1. Pneumonia

2. Community-acquired pneumonia (CAP)
UK figures suggest that an estimated 5-11/1000 adults suffer from CAP each year, accounting for around 5-12% of all lower respiratory tract infections.
The incidence varies with age, being much higher in the very young and very old, in whom the mortality rates are also much higher.
World-wide, CAP continues to kill more children than any other illness.

3. Community-acquired pneumonia (CAP)
Most cases are spread by droplet infection and occur in previously healthy individuals but several factors may impair the effectiveness of local defences and predispose to CAP. 
Strep. Pneumoniae remains the most common infecting agent, and thereafter, the likelihood that other organisms may be involved depends on the age of the patient and the clinical context.
Viral infections are an important cause of CAP in children, and their contribution to adult CAP is increasingly recognised.

4. Clinical features
Pneumonia usually presents as an acute illness in which systemic features such as fever, rigors, shivering and vomiting predominate .
Pulmonary symptoms breathlessness and cough, painful and dry, but later accompanied by the expectoration of mucopurulent sputum.
Proteinaceous fluid and inflammatory cells congest the airspaces, leading to consolidation of lung tissue.
This improves the conductivity of sound to the chest wall (bronchial breathing and whispering pectoriloquy).
Crackles are often also detected

5. Common clinical features of community-acquired pneumonia (CAP)
Streptococcus : Rapid onset, high fever and pleuritic chest pain;.
Mycoplasma pneumoniae: Children and young adults.
Rare complications include haemolytic anaemia, Stevens- Johnson syndrome, erythema nodosum, myocarditis, pericarditis, meningoencephalitis, Guillain-Barré syndrome.
Legionella pneumophila:Middle to old age. Local epidemics around contaminated source, e.g. cooling systems in hotels, hospitals. Person-to-person spread unusual. Chlamydia pneumoniae, Haemophilus influenzae, Staphylococcus aureus.

6. Investigations
The objectives are to exclude other conditions that mimic pneumonia ,assess the severity, and identify the development of complications.
A chest X-ray usually provides confirmation of the diagnosis. In lobar pneumonia, a homogeneous opacity localised to the affected lobe or segment usually appears within hours of the onset of the illness .
Radiological examination is helpful if a complication such as parapneumonic effusion, intrapulmonary abscess formation or empyema is suspected.

7. Pneumonia of the right middle lobe

8. Investigations
Many cases of CAP can be managed successfully without identification of the organism, particularly if there are no features indicating severe disease.
A full range of microbiological tests should be performed on patients with severe CAP .
The identification of Legionella pneumophila has important public health implications and requires notification. In patients who do not respond to initial therapy, microbiological results may allow its appropriate modification.
Microbiology also provides useful epidemiological information

9. Gram stain of sputum showing Gram-positive diplococci characteristic of Strep. pneumoniae (arrows).

10. Investigations All patients:
Sputum:direct smear by Gram and Ziehl-Neelsen stains. Culture and antimicrobial sensitivity testing
Blood culture: frequently positive in pneumococcal pneumonia
Serology: acute and convalescent titres for Mycoplasma, Chlamydia, Legionella, and viral infections. Pneumococcal antigen detection in serum or urine
PCR: Mycoplasma can be detected from swab of oropharynx

11. Investigations
Severe community-acquired pneumonia The previous tests plus consider:
Tracheal aspirate, induced sputum, bronchoalveolar lavage, protected brush specimen or percutaneous needle aspiration. Direct fluorescent antibody stain for Legionella and viruses
Serology: Legionella antigen in urine.
Pneumococcal antigen in sputum and blood. Immediate IgM for Mycoplasma
Cold agglutinins: positive in 50% of patients with Mycoplasma

12. Investigations
Pulse oximetry provides a non-invasive method of measuring arterial oxygen saturation (SaO2) and monitoring response to oxygen therapy.
Arterial blood gas is important in those with SaO2 < 93% or with features of severe pneumonia, to identify ventilatory failure or acidosis.
The white cell count may be normal or only marginally raised in pneumonia caused by atypical organisms, whereas a neutrophil leucocytosis of more than 15 × 109/L favours a bacterial aetiology.
A very high (> 20 × 109/l) or low (< 4 × 109/l) white cell count may be seen in severe pneumonia.
Urea and electrolytes and liver function tests should also be checked.
The C-reactive protein (CRP) is typically elevated

13. Management
Oxygen: should be administered to all patients with tachypnoea, hypoxaemia, hypotension or acidosis with the aim of maintaining the PaO2 ≥ 8 kPa (60 mmHg) or SaO2 ≥ 92%. High concentrations (≥ 35%), preferably humidified, should be used in all patients who do not have hypercapnia associated with COPD.
Assisted ventilation should be considered at an early stage in those who remain hypoxaemic despite adequate oxygen therapy.
Noninvasive Ventilation (NIV ) may have a limited role but early recourse to mechanical ventilation is often more appropriate

14. Management Fluid balance:
Intravenous fluids should be considered in those with severe illness, in older patients and in those with vomiting.
Otherwise, an adequate oral intake of fluid should be encouraged.
Inotropic support may be required in patients with circulatory shock.

15. Antibiotic treatment
Prompt administration of antibiotics improves outcome.
The initial choice of antibiotic is guided by clinical context, severity assessment, local knowledge of antibiotic resistance patterns, and at times epidemiological information, e.g. during a mycoplasma epidemic.
In most patients with uncomplicated pneumonia a 7-10-day course is adequate, although treatment is usually required for longer in patients with Legionella, staphylococcal orKlebsiella pneumonia.
Oral antibiotics are usually adequate unless the patient has severe illness, impaired consciousness, loss of swallowing reflex or malabsorption.

16. Management Most patients respond promptly to antibiotic therapy.
However, fever may persist for several days and the chest X-ray often takes several weeks or even months to resolve, especially in old age.
Delayed recovery suggests either that a complication has occurred or that the diagnosis is incorrect .
Alternatively, the pneumonia may be secondary to a proximal bronchial obstruction or recurrent aspiration.
The mortality rate in adults managed at home is very low (< 1%); hospital death rates are typically between 5 and 10%, but may be as high as 50% in severe illness

17. Antibiotic treatment for CAP
Uncomplicated CAP :Amoxicillin 500 mg 8-hourly orally.
If patient is allergic to penicillin: Clarithromycin 500 mg 12- hourly orally or Erythromycin 500 mg 6-hourly orally.
If Staphylococcus is cultured or suspected: Flucloxacillin 1-2 g 6- hourly i.v. plus Clarithromycin 500 mg 12-hourly i.v.
If Mycoplasma or Legionella is suspected: Clarithromycin 500 mg 12-hourly orally or i.v. or Erythromycin 500 mg 6-hourly orally or i.v. plus Rifampicin 600 mg 12-hourly i.v. in severe cases.
Severe CAP: Clarithromycin 500 mg 12-hourly i.v. or Erythromycin 500 mg 6-hourly i.v. plus Co-amoxiclav 1.2 g 8-hourly i.v. or Ceftriaxone 1-2 g daily i.v. or Cefuroxime 1.5 g 8-hourly i.v. or Amoxicillin 1 g 6-hourly i.v. plus flucloxacillin 2 g 6-hourly i.v.

18. Management

19. Complications of pneumonia
Para-pneumonic effusion-common
Empyema .
Retention of sputum causing lobar collapse
DVT and pulmonary embolism
Pneumothorax, particularly with Staph. aureus
Suppurative pneumonia/lung abscess
ARDS, renal failure, multi-organ failure
Ectopic abscess formation (Staph. aureus)
Hepatitis, pericarditis, myocarditis, meningoencephalitis
Pyrexia due to drug hypersensitivity