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Infectious Diseases Flashcards

1
Q

Most common cause of Otitis Externa

A

Pseudomonas aeruginosa

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2
Q

What is Antigenic Shift (and which virus does it occur in?)

A

Reassortment of viral genome from two different strains of Influenza B, leading to an abrupt change in structure/familiarity to immune system

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3
Q

What is antigenic drift?

A

Continuous mutations of haemagglutinin proteins, prevents formation of long lasting immune response to Influenza as specific IgA antibodies formed won’t continue to work

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4
Q

When is Oseltamivir most useful?

A

Only works in first 12 hours post infection, as well as in prophylactic role.

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5
Q

What organism is associated with UTI following bladder instrumentation?

A

Staphylococcus aureus

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6
Q

What’s the most sensitive test of osteomyelitis in diabetic foot infections?

A

Positive probe-to-bone test

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7
Q

Which antibiotics are best at penetrating biofilms?

A

Quinolones (Ciprofloxacin, norfloxacin, moxifloxacin)
Rifampicin
Linezolid

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8
Q

What beta lactams have high oral bioavailability?

A

Amoxicillin and Cephalexin

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9
Q

What organisms become more likely in an early acute PJI?

A

More likely to include gram negatives such as E coli and enterococci

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10
Q

Which Malaria species can develop dormant liver stage?

A

Vivax (2 years) and Ovale (4 years)

Asymptomatic interval in brackets

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11
Q

Gold standard investigation for Malaria

A

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

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12
Q

Malaria antigen testing

A

Faster
Less sensitive
Doesn’t determine density
Can stay positive post treatment
Can have false negatives due to gene mutations

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13
Q

Most virulent Malaria species

A

Plasmodium falciparum

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14
Q

Dominant malaria species outside sub Saharan Africa

A

Plasmodium vivax

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15
Q

Markers of severe Malaria

A

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

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16
Q

Antifungal for Moulds

A

Voriconazole

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17
Q

Septate dichotomous hyphae

A

Aspergillus
Treat with Voriconazole

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18
Q

What are the two key yeast infections, and what antimicrobial is indicated?

A

Cryptococcus and Candida
Fluconazole

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19
Q

Treatment for severe Malaria

A

Artesunate

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20
Q

Dengue Fever

A

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)

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21
Q

What impact does serotype have on recurrent Dengue Fever infection?

A

Same serotype = protective
Different serotype = increased risk of severe disease

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22
Q

Abrupt onset illness with non productive cough, coryza, conjunctival suffusion, fevers, delayed development of rash starting on face and spreading to body

A

Measles

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23
Q

Dengue Fever Incubation

A

7 days, rarely >14

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24
Q

Measles incubation period

A

10-14 days

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25
Yellow Fever Vaccination
Single dose required for lifelong protection 90% of individuals protected within 10 days, nearly 100% within 3-4 weeks
26
Febrile illness with black eschar after return from rural SE Asia/Northern Australia
Scrub typhus
27
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
28
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
29
A returning traveller from a safari trip to Zambia. Fever, HA, photophobia, altered mental status. Blood smear
African trypanosomiasis
30
Indian gnetleman from India with thickening of skin on face
Leprosy
31
Meningoencephalitis after swimming in a fresh and warm water source
Primary amoebic meningoencephalitis (Naegleria fowleri)
32
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
33
MSM (men having sex with men) presents with liver abscess following trip to Southeast Asia
Amoebic Liver abscess (entamoeba hystolytica)
34
Fever, headache, agitation, confusion, following a dog bite in Indonesia
Rabies
35
Immigrant from Caribbean, wheezing and cough, deteriorates after treated with prednisone
Strongyloidiasis (Strongyloides hyperinfection)
36
White water rafting in Hawaii, fever, headaches, conjunctival suffusion, thrombocytopaenia, raised LFTs
Leptospirosis
37
Mechanism of MRSA
Altered penicillin binding protein 2a (PBP2a), often due to genetic change of mecA gene
38
Clavulanic Acid and MRSA
Beta lactamase inhibitors such as clavulanic acid do not overcome MRSA's mechanism of resistance as it is not enzymatic
39
Mechanism of penicillin resistance
Beta lactamase enzyme hydrolyses penicillin
40
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
41
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
42
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
43
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
44
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
45
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
46
Macrolide and Penicillin use in resistant Pneumococcal Infection
Higher doses of penicillin can overcome resistance Higher dose of Macrolides don't overcome resistance
47
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
48
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
49
What antibiotic resistance do ESCHAPPM Organisms have?
AmpC Beta-Lactamase
50
Which key Cephalosporin is active against AmpC?
Cefepime
51
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
52
What mechanisms of antibiotic resistance develop during treatment?
Inducible cephalosporinase Selection of derepressed mutant via the antibiotic therapy
53
Which HIV patients should receive ART?
All patients
54
Normal CD4 count
>500
55
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
56
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
57
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
58
Tenofovir Disoproxil Fumarate - drug type/mechanism/indication - Key side effect
NRTI Causes Fanconi Syndrome
59
In addition to HIV, what else does Tenofovir treat?
HBV
60
Naming conventions of HIV drugs
NRTIs: variable NNRTIs: -virine or -verine Proteinase Inhibitors: - navir Integrase Inhibitors: -gravir
61
Starting Regimens for HIV treatment
Integrase Inhibitor + 2x NRTI Or can go single NRTI if no resistance and no HBV
62
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
63
Why doses PJP cause Tension Pneumothorax?
Cyst formation → pneumothorax
64
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
65
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
66
Treatment of Cryptococcus Meningitis
Amphotericin plus Flucytosine initially then followed by high dose Fluconazole. Total therapy 1 year. Superior to fluconazole or amphotericin monotherapy
67
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
68
What form of disease does MAC cause in HIV?
Disseminated disease and focal lymphadenitis

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