Lower repsiratory tract

what counts as the lower respiratory tract?

Trachea → bronchi → bronchioles → lungs/alveoli

what are some host defence systems do we have

elaborate system of host defenses, including humoral immunity, cellular immunity, and anatomic mechanisms

when does infection occur

if one of these systems fail

what are the 3 common lower repsiratory track infections

1. Bronchitis
2. Bronchiolitis
3. Pneumonia

what is humoral immunity

protective substances/antibodies found in body fluids and secretions.

what is cellular immunity

immune cells that recognize and eliminate pathogens.

what is Anatomic/mechanical defenses

physical ways the respiratory system prevents pathogens from reaching the lungs, such as mucus, cilia, coughing, and the structure of the airways.

what is main site affected with bronchitis

Bronchi

main site affected if you have Bronchiolitis

Bronchioles

main site affected if you pneumonia?

Lung tissue, especially alveoli

how do pulmonary infections usually occur?

Bacteria or other pathogens can live in the upper respiratory tract (mouth/throat). Small amounts of saliva or mucus containing those pathogens can accidentally be aspirated (breathed) into the lungs, where they may cause a pulmonary infection such as pneumonia.

what is a less common way?

Less common, microbes enter the lung via the blood from an extrapulmonary source or by direct inhalation of infected
aerosolized particles

how come if a agent reaches the target it still may not cause infection?

Just because a microorganism reaches the lungs doesn't guarantee infection.

Whether it establishes an infection depends on things like age, lifestyle/habits, airway anatomy, and characteristics of the pathogen.

LRIs in children and adults
most commonly result from?

either viral or bacterial invasion
of lung parenchyma

what is bronchitis

is an inflammatory condition of the large and small airways → the tracheobronchial tree

• excludes alveoli

what structures are in the tracheobronchial tree

Trachea → primary bronchi → smaller bronchi → bronchioles

what are the 2 types of bronchitis?

1. Acute bronchitis (AB)

2. Chronic bronchitis (CB)

what is Acute bronchitis (AB)

inflammation of the epithelium of the large airways resulting from infection or smoke inhalation

• AB symptoms are short-lived and last <1 month

what is Chronic bronchitis (CB)

chronic cough producing sputum lasting more than 3 months for 2 consecutive years without an underlying etiology of bronchiectasis or tuberculosis

what type of infection is AB most of the time?

About 85–95% of acute bronchitis cases are associated with respiratory viruses.

• Acute bronchitis → think VIRUS first, not bacteria.

• The common viral causes listed are influenza A, RSV, and parainfluenza virus. Rhinovirus and adenovirus can also cause it.

whats something that can happen to patient if they bacterial bronchititis

a secondary bacterial infection can sometimes occur, particularly in someone with an underlying co-morbidity.

• Co-morbidity = another disease/condition that the patient already has at the same time.

signs and symptoms of acute brochitits?

• Acute bronchitis often starts as a URI

• The key symptom of acute bronchitis is cough.

can fever occur?

Fever can occur, but it rarely exceeds 39°C.

It's particularly associated with infections such as influenza, adenovirus, SARS-CoV-2, and Mycoplasma pneumoniae.

• So a very high or persistent fever could make clinicians consider diagnoses beyond uncomplicated acute bronchitis, such as pneumonia.

Distinguishing bronchitis from asthma/bronchiolitis

Acute bronchitis primarily involves the bronchi and is dominated by cough.

Asthma and bronchiolitis are more likely to produce prominent:

Wheezing = whistling sound caused by narrowed airways
Dyspnea = shortness of breath/difficulty breathing
Hypoxemia = abnormally low oxygen in the blood

• For acute bronchitis, think:

  URI → bronchial inflammation → persistent cough ± sputum

why are Bacterial cultures of expectorated sputum not useful for acute bronchitis?

Expectorated sputum = mucus/phlegm that the patient coughs up.

• 85–95% of acute bronchitis is viral.

• sputum passes through the mouth and upper respiratory tract, so the sample can contain organisms that are colonizing those areas rather than actually causing the bronchitis.

What about viral testing? for acute bronchitits?

Routine viral testing/cultures also usually aren't necessary because knowing the exact virus often doesn't change management for uncomplicated acute bronchitis.

Testing becomes more relevant when patients have important risk factors such as:

• COPD

• Congestive heart failure

• Immunocompromise

why is etiologic diagnosis unessecary for acute broncitits?

For most patients, we don't need to determine the exact microorganism causing their acute bronchitis

• Why? Because regardless of which respiratory virus caused it, uncomplicated AB is generally treated with supportive care.

how do you treat bacterial acute bronchitits

• If bacterial infection is suspected/confirmed, the antibiotic should ideally be chosen based on the specific pathogen.

• due to the increasing antimicrobial resistance, antibiotics should be only be administered upon culture serology or PCR confirmation in patients not responding to supportive care

what about Viral acute bronchitis?

Since most acute bronchitis is viral, antibiotics won't work.

Antiviral drugs are available for certain viruses, particularly influenza, but antiviral resistance can occur, especially with inappropriate/overuse.

That's why antivirals aren't simply given for every respiratory viral infection.

What is bronchiolitis?

Bronchiolitis = acute viral infection and inflammation of the bronchioles.

Remember the airway pathway:

Trachea → bronchi → bronchioles → alveoli

Why is bronchiolitis especially important in infants?

Infants naturally have very small bronchioles. During a viral infection:

Virus infects bronchioles → inflammation → bronchiolar wall swells + mucus production → airway lumen becomes narrower

• Because an infant's bronchiole is already tiny, even a relatively small amount of swelling and mucus can substantially obstruct airflow.

who are most affected by bronchiolitits

• infants within first year of life

• elderly

• immunocompromised

symptoms of bronchiolitis

often starts like an upper respiratory infection

For the first 1–4 days, the child may have symptoms that look like a regular URI:

Nasal congestion + rhinorrhea (runny nose) + cough + low-grade fever

• self-limiting and symptoms diminish within 7 to 10 days with resolution within 28 days

• treatment in many uncomplicated cases is mainly supportive rather than antibiotics.

Why can infants become dehydrated from bronchiolitis

Infants with bronchiolitis may have:

Coughing/difficulty breathing → harder to feed/drink

At the same time, fever, vomiting, or diarrhea can increase fluid losses.

what is RSV?

Respiratory syncytial virus

• is the most common cause of pediatric bronchiolitis, accounting for up to 75% of all cases

• Bacteria serve as secondary pathogens in a minority of cases

what are different ways we can identify the pathogen causing bronchiolitis/LRIs?

1. culture based method (gold standard) - Growing the actual pathogen

2. ELISA and fluorescent antibody staining - Viral antigens

3. PCR - Viral genetic material

4. Chest X-ray

what is ELISA and fluorescent antibody staining?

hey look for viral antigens.

An antigen is a component of the pathogen that can be recognized by antibodies.

For bronchiolitis, a sample of nasopharyngeal secretions can be collected.

• Prone to false-negative detection depending on infection stage

how does PCR work?

PCR detects the pathogen's genetic material (DNA/RNA).

Bronchiolitis treatments for healthy patients

Bronchiolitis is usually self-limiting, meaning the immune system eventually clears the viral infection.

Treatment therefore focuses on symptoms:

Antipyretics → reduce fever
Adequate fluids → prevent/treat dehydration

what about for n hospitalized patients for Bronchiolitis

• oxygen therapy and intravenous (IV) fluids to treat dehydration

• - Clinicians also consider whether underlying cardiac or pulmonary disease is making the respiratory illness more severe.

what is Ribavirin

antiviral medication.

an antiviral against a variety of RNA and DNA viruses, including RSV, influenza A, influenza B, parainfluenza, and adenovirus

when can you use ribavirin

• it is approved only in aerosolized form against RSV
• Only used for severely ill patients
• Preventative: Vaccines for influenza A/B and now RSV

What is pneumonia?

infection and inflammation of the lung parenchyma.

• It is a year-round illness due to different infectious agents that vary with seasons
• occurs in persons of all ages but most severe in the very young, the elderly, and the chronically ill

how pneumonia caused?

Is caused by inspiration of ambient air into the lower respiratory tract with contaminated environmental and infectious particulate matter

Why can pneumonia cause sepsis?

If the infection becomes severe, the body's response may become systemic rather than remaining localized to the lungs.

• sepsis = Sepsis is a dangerous, systemic response to an infection where the immune response becomes dysregulated and starts causing organ dysfunction.

  
  

Three routes of infection for pneumonia

1. Direct inhalation of infectious droplets

2. Aspiration of oropharyngeal contents (URI)

3. Hematogenous (bloodstream) spread from another infection site

why dont pathogens automatically cause pneumonia?

Your lungs have host defenses, including both:

Innate immunity = immediate, nonspecific defenses
→ mucus/cilia, cough reflex, alveolar macrophages, etc.

Adaptive immunity = specific immune responses
→ B cells/antibodies and T cells.

what is Community-acquired pneumonia (CAP)

CAP = pneumonia acquired outside of a hospital, or that becomes apparent within the first 48 hours of hospitalization.

what is Hospital-acquired Pneumonia (HAP

occurs in the hospital after at least 48 hours of hospitalization

what is Ventilator-acquired Pneumonia (VAP

occurs following 48 hours of endotracheal intubation

is pneumonia that develops in someone who is on a mechanical ventilator to help them breathe.

Normally, your upper airway has defenses that help prevent pathogens from reaching the lungs. With a ventilator, a breathing tube goes into the airway, which can make it easier for microorganisms to reach the lower respiratory tract.

pneumonia symptoms

high fever, chills, malaise with cough, increased sputum production, dyspnea, chest pain

• Dyspnea = difficulty/shortness of breath, which can occur because alveolar inflammation impairs gas exchange.

• immune activation → WBC count may increase

What is a pulmonary infiltrate?

A pulmonary infiltrate is an abnormal area seen on lung imaging where normally air-filled lung tissue has become denser because it contains things such as fluid and inflammatory cells.

how can chest xrays help

help identify pulmonary infiltrates

what is recommended for HAP or VAP

Blood cultures and non-invasive sputum cultures are recommended

• Confirmation of CAP etiology is only for severe CAP

what is primary goal of pneumonia treatment?

Eradication of the offending organism through selection of the appropriate antibiotic(s) or antiviral(s) and subsequent complete clinical cure is the primary goal.

• Secondary goals include minimization of the unintended consequences of therapy, including toxicities and risk of acquiring secondary infection

Why use combination antibiotic therapy for treating pneumonia

For some serious bacterial pneumonias, especially when multidrug-resistant (MDR) bacteria are a concern, more than one antibiotic may be used.

Multidrug-resistant bacteria = bacteria resistant to multiple classes of antibiotics.

Older antibiotics considered as last-resort drugs due to their toxic side-effects are increasingly being used ex. polymyxins and aminoglycosides

how to treat viral pneumonia

specific antiviral therapy, supportive care, or prevention through vaccination/other preventive measures.

• Acyclovir used to treat varicella (chickenpox) and herpes simplex related viral pneumonias