Infectious Diseases Flashcards
Most common cause of Otitis Externa
Pseudomonas aeruginosa
What is Antigenic Shift (and which virus does it occur in?)
Reassortment of viral genome from two different strains of Influenza B, leading to an abrupt change in structure/familiarity to immune system
What is antigenic drift?
Continuous mutations of haemagglutinin proteins, prevents formation of long lasting immune response to Influenza as specific IgA antibodies formed won’t continue to work
When is Oseltamivir most useful?
Only works in first 12 hours post infection, as well as in prophylactic role.
What organism is associated with UTI following bladder instrumentation?
Staphylococcus aureus
What’s the most sensitive test of osteomyelitis in diabetic foot infections?
Positive probe-to-bone test
Which antibiotics are best at penetrating biofilms?
Quinolones (Ciprofloxacin, norfloxacin, moxifloxacin)
Rifampicin
Linezolid
What beta lactams have high oral bioavailability?
Amoxicillin and Cephalexin
What organisms become more likely in an early acute PJI?
More likely to include gram negatives such as E coli and enterococci
Which Malaria species can develop dormant liver stage?
Vivax (2 years) and Ovale (4 years)
Asymptomatic interval in brackets
Gold standard investigation for Malaria
Thick and thin films
Thick film: high sensitivity
Thin film: higher specificity, can determine species and density
Schuffner granules, crescent shaped granules
If negative, repeat 12-24hrly for 3 tests
Malaria antigen testing
Faster
Less sensitive
Doesn’t determine density
Can stay positive post treatment
Can have false negatives due to gene mutations
Most virulent Malaria species
Plasmodium falciparum
Dominant malaria species outside sub Saharan Africa
Plasmodium vivax
Markers of severe Malaria
High parasitaemia- >2%
Anaemia: Hb <50, Hct <0.20 with parasite count >10,000
Jaundice
Seizures
Kidney Injury
Shock
Impaired consciousness
Prostration
Hypoglycaemia <2.2mmol/L
Antifungal for Moulds
Voriconazole
Septate dichotomous hyphae
Aspergillus
Treat with Voriconazole
What are the two key yeast infections, and what antimicrobial is indicated?
Cryptococcus and Candida
Fluconazole
Treatment for severe Malaria
Artesunate
Dengue Fever
Fevers, myalgia, retro-orbital pain, malaise, thrombocytopaenia, macular rash
Mosquito transmitted flavivirus: aedes aegypti, A. albopictus, A polynesiensis
Most common arbovirus infection in humans, transmitted in urban environments during the day (unlike Malaria)
What impact does serotype have on recurrent Dengue Fever infection?
Same serotype = protective
Different serotype = increased risk of severe disease
Abrupt onset illness with non productive cough, coryza, conjunctival suffusion, fevers, delayed development of rash starting on face and spreading to body
Measles
Dengue Fever Incubation
7 days, rarely >14
Measles incubation period
10-14 days
Yellow Fever Vaccination
Single dose required for lifelong protection
90% of individuals protected within 10 days, nearly 100% within 3-4 weeks
Febrile illness with black eschar after return from rural SE Asia/Northern Australia
Scrub typhus
Scrub typhus
Mite borne disease from rural areas of southeast or east Asia and northern Australia
Gram -ve coccobacillus
Symptoms within 10 days: fever, headaches, myalgia, mental status change, lymphadenopathy, pneumonia
Non pruritic macular or maculopapular rash with characteristic eschar
Treat with Doxycycline, often fever will resolve dramatically after a single dose
Lyme Disease
Tick borne illness caused by Borreliella species in America, Europe and Asia
Erythema migrans is classic rash and occurs within 1-2 weeks at site of bite
Neuroborreliosis: Lymphocytic meningitis, cranial nerve palsies, encephalomyelitis
Carditis: AV block +/- myopericarditis
Ceftriaxone, Cefotaxime, penicillins for CNS disease
Doxy for isolated facial nerve palsy
A returning traveller from a safari trip to Zambia. Fever, HA, photophobia, altered mental status. Blood smear
African trypanosomiasis
Indian gnetleman from India with thickening of skin on face
Leprosy
Meningoencephalitis after swimming in a fresh and warm water source
Primary amoebic meningoencephalitis (Naegleria fowleri)
Vomiting, diarrhoea, peri-oral paresthesias, metallic taste, blurred vision, temperature-related dysesthesias (cold stimuli perceived as hot) after eating coral fish in Fiji
Ciguatera fish poisoning
MSM (men having sex with men) presents with liver abscess following trip to Southeast Asia
Amoebic Liver abscess (entamoeba hystolytica)
Fever, headache, agitation, confusion, following a dog bite in Indonesia
Rabies
Immigrant from Caribbean, wheezing and cough, deteriorates after treated with prednisone
Strongyloidiasis (Strongyloides hyperinfection)
White water rafting in Hawaii, fever, headaches, conjunctival suffusion, thrombocytopaenia, raised LFTs
Leptospirosis
Mechanism of MRSA
Altered penicillin binding protein 2a (PBP2a), often due to genetic change of mecA gene
Clavulanic Acid and MRSA
Beta lactamase inhibitors such as clavulanic acid do not overcome MRSA’s mechanism of resistance as it is not enzymatic
Mechanism of penicillin resistance
Beta lactamase enzyme hydrolyses penicillin
Linezolid
Bacteriostatic antibiotic
Inhibits bacterial protein synthesis by binding to both 30S and 50S ribosomal subunits
Can suppess toxin production
Broad spectrum against gram positives
Reversible bone marrow suppression, irreversible neuropathy
Serotonin syndrome
100% bioavailability, good bone, lung, CNS penetration
Daptomycin
Cyclic lipopeptide
Bactericidal
Depolarises bacterial cell membranes
Inactivated by surfactant -> doesn’t work for respiratory tract infection
SEs: Myopathy, eosinophilic pneumonia, peripheral neuropathy
CK monitoring required
Loading and renal dose adjustment necessary
Tigecycline
Bacteriostatic
Eliminated via biliary tract -> not effective for UTI
Covers gram positives and negatives, including MRSA, VRE, ESML, AmpC, anaerobes, atypicals
Doesn’t work against Pseudomonas
Not good for bacteraemia due to high volume of distribution
Doesn’t get into CNS well
Mechanism of Vancomycin Resistance
Change in protein structure in bacterial cell walls from
D-Ala D-Ala to D-Ala D-Lac
Vancomycin then can’t bind and inhibit bacterial wall synthesis
Teicoplanin versus Vancomycin
Both glycopeptides
Similar efficacy
Teicoplanin can be given IM and has long half life so daily dosing
Teicoplainin fewer side effects
But expensive
Mechanism of Pneumococcal Penicillin resistance
Similar to MRSA - due to changes in penicillin binding proteins
Thus beta lactamase inhibitors such as Clavulanic acid don’t work
However can be overcome if penicillin concentration at site of infection is higher than MIC of organism for 40-50% of dose interval
Respiratory infections can often still be treated with penicillins, but harder to treat CNS infections as resistance occurs at a lower MIC
Macrolide and Penicillin use in resistant Pneumococcal Infection
Higher doses of penicillin can overcome resistance
Higher dose of Macrolides don’t overcome resistance
Most common mechanism of beta lactam resistance in Gram Negative bacteria
Beta lactamases are the most common mechanism of resistance.
ESBL, AmpC, KPC, etc. all beta lactamase driven
ESCHAPPM Organisms
Enterobacter
Serratia marcescens
Citrobacter freundii
Hafnia alvei
Acinetobacter and Aeromonas
Proteus vulgaris
Providencia
Morganella morganii
First three most important. For Proteus and Citrobacter it is species specific, so other Citrobacters and Proteus organisms don’t have same resistance
What antibiotic resistance do ESCHAPPM Organisms have?
AmpC Beta-Lactamase
Which key Cephalosporin is active against AmpC?
Cefepime
What antibiotics should be used for ESCHAPPM Organisms?
Carbapenems are empiric antibiotic of choice
Cefepime suitable
Quinolones, Bactrim and aminoglycosides can be appropriate once sensitivities done
What mechanisms of antibiotic resistance develop during treatment?
Inducible cephalosporinase
Selection of derepressed mutant via the antibiotic therapy
Which HIV patients should receive ART?
All patients
Normal CD4 count
> 500
How does HIV infect humans?
HIV glycoprotein120 binds to CD4 receptors on immune cells as well as to co receptor CCR5 or CXCR4. Then Glycoprotein 41 attaches to cell membrane and fuses to enter cells. HIV then has a reverse transcriptase enzyme which turns HIV RNA into DNA to be integrated in host cell chromosome
Testing for HIV
Antigen and antibodies should both be tested - 4th generation testing.
Then confirmatory testing if possible.
If combination Ag/Ab testing is negative two weeks post exposure, HIV is essentially excluded
What specific presentations of HIV indicate a need to delay ART?
Cryptococcal meningitis - survival improved if ART commencement delayed 6 weeks, likely due to immune reconstitution syndrome
CNS TB
Tenofovir Disoproxil Fumarate
- drug type/mechanism/indication
- Key side effect
NRTI
Causes Fanconi Syndrome
In addition to HIV, what else does Tenofovir treat?
HBV
Naming conventions of HIV drugs
NRTIs: variable
NNRTIs: -virine or -verine
Proteinase Inhibitors: - navir
Integrase Inhibitors: -gravir
Starting Regimens for HIV treatment
Integrase Inhibitor + 2x NRTI
Or can go single NRTI if no resistance and no HBV
Ritonavir
Protease Inhibitor for HIV
Part of Paxlovid for COVID
Inhibits CYP3A4 → many interactions
Very poorly tolerated
Prolongs half life of the other Protease Inhibitors
Why doses PJP cause Tension Pneumothorax?
Cyst formation → pneumothorax
Steroids and PJP infection
While prolonged steroid use is a risk factor for PJP, also important role in patients with infection. Reduce mortality in hypoxic patients
When should PJP prophylaxis be given?
Medications, Conditions, etc.
HIV patients with CD4 <200
Prolonged steroid use - ≥20mg for more than a few weeks
HIV patients who’ve had PJP and now recovered
Treatment of Cryptococcus Meningitis
Amphotericin plus Flucytosine initially then followed by high dose Fluconazole. Total therapy 1 year.
Superior to fluconazole or amphotericin monotherapy
Most common CNS infection in HIV patients not on treatment or prophylaxis
Toxoplasmosis
Causes enhancing lesions in brain, can treat without biopsy with bactrim
Intracellular protozoan parasite
What form of disease does MAC cause in HIV?
Disseminated disease and focal lymphadenitis
