Pneumonia

Definition
Pneumonia denotes infection of the lung tissue and may be caused by bacteria, viruses or fungi. It is classified into community-acquired pneumonia (CAP) or health care associated pneumonia (HCAP).

Epidemiology
In Singapore, pneumonia is the third leading cause of death and is the fifth most common cause of hospitalisations. There are roughly 11,000 patients a year admitted to hospitals with pneumonia. It is most serious for infants, young children, adults > 65 years, people who have underlying health conditions and those whose immune systems are compromised.

Common pathogens

  • Community-acquired pneumonia: This is the most common type of pneumonia. It can be classified into atypical and typical community-acquired pneumonia
    1. Typical: It is most often caused by Streptococcus pneumoniae which usually affects one lobe of the lung. Bacterial pneumonia can occur on its own or after a preceding common cold or “flu”.
    2. Atypical: Bacteria such as Mycoplasma pneumoniae cause pneumonia. Other causes of atypical pneumonia are Chlamydia pneumoniae, Legionella pneumophilia. Viruses such as influenza, adenovirus, SARS virus or more recently, the MERS coronavirus, can also cause atypical pneumonia.
  • Health care associated pneumonia: This form of pneumonia occurs in people who have recently stayed in the hospital, nursing home or used a day surgery facility. HCAP also covers persons who regularly attend outpatient medical facilities such as dialysis centres. The illness can be more severe as the bacteria causing HCAP are often more resistant to antibiotics and the persons who fall ill with HCAP often have an underlying medical condition. Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas aeruginosa are frequent pathogens. People in long-term facilities (such as nursing homes) or are on kidney dialysis at a dialysis facility are also at higher risk for HCAP.
  • Aspiration pneumonia: This type of pneumonia may occur both in the setting of CAP and HCAP. It occurs when you inhale food, drink, vomit or saliva into the lungs. This is often associated with impaired conscious state such as with brain injury, excessive alcohol or drugs. It can also occur when there is an underlying swallowing problem. Streptococcus pneumoniae, Staphylococcus aureus and oral flora such as Fusobacterium can be potential causes.

Clinical Symptoms

  • Cough productive of greenish or reddish phlegm
  • Chest pain, especially with breathing
  • High fever
  • Breathlessness
  • Difficulty breathing and reduced effort tolerance

Diagnostic Tests

  • Blood tests for elevated white blood cells indicating infection, serology tests for identification of bacteria and oxygen and carbon dioxide levels in the blood. In severe pneumonia, the bacteria may spread into the blood stream and this can be detected in the blood.
  • Chest X-ray to check for the presence of pneumonia
  • Examination of sputum sample where a sample of the sputum (phlegm) is obtained to determine which organism is causing the infection
  • If treatment does not improve the infection, a bronchoscopy may be needed.

Treatment
Pneumonia can be a life threatening illness. Community-acquired pneumonia due to bacteria are treated with antibiotics. There are various simple scoring systems that doctors use to stratify the severity of pneumonia in each patient and this helps to assist with the decision for inpatient or outpatient care. Hospitalisation is often required if children are younger than 3 months who are breathless and drowsy. If adults are confused, have rapid breathing, have low blood pressure and are at least 65 years old, inpatient care is usually recommended. The specific antibiotic to be prescribed is individualized depending on risk factors and severity of illness.

For HCAP, antibiotics are prescribed and other supportive care is important. In patients with severe pneumonia and who exhibit worsening parameters, the doctor may advise intubation and taking over the breathing function using a machine (ventilator support) to improve the chances of survival.

Prevention
Pneumonia can be prevented by:

  • Getting annual influenza immunization as pneumonia can occur following influenza
  • Getting pneumococcal vaccination (against Streptococcus pneumoniae). It is recommended for everyone 65 years old and above, those with a weakened immune system due to HIV or cancer, anyone living in nursing homes and long-term care facilities and smokers.

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