Lower Respiratory Tract Infections - Clinical syndromes, Bronchitis, Bronchiolitis, Pneumonia, Pleural infections

Clinical syndromes of Lower Respiratory Tract Infection (LRTI)

Lower respiratory tract infection (LRTI) can clinically manifest as

• Bronchitis

• Bronchiolitis

• Pneumonia

• Pleural infection

Bronchitis

Bronchitis, a manifestation of Lower Respiratory Tract Infection (LRTI), is an infection of the main airways of the lungs (bronchi) resulting in inflation and irritation of the bronchus. It can be divided into two types:

Acute bronchitis

Acute bronchitis is characterized by inflammation of the tracheobronchial tree. It may be a part of or preceded by upper respiratory tract infections such as influenzae (the “flu”) or the common cold.

It is characterized by cough, variable fever, croup, and sputum production. Sputum (pus from the lungs) is often clear at the onset but may become purulent as the illness persists.

Major causes of acute bronchitis

Bacteria:

• Bordetella pertussis (in infants and school children)

• B. parapertussis

• Mycoplasma pneumoniae

• chlamydia pneumoniae

Viruses: commonly influenzae virus, adenovirus, rhinovirus, coronavirus

less commonly = RSV, human metapneumovirus, coxsackie A21 virus

Chronic bronchitis

Chronic bronchitis is a common condition affecting about 10-25% of adults. This disease is defined by clinical symptoms in which excessive mucus production leads to coughing up sputum on most days for at least 3 consecutive months for more than 2 successive years.

Cigarette smoking, previous respiratory infection, and inhalation of dust or fumes are important contributing factors, and patients with chronic bronchitis can suffer from acute flare-ups of infection.

Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis are the causative agents.

Bronchiolitis

Bronchiolitis is an acute viral lower respiratory tract infection, in which the inflammation of the smaller diameter bronchiolar epithelial surfaces primarily occurs during the first 2 years of life.

Clinical manifestations include acute onset of wheezing and hyperinflation, cough, rhinorrhea (running nose), tachypnea (rapid breathing), respiratory distress, etc.

It is primarily caused by viruses and the viruses that cause bronchiolitis include:

• RSV (accounts for 40-80% of cases; cases increase during winter to early spring)

• Parainfluenza viruses type 1-3

• Rhinovirus

• Adenovirus

• Influenza virus

• Enterovirus

• Human metapneumovirus

Initially, the viruses replicate in the epithelium of the upper respiratory tract. In the case of infants, it rapidly spreads to the lower tract airways. Early inflammation of the bronchial epithelium progresses to necrosis.

A specific viral etiology is identified by viral isolation (mostly from infants) from respiratory secretions (preferably from the nasal wash) and if required, hospitalization is recommended.

Pneumonia

Pneumonia is the inflammation of the lower tract involving the lung's airways and supporting structures. It is the major cause of illness and death. There are major categories of pneumonia -

• Community-acquired pneumonia

• Hospital-acquired pneumonia (within 2 days of admission)

• Ventilator-associated (within 2 days of admission)

• healthcare-associated – affects only patients hospitalized

Symptoms include fever, chills, chest pain, and cough.

In past, pneumonia was classified into 2 groups based on whether the cough was productive or non-productive for mucoid sputum.

1. Typical or acute pneumonia (eg: Streptococcus pneumoniae)

2. Atypical pneumonia

* Atypical pneumonia pathogens include (Mycoplasma pneumoniae, Legionella pneumophila, and Chlamydophila pneumoniae) and symptoms are similar to that of typical bacterial pneumonia.

Pleural infections

Microorganisms when infecting the lungs, subsequently gain access to the pleural space through an abnormal passage (fistula). The patient may then develop empyema (pus in the body cavity such as the pleural cavity).

Symptoms are insidious as an early course of the Lower Respiratory Tract Infection (LRTI) is related to the primary infection of the lung and can be detected by physical and radiography (empyema).

Pleural cavity

Pleura is the thin covering that protects and cushions the lungs. The pleural cavity/space is the tiny area between two layers of pleura. It is normally filled with a small amount of fluid.