Infection Flashcards
1
Q
What is MRSA? What abx are used to treat it?
A
- Staph aureus bacteria that have become resistant to beta-lactam abx
- Doxycycline, vancomycin, clindamycin, teicoplanin, linezolid
2
Q
What causes TB? Shape? Gram staining?
A
- Mycobacterium tuberculosis
- Rod shaped
- Zeihl-Neelsen stain (bright red against blue background)
3
Q
What is MDR-TB?
A
- Multidrug-resistant TB
- Strains resistant to more than one TB drug
4
Q
How is TB spread? What are possible outcomes of infection?
A
- Saliva droplets
- Immediate clearance
- Primary active TB
- Latent TB
- Secondary TB
5
Q
What normally causes reactivation of latent TB? What is this then called?
A
- Immunosuppression
- Secondary TB
6
Q
What is a cold abscess? How does it present?
A
- Abscess caused by TB
- Firm, painless abscess in the neck
7
Q
What is the BCG vaccine?
A
Live attenuated Mycobacterium bovis bacteria (close relative of M tuberculosis)
8
Q
What tests are used to detect an immune response to TB?
A
- Mantoux test
- Interferon-gamma release assay
9
Q
What is check before someone is given a BCG vaccine?
A
- Mantoux test
- HIV status
- Possibility of immunosuppression
10
Q
What investigations are useful where active TB infection is suspected?
A
- CXR
- Cultures
11
Q
What is involved in the Matoux Test? What is a positive result? What does this indicate?
A
- Tuberculin (a collection of tuberculosis proteins isolated from the bacteria) is injected into the intradermal space on the forearm. This creates a bleb under the skin which is measured 72 hrs later
- An induration of 5mm or more
- Immune response to TB caused by active, latent or previous TB infection
12
Q
What is involved in the Interferon-Gamma Release Assays? What is a positive result? Why does this occur?
A
- Mixing a blood sample with antigens from the M. tuberculosis bacteria
- When interfon-gamma is released
- After previous contact with M. tuberculosis, white blood cells becomes sensitised to the bacteria antigens are will release interferon-gamma on further contact
13
Q
What indicated primary TB on CXR
?
A
- Patchy consolidation
- Pleural effusions
- Hilar lymphadenopathy
14
Q
What indicated reactivated TB on CXR?
A
- Patchy/nodular consolidation
- Cavitation (gas filled spaces) typically in the upper zones
15
Q
What indicates disseminated miliary TB on CXR?
A
- ‘Millet seeds’ (small 1-3mm nodules) disseminated throughout the lung fields
16
Q
Why are culture samples required in TB? When are the collected? How long do the results take to come back?
A
- Cultures are used for testing drug resistance
- Ideally collected before starting treatment
- Can take several months - tx is normal started while waiting for culture results
17
Q
What is the treatment of active TB?
A
- Rifampicin (6 months)
- Isoniazid (6 months)
- Pyrazinamide (2 months)
- Ethambutol (2 months)
18
Q
What is the treatment of latent TB?
A
Either:
- Rifampicin and Isoniazid for 3 months
- Isoniazid for 6 months
19
Q
What can rifampicin cause? What drugs can it interact with?
A
Red/orange discolouration of secretions (‘red-an-orange-pissin’’)
Contraceptive pills
20
Q
What can isoniazid cause?
A
Peripheral neuropathy (‘I’m-so-numb-azid’)
21
Q
What can pyrazinamide cause?
A
Hyperuricaemia resulting in gout
22
Q
What can ethambutol cause?
A
Colour blindness and reduced visual acuity (‘eye-thambutol’)
23
Q
What type of virus is HIV?
A
RNA retrovirus
24
Q
What are the two types of HIV? Which is more common?
A
- HIV-1 (more common)
- HIV-2
25
What is AIDS? When does it occur?
Acquired immunodeficiency syndrome
- Occurs when HIV is not treated -> disease progression -> person becomes immunocompromised
- This leads to opportunistic infections and AIDS-defining illnesses
26
What is the basic pathophysiology of HIV?
- The virus enters and destroys CD4 T-helper cells
- This causes progressive immunocompromise resulting in a number of AIDS defining conditions
27
What are examples of AIDS-defining illnesses?
- Kaposi's sarcoma
- Pneumocystitis jirovecii pneumonia
- CMV infection
- Candidiasis (oesophageal/bronchial)
- Lymphomas
- TB
28
What are the stages of HIV infection?
1. Acute seroconversion: 2-6 wks following infection, 50% develop flu like symptoms (sore throat, fever, malaise, maculopapular rash, lymphadenopathy)
2. Asymptomatic: can last 8-10 years, may have generalised lymphadenopathy
3. Symptomatic: as the immune system fails and the virus mutates, the pt becomes more susceptible to common pathogens (colds/gastroenteritis), constitutional symptoms inc. wt loss/fatigue
4. AIDS - diagnosis with an AIDS defining illness
29
How can HIV be transmitted?
Blood borne;
- Mother to child
- Sexual intercourse
- IVDU
- Needle stick injuries
- Blood products
30
What is an example of vertical HIV transmission?
Mother to child at any stage of pregnancy, birth or breastfeeding
31
What screening tests are used for HIV?
- Fourth-generation laboratory test
- Point of care test
32
What does the fourth generation laboratory test involve? When is a negative test unreliable?
- Tests for antibodies to HIV and the p24 antigen
- A negative result within 45 days of exposure is unreliable
- This is because it had a window period of 45 days
33
What is involved in the point-of-care test for HIV? Any window period?
- Test for HIV antibodies
- Gives a result within minutes
- 90 day window period
34
Who has a bigger willy, Maddie or Emma
Maddie
35
What tests are used to monitor and plan treatment in HIV?
- CD4 count
- Viral load
36
What is the CD4 count used to assess?
Risk of opportunistic infection
37
What is the normal CD4 count? What would indicate patients are at high risk of opportunistic infections?
- 500-1200 cells/mm3
- Under 200 cells/mm3
38
What is measured to determine the viral load in HIV? What level indicates an undetectable viral load?
- HIV RNA per ml of blood
- <20 copies/ml
39
What is the aim of HIV treatment?
To achieve and normal CD4 count and an undetectable viral load
40
What is the treatment of HIV?
A combination of antiretroviral therapy (ART) medications
41
What are the classes of ART medications?
- Protease inhibitors (PI)
- Integrase inhibitors (II)
- Nucleoside reverse transcriptase inhibitors (NRTI)
- Non-nucleoside reverse transcriptase inhibitors (NNRTI)
- Entry inhibitors (EI)
42
What is the usual starting regime in HIV management?
Two NRTIs (e.g. tenofovir plue emtricitabine) PLUS a tri agent (e.g. bictegravir)
43
What are all HIV positive patients with a CD4 count <200/mm3 treated with?
Prophylactic co-trimoxazole to protect against pneumocystis jirovecii pneumonia
44
What are the recommendations surrounding cervical smears for HIV positive people?
Yearly cervical smears due to increased risk of HPV and cervical cancer
45
What are the recommendations surrounding vaccinations for HIV positive people?
- Ensure vaccinations are up to date
- Yearly influenza vaccine
- Avoid live vaccines e.e. BCG and typoid
46
What viral load would indicate VD vs CS in HIV positive pregnant women?
- <50 copies/ml = normal VD
- >50 copies/ml = consider CS
- >400 copies/ml - recommend CS
47
What is the management of HIV positive women in labour with a viral load >1000 copies/ml?
- CS
- IV zidovudine during labour and delivery
48
What indicates a newborn is low-risk of HIV? What is given as HIV prophylaxis to low-risk vs his-risk babies?
- Low-risk if the mother's viral load is <50 copies/ml
- Low-risk prophylaxis = zidovudine for 2-4 weeks
- High-risk prophylaxis = zidovudine, lamivudine and nevirapine for 4 weeks
49
Is breast feeding recommended in HIV positive mothers?
- No
- HIV can be transmitted during breastfeeding
50
What is PEP? What does it consist of? When should it be taken? How long for?
- Post exposure prophylaxis
- A combination of ART
- PEP should be commenced within a short window of opportunity (<72 hrs)
- Current regime is for 28 days
51
What is PrEP?
- Pre-exposure prophylaxis
52
Kapsoi's sarcoma:
1. What is it caused by?
2. How does it present?
3. What is the management?
1. HHV-8
2. Purple papules/plaques on the skin or mucosa (GI/resp tract). Lesions may ulcerate. Resp involvement can lead to pleural effusion and massive haemoptysis
3. Radiotherapy + resection
53
Is HIV a notifiable disease?
No
54
What causes malaria? Which is the most severe subtype?
Malaria is caused by members of the Plasmodium family of protozoan parasites
- Plasmodium falciparum (most severe)
- Plasmodium vivax
- Plasmodium ovale
- Plasmodium malariae
- Plasmodium knowlesi
55
What is malaria spread by?
Female Anopheles mosquito
56
What is the life cycle of malaria?
- Feeding mosquito sucks up parasites
- Parasite reproduce in mosquito producing sporozoites
- These are injected into human when bitten by mosquito
- Sporozoites travel to the liver where they lie dormant as hypnozoites (this can be for 4 yrs if P. ovale / P. vivax)
- In the liver the parasites mature into merozoites which infect red blood cells -> reproduce -> rupture -> merozoites released into blood -> haemolytic anaemia
- The rupture and release of merozoites is responsible for fever spikes
57
What are the patterns of fever spikes for different malaria causing parasites?
- Every 48 hrs = P. vivax, P. ovale (tertian malaria)
- More frequent, irregular fever spikes = P. falciparum (subtertian)
- Every 72 hrs = P. malariae (quartan)
58
What is the typical incubation period for malaria?
1-4 weeks
59
Give some symptoms and signs of malaria
Symptoms:
- Fever (up to 41)
- Fatigue
- Myalgia
- Headache
- N+V
Signs:
- Pallor (due to anaemia)
- Hepatosplenomegaly
- Jaundice (rupture of RBC -> bilirubin release)
60
How is malaria diagnosed?
- Malaria blood film
- Will show the parasites, the concentration (as percentage) and the type
61
What is required to exclude a diagnosis of malaria?
- Three negative samples taken over three consecutive days
- This is because the parasites are released into the blood every 48-72 hrs meaning they may be missed
62
When should patients with malaria be admitted?
- Any patients with P. falciparum malaria
- Severe/complicated malaria
63
What is the first line oral and first and second line IV treatment for malaria?
Oral:
- Artemether with lumefantrine
IV:
- Artesunate (first)
- Quinine dihydrochloride
64
What is a side effect of IV artesunate for malaria?
Haemolysis
65
What are possible complications of P. falciparum malaria?
- Cerebral malaria
- Seizures
- Reduced consciousness
- AKI
- Pulmonary oedema
- DIC
- Severe haemolytic anaemia
- Multi-organ failure and death
66
What are the most common medications used for malaria prophylaxis? Include potential side effects
- Proguanil with atovaquone (Malarone)
- Doxycycline (diarrhoea/thrush/photosensitivity)
- Mefloquine (anxiety/depression/abnormal dreams)
67
What are protective factors against malaria?
- Sickle cell trait
- GP6D deficiency
- HLA-B53
- Absence of Duffy antigens
68
What is clostridium difficile?
A gram positive, rod-shaped, anaerobic bacteria
69
What are the main causes of C. diff?
- Antibiotics
- Clindamycin
- Ciprofloxacine
- Cephalosporins
- Carbapenems
- PPIs
70
C. diff produces toxins which cause symptoms and complications. What are the main two?
- Toxin A (enterotoxin)
- Toxin B (cytotoxin)
71
How do you test for C. diff?
Stool sample:
- C. diff antigen (screening test)
- A and B toxins (diagnostic)
72
What is the first and second line management of C. diff?
1. Oral vancomycin
2. Oral fidaxomicin
73
What are complications of C. diff?
- Pseudomembranous colitis
- Toxic megacolon
- Bowel perforation
- Sepsis
74
What are ddx for intra-abdominal infections?
- Acute diverticulitis
- Acute cholecystitis
- Ascending cholangitis
- Appendicitis
- SBP
- Intra-abdominal abscess
75
Intra-abdominal infections are caused by a range of different bacteria. They require broad-spectrum abx whilst awaiting culture results. 2/3 broad spec abx are often used to cover for gram +ve, gram -ve, anaerobic and atypical bacteria. What abx covers for all three of these apart from atypical bacteria?
Co-amoxiclav
76
What is cellulitis?
An infection of the skin and the soft tissues underneath
77
What feature of cellulitis indicates a staph aureus infection?
Golden yellow crust
78
What are the most common causes of cellulitis?
- Staph aureus
- Group A strep
- Group C strep (strep dysgalactiae)
79
What classification system can be used to assess the severity of cellulitis?
Eron classification
- Class 1-4
- Class 4 = sepsis or life threatening infection
80
Which cellulitis pts require admission for IV abx?
- Class 3/4 cellulitis
- Frail
- V young
- Immunocompromised
- Facial, periorbital or orbital cellulitis
81
What is the first line abx for cellulitis? What is favoured for cellulitis near the eyes of nose?
- Flucloxacillin
- Co-amoxiclav
82
What is the pathophysiology of sepsis?
- Macrophages, lymphocytes and mast cells recognise pathogens -> release cytokines (interleukins/TNF) -> activate immune system -> systemic inflammation
- Cytokines -> endothelial lining of blood vessels -> more permeable -> fluid leaks out into extracellular space -> oedema and reduced intravascular volume -> decreased oxygen supply to tissues -> anaerobic respiration -> serum lactate rises + metabolic acidosis occurs
- Activation of the coagulation system -> formation of blood clots throughout the body -> platelets and clotting factors used up -> thrombocytopenia + haemorrhage = DIC
83
What happens in septic shock?
The arterial blood pressure drops despite adequate fluid resuscitation -> organ hypo perfusion
84
How is septic shock diagnosed?
- Low mean arterial pressure despite fluid resuscitation (<65mmHg)
- Raised serum lactate (>2mmol/L)
85
What is the management of septic shock?
- Aggressive treatment with IV fluids
- Escalate to HDU/ICU for treatment with vasopressors (e.g. noradrenaline) to increase systemic vascular resistance and MAP
86
What is the sepsis 6?
3 test:
- Serum lactate
- Blood cultures
- Urine output
3 treatments:
- Oxygen
- Broad spec abx
- IV fluids
87
What is neutropenic sepsis?
Sepsis in someone with a neutrophil count below 1x10^9/L
88
What medications can cause neutropenia?
- Chemotherapy
- Clozapine
- DMARDs
- Biologics
89
What is treated as neutropenic sepsis until proven otherwise?
Temp >38 in pts on chemo or meds that may cause neutropenia
90
What is the treatment of neutropenic sepsis?
- Broad spec abx e.g. Piperacillin with tazobactam (tazocin is name for both together)
- Refer to local guidelines
91
What is infectious mononucleosis? What is it aka?
- Condition caused by infection with EBV
- Glandular fever
92
What are the features of infectious mononucleosis?
- Fever
- Sore throat
- Fatigue
- Lymphadenopathy
- Tonsillar enlargement
- Splenomegaly
93
What antibiotics cause an itchy maculopapular rash in patients with infectious mononucleosis?
- Amoxicillin
- Cefalosporins
94
How can you investigate IM?
1. Test for heterophile antibodies:
- Monospot test
- Paul-Bunnell test
- These tests are not 100% sensitive as not everyone with IM produces heterophile antibodies
2. Test for EBV antibodies:
- IgM rises early suggesting acute infection
- IgG persists after the condition suggesting immunity
95
What is the management of IM?
- Self limiting - acute illness lasts 2-3 weeks
- Avoid alcohol - EBV affects livers ability to process alcohol
- Avoid contact sports - risk of splenic rupture
96
How does scabies present?
- Itchy small red spots
- Track marks where the mites have burrowed
- The classic location is between the finger webs
- Can take up to 8 weeks for symptoms to appear after the initial infection
97
What is the management of scabies?
- Permethrin cream - apply to whole body and leave on for 8-12 hours, repeat a week later to kill the eggs that survived
- Oral ivermectin as a single dose can be repeated a week later for difficult to treat/crusted scabies
- Wash all clothes etc on a hot wash to destroy mites, hoover carpets and furniture
- Note itching can continue for 4 weeks after successful treatment
98
What is crusted scabies?
- A serious infestation with scabies in patients that are immunocompromised
- Rather than individual spots they have patches of red skin that turn into scaly plaques (misdiagnosed as psoriasis)
- Immunocompromised patients may not have an itch as they do not mount an immune response to infestation
- Tx = oral ivermectin
99
What causes Lyme disease?
The spirochaete Borrelia burgdorferi which is spread by ticks
100
What are early features of Lyme disease? (within 30 days)
- Erythema migrant (build eye rash at the site of tick bite)
- Systemic features - headache, lethargy, fever, arthralgia
101
What are late features of Lyme disease? (after 30 days)
- Cardiovascular - heart block, peri/myocarditis
- Neurological - facial nerve palsy, radicular pain, meningitis
102
What is the first line test for Lyme disease?
- Enzyme-linked immunosorbent assay (ELISA) antibodies to Borrelial burgdoferi
- If -ve test and within first 4 weeks of symptoms onset, retest in 4-6 weeks
103
When can you commence abx for Lyme disease without antibody testing?
If erythema migrans is present
104
What is the management of Lyme disease?
- Doxycycline if early disease
- Ceftriaxone if disseminated disease
105
What reaction can be seen after commencing abx therapy for Lyme disease?
- Jarisch-Herxheimer reaction
- Fever, rash, tachycardia after first dose of abx
106
What is toxic shock syndrome?
- A severe systemic reaction to bacterial toxins
- Toxins are produced by staph aureus or Group A strep
107
What can cause toxic shock syndrome?
- Tampons
- Soft tissue infections
- Post-surgical infections
- Burns
- Retained foreign objects e.g. nasal packing, dialysis catheters
108
What is the diagnostic criteria for toxic shock syndrome?
- Fever - temp >38.9
- Hypotension - systolic <90
- Diffuse erythematous rash
- Desquamation of rash - especially palms and soles
- Involvement of 3 or more organ systems - e.g. CNS involvement (confusion), mucous membrane erythema, D+V, hepatitis, renal failure, thrombocytopenia
109
What is the management of toxic shock syndrome?
- Removal of infection focus
- IV fluids
- IV antibiotics
110
How can necrotising fasciitis be classified?
- Type 1 - caused by mixed anaerobes and aerobes (often post-surgery in diabetics) (more common)
- Type 2 - caused by strep pyogenes
111
What are RF for necrotising fasciitis?
- Skin factors - recent trauma, burns, soft tissue infections
- DM - particularly if treated with SGLT-2 inhibitors
- IVDU
- Immunosuppression
112
What is the most commonly affected site in necrotising fasciitis?
Perineum
113
How does necrotising fasciitis present?
- Acute onset
- Pain, swelling, erythema of affected site
- Skin necrosis is a late sign
- Fever and tachycardia may occur late in the presentation
114
What is the management of necrotising fasciitis?
- Urgent surgical referral for debridement
- IV abx
115
What is the prognosis of necrotising fasciitis?
Average mortality = 20%
116
