Pneumonia

What is it?
An inflammation of the substance of the lungs, usually due to bacteria

Classification by site
Localised – one or more lobes affected
Diffuse – affect lung lobules and bronchii and bronchioles (bronchopneumonia)

Classification by aetiology

Typical pneumonia
Due to streptococcus pneumoniae – most common

Atypical pneumonia
Due to organisms such as mycoplasma pneumoniae, legionella pneumophila, Chlamydia pneumoniae, Chlamydia psittaci, coxiella burnetti
Accounts for 1/5 of the cases of pneumonia (Kumar and Clarke).
Overlaps in clinical presentation with typical pneumonia

Viral pneumonia
Influenza and adenovirus infection are the most common causes. It can often predispose parients to bacterial pneumonia (damages epithelium - facilitates bacterial infection).

Pneumonia due to opportunistic infections
Occurs in immunocompromised patients (e.g. AIDS). It is due to Pneumocytis carinii (bacterium), actinomyces isralli (bacterium), nocardia asteroids (bacterium), cytomegalovirus, aspergillus fumigates (fungus), mycobacterium avium-intracellulare (bacterium), crytptococcus (fungus) and Karposi’s sarcoma.

Rare causes
Bordetella pertussis, typhoid bacillus, paratyphoid bacillus, brucellosis, leptospirosis, measles, chicken pox, glandular fever

Aspiration pneumonia
Occurs when gastric contents enters the lungs. Due to a trachea-oesophageal fistula, periods of impaired consciousness (e.g. sleep), reflux oesophagitis with an oesophageal stricture, or in bulbar palsy (problems with cranial nerves 7-12). The pneumonia is often due to anaerobes.

Risk factors
· Cigarette smoking – strongest independent factor for invasive pneumococcal disease
· Strep. Pneumoniae - often follows a viral infection with influenza/parainfluenza
· Hospitalised patients – infected with Gram negative organisms
· Alcohol excess
· Bronchiectasis (abnormal and permanently dilated airways – impairs the mucocillary transport mechanism, and thus frequent bacterial infections occur)
· Bronchial obstruction, such as a carcinoma
· Immunosuppresion (AIDS, cytotoxic agents) – infection by Pneumocystis carinii, Mycobacteirum avium intracellulare and cytomegalovirus
· IV drug abuse – associated with staph.aureus infection
· Inhalation from oesophageal obstruction – associated with infection from anerobes

Clinical presentation (with strep. pneumoniae)
· Preceding history of viral infection
· High temperature – 39.5°C
· Pleuritic pain
· Dry cough
· Rusty-coloured sputum
· Breathing is rapid and shallow
· Affected side of chest moves less
· Pleural rub
· Signs of consolidation in the lungs

Diagnosis of severe community-acquired pneumonia
· Respiratory rate is greater than or equal to 30/min
· Diatolic BP is less than 60 mmHg
· Confusion
· High mortality, particularly in those over 65
· Co-morbidities

Investigations
· Chest x-ray
· In strep. pneumoniae:
o White blood cell count – is greater than 15 x 109/L (normal = 4-11 x 109/L)
o Erythrocyte sedimentation rate – greater than 100mm/h (normal = less than 20 mm/h) – measure of the settling of RBCs during 1 hour
· To detect certain types of pneumonia:
o Pneumococcal antigen – counter-immunoelectrophoresis of sputum, urine and serum (more sensitive than sputum or blood cultures)
o Mycoplasma antibodies (IgM and IgG)
o Legionella and Chlamydia antibodies – immunoflouresence tests
o Legionella antigen – in urine
· Blood gases – check for respiratory failure, and is also baseline for comparison if the patient deteriorates

Management
· Antibiotics
o Should be started once diagnosis is made
o Largely directed against strep. pneumoniae
o Mild community-acquired pneumonia – oral amoxicillin, oral erythromycin if sensitive to penicillin
o Staph. Aureus infection
§ intravenous flucloxacillin
§ if intolerant to penicillin and macrolides – fluroquinalone
o Severe cases
§ Broad-spectrum lactamase-stable beta-lactam (co-amoxiclav or cefuroxime)
§ Clarythromycin
o Antibiotics can be narrowed once test results received (however, 10% are mixed infections)
· General measures
o Fluids – avoid dehydration
o Sitting upright or where comfortable
o Cough should be encouraged (physiotherapy may be needed.)
§ If it is distressing or unproductive – codeine linctus
o Analgesia from pleuritic pain
· Hospital-acquired
o Commonly gram negative bacteria
§ Third-generation cephalosporin (cefuroxime)
§ Aminoglycosdies (gentamicin)
o Pseudomonas infection
§ IV xiprofloxacin or ceftazidime (cephalosporin)
o Aspiration pneumonia (multiple bacteria, often anaerobic)
§ Metronidazole (nitromidazole)
§ Co-amoxiclav or cefuroxime