Respiratory Tract Infections Flashcards
Distinguish between URTI and LRTI
URTI: Common and relatively trivial - illnesses caused by an acute infection which involves the upper respiratory traccts including the nose, sinuses, pharynx or larynx.
LRTI: Potentially life-threatening, virus and bacteria - infection bellow level of larynx; Bronchiolitis, Bronchitis, Pneumonia
Some causes of common cold Coryza
- Coronaviruses e.g.g SARS, MERS
- Rhinoviruses
- Adenoviruses
- Parainfluenza virus 1-4
- Enteroviruses - coxsackie
- RSV (respiratory synctial virus
CRAPER
Common causes of Pharyngitits and Tonsilitis
- Viruses (adenoviruses)
- Bacteria - Strep Pyogens
Enlarges, white tonsils
Causes of epiglottitis
- Bacterial, potentially life threatening
- And rearely Haemophilus influenza type B
Causes and symptoms of Croup
- In young children
- Inspiratory stridor due to narrowed airways - noisy expiration
- Viruses e.g. paraflu, RSV
Characteristics and causes of infectious mononucleosis
=Glandular fever
- Syndrome, not aetiological diagnosis
- Pharyngitis, lymphadenopathy, fever, malaise
- Atypical mononuclear cells in peripheral
- Caused by EBV, cytomegalovirus, tomxoplasmosis, HIV
Causes of LRTI
- Influenza
- Respiratory synctial virus
Rarely:
- Varicella zoster
- Measles
- SARS, MERS
Clinical features of influenza virus infection
- A,B,C only A has subtypes
- Respiratory tract symptoms e.g. rhinits, cough, SOB
- Systemic symptoms fever, headaches myalgia
Pathogenesis of influenza virus
- Segmented single stranded RNA genome
- 8 segments encoding 11 proteins e.g. segment 4=haemaglutinin which binds sialic acids on cells to intiate infection
- 6= Neuroaminidase
- Pneumotropic - infects cells lining respiratory tract down to alveoli
- Lytic - strips off resp epithlium
- Removes innate defence mechanisms - mucous secretion
- Increased inhalation of bacteria
- Interferon induced by virus circulates in blood
Complications of influenza virus
- Pneumonia: primary viral -> mononuclear cell infiltration,
- Secondary bacterial ->PMNL infiltrate
- Caridovascular, potential myocarditis
- CNS - encephalitis
Describe Antigenic drift in influenza
- Occurs in inlfuenza A and B
- random spontaneous mutations by RNA polymerase in viral genes encoding HA and NA; 1-2% AA sequence change
- Mutations clustered in key HA and NA apitoptes, true darwinian evolution, selected by host immune response
Describe antigenic shift in influenza
- Only in influenza A and
-
genetic reassortment
- Between human and non-human(avian) viruses-> new subtypes
- >20% AA differences -> new pandemic strain emerges with no existing immunity in population
Define epidemic
A widespread occurence of an influenza in a community ata particular time e.g. annual flu epidemic
Define pandemic
An infleunza pandemic is an epidemic of an influenza virus that spreads on a worldwide scale and infects a large proportion of the human population
Clinical features of RSV (Respiratory Synctial Virus)
- LRTI in infants - bronchitis, pneumonia
- High hospitalisation rates, low mortality
- Re-infection occurs during life due to antigenic drift
Main route of trnasmission for SARS, influenza and other respiratory viruses
Droplets
Usually under 1m spread
Two main types of pneuomonia
Community acquired pneuomonia CAP
Hospital acquired pneumonia
Demographics more prone to CAP
Males
Elderly
Alcoholics and smokers (poor neutrophils)
Common bacteria that can cause CAP
-
S. pneumonia
- Most common in those without COPD
- Major virulence factor = the capsular polysaccharide
- Relative resistant to penicillin
- Can be vaccinated
-
H influenza
- capsulated
- Primary cause of CAP in children and immigrants without HIB vaccination
- Non-capsulated
- Important cause in COPD patients
- capsulated
Atypical bacteria causing CAP
- Mycoplasma pneumonia
- Chlamydia pneumonia
- Legionella pneumonia
- S. auerues
Mycoplasma pneumonia characteristics in CAP
- Second most common cause of CAp
- Characteristic extra-pulmonary features
- Skin
- Can occur seasonally and epidemic
- Tetracycline
Characteristics of legionella Pneumonia in CAP
- Not as common as S.pneumonia, but severe as poorly treated with antibiotics
- Sporadic cases occur in smokers and immunocompromised
- Outbreak cases often water borne.
- Treat legionellossis
- High dose macrolide
- Up to 4g erythromycin per day
- Rifampicin
Characteristics of S.aureus CAP
- Common cause of CAP during influenza outbreak
- Cause of necrotising haemorrhagic pneumonia
- CXR: Not lobular/standard presentation, pulmonary abcesses
