MI: Respiratory Tract Infections Flashcards
List some ways in which the body can be compromised, thereby increasing the risk of respiratory tract infection.
- Poor swallow (aspiration)
- Abnormal ciliary function (e.g. smoking)
- Abnormal mucus (e.g. CF)
- Dilated airways (e.g. bronchiectasis)
- Defect in host immunity
What type of bacterium is Streptococcus pneumoniae?
- Gram-positive cocci in chains
- Alpha-haemolytic and optochin-sensitive
What is optochin used for?
Used to differentiate S. pneumoniae from other alpha-haemolytic streptocci
Epidemiology of S. Pneumoniae infection in CAP
20-50% of CAP
Almost always penicillin sensitive
What is pneumonia and what are its presenting symptoms
Inflammation of alveoli due to infection
Presentation:
- Fever
- Cough
- SoB
- Pleuritic chest pain
Why is no microbiological identification of the pathogen made in the most cases of CAP?
Difficult to obtain a good sputum sample and early treatment is usually initiated with empirical antibiotics
List the main organisms that cause CAP.
- VIRUSES
- Streptococcus pneumoniae
- Haemophilus influenzae
- Mycoplasma pneumoniae
- Moraxella catarrhalis
- Staph aureus
List the most prevalent pathogens causing CAP in the following age groups:
- 0-1 months
- 1-6 months
- 6 months - 5 years
- 16 - 30 years
0 - 1 months:
- Escherichia coli
- Group B Streptococcus
- Listeria monocytogenes
1-6 months:
- Chlamydia trachomatis
- Staphylococcus auerus
- RSV
6 months - 5 years:
- Mycoplasma pnaeumoniae
- Influenza
16-30 years:
- Mycoplasma pneumoniae
- Streptococcus pneumoniae
List the causes of CAP that fall into the following two categories:
- Typical
- Atypical
Typical (85%):
- Streptococcus pnaeumoniae - lobar
- Haemophilus influenzae - bronchopneumonia
Atypical:
- Legionella - Summer/ Water exposure
- Mycoplasma - barking cough, normal CXR
- Coxiella burnetii (Q fever) - farm animals, hepatitis
- Chlamydia psittaci - Exposure to birds, splenomegaly, rash, haemolytic anaemia
What investigations would you consider in pneumonia
FBC, U&E, CRP
Blood culture, sputum culture
ABG
CXR
What is the CURB-65 score? How is it interpreted?
- Confusion
- Urea > 7 mmol/L
- Respiratory rate > 30/min
- BP < 90 systolic, < 60 diastolic
Score of 2 = consider hospital admission
Score of more than 2 = severe pneumonia that may need ITU admission
What is bronchitis and in which group of people does it most likely occur
Inflammation of bronchi and medium-sized airways
Mainly affects smokers
Outline the presentation of bronchitis.
- Cough
- Fever
- Increased sputum production
- Increased SOB
- CXR often normal
Which organisms cause bronchitis?
- Viruses
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
How is bronchitis managed
- Smoking cessation
- Bronchodilators
- Physiotherapy
- +/- Antibiotics
List some bacterial causes of cavitating lung lesions.
- Staphylococcus aureus
- Klebsiella pneumoniae
- TB
What type of bacteria is H. influenzae and what kind of agar is it cultured on
- Gram negative coccobacillus
- Cultured on chocolate agar
More common with preexisting lung disease
15-35% CAP
May produce beta-lactamase
How is Legionella spread and what abnormal symptoms can it present with?
Inhalation of infected water droplets
Can present with confusion, abdominal pain and diarrhoea
What electrolyte derangement commonly occurs with Legionella pneumonia
Hyponatraemia (can cause neurological symptoms like confusion or drowsiness)
What would you see on FBC in Legionella infection?
Lymphopaenia
How does Legionella pneumonia appear on CXR
Bilateral interstitial shadowing
What medium is Legionella grown on?
Buffered charcoal yeast extract
How is Legionella pneumoniae diagnosed and treated
Diagnosed by urine antigen detection
Treated with macrolides
What is a feature of bacteria that cause atypical pneumonia and how does it affect treatment?
They have NO cell wall
Therefore not susceptable to cell wall targetting antibiotics e.g. penicillins
List four atypical organisms.
- Mycoplasma pneumoniae
- Legionella pneumophilia
- Chlamydia psittaci
- Coxiella burnetii
Which type of antibiotics do work on atypical bacteria?
Antibiotics that interfere with protein synthesis (macrolides, tetracyclines)
How is Coxiella burnetii spread and treated
Spread by domestic/farm animals and transmitted by infected aerosol or milk
Treated with macrolides
How is Chlamydia psittaci spread and treated
Spread from birds by inhalation
Treated with macrolides
Which investigation is used for Coxiella and Chlamydia psittaci?
Serology
NOTE: serology looks at the development of antibodies after an infection. Therefore it requires paired samples (usually collected on presentation and then 10-14 days later)
It is useful for investigating bacteria that are difficult to culture.
What is an empyema?
Collection of pus within the pleural cavity
List some reasons for failure to respond to treatment.
- Empyema/abscess
- Proximal obstruction (e.g. tumour)
- Resistant organisms
- Not absorbing antibiotics
- Immunosuppression
- Alternative diagnosis (e.g. lung cancer)
What is the classical CXR feature of TB?
Upper lobe cavitation
What clues in history might point you towards TB?
- Ethnicity/recent travel to endemic regions
- Prolonged course
- Fevers
- Weight loss
- Haemoptysis
How is TB diagnosed?
Primary latent TB: TST, IGRA
Active (primary or secondary) TB: PCR, sputum culture, CXR
Which types of staining are used when investigating TB?
- Auramine stain
- Ziehl-Neelsen stain
NOTE: they are red rods
Define hospital-acquired pneumonia.
A pneumonia that presents > 48 hours after hospital admission
List some organisms that cause HAP.
- Enterobacteriaciae 31% (MOST COMMON - e.g. E. coli, K. pneumoniae)
- Staphylococcus aureus 19%
- Pseudomonas 17%
- Haemophilus influenzae
- Acinetobacter baumanii
- Fungi (e.g. Candida)
Classical PCP CXR presentation
Bilateral consolidation “Bats wing”
Describe the typical presentation of Pneumocystic jirovecii pneumonia.
- Dry cough
- Weight loss
- SOB
- Malaise
- Walk test - desaturation on exertion
How is PCP diagnosed?
- Blood PCR (early detection in HIV patients)
- Sputum staining with silver-based stains
- Bronchoalveolar lavage and immunofluorescence
What is the treatment for PCP?
Co-trimoxazole (septrin)
What are the main features of allergic bronchopulmonary aspergillosis?
- Chronic wheeze
- Eosinophilia
- Bronchiectasis
What is an aspergilloma?
- Fungal ball often forming within a pre-existing cavity
- May cause haemoptysis
Who is affected by invasive aspergillosis and how is it treated?
Affects immunocomprimised individuals
Treated with amphotericin B
Flowering spores?
Aspergillus
Which organisms cause pneumonia in the following subgroups of patients:
- HIV
- Neutropenia
- Bone marrow transplant
- Splenectomy
- HIV: PCP, TB, Atypical mycobacteria
- Neutropaenia: Fungal (e.g. Aspergillus)
- Bone marrow transplant: CMV
- Splenectomy: Encapsulated organisms (e.g. Streptococcus pnaeumoniae, Haemophilus influenzae)
What is the emprical treatment for mild-to-moderate CAP?
Amoxicillin
(macrolide if penicillin allergic)
What is the emprical treatment for moderate-to-severe CAP?
Co-amoxiclav AND clarithromycin
What are the 1st and 2nd line treatment options for HAP?
Check local guidelines
Mild = co-amoxiclav
Severe = tazocin
(glycopeptides if MRSA)
Which antibiotics are used to treat HAP caused by:
- MRSA
- Pseudomonas
- MRSA - Vancomycin
- Pseudomonas - Tazocin OR ciprofloxain +/- gentamicin
How can pneumonia be prevented
Vaccinations
Smoking advice
