RTIs (Pt 2) Flashcards
What age groups are most affected by fatal lower respiratory tract infections ?
- Elderly in developed countries
- Children under five in developing countries
Pneumonia:
- Define
- Transmission
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
What is the most common cause of infection-related death in UK and USA ?
Pneumonia
Describe the aetiology of pneumonia depending on age.
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
Identify the main pathogens in viral pneumonia.
Rhinoviruses
Coronaviruses
Influenza virus
Measles virus
Identify the main pathogens in bacterial pneumonia.
Streptococcus pneumoniae
Mycobacterium tuberculosis
Haemophilus influenzae
Pseudomonas aeruginosa
Define atypical pneumonia. What organisms can cause atypical pneumonia ?
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
Identify the main anatomical classifications of pneumonia.
- Lobar pneumonia
- Bronchopneumonia
- Interstitial pneumonia
- Necrotising pneumonia
Define lobar pneumonia.
Pneumonia involving a distinct region of the lung ie. lobe.
Define bronchopneumonia.
Diffuse, patchy consolidation, associated with bronchi and bronchioles.
Define interstitial pneumonia.
Invasion of lung interstitium, usually characteristic of viral infection.
Define necrotising pneumonia.
Lung abscesses and destruction of parenchyma
Identify the main clinical features of Streptococcus pneumoniae pneumonia.
1) Initially:
- Abrupt onset
- Rigors
- Fever
- Malaise
- Tachycardia
- Dry cough
2) Followed by:
- Productive cough with rusty sputum
- Spiky temperature
- Lobular consolidation
Identify the main clinical features of Mycoplasma pneumoniae pneumonia.
- Fever
- Dry cough
- Dyspnoea
- Lymphadenopathy
Identify the main clinical features of Haemophilus influenzae pneumonia.
- Mainly occurs in children
- Consolidation or patchy bronchopneumonia
- Persistent purulent sputum and malaise
Identify the main clinical features of Legionella pneumophila pneumonia.
=Legionnaire’s disease (form of atypical pneumonia), i.e. severe systemic infection with pneumonia
- Tachypnoea
- Purulent sputum
- Consolidation
Legionella pneumophila:
- What type of bacteria ?
- What is its mechanism of action ?
- How is transmitted ?
- Special features ?
- 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
Describe the laboratory diagnosis of Legionnaire’s Disease.
Detection of antigen in urine (4-fold rise in antibody)
What are the main clinical features of Measles ?
- Fever
- Characteristic rash
- Runny nose
- Koplik’s spots
What are possible complications of measles ?
→ Neurological complications
→ “Giant cell” (Hecht’s) pneumonia in the immunocompromised – usually fatal
Do people usually die from measles ?
In developing countries, yes.
MEASLES virus:
- Class of virus
- Transmission
- Where does it replicate ?
- Incubation period
- Is infection localised or sytemic ?
- Class of virus: Paramyxovirus
- Transmission: via aerosol
- Where it replicates: Replicates in LRT
- Incubation period: 10-14 days
- Multisystem infection
Describe diagnosis of measles.
- Clinical mainly
- Serology for measles-specific IgM (easiest way)
- Virus isolation
- Viral RNA detection
Describe treatment and prevention of measles.
TREATMENT
♣ If severe, ribavarin treatment available
♣ Antibiotics for secondary bacterial infection
PREVENTION
♣ Immunisation with highly effective, live, attenuated MMR vaccine
List the main risk factors for pneumonia. Identify the pathogen associated with each risk factor.
- Travel, air conditioning (L. pneumophila)
- CF (Pseudomonas)
- Bird contact (C. psitacci)
- Immigration (M. tuberculosis)
- Farming (sheep) (Coxiella burnetti)
- Recent influenza (S. pneumoniae, St. aureus)
What are the main symptoms, and signs of pneumonia ?
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
How is pneumonia diagnosed ?
- 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)
Define and explain how to calculate a CURB score.
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)
Distinguish between endemic, epidemic and pandemic disease. Giving an example of disease which causes all three.
- 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.
INFLUENZA VIRUS
- Class of virus
- Types
- Structure
-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.
Explain the terms antigenic shift and antigenic drift, and explain how they apply to the Influenza virus.
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
Briefly explain how a pandemic influenza strain can be generated.
“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”
What are the main characteristics of a pandemic ?
- Antigenic shift
- Most people have no immunity
- Attack rate is high- spreads rapidly
- Mortality rate can be high
What is the virus of swine flu ? Describe the epidemiology of swine flu. Also describe the attack and mortality rate of swine flu.
-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
Distinguish between pandemic and seasonal flu.
Seasonal ‘flu – different serotypes
Pandemic flu - almost exclusively pandemic
H1N1
How is influenza diagnosed ?
- Point of care diagnosis (medical diagnosis at or near the point of care)
- Nasopharyngeal aspirate
- Serum (serology)
How is influenza treated and managed ?
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
How is influenza prevented ? Describe the main features of this method.
-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
What groups are particularly critical in the vaccination process of influenza.
Elderly, immunosuppressed and others with respiratory risk (e.g. asthmatics and bronchitics) require an annual vaccine
How long does it take to develop a new flu vaccine ? (given that new flu vaccine is required each year)
New recombination methods speed up the process of developing a new vaccine - this was used in the recent swine flu pandemic
SARS:
- Definition
- Symptoms
- Incubation period
- Transmission
- Pathogen
♠ 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)
What are the main structural features of SARS coronavirus ? How can SARS coronavirus be identified ?
• Structure:
- Enveloped
- RNA virus
- Characteristic halo
- Receptor for spike protein is ACE2
• Identified by:
- virus isolation in cell culture
- electron microscopy
- molecular techniques
What is the treatment for SARS ?
• 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
MERS
- Pathogen
- Symptoms
- Pathogen: MERS-CoV
- Symptoms: Same as SARS
What is the leading cause of death globally from a single infectious agent ?
Tuberculosis
What are risk factors for TB ?
- 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
What pathogen is responsible for TB ?
Mycobacterium tuberculosis
Clinically, what are the main types of TB ? What are the main clinical features of each of these ?
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
Mycobacterium tuberculosis:
- Type of bacteria
- Transmission
- Location in body
-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)
How is TB diagnosed ?
♠ 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.
Explain the significance of bacterial load in diagnostics.
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
Identify some important diagnostic tools and rank them in order of sensitivity with increased bacterial load.
- Culture most sensitive (can detect even low bacterial load)
- PCR intermediate
- Smear least sensitive (requires high bacterial load to detect it)
Explain how “visualising acid-fast bacilli in sputum smears” works as a way of diagnosing TB.
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
Identify the main ways to culture myobacterium tuberculosis, and explain how culturing can lead to diagnosis.
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)
Identify the function, pros and cons of Rapid Automated TB Culture System (Xpert MTB/RIF) for TB diagnosis.
♦ Function: Detects TB bacilli + determines RIF resistance
♦ PROS: • A two hour test (quick) • 95% sensitive • 95% specific • Little technical expertise required
CONS:
• Expensive
Describe treatment and prevention for Tuberculosis.
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”)
Identify possible fungal infections of the lower respiratory tract.
- Aspergillus fumigatus
* Pneumocystis jiroveci (previously P. carinii)
Identify possible infections of the lower respiratory tract.
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
Identify possible parasitic infections of the lower respiratory tract.
- Ascaris
- Strongyloides
- Schistosoma
- Echinococcus granulosus
