Chapter 21


Infectious Diseases Affecting the Respiratory System



Upper Respiratory Tract Infections: Common Cold

   Also called Rhinitis

   Most commonly caused by rhinoviruses, coronaviruses, and adenoviruses

   There is typically no fever, but malaise, scratchy throat, runny nose, sneezing, and cough are frequently exhibited

   Involve local inflammatory reactions characterized by swelling of nasal mucosa and increased production of mucus

   Transmitted by inhalation or fomites

   Most treatments alleviate the symptoms but dont affect the virus

   Can predispose patient to secondary infections by other microorganisms





   Pain and pressure in the sinus region with drainage that may be greenish, headache, or facial tenderness

   Bacterial causes include: Haemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus

   Fungal causes include Aspergillis




Otitis Media (Ear Infection)

   Viral infections may lead to inflammation of the eustachian tubes and buildup of fluid in the middle ear

   Earache, fever, vomiting, loss of hearing, may lead to ruptured eardrum

   Causative agents include: Haemophilus influenzae and Streptococcus pneumoniae

   Treatments include removal of adenoids, ear tubes, and antibiotics




Streptococcal Pharyngitis (Strep Throat)

   Caused by Streptococcus pyogenes

   Results in redness, swelling and tenderness of throat, fever, headache, nausea, and difficulty swallowing

  May also result in white pus-filled nodules on the tonsils

   Transmitted via respiratory droplets or contact with mucus secretions

   Treat with antibiotics early

   Untreated S. pyogenes infections can lead to several complications:

  Scarlet fever

  erythrogenic toxin causes sandpaperlike rash on the skin and high fever

  Rheumatic fever

  fever, joint pain, rash, chest pain

  involves the heart, skin, joints, and brain

  Subacute bacterial endocarditis

  damaged heart valves subject to infection

  Acute glomerulonephritis

  antigen-antibody complexes cause inflammation of the kidneys





   Caused by the bacterium Corynebacterium diphtheriae

   Symptoms include low-grade fever, sore throat, vomiting, and lymph node enlargement

   Diptheria exotoxin - absorbed into the blood stream causing damage to the heart, nerves, and kidneys

   A characteristic pseudomembrane  usually forms on the tonsils or pharynx

  a grayish film consisting of inflammatory cells and fluid

  can block airway resulting in asphyxiation

   Prevented with DPT toxoid vaccine

  treat with anti-toxin or antibiotics if exposed





Lower Respiratory Tract Infections: Pertussis

   Whooping cough is caused by Bordetella pertussis

   Disease has 3 distinct stages:

  Catarrhal Stage symptoms include nasal drainage, congestion, and sneezing

  Paraoxysmal stage - violent, uncontrollable coughing followed by deep inspiration which gives off a whoop sound

  Convalescent stage bacteria and symptoms are gone, but patient is susceptible to secondary infections

   Virulence factors include: filamentous hemagglutinin (Fha), pertussis toxin (Ptx) and tracheal cytotoxin

  help the bacteria to attach to and destroy the respiratory epithelium resulting in a build-up of mucus

   Secondary bacterial infection is chief cause of death due to damage in respiratory tract

   Transmitted via respiratory droplets

   Acellular DPT vaccine prevents infection

  treated with antibiotics




Respiratory Syncytial Virus

   Children under 6 months of age and premature babies are susceptible to disease

   The virus enters the respiratory tract and causes cells to fuse together creating a clump of cells known as a syncytia

  cells die and slough off causing a clogging of the bronchi; patients are often susceptible to secondary infections because of this

   Experience symptoms of croup and bronchiolitis:  runny nose, cough, fever, wheezing, difficulty breathing, and a dusky skin color from lack of oxygen

   Transmitted by droplets or fomites

   Treated with antivirals or passive antibodies




Influenza (Flu)

   Caused by influenza viruses A, B, and C

  Most epidemics and pandemics of influenza are the result of influenza A virus because it can undergo antigenic drifts and shifts

  virus constantly mutates hemagglutinin (H) and neuraminidase (N) receptor genes to     evade host immunity

   Symptoms include fever, head and muscle aches, chills, lack of energy, and dry cough

   Virus damages respiratory epithelium and deaths are commonly attributed to secondary bacterial infections such as pneumonia

   Spread via respiratory droplets and fomites

   Prevented with subunit vaccine, attenuated nasal vaccine, or anti-virals early





   Caused by the airborne bacteria Mycobacterium tuberculosis

  an acid-fast, rod shaped bacterium

  the bacteria are inhaled, phagocytized by macrophages of the lung tissue, and multiply within them

   Most infections are asymptomatic, but clinical tuberculosis is divided into 3 stages:

  Primary tuberculosis - leukocytes surround the bacteria-containing macrophages resulting in the formation of a tubercle

  Lesions can form when tissue-damaging enzymes are released from leukocytes

  Cell-mediated immune response to the bacteria can be detected using the TB skin test

  Reactivation tuberculosis - results when tubercles expand and bacteria drain into the respiratory tract

  symptoms include violent coughing, greenish or bloody sputum, low grade fever, weight loss, extreme fatigue, night sweats, and chest pain leading to body wasting called consumption

  Disseminated tuberculosis can involve kidneys, bones, genital tract, brain, and meninges and is usually fatal

   Transmitted via respiratory droplets

   Treat with a combination of antibiotics for 2-12 months

  multi-drug-resistant TB (MDRTB) are common due to noncompliance

  an attenuated BCG vaccine is available

  a new extensively drug resistant strain called   XDR-TB was identified in 2006





   Inflammatory condition where fluid fills the alveoli of the lung

   Can be caused by a variety of microorganisms

   Symptoms include fever, headache, cough, painful breathing, and sputum containing blood & pus


Pneumonia:  Causes

   Streptococcus pneumoniae (Pneumococcal)

  Gram-positive, alpha-hemolytic diplococcus in the upper respiratory tract of 5-50% of healthy people

  Is the leading cause of community-acquired pneumonia in older adults

  The capsule is its primary virulence factor but pneumolysin is similar to streptolysin of S. pyogenes

  Complications include:  pleurisy, septicemia, endocarditis and meningitis

  Polysaccharide conjugate vaccine is available or antibiotics early

   Legionella pneumophila

  Commonly found in amoeba in warm natural waters and resists heating, cooling, and some chlorines

  allows the bacteria to survive in air conditioners, poorly treated pools, showers, and vegetable sprayers in supermarkets

  Can cause lung abscesses, pneumonia and fatal respiratory failure

  Treat with combination of antibiotics

   Mycoplasma pneumoniae

  A small bacterium lacking a cell wall

  Leading cause of pneumonia in college students and is also common among military recruits

  Generally mild disease and is often referred to as walking pneumonia


  Zoonosis involves humans in close proximity to mouse populations

  transmission via airborne dust containing urine, feces, or saliva of infected rodents

  Can cause pulmonary edema and acute respiratory distress syndrome (ARDS)

  severe breathing difficulties and drop in blood pressure

   Histoplasma capsulatum

  Fungal spores are widespread and mainly found in soils contaminated by bird or bat droppings

  A small inhaled dose survives in macrophages and is carried to other sites

  Usually produces mild respiratory symptoms, but a few develop more severe symptoms

  Chronic pulmonary histoplasmosis signs and symptoms similar to tuberculosis

  Infections in immunocompromised individuals can lead to lesions in the brain, intestines, heart, liver, spleen, bone marrow, and skin

  Treat with anti-fungal medications for weeks

   Pneumocystis jiroveci

  Pneumocystis pneumonia is the most frequent opportunistic infection in AIDS patients

  Most infections in immunocompetent individuals are asymptomatic

  Treat with anti-fungals

   Klebsiella pneumoniae

  Primary cause of most nosocomial infections

  bacteria access LRT through abnormal breathing, aspiration of normal flora from URT, or mechanical ventilation

  Can cause lung abscesses and endotoxic shock

  Treat with antibiotics early