Introduction

• Pneumonia is the most fatal hospital acquired infection
• As well as bacteria, other causes include viruses, fungus and parasites.

Epidemiology

• Pneumonia is a dangerous condition, and is responsible for many deaths of patients over the age of 80
• Deaths amongst younger populations have dramatically decreased with the advent of antibiotics.
• Incidence is 1-3 per 1000 (i.e.. 0.1-03% of people have pneumonia at any one time)
• The incidence of bacterial pneumonia amongst those with HIV is higher than in the general population, particularly in IV drug users with HIV. However, the causatory organisms are the same.
• Most cases caused by bacteria, about 15% are viral

Classification

Precipitating factors

• Strep pneumoniae infection often follows viral infection with influenza or parainfluenza.
• Hospitalisation! – hospital acquired infection is often with Gram-negative organisms
• Cigarette smoking – this is the most important risk factor for pneumococcal disease
• Alcohol excess
• Bronchiectesis (e.g. in CF)
• Bronchial obstruction (e.g. carcinoma)
• Immunosupression
• IV drug use
• Dysphagia (both oesophageal and co-ordination disorders – leading to aspiration)

Symptoms

• Typically the same for hospital acquired / non-hopsital acquired cases
• Shortness of breath
• Cough
  • May be productive in adolescents and adults –  Purulent sputum possible
  • Often dry in infants and the elderly
• Fever
• Rigors
• Vomiting
• Headache
• Loss of appetite
• Very occasionally – haemoptysis
• Pleuritic chest pain – which may on occasion radiate to the shoulder (if diaphragm is involved) or the anterior abdominal wall
  • Pleuritic chest pain – a sharp shooting or stabbing pain, usually in the side, that is most painful on inspiration, but can also be felt on expiration, or even whilst talking.
• Upper abdominal tenderness in some patients with lower lobe pneumonia
• Signs of consolidation – both on examination and CXR
• Dyspnoea
• Tachypnoea
• Tachycardia
• Increased secretions – noticeable in ventilated patient in hospital acquired cases

Signs

• Vary with the type of pneumonia present
• In strep pneumoniae
  • Rapid shallow breathing
  • Pleural rub
• Confusion – may be the only sign in elderly patients

Diagnosis

Oxygen saturation – <92% is worrying
Usually an x-ray is performed after clinical suspicion to confirm the diagnosis. The x-ray may show:

• Evidence of infiltrate in the form of consolidation on the x-ray – can also show the spread of any infection by distribution of the infiltrate
• Changes may not appear on x-ray for up to 48 hours after symptoms, however, after effective treatmnet, consolidation may still be seen on x-ray for up to 6 weeks
  • Persistent x-ray changes may suggest underlying carcinoma with secondary pneumonia
  • X-ray should be repeated at least weekly as an inpatient, and then at 6 weeks follow-up. Any signs still present indicate the need for a further x-ray.

Blood cultures may be taken to asses for bacteraemia.
It is not routine practice to attempt to identify the causatory organism in community acquired infection.
FBC

• ↑WCC
• ↑ESR (>100mm/h) and ↑CRP
• Possible anaemia (sign of abscess)
• Blood cultures – in ill patients to check for septicaemia

Urine – in severe cases of pneumonia, where legionella is suspected, urine testing for legionella antigen may be indicated
Pleural fluid aspiration – to asses for organisms. Transthoracic aspiration may be performed (often with CT guidance) to identify lesions (e.g. empyema, abscess) and to gain samples.
The CURB-65 score – is a scale used to assess the severity of community-acquired pneumonia. It predicts the risk of mortality (CURB score 0 = <1% risk, CURB score 5= 60% risk). Each factor of the score is worth 1 point.

• C – Confusion – use the abbreviated mental test (score ≤8)
• U – Urea – >7mmol/L
• Respiratory rate – ≥30/min
• Blood Pressure <90 systolic, or <60 diastolic
• 65 – age >65 years
  • A score ≥3 is severe pneumonia. ≥2 requires hospitalisation.

Differentials

• Pulmonary embolism (PE) – patient is not usually systemically unwell. Shortness of breath is more likely to be sudden onset.
• Pulmonary / pleural TB
• Pulmonary oedema

Treatment

• If not vomiting, and CURB65 score ≤2, oral antibiotics. If severe and/or vomiting, IV antibiotics required, as per sensitivities.
• Keep Oxygen saturation >92%, using oxygen therapy as required
• IV fluids, to prevent dehydration and shock
• Monitor progress – don’t be afraid to repeat CXRs as necessary
• All patients should receive 6 week follow-up including repeat CXR

Complications

Respiratory failure – PaO₂ <8kPa. The most common complication. Relatively easy to treat, with 60% oxygen (high flow).

• If the PaCO₂ rises to >6kPa, or the hypoxia does not resolve with oxygen therapy, transfer to ITU.
• Be careful using O₂ in COPD patients – can reduce the drive to breathe.
• Aim to keep sats at 90-94%
• Do regular ABG testing, and consider intubation if situation not improving

Hypotension – another relatively common feature, thought to be the result of dehydration, and vasodilation due to sepsis. This should be treated if systolic BP drops below 90mmHg, with 250ml of crystalline infusion over 15mins. If systolic BP does not improve, consider transfer to ITU.
Atrial fibrillation – is a common complication in the elderly. It usually resolves with treatment of the pneumonia, but digoxin may be given to reduce the heart rate as short-term therapy.

Pleural effusion – the pleura may become inflamed, which can result in excess fluid production, causing a pleural effusion. In many cases, this will not require treatment, but in some individuals, it may require drainage. Clinical signs (see below) are not usually present until the volume of fluid is >500ml. Rarely, the fluid may become infected, resulting in empyema.
Empyema – typically presents in a patient who has partially recovered, but then develops a spike in temperature. Signs of pleural effusion may be present (decreased chest expansion, dullness, reduced breath sounds, pleural rub – all on affected side. The lung above the effusion can becomes compressed.)

• Fluid aspiration – the fluid is usually yellow, with a pH <7.2, and low levels of glucose. Samples can be obtained via aspiration, bronchoscopy, or sometimes via transthoracic aspiration using ultrasound/CT guidance. About 70% of cases of empyema consist purely of anaerobes, and in the other 30% both aerobic and anaerobic bacteria are present.
• Chest drainage – treatment is with the insertion of a chest drain – usually with radiological guidance. Reducing the risk of adhesions – it was thought that using streptokinase in a wash reduced the risk of adhesions, but there is not much evidence for this, and its use is not routinely recommended.
• Antibiotic therapy – should also be given, usually for 4-6 weeks. This should be something that is effective against both aerobic and anaerobic bacteria, and a typical regimen might include iv doses of cefuroxime and co-amoxiclav for 5 days, followed by 3-5 weeks of metronidazole alone. The treatment of empyema and abscess is typically very similar, however, rarely, abscess might require surgery, whilst empyema does not.

Lobar collapse – most commonly the result of sputum retention
Thromboembolsim
Pneumothorax – particularly with Staph Aureus

Lung abscess

• Is a serious complication.
• A lung abscess is a cavitating lesion containing pus, within the lung.
• Commonly results from aspiration (e.g. alcoholism, inhaled foreign body, oesophageal blockage, bulbar palsy) and also occurs in other instances of bronchial obstruction, e.g. – bronchial carcinoma. Most likely to occur if the pneumonia was not adequately treated.
• Pathology – certain causatory organisms are more likely to cause abscess than others, particularly staph aeurus  and klebsiella pneumoniae.
• In some instances, septic emboli, particularly in the case of staphylococci, can result in multiple lung abscesses.
• More rarely, pulmonary infarction can cavitate, and may become infected, resulting in abscess formation.
• Presentation – this would usually be a pneumonia that worsens despite treatment, with the production of purulent sputum, as a result of the growth of smelly anaerobic organisms. There is likely to be fever, malaise, anaemia and weight loss. Clubbing can occur if the abscess has been present for long enough.
• Investigations
  • X-ray – a walled cavity is visible, usually with a fluid level.
  • Bloods – FBC for anaemia and neutrophilia
  • ESR + CRP – will be raised
  • Sputum sample – microscopy to identify organism
  • Bronchoscopy – sometimes performed to get samples
• Treatment
  • Treat the infection as per antibiotic sensitivities for 4-6 weeks
  • Consider postural drainage to remove excess sputum
  • In serious cases, antibiotic instillation / aspiration, and sometimes even surgical excision may be required

Septicaemia

• Can occur if the bacteria enter the blood stream. May result in infective endocarditis and meningitis, and requires urgent treatment
• Patient will be very systemically unwell
• Take blood cultures to identify the causatory organism, and treat with IV antibiotics

ARDS / renal failure / multi-organ failure
Ectopic abscess – particularly with Staph aureus
Hepatitis, Pericarditis, Myocarditis and meningitis are seen most commonly in mycoplasma pneumoniae infection, which is most prevalent in young adults.

Types of infection in further detail

References

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