Respiratory infections 2 Flashcards
M2 inhibitors amantadine and rimantadine are no longer used for influenza.
They block formation of influenza-derived ion channels, which are important in virus uncoating.
Why is this?
Only reduced length of disease by 1 day
Do not work on influenza B
Rapidly increasing resistance since 2009
1 year old child presents with SOB/ fever
Diagnosed bronchiolitis.
What are most likely causes?
RSV -70% of cases. Causes most severe disease if <6 months of age. Usually Dec-Feb. 160k deaths occur annually due RSV.
Approx 2/3 of infants are infection during first year of life. All infants infected by age 2
Starts as URTI. Can progress to LRTI in 50% cases
Influenza Parainfluenza Coronavirusees Rhinoviruses Metapneumovirus Mycoplasma Bordetella pertussis
Where does RSV get its name from?
Virus attaches to cell membrane using viral G protein
viral F protein along with cellular receptor mediates viral entry
fusion protein causes neighbouroing cells to coalesce, resulting in multinucleated cells - termed syncytia
End result is damage to airway epithelium, and loss of ciliated epithelial cells
Cytokines cause oedema and immune response which can lead to narrowing of bronchioles - causing stridors
What treatment is there for RSV infection in children/ immunocompromised?
Ribavirin - aerosolised
IVIG - give with ribavirin, if patient immunocompromised for another reason
Palivizumab - humanised mouse monoclonal antibody given in summer as prophylaxis for winter. Not used as treatment
Reduces hospitalisation by 50%, and wheezing by 60%
Child with RSV.
What are infection control issues?
Droplet precautions in side room
Can have healthcare spread
Which patient groups should receive palivizumab RSV prophylaxis?
Palivizumab is a monoclonal antibody licensed for preventing serious lower respiratory-tract disease caused by respiratory syncytial virus in children at high risk of the disease; it should be prescribed under specialist supervision and on the basis of the likelihood of hospitalisation. Palivizumab is recommended for:
- children under 9 months of age with chronic lung disease (defined as requiring oxygen for at least 28 days from birth) and who were born preterm
- children under 6 months of age with haemodynamically significant, acyanotic congenital heart disease who were born preterm.
Palivizumab should be considered for:
- children under 2 years of age with severe combined immunodeficiency syndrome
- children under 1 year of age who require long-term ventilation
- children 1–2 years of age who require long-term ventilation and have an additional co-morbidity (including cardiac disease or pulmonary hypertension).
Daptomycin has good efficacy against gram positives which can cause pneumonia.
Why is daptomycin not used in pulmonary infections?
Can cause daptomycin- induced acute eosinophilic pneumonia
The precise mechanism for daptomycin-induced lung injury is unknown, but is believed to be related to daptomycin binding to pulmonary surfactant culminating in epithelial injury
35 year old feels unwell with malaise, headache, fever, chills, vomiting. Then develops cough and SOB.
CXR shows diffuse bilateral pulmonary infiltrates
Mycoplasma serology pending
Legionella urinary Ag neg
Sputum culture pending
Blood culture pending
What is most likely cause?
Legionella
Legionella Ag is part of cell wall that is excreted in urine
Only detects L. pneumophila serogroup 1 - which causes approx 80% of infections.
LegAg can be secreted in urine for weeks/ months after initial infection
Legionella urinary antigen is only positive in 80% patients.
What plates can be used to attempt to culture it?
How does it appear under microscopy?
buffered charcoal-yeast extract (BCYE) - although not routinely used. BAL fluid is best for this
will not grow on 5% blood agar
Microscopy - appears as long thin gram neg rod
How is legionella adapted for the environment?
What is its pathogenesis of infection?
Live in free water
Lives inside amoeba, and utilises their resources
Inhaled, enters pulmonary macrophages.
Releases proteins which block phagolysosome fusion, preventing death of bacteria
Why are beta-lactams not used against legionella infection?
- do not penetrate infected macrophages well
- legionella produces beta-lactamase
- macrolides/ quinolones are used
Patient diagnosed with legionella pneumonia on ITU.
What are infection control measures?
Not spread person-person, so no personal protection needed
Need to ensure outbreak is not hospital related - check water/ air conditioning
PCP normally diagnosed by BAL PCR
What would microscopy findings be?
Silver stain will show dark cyst like structures 5microns diameter
AML patient with SOB.
CXR bilateral patchy changes
BAL shows septate hyphae with acute-angle branching
What is the organism?
Aspergillus - septate hyphae with acute-angle branching
Fusarium can have similar appearance
Candida/ Trichosporon are yeasts
PCP is yeast-like
Often BAL is negative in invasive aspergillus. Fungi invades the pneumocytes, so biopsy is required
What are most common species of aspergillus which cause invasive infection?
A. fumigatus
A. flavus
A. niger
What tests can be used for diagnosis of invasive aspergillosis?
Sputum/ BAL
Lung biopsy
Serum/BAL B-D-glucan and galactomannan
Both serum carbohydrates found in aspergillus cell walls
B-D-glucan goes up in candida infection as well. Galactomannan is more specific to aspergillus