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MD3001 > RTIs (Pt 2) > Flashcards

RTIs (Pt 2) Flashcards

1
Q

What age groups are most affected by fatal lower respiratory tract infections ?

A
  • Elderly in developed countries

- Children under five in developing countries

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2
Q

Pneumonia:

  • Define
  • Transmission
A

PNEUMONIA

  • Definition: Inflammation of the substance of the lungs
  • Transmission: Access to LRT by inhalation of aerosolised (e.g. sneezing, cough) microbes or by aspiration of normal flora of the URT
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3
Q

What is the most common cause of infection-related death in UK and USA ?

A

Pneumonia

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4
Q

Describe the aetiology of pneumonia depending on age.

A

CHILDREN
• Mainly viral
• Neonates may develop pneumonia caused by Chlamydia trachomatis acquired from mother during birth

ADULTS
• Mainly bacterial
• Aetiology varies with age, underlying disease, occupational and geographic risk factors

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5
Q

Identify the main pathogens in viral pneumonia.

A

Rhinoviruses
Coronaviruses
Influenza virus
Measles virus

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6
Q

Identify the main pathogens in bacterial pneumonia.

A

Streptococcus pneumoniae
Mycobacterium tuberculosis
Haemophilus influenzae
Pseudomonas aeruginosa

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7
Q

Define atypical pneumonia. What organisms can cause atypical pneumonia ?

A

Pneumonia which fails to respond to treatment with penicillin (i.e. “not caused by one of the pathogens most commonly associated with the disease”)

  • Mycoplasma pneumoniae
  • Legionella pneumophilia
  • Chlamydia psittaci
  • Chlamydia pneumoniae
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8
Q

Identify the main anatomical classifications of pneumonia.

A
  • Lobar pneumonia
  • Bronchopneumonia
  • Interstitial pneumonia
  • Necrotising pneumonia
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9
Q

Define lobar pneumonia.

A

Pneumonia involving a distinct region of the lung ie. lobe.

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10
Q

Define bronchopneumonia.

A

Diffuse, patchy consolidation, associated with bronchi and bronchioles.

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11
Q

Define interstitial pneumonia.

A

Invasion of lung interstitium, usually characteristic of viral infection.

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12
Q

Define necrotising pneumonia.

A

Lung abscesses and destruction of parenchyma

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13
Q

Identify the main clinical features of Streptococcus pneumoniae pneumonia.

A

1) Initially:
- Abrupt onset
- Rigors
- Fever
- Malaise
- Tachycardia
- Dry cough

2) Followed by:
- Productive cough with rusty sputum
- Spiky temperature
- Lobular consolidation

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14
Q

Identify the main clinical features of Mycoplasma pneumoniae pneumonia.

A
  • Fever
  • Dry cough
  • Dyspnoea
  • Lymphadenopathy
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15
Q

Identify the main clinical features of Haemophilus influenzae pneumonia.

A
  • Mainly occurs in children
  • Consolidation or patchy bronchopneumonia
  • Persistent purulent sputum and malaise
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16
Q

Identify the main clinical features of Legionella pneumophila pneumonia.

A

=Legionnaire’s disease (form of atypical pneumonia), i.e. severe systemic infection with pneumonia

  • Tachypnoea
  • Purulent sputum
  • Consolidation
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17
Q

Legionella pneumophila:

  • What type of bacteria ?
  • What is its mechanism of action ?
  • How is transmitted ?
  • Special features ?
A
  • Type of bacteria: Gram negative bacillus
  • Mechanism of action: Secretes protease causing lung damage
  • Transmission: transmitted by aerosol, but not person-person
  • Special feature: usually occurs as outbreaks
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18
Q

Describe the laboratory diagnosis of Legionnaire’s Disease.

A

Detection of antigen in urine (4-fold rise in antibody)

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19
Q

What are the main clinical features of Measles ?

A
  • Fever
  • Characteristic rash
  • Runny nose
  • Koplik’s spots
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20
Q

What are possible complications of measles ?

A

→ Neurological complications

→ “Giant cell” (Hecht’s) pneumonia in the immunocompromised – usually fatal

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21
Q

Do people usually die from measles ?

A

In developing countries, yes.

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22
Q

MEASLES virus:

  • Class of virus
  • Transmission
  • Where does it replicate ?
  • Incubation period
  • Is infection localised or sytemic ?
A
  • Class of virus: Paramyxovirus
  • Transmission: via aerosol
  • Where it replicates: Replicates in LRT
  • Incubation period: 10-14 days
  • Multisystem infection
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23
Q

Describe diagnosis of measles.

A
  • Clinical mainly
  • Serology for measles-specific IgM (easiest way)
  • Virus isolation
  • Viral RNA detection
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24
Q

Describe treatment and prevention of measles.

A

TREATMENT
♣ If severe, ribavarin treatment available
♣ Antibiotics for secondary bacterial infection

PREVENTION
♣ Immunisation with highly effective, live, attenuated MMR vaccine

25
Q

List the main risk factors for pneumonia. Identify the pathogen associated with each risk factor.

A
  • Travel, air conditioning (L. pneumophila)
  • CF (Pseudomonas)
  • Bird contact (C. psitacci)
  • Immigration (M. tuberculosis)
  • Farming (sheep) (Coxiella burnetti)
  • Recent influenza (S. pneumoniae, St. aureus)
26
Q

What are the main symptoms, and signs of pneumonia ?

A

SYMPTOMS

  • Weakness and malaise
  • Breathlessness
  • Cough
  • Purulent sputum
  • Chest pain (sharp, due to pleural inflammation)

SIGNS

  • Raised temperature
  • Purulent sputum
  • Tachypnoea
  • Signs of lung consolidation
  • Cyanosis
  • Shock
27
Q

How is pneumonia diagnosed ?

A
  • Primarily by history and examination
  • Radiology can help figure out specific anatomical classification of the pneumonia + rule out other conditions which can mimic pneumonia
  • Sputum can also be taken (but retrospective, because it takes 48 hours)
28
Q

Define and explain how to calculate a CURB score.

A

Estimation of mortality of community-acquired pneumonia to help determine inpatient vs. outpatient treatment:

1 point for each feature present:
• Confusion of new onset (defined as an AMTS of 8 or less)
• Blood Urea nitrogen greater than 7 mmol/l (19 mg/dL)
• Respiratory rate of 30 breaths per minute or greater
• Blood pressure less than 90 mmHg systolic or diastolic blood pressure 60 mmHg or less
• Age 65 or older

  • If 0 to 1 points, low severity, low mortality, home treatment (1 drug)
  • If 0 to 1 points, low severity, low mortality but hospital treatment due to reasons other than pneumonia (e.g. social reasons or comorbidity) (1 drug)
  • If 2 points, moderate severity, moderate mortality, hospital treatment (2 drugs)
  • If 3-5 points, high severity, high mortality, hospital treatment (and possibly critical care)
29
Q

Distinguish between endemic, epidemic and pandemic disease. Giving an example of disease which causes all three.

A
  • Endemic: Present in a community at all times; at a relatively low to medium frequency but at a steady-state
  • Epidemic: Sudden severe outbreak within a region or a group
  • Pandemic: Occurs when an epidemic becomes widespread and affects a whole region, a continent, or the entire world.

Influenza causes endemic, epidemic and pandemic disease.

30
Q

INFLUENZA VIRUS

  • Class of virus
  • Types
  • Structure
A

-Class of virus: Orthomyxovirus

-Types:
• Type A: epidemics and pandemics, animal reservoir
• Type B: epidemics, no animal hosts
• Type C: minor respiratory illness

-Structure:
♦ Type-specific antigens on cell surface (spikes) (i.e. haemagglutinin (H) and neuraminidase (N))
♦ Segmented, single stranded RNA. Reassortment gives rise to novel combinations of H and N antigens.

31
Q

Explain the terms antigenic shift and antigenic drift, and explain how they apply to the Influenza virus.

A

Influenza virus undergoes genetic changes during spread through the host species.

1) Antigenic drift
- Small point mutations are constantly occurring in N and H antigens
- Allows virus to multiply in individuals with immunity to preceding strains
- New sub-type can re-infect community
- Occurs with all influenza types

2) Antigenic shift
- Sudden major change based on recombination between two different virus strains when they infect the same cell.
- New virus has novel surface glycoproteins
- New strains can infect previously immune populations, and cause pandemic

32
Q

Briefly explain how a pandemic influenza strain can be generated.

A

“Major changes in the influenza type A HA antigen (antigenic shift) are caused by reassortment from different influenza A subtypes, such as between animal and human subtypes, and in rare events, such shifted viruses can result in strains capable of causing large regional or global pandemic outbreaks”

33
Q

What are the main characteristics of a pandemic ?

A
  • Antigenic shift
  • Most people have no immunity
  • Attack rate is high- spreads rapidly
  • Mortality rate can be high
34
Q

What is the virus of swine flu ? Describe the epidemiology of swine flu. Also describe the attack and mortality rate of swine flu.

A

-Influenza A virus H1N1 virus
-Infection largely limited to individuals under the age of 40
-Attack rate was high but mortality low because many had a degree of immunity because a) Older people had been infected with older H1N1 viruses in childhood b)
Vaccine had contained H1N1 components

35
Q

Distinguish between pandemic and seasonal flu.

A

Seasonal ‘flu – different serotypes

Pandemic flu - almost exclusively pandemic
H1N1

36
Q

How is influenza diagnosed ?

A
  • Point of care diagnosis (medical diagnosis at or near the point of care)
  • Nasopharyngeal aspirate
  • Serum (serology)
37
Q

How is influenza treated and managed ?

A

TREATMENT
• Amantadine
• Zanamavir
• Oseltamivir (“Tamiflu”)

MANAGEMENT

  • Warmth, rest, hydration, analgesia
  • Anti-virals within 48 hours has some effect on duration of fever
  • No antibiotics unless secondary bacterial infection suspected
38
Q

How is influenza prevented ? Describe the main features of this method.

A

-Killed vaccine (70% efficacy)
Trivalent vaccine
Antigenic variation means that a new vaccine is required each year
New vaccine is based on the PREDICTED strains

39
Q

What groups are particularly critical in the vaccination process of influenza.

A

Elderly, immunosuppressed and others with respiratory risk (e.g. asthmatics and bronchitics) require an annual vaccine

40
Q

How long does it take to develop a new flu vaccine ? (given that new flu vaccine is required each year)

A

New recombination methods speed up the process of developing a new vaccine - this was used in the recent swine flu pandemic

41
Q

SARS:

  • Definition
  • Symptoms
  • Incubation period
  • Transmission
  • Pathogen
A

♠ Definition: Outbreak of severe respiratory disease with no identifiable cause

♠ Symptoms: 
• High fever
• Cough
• Shortness of breath
• CXRs consistent with pneumonia

♠ Incubation period:
2-7 days (10 max)

♠ Transmission:
droplets, faeces, infected animals

♠ Pathogen:
SARS-associated Coronavirus (SARS CoV)

42
Q

What are the main structural features of SARS coronavirus ? How can SARS coronavirus be identified ?

A

• Structure:

  • Enveloped
  • RNA virus
  • Characteristic halo
  • Receptor for spike protein is ACE2

• Identified by:

  • virus isolation in cell culture
  • electron microscopy
  • molecular techniques
43
Q

What is the treatment for SARS ?

A

• No specific anti-viral treatment available

  • Ribavirin
  • Corticosteroids
  • Interferons
  • Anti-retroviral therapies (e.g. protease inhibitors)

• Whole inactivated virus vaccine and recombinant vaccine now been developed

44
Q

MERS

  • Pathogen
  • Symptoms
A
  • Pathogen: MERS-CoV

- Symptoms: Same as SARS

45
Q

What is the leading cause of death globally from a single infectious agent ?

A

Tuberculosis

46
Q

What are risk factors for TB ?

A
  • AIDS
  • Increased use of immunosuppressive drugs
  • Decreased socio-economic conditions
  • Increased immigration from areas of high endemicity
  • Multiple drug resistance (MDR)
  • Overcrowding and poor nutrition
47
Q

What pathogen is responsible for TB ?

A

Mycobacterium tuberculosis

48
Q

Clinically, what are the main types of TB ? What are the main clinical features of each of these ?

A

1) Primary TB
- Usually asymptomatic
- Possible cough and/or wheeze
- Possible small transient pleural effusion

2) Miliary TB
- Due to acute diffuse dissemination of bacillus
- Fatal without treatment

3) Post-primary TB
- Onset of symptoms over weeks/months
- Malaise
- Fever
- Weight loss
- Mucoid, purulent or blood-stained sputum (productive cough)
- Pleural effusion

49
Q

Mycobacterium tuberculosis:

  • Type of bacteria
  • Transmission
  • Location in body
A

-Type of bacteria: Neither Gram positive nor Gram negative, obligate anaerobe, human pathogen, acid-fast bacilli
-Transmission: Spread by inhalation of organisms from dust / aerosols
-Location in body: TB primarily affects lungs (especially well-aerated upper lobes of
lungs since obligate aerobe) but can process to other sites (e.g. GI tract)

50
Q

How is TB diagnosed ?

A

♠ Mantoux test:
• Used to detect latent TB infection
• Tuberculin injected intradermally
• Immune response if individual previously exposed to bacterium (swelling)
• Induration (palpable hardened area) measured after 48-72 hours

♠ Specimens (but problem: TB is very slow growing so may have to wait weeks)
-Respiratory- sputum, laryngeal, gastric contents, broncho-alveolar lavage, induced sputum
-Pus
-CSF
-Stools
Wrt specimens, primary diagnosis is made from visualising acid-fast bacilli in sputum smears. Cultures can also be used.

51
Q

Explain the significance of bacterial load in diagnostics.

A

1) Patients present at different bacteria loads
2) Diagnostic test become positive at different bacterial loads
3) Reducing bacterial load can delay diagnosis
4) Symptoms differ at different bacterial loads

52
Q

Identify some important diagnostic tools and rank them in order of sensitivity with increased bacterial load.

A
  • Culture most sensitive (can detect even low bacterial load)
  • PCR intermediate
  • Smear least sensitive (requires high bacterial load to detect it)
53
Q

Explain how “visualising acid-fast bacilli in sputum smears” works as a way of diagnosing TB.

A

1) Auramine
- Positive organisms fluoresce bright yellow,
- More sensitive than Z/N for initial diagnosis because the whole smear can be examined under low power magnification
- Tells you about presence or absence

2) Ziehl-Neelsen (Z/N)
- High power magnification
- Semi-quantification

54
Q

Identify the main ways to culture myobacterium tuberculosis, and explain how culturing can lead to diagnosis.

A

1) Solid culture:
• Lowenstein-Jensen (LJ) slopes: 6 weeks
• Middlebrook agar plates: 2-3 weeks

2) Liquid culture:
• Mycobacteria Growth Indicator Tube (MGIT): 5-15 days
(allows continuous monitoring of positive cultures)

Bacterial growth is measured by the consumption of oxygen in the media. Tubes contain a fluorescence compound sensitive to the presence of oxygen. Actively respiring bacteria consume oxygen from the media allowing fluorescence to be detected.

NOW, Rapid Automated TB Culture System (Xpert MTB/RIF)

55
Q

Identify the function, pros and cons of Rapid Automated TB Culture System (Xpert MTB/RIF) for TB diagnosis.

A

♦ Function: Detects TB bacilli + determines RIF resistance

♦ PROS: 
• A two hour test (quick) 
• 95% sensitive
• 95% specific
• Little technical expertise required

CONS:
• Expensive

56
Q

Describe treatment and prevention for Tuberculosis.

A

TREATMENT: Prolonged, combination Therapy

  • isoniazid, rifampicin, ethambutol, pyrazinamide
  • To prevent emergence of resistance
  • However, multi-drug resistant TB (MDR-TB) is a major global problem
  • Minimum of 6 months to eradicate slow growing organisms

PREVENTION

  • Childhood immunisation: live, attenuated, BCG vaccine
  • Prophylaxis with isoniazid for 1 year (“for the treatment of latent TB infection among people living with HIV and children under five years of age who are contacts of patients with TB”)
57
Q

Identify possible fungal infections of the lower respiratory tract.

A
  • Aspergillus fumigatus

* Pneumocystis jiroveci (previously P. carinii)

58
Q

Identify possible infections of the lower respiratory tract.

A

Viral:
Viral pneumonia
Measles
Influenza (e.g. swine flu, avian flu, SARS, MRES)

Bacterial:
Bacterial pneumonia
TB

Fungal:
• Aspergillus fumigatus
• Pneumocystis jiroveci (previously P. carinii)

Parasitic: 
• Ascaris
• Strongyloides
• Schistosoma
• Echinococcus granulosus
59
Q

Identify possible parasitic infections of the lower respiratory tract.

A
  • Ascaris
  • Strongyloides
  • Schistosoma
  • Echinococcus granulosus

MD3001 (75 decks)

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