Pneumonia is an infection of the pulmonary parenchyma.
Despite being the cause of significant morbidity and
mortality, pneumonia is often misdiagnosed, mistreated,
It is usually caused by bacteria.
Clinically it presents as an acute illness characterized in the
majority of cases by the presence of cough, purulent
sputum and fever together with physical signs or
radiological changes compatible with consolidation of the
Pneumonia can be classified both anatomically and on the
basis of the aetiology.
Anatomical classification :
Pneumonias are either localized, with the whole of one or
more lobes affected (lober pneumonia) , or diffuse, when
they primarily affect the lobules of the lung, often in
association with the bronchi and bronchioles - a condition
referred to as 'bronchopneumonia'.
Aetiological classification :
An aetiological factor can be discovered in
approximately 75% of patients.
The term 'atypical pneumonia' has been used to
describe pneumonia caused by agents such as
Mycoplasma, Legionella, Chlamydia and Coxiella
While these pneumonias can differ from
pneumococcal disease, there is a considerable
overlap in clinical presentation and as these agents
account for almost one-fifth of the cases of
pneumonia , the term 'atypical' has been dropped.
Pneumonias may also result from:
I. chemical causes, such as in the aspiration of vomitus
III. allergic mechanisms.
Precipitating factors :
Strep. pneumoniae - often follows viral infection with
influenza or para-influenza.
Hospitalized 'ill' patients - often infected with Gram-
Cigarette smoking (the strongest independent risk
factor for invasive pneumococcal disease).
Bronchiectasis (e.g. in cystic fibrosis).
Bronchial obstruction (e.g. carcinoma) -
occasionally associated with infection with 'non-
Immunosuppression (e.g. AIDS or treatment with
cytotoxic agents) - organisms include
Pneumocystis carinii, Mycobacterium avium,
Intravenous drug abuse - frequently associated
with Staph. aureus infection.
Inhalation from oesophageal obstruction - often
associated with infection with anaerobes.
Classic pneumonia evolves through a series of pathologic
The initial phase is one of edema, with the presence of a
proteinaceous exudate—and often of bacteria—in the
alveoli. This phase so rapidly followed by
Red hepatization phase. The presence of
erythrocytes in the cellular intra-alveolar exudate gives
this second stage its name, but neutrophils are also present
and are important from the standpoint of host defense.
Bacteria are occasionally seen in cultures of alveolar
specimens collected during this phase.
Gray hepatization, no new erythrocytes are
extravasating, and those already present have been lysed
and degraded. The neutrophil is the predominant cell,
fibrin deposition is abundant, and bacteria have
This phase corresponds with successful elimination of
the infection and improvement in gas exchange.
Resolution, the macrophage is the dominant cell type
in the alveolar space, and the debris of neutrophils,
bacteria, and fibrin has been cleared, as has the
This pattern has been described best for pneumococcal
pneumonia and may not apply to pneumonias of all
The clinical presentation varies according to the
immune state of the patient and the infecting agent.
In the most common type of pneumonia - caused
by Strep. pneumoniae - there is often a preceding
history of a viral infection.
The patient rapidly becomes ill with a high fever
Dry cough. A day or two later, rusty-coloured
sputum is produced and at about the same time the
patient may develop labial herpes simplex.
high temperature (up to 39.5°C)
Rapid and shallow breathing
the affected side of the chest moves less, and signs of
consolidation may be present together with a pleural
- Plain, X-ray
confirms the area of consolidation but radiological
changes lag behind the clinical course so that X-ray
changes may be minimal at the start of the illness.
Conversely, consolidation may remain on the chest
X-ray for several weeks after the patient is clinically
The chest X-ray usually returns to normal by 6
weeks, except in patients with severe airflow
- Persistent changes on the chest X-ray after this
time suggest a bronchial abnormality, usually a
carcinoma, with persisting secondary pneumonia.
Chest X-rays should rarely be repeated more
frequently than at weekly intervals during the
acute illness and then at 6 weeks after discharge
- CT chest may be needed .
• Gram's Stain and Culture of Sputum :
The main purpose of the sputum Gram's stain is to ensure
that a sample is suitable for culture. However, Gram's
staining may also help to identify certain pathogens (e.g., S.
pneumoniae, S. aureus, and gram-negative bacteria) by
their characteristic appearance.
The sensitivity and specificity of the sputum Gram's stain
and culture are highly variable; even in cases of proven
bacteremic pneumococcal pneumonia, the yield of positive
cultures from sputum samples is 50%.
Blood Culture in the presence of bacteramia .
Two commercially available tests detect pneumococcal and
certain Legionella antigens in urine.
Polymerase Chain Reaction
Polymerase chain reaction (PCR) tests are available for a
number of pathogens. However, the use of these PCR
assays is generally limited to research studies.
A fourfold rise in specific IgM antibody titer between acute-
and convalescent-phase serum samples is generally
considered diagnostic of infection with the pathogen in
question, such as Coxiella burnetii.
Recently, however, they have fallen out of favor because of
the time required to obtain a final result for the convalescent-
TYPES OF PNEUMONIA
• Mycoplasma pneumonia is relatively common and often
occurs in patients in their teens and twenties.
• Generalized features such as headaches and malaise often
precede the chest symptoms by 1-5 days.
• Cough may not be obvious initially and physical signs in
the chest may be scanty.
• On chest X-ray, usually only one lobe is involved but
sometimes there may be dramatic shadowing in both
lungs. There is frequently no correlation between the X-ray
appearances and the clinical state of the patient.
• The white blood cell count is not raised.
• Cold agglutinins occur in 50% of the cases.
• The diagnosis is confirmed by a rising antibody
• Treatment is with macrolides, e.g. erythromycin
500 mg four times daily for 7-10 days. Tetracycline
is also effective. Although most patients recover in
10-14 days, the disease can be protracted for weeks
and relapses occurring.
• Lung abscesses and pleural effusions are rare.
Primary viral pneumonia is uncommon in adults,
influenza A virus or adenovirus infection being the
It predisposes patients to bacterial pneumonia by
damaging the respiratory epithelium and
facilitating bacterial infection. Influenza A (HSNI)
normally does not affect humans but recently has
been transmitted from fowls (Avian flu), crossing
the species barrier. Patients present with fever,
breathlessness, cough and diarrhoea.
Lymphopenia and thrombocytopenia are present
and pulmonary infiltrates are seen on chest X-ray.
The mortality rate is high.
Severe acute respiratory syndrome (SARS) is due to
a novel coronavirus. The incubation period is
approximately 5 days with spread between humans
mainly by droplet infection.
The outbreak in 2003 affected many healthcare
workers. Fever, malaise, headache and rigors were
followed in the second week by cough,
breathlessness and diarrhoea.
Lymphopenia, thrombocytopenia and pulmonary
infiltrates (mainly in the lower zones) occur.
At the end of the second week 20% of patients
deteriorate, developing ARDS, and the mortality is
H. influenzae is a frequent cause of exacerbation of chronic
bronchitis and can cause pneumonia in COPD patients.
The pneumonia can be diffuse or confined to one lobe.
There are no special features to separate it from other
It responds well to treatment with oral amoxicillin 500 mg
× 4 daily.
Staph. aureus rarely cause pneumonia except after a
preceding influenzal viral illness.
The infection starts in the bronchi, leading to patchy areas of
consolidation in one or more lobes, which break down to
form abscesses. These may appear as cysts on the chest X-
Pneumothorax, effusion and empyemas are
Septicaemia develops with metastatic abscesses in
Fulminating staphylococcal pneumonia can lead
to death in hours.
Areas of pneumonia (septic infarcts) are also seen
in staphylococcal septicaemia. This is frequently
seen in intravenous drug abusers.
Pulmonary symptoms are often few but
breathlessness and cough occur and the chest X-
ray reveals areas of consolidation.
Abscess formation is frequent.
These are the cause of many hospital-acquired pneumonias but
they are occasionally responsible for cases in the community.
• Pneumonia due to Klebsiella usually occurs in elderly people
with a history of heart or lung disease, diabetes, alcohol excess
• The onset is often sudden, with severe systemic upset.
• The sputum is purulent, gelatinous or blood-stained.
• The upper lobes are more commonly affected and the
consolidation is often extensive.
• The organism can be found in the sputum or in the blood.
• Treatment is dependent on the sensitivity of the organism, but
a cephalosporin is usually required.
• The mortality is high, partly owing to the presence of the
• Pneumonia due to Pseudomonas is of considerable
significance in patients with cystic fibrosis, since it
correlates with a worsening clinical condition and
• It is also seen in patients with neutropenia following
• The isolation of P. aeruginosa from sputum must be
interpreted with care because may simply represent
contamination from the upper airways.
• Treatment with the 4-quinolone antibiotic ciprofloxacin
(200-400 mg i.v. over 30-60 minutes twice daily) or
ceftazidime (2 g bolus i.v. 8-hourly). Ticarcillin (15-20 g
daily i.v. infusion) and piperacillin are active against these
bacilli. These penicillins are usually given in combination
with an aminoglycoside, e.g. gentamicin, for maximum
GENERAL MANAGEMENT OF PNEUMONIA:
Sputum and blood should always be sent for culture but
antibiotic treatment should not be delayed.
Severe cases need to be admitted to hospital and a chest X-ray
performed. Other investigations, e.g. blood gases, are useful to
detect respiratory failure and provide a baseline for
comparison if the patient deteriorates.
The choice of antibiotics is inevitably empirical, and is
largely directed at Strep. pneumoniae infections.
For treatment of mild community-acquired pneumonia, oral
amoxicillin at a dose of at least 500 mg 8-hourly. Oral
erythromycin (or clarithromycin, which is better tolerated) is
an alternative choice for those sensitive to penicillin.
For more severe cases treated in hospital, combined
therapy with amoxicillin and a macrolide (erythromycin or
clarithromycin) is recommended. When oral therapy is
contraindicated, parenteral ampicillin or benzylpenicillin
should be combined with clarithromycin.
ForStaph. aureus infection intravenous flucloxacillin ±
sodium fusidate should be added. Fluoroquinolones are
recommended for those intolerant of penicillins or
For severe cases, parenteral antibiotics should be given
with the combination of a broad-spectrum lactamase-
stable beta-lactam antibiotic (co-amoxiclav or cefuroxime)
Parenteral antibiotics should be switched to oral once the
temperature has settled for a period of 24 hours and
provided there is no contraindication to oral therapy.
The choice of antibiotics may be narrowed once
microbiological results are available but it should be
remembered that up to 10% of pneumonias may have
Criteria for the diagnosis of severe community-
Respiratory rate ≥ 30/min
Diastolic blood pressure ≤ 60 mmHg
Old age particularly in those > 65 years old
Chest X-ray - more than one lobe involved
Pao2 < 60 mmHg
Low albumin (< 35 g/L)
White cell count (low <4 × 109/L or high > 20 ×
Raised serum urea (> 7 mmol/L)
Blood culture - positive
For more severe cases treated in hospital in addition to
antibiotic therapy fluids should be given to avoid dehydration,
care of the mouth and skin.
Cough should normally be encouraged, but if it is
unproductive and distressing, cough suppressants can be
Physiotherapy is needed to help and encourage the patient to
Pleuritic pain may require analgesia, but powerful analgesia
(e.g. opiates) should be used with care because they cause
severe hypoxia, oxygen therapy should be given.
COMPLICATIONS OF PNEUMONIA
This term is used to describe severe localized suppuration in the
lung associated with cavity formation on the chest X-ray, often
with the presence of a fluid level.
Abscesses may develop during the course of specific pneumonias,
particularly when the infecting agent is Staph. aureus or Klebsiella
pneumoniae. Septic emboli, usually staphylococci, result in
multiple lung abscesses.
Infarcted areas of lung occasionally cavitate and rarely become
Amoebic abscesses may occasionally develop in the right lower
lobe following transdiaphragmatic spread from an amoebic liver
The patient is often anaemic with a high ESR.
Empyema means the presence of pus within the pleural
This usually arises from bacterial spread from a severe
pneumonia or after the rupture of a lung abscess into the
Typically an empyema cavity becomes infected with
anaerobic organisms and the patient is severely ill with a
high fever and a neutrophil granulocytosis.
Empyemas should be treated by prompt tube drainage or
by rib resection and drainage of the empyema cavity under