Respiratory Infections Flashcards
What kind of infections is the respiratory tract prone to?
Air borne infections
Terms for an infection of the lung
Pneumonia or Pneumonitis
How many L of air inhaled each day?
10,000L
Where and how many bacterial microns are held in the respiratory tract?
- > 10 in upper airways
- 3-10 trapped in tracheobronchial mucus
- 1-5 deposited in terminal airways and alveoli
- <1 in suspended alveolar air as exhaled
Defence mechanisms of the respiratory tract
- nasal clearance
- mucociliary action in tracheobronchials
- alveolar macrophages
What can suppress the cough reflex?
- coma
- anaesthesia
- drugs
- chest pain
- neuromuscular disease
What can injure the mucociliary apparatus?
- smoking
- inhalation of hot/corrosive gases
- congenital
What can disturb macrophage function?
- smoking
- alcohol
- anoxia
- O2 toxicity
What other things can disturb normal lung defence?
- pulmonary congestion
- pulmonary oedema
- accumulation of secretions
- general immune suppression
- unusually virulent organisms
Define pneumonia
Alveolar inflammation due to lung infection
3 types of pneumonia
- lobar
- bronchopneumonia
- atypical pneumonia
Lobar pneumonia features
- affects large part of lobe or entire
- previously healthy males age 20-50
- 90% strep penumonie cause
Clinical features of lobar pneumonia
- high grade fever with rigors
- productive cough
- rusty sputum
- pleuritic chest pain
- signs of consolidation
4 stages of lobar pneumonia
- congestion
- red hepatisation
- grey hepatisation
- resolution
Congestion stage of lobar pneumonia
- first
- 24 hours
- vessels engorged
- alveolar oedema
- heavy red lung
Red hepatisation in lobar pneumonia
- 2-4 days
- outpouring neutrophils and RBCs into alveoli
- red, solid, airless, liver like lung
Grey hepatisation in lobar pneumonia
- 4-8 days
- fibrin and macrophages replace neutrophils and RBCs
- grey, solid, airless lung
Resolution stage in lobar pneumonia
- last
- 8-10 days
- gradual return to normal
Complications of lobar pneumonia
- lung abscess
- empyema
(rare but more likely with Klebsiella or Staph infections)
What is the commonest type of pneumonia?
- bronchopenumonia
What does bronchopneumonia begin as?
- bronchitis and bronchiolitis
- then spreads to alveoli
Bacteria causing bronchiolitis
- staph
- strepto viridans
- H influenzae
- pseudomonas
- coliforms
4 typical clinical settings of bronchopneumonia
- infancy
- old age
- secondary to viral infection
- chronic debilitating illness
Pathology of bronchopneumonia
- bilateral
- basal
- patchy
- grey/grey-red spots of consolidation
- microscopic = acute inflammatory infiltrate in bronchioles and alveoli
Complications of bronchopneumonia
- death (as usually old age or debilitating illness)
- resolution
- scarring
- abscess/empyema (rare)
Differences between lobar and bronchopneumonia
lobar = Afflicts large portion or entire lobe vs.
Patchy, usually bilateral basal distribution
Previously healthy individuals vs. Pre-existing suppressed immune defense
90-95% Streptococcus pneumoniae vs. Any pathogen (staph, strept, pneumo, hamophilus, pseudomonas, coliforms) Xray and clinical signs: Complete lobar opacity vs. Xray: Focal opacities; clinical signs less pronounced
Generally complete resolution vs.
Variable; often fatal; determined by preexisting illness
Most important distinctions between lobar and bronchopneumonia?
- identifying causative agent
- extent of disease
Features of interstitial pneumonia
- patchy or extensive
- congested/subcrepitant lungs
Site of inflammation in interstitial pneumonia
- alveolar septa and interstitial tissues
Why is interstitial pneumonia atypical?
- no/minimal alveolar exudate
Causative agents of interstitial pneumonia
- mycoplasma pneumoniae
- influenza A and B
- rhino
- rubeola
- varicella
- chlamydia
- coxiella
- undetermined often
Predisposing conditions to interstitial pneumonia
- malnutrition
- alcoholism
- debilitating illnesses
Clinical presentation of interstitial pneumonia
- variable
- general symptoms
- sporadic change from mild to self limiting
- secondary bacterial infections common
Cause of pulmonary TB
- Mycobacterium tuberculosis or M bovis infecting the lungs
Commonest site of TB
Lungs
Why is there a UK rise in pulmonary TB cases
HIV rise
immunosuppression
low socioeconomic status
drug resistance
What does clinical pulmonary TB represent?
- reinfection or reactivation
- rarely progressive primary TB
Pathogenesis of TB
See video/last year
Primary TB
- response to first contact with tubercle bacilli
- asymptomatic
- Ghon complex = 1cm focus in midzone with draining lymph node
- fibrosis and calcification heals
Secondary TB
- reinfection or reactivation
- sometimes progressive primary TB
- bacteria relocate to oxygen rich areas
- usually apical about 3cm
Microscopic pathology of TB
- Type 4 hypersensitivity
- granulomas with caseous necrosis, langhan’s giant cells, epithelioid macrophages
- acid fast bacilli with Ziehl-Neelsen
What provides definitive diagnosis of TB
sputum culture
Complications of pulmonary TB
- progressive fibrocavitary = destroying lungs through necrosis, cavitation and fibrosis
- military TB = bloodborne dissemination within lung or throughout body, throughout body = meninges, bone marrow, liver
Fungal infections
- in immunocompromised
- HIV = pneumocystis carinii
- histoplasma, coccidio, candida, aspergillus, mucor, cryptococcus
Aspiration pneumonia
- route of infection via aspiration or blood borne
