatal herpes is very rare but can have high morbidity and mortality - highest risk with maternal genital HSV in third trimester
genital herpes in pregnancy is treated with single dose aciclovir unless in third trimester in which case give acicolvir until delivery and plan caesarean
measles presentation
prodrome of fever, malaise, conjunctivitis and cough. Blue-grey spots called Koplik spots appear inside the buccal mucosa but disappear early on
rash appears as a maculopapular rash that starts on the face and spreads down the body
measles complications
include bacterial pneumonia, otitis media, and acute encephalitis
primary HIV infection
also called seroconversion
flu like illness but can be entirely asymptomatic
when antibodies appear in the serum the pt is said to be seroconverted
glandular fever
Glandular fever is a syndrome of fever, sore throat and lymphadenopathy. Most cases are caused by Epstein-Barr virus with a minority being caused by cytomegalovirus. Most people acquire these infections in infancy but there is a second peak in the teenage years
monkey pox
transmission via contact with animal, human, or materials contaminated with the virus which enters through broken skin, resp tract or mucous membranes
The infection is usually self-limiting with fever, malaise, lymphadenopathy, and headache. The incubation period is usually 5-21 days. Treatment is mainly supportive
how are viruses classified
as DNA or RNA viruses
and further on single or double strand
tests to diagnose viral infection
PCR
antigen testing
antibody testing
histology - via end organ damage
viral culture (not routine)
respiratory viruses
adenovirus
respiratory syncytial virus
influenza viruses
coronaviruses
rhinovirus
parainfluenza virus (viral croup)
human metapneumovirus
causes of viral gastroenteritis
norovirus
rotavirus
treatment of viral gastroenteritis
mainstay is hydration - oral rehydration solutions
in severe cases may need IV rehydration
concerns of cellulitis in hands
nerve and blood vessel damage due to swelling and compression in small spaces
first line antibiotic uncomplicated cellulitis
flucloxacillin - staph aureus most common organism
clarithromycin/clinda if allergic
first line antibiotic mammal bites
co amoxiclav
what antibiotics are effective against MRSA
vancomycin and doxycycline
teicoplanin and linezolid
sign of deep soft tissue infection
pain in excess of erythema
investigating tissue infection
FBC
blood cultures
ABG
CK
imaging; xray, USS
screen for blood borne viruses
management necrositing fascitis
surgical debridement
+ ABx and fluids, and analgesia supportive
what micro-organisms can cause skin and soft tissue infections commonly
staph aureus
group A strep (pyogenes)
pseudomonas aeriginosa
what is gas gangrene
rapidly progressive and life-threatening.
Wounds become contaminated with Clostridium spores
Management is similar to necrotising fasciitis with surgical debridement and antibiotics to cover the most likely bacteria.
management of severe septic diarrhoea presentation
IV fluids
oral rehydration salts
IV hydrocortisone to prevent addisonian crisis
intravenous piperacillin / tazobactam with metronidazole to cover for translocation of gut pathogens
tests in severe diarrhoea presentation
FBC, U+E, LFT, CRP, lactate
Blood culture - if septic
Urine culture and analysis
Stool culture and microscopy
ABG if septic
HIV test, CMV if immunocompromised and refer to gastro
what is dysentery
bloody diarrhoea
CMV colitis
caused by reactivation and proliferation of cytomegalovirus
in an immunocompetent host infection does not cause significant clinical signs
Acute symptomatic infection or reactivation of a latent infection can occur in patients who are immunosuppressed, causing a variety of symptoms including pyrexia, dehydration, vomiting and bloody diarrhea
treatment is Ganciclovir
CMV presentations
depend on site of infection
spread by infected secretions
- CMV mononucleosis
- CMV colitis
when should malaria be considered
anyone with a fever/Hx of one returned from an endemic area within the last year
hep C transmission
blood borne virus
IVDU are highest risk
there is no vaccine
hep C natural course
incubation period 2 weeks - 6 months
2/3 asymptomatic in acute phase. if symptomatic usually mild right upper abdominal pain, fever, lethargy, jaundice, joint pain and confusion
ALT can be 10-20x upper limit
chronic infection is common
liver cirrhosis and hepatocellualr carcinoma high risk
hep C diagnosis
anti-HCV antibody is the best initial test, followed by HCV RNA detection in the blood by PCR tests to identify chronic active infection
hep C treatment
interferon and ribavirin have been mainstay
direct antivirals coming in
amoebic liver abscess cause
caused by a parasite transmitted by the faecal oral route
incubation period can vary weeks up to years
amoebic liver abscess diagnosis and treatment
Ultrasound of the liver will usually reveal a single, round hypoechoic lesion
raised ALP and WCC
treatment is metronidazole 7-10 days
Pneumocystis Jirovecii Pneumonia
yeast like fungal pathogen that can cause a pneumonia in those who are immunocompromised
one of the most common opportunistic infection
presents with exertion dyspnoea, dry cough, and malaise
can be first presentation of HIV
test bloods, HIV test, Beta-d glucan, CXR
PJP prophylaxis
can’t prevent exposure
Patients infected with HIV who have a CD4 count <200 cells/mm3 are advised to take PCP prophylaxis. The first line medication is low dose co-trimoxazole 960mg OD
breastfeeding HIV +ve
vaginal birth?
advised against even if undetectable viral load - possible risk of transmission
vaginal birth is fine if viral load undetectable
how many HIV drugs are typically given
3 different drugs in combination
typically two nucleoside reverse transcriptase inhibitors (NRTI) and either a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI)
PPIs and Rilpivirine
PPIs must never be used with this HIV drug as they reduce concentration so make it ineffective
many ARVs can react with other medications and also recreational drugs - always check
Post-Exposure Prophylaxis (PEP)
when an individual has had a exposure at high risk of HIV e.g. sexual behaviour of high risk or a needle stick injury
must be started within 72 hours
Pre Exposure Prophylaxis (PrEP)
can be taken regularly by individuals at high risk of HIV
travel history important questions
- countries visited or transited through
- dates of travel and illness onset
- pre-travel vaccines/malaria proph
- type of travel
- activities whilst abroad
- Viral Haemorrhagic Fever risk assessment
- immune status
hep B transmission and course
blood borne, sex, vertical, close household contact
acute viral hepatitis
can progress to chronic
complications HCC and cirrhosis
vaccine available
hep D
sub viral particle
requires HBV co-infection
HBV vaccine is protective
hep E
faecal oral route
usually mild but can be severe especially risk in pregnant women
chronic infection only in immunocompromised
hep A
faecal oral, blood, sex
acute viral hepatitis with fever, jaundice and hepatomegaly
vaccine available
dengue fever
viral infection transmitted by a mosquito that can progress to viral haemorrhagic fever (severe dengue) where disseminated intravascular coagulation is seen
treatment is entirely symptomatic
typhoid/paratyphoid
caused by salmonella viruses transmitted by faecal oral route
what diseases can E.Coli cause
diarrhoeal illnesses
UTIs
neonatal meningitis
syphilis cause and treatment
syphilis, caused by Treponema pallidum
IM benzathine benzylpenicillin given as a single dose
can cause a Jarisch-Herxheimer reaction within 24 hrs of starting treatment - give antipyretics
gonorrhoea treatment
IM ceftriaxone
Disseminated gonococcal infection
triad = tenosynovitis, migratory polyarthritis, dermatitis
what is malaria
symptoms of malaria
protazoan parasitic infection transmitted by mosquitos
symptoms are of general malaise (fever, headache, N&V, muscle pain) + splenomegaly
Lyme disease
- causative organism
- features of disease
tick-born spirochaetial infection caused by Borrelia burgdorferi
stage 1 - early disease with non-specific systemic symptoms such as fever, arthralgia and malaise, often associated with the typical rash.
stage 2- occurs several weeks later, with possible aseptic meningitis, facial palsy, arthritis and a carditis.
stage 3 - may occur months to years later, with neuropsychiatric manifestations and chronic fatigue (this is rare in children).
The rash is pathognomic of Lyme Disease, and treatment can be given without serological confirmation
treatment Lyme disease
Cefuroxime and amoxicillin
Blood tests are indicated if symptoms persist and there is uncertainty about the diagnosis.
infections to consider with an animal bite
tetanus - make sure vaccinations are up to date
rabies if abroad
gas gangrene
some soft tissue infections can lead to gas gangrene as bacteria produce gas - this is an emergency; surgical debridement and Abx
The commonest two bacteria implicated in skin and soft tissue infections
staph aureus and strep pyogenes(group A strep)
how to determine if a hepatitis C infection is active
HCV antibody just confirms previous exposure to HCV
to work out if active need to send blood for Hepatitis C RNA PCR
any detectable level indicates active infection
what defines a late HIV diagnosis
defined as a CD4 count <350 cells/mm3 within 3 months of diagnosis; likely to have had it for >3 years and high risk of transmission
HIV test counselling
need to explain whether screen due to the patient living in a high prevalence area but without any particular suspicion of HIV or if HIV is suspected due to an indicator disease or high-risk life style
Lengthy pre-test HIV counselling is not a requirement in either case, unless a patient requests or needs this. The essential elements that the pre-test discussion should cover are:
- The benefits of testing to the individual
- Details of how the result will be given
another way in areas on high prevalence is information about routine HIV testing at the department is provided using posters and leaflets and this is emphasised by stating the same verbally
Notional consent is used in opt-out HIV testing in which tests are routinely offered to all patients, with the offer to decline
