respiratory system infections - humsc
TRANSCRIPT
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Respiratory system infections
Microbiology Lecture 1 RS Module
Ashraf KhasawnehFaculty of Medicine
The Hashemite University
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THE RESPIRATORY SYSTEM
• A major portal of entry for infectious organisms
• It is divided into three tracts – upper , middle and lower.– The division is based on structures and functions in each part.
• The three parts have different types of infection.
• The upper respiratory tract:– Mouth, nasal cavity, sinuses and pharynx
– Infections are fairly common.
– Usually nothing more than an irritation
• The middle respiratory tract:– Epiglottis, larynx, trachea, bronchi and bronchioles
– 80-90% of infections are viral
• The lower respiratory tract:– Lungs and alveoli
– Infections are more dangerous.
– Can be very difficult to treat
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ANATOMY OF THE RESPIRATORY SYSTEM
• The most accessible system in the body:– Breathing brings in clouds of potentially
infectious pathogens.
• The body has a variety of host defense
mechanisms:– Innate immune response
– Adaptive immune response
• Upper respiratory tract is continuously
exposed to potential pathogens.
• Lower respiratory tract is essentially a
sterile environment.
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NORMAL FLORA OF THE RESPIRATORY TRACT
• Generally limited to the upper respiratory tract
• Gram-positive bacteria (streptococci and staphylococci)
very common
• Disease-causing bacteria are present as normal flora; can
cause disease if their host becomes immunocompromised
or if they are transferred to other hosts (Streptococcus
pyogenes, Haemophilus influenza, Streptococcus
pneumonia, Neisseria meningitides, Staphylococcus
aureus)
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PATHOGENS OF THE RESPIRATORY SYSTEM
• Many bacterial organisms infect the
respiratory system.
• Upper respiratory tract also portal of entry for
viral pathogens.
• Vaccination has eliminated many respiratory
infections.– Some still seen in underdeveloped parts of the
world.
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PATHOGENS OF THE RESPIRATORY
SYSTEM
• Respiratory pathogens are easily transmitted from human to human.
– They circulate within a community.
– Infections spread easily.
• Some respiratory pathogens exist as part of the normal flora.
• Others are acquired from animal sources –zoonotic infections.
– Q fever from farm animals
– Psittacosis from parrots and other birds
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PATHOGENS OF THE RESPIRATORY SYSTEM
• Water can be a source of respiratory infections.– Legionellosis– Contaminated water can be aerosolized.– Droplets can be inhaled, and infection can result.
• Fungi are also a source of respiratory infection.– Usually in immunocompromised patients– Most dangerous are Aspergillus and Pneumocystis.
• Some pathogens are restricted to certain sites.– Legionella only infects the lung.
• Other pathogens cause infection in multiple sites.– Streptococcus can cause:
• Middle ear infections.• Sinusitis.• Pneumonia.
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DEFENSES OF THE RESPIRATORY SYSTEM
• The respiratory system has significant
defenses.
• The upper respiratory tract has:– Mucociliary escalator.
– Coughing.
• The lower respiratory tract has:– Alveolar macrophages.
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DEFENSES OF THE RESPIRATORY SYSTEM
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BACTERIA INFECTING THE RESPIRATORY
SYSTEM
• Can be divided into groups depending on the
infections they cause– Otitis media, sinusitis, and mastoiditis
– Pharyngitis
– Typical and atypical community-acquired
pneumonia
– Hospital-acquired (nosocomial) pneumonia
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Upper Respiratory Tract Diseases Caused by
Microorganisms
• Rhinitis, or the Common Cold
– Symptoms: sneezing, scratchy throat, runny nose
(rhinorrhea)
– Symptoms begin 2-3 days after infection
– Usually not accompanied by fever
– Net result: nasal obstruction, nasal discharge
– Causative agents: Rhinovirus, Adenovirus, Coronavirus,
Parainfluenza virus, Influenza virus, RSV
– Rarely caused by bacteria or Fungi
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Pharyngitis
• Inflammation of the throat
• Pain and swelling, reddened mucosa, swollen tonsils,
sometime white packets of inflammatory products
(exudate), petechial hemorrhages
• Mucous membranes may swell, affecting speech and
swallowing
• Often results in foul-smelling breath
• Incubation period: 2-5 days
• DDx of follicular tonsillitis: Strep. Pyogens,
Adenoviral infection, Candida albicans.
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Sinusitis• Commonly called a sinus infection
• Most commonly caused by
• Local: URTI produce edema of antral tissues, nasal septum deviation, enlarged adenoids, tumor or foreign body in the nasal cavity
• Systemic: Allergy, cystic fibrosis and immunodeficiency.
• Symptoms: nasal congestion, pressure above the nose or in the forehead, feeling of headache or toothache
• Facial swelling and tenderness common, +/- fever
• Discharge appears opaque with a green or yellow color in case of bacterial infection
• Discharge caused by allergy is clear and may be accompanied by itchy, watery eyes
• Causative microorganisms: Strep. Pneumonia, H. Influenza. Less common Strep. Pyogens, Staph. Aureus and M. catarrhalis
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Dx: Gram stain and culture of direct sinus aspirate
Rx:
•Acute: Empirical Antibiotic
•Chronic or complicated: obtain cultures and determine
antibiotic sensitivity
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Otitis Externa
• Predisposing factors: local trauma, furunculosis, foreign body and
excessive moisture (swimmer’s ear).
• Symptoms: Pain and redness (cellulitis)
• Malignant otitis externa: P aeruginosa
• Most commonly caused by P aeruginosa
• Dx: Clinical examination.
• Rx: Topical agents containing antibiotics.
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Acute Otitis Media (Ear Infection)
• Also a common sequel of rhinitis
• Viral infections of the upper respiratory tract lead to inflammation of the
Eustachian tubes and buildup of fluid in the middle ear- can lead to
bacterial multiplication in the fluids
• Bacteria can migrate along the eustachian tube from the upper respiratory
tract, multiply rapidly, leads to pus production and continued fluid secretion
(effusion)
• Chronic otitis media: when fluid remains in the middle ear for indefinite
periods of time (may be caused by biofilm bacteria)
• Symptoms: Fever, sensation of fullness or pain in the ear
• Untreated or severe infections can lead to eardrum rupture or mastoiditis
and CNS involvement.
• Causative microorganisms:
– < 3 months: S pneumonia, group B strep., S aureus, P aeruginosa
– > 3 Months: S pneumonia, H influenza. Less common Strep. Pyogens, Staph.
Aureus and M. catarrhalis
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Diphtheria
• Symptoms initially experienced in the upper
respiratory tract
• Sore throat, lack of appetite, low-grade fever
• Pseudomembrane forms on the tonsils or pharynx
• DDx of pseudomembrane:
– Diphtheria
– Vincent’s angina: Oral lesion caused by fusospirochetal
infection (anaerobes)
– EBV: Infectious mononucleosis
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Middle respiratory tract infections
• The middle respiratory tract infections include:
• Acute Epiglotitis
• Laryngitis and croup
• Tracheitis
• Bronchitis and Bronchiolitis
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Acute Epiglottitis• Abrupt onset of throat and neck pain, fever and inspiratory
stridor, muffled phonation or aphonia and difficult swallowing,
drooling.
• Caused mostly by bacteria (90%). H influenza type b (85%)
and S pneumonia. Less common C diphtheriae and N
meningitidis.
• Medical emergency: Do not use tongue depressor or attempt
throat swab.
• Dx: Blood culture
X-ray: thumb sign
• Rx: adequate airway, humidified air and oxygen.
Specific antimicrobial therapy.
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Laryngitis and croup
• Sudden onset or slow onset.
• Fever and inspiratory stridor, hoarse phonation and harsh
barking cough. Croup associated with chest pain and sputum
production.
• Caused mostly by viruses (90%). Parainfluenza, influenza,
adenovirus. Less common RSV, rhinovirus and coronavirus.
• Acute bacterial tracheitis (purulent process).
• Dx: Bacterial cause; Gram stain and culture of secretions
obtained by direct laryngoscopy. Blood culture.
• Rx: adequate airway, humidified air and oxygen.
Specific antimicrobic therapy (bacterial only).
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bronchitis and bronchiolitis• Spread from URTI.
• Fever, cough and sputum production clear at the beginning then turns
purulent.
• Predisposing factors to Chronic bronchitis: smoking, environmental
pollutants, chronic infection (TB), defective clearance of secretions and
bacteria (cystic fibrosis).
• Acute bronchitis: persistent dry cough, rapid or noisy breathing (wheezing)
brief pauses in breathing, feeding less and having fewer wet nappies
vomiting after feeding, being irritable
• caused mostly by viruses (80%). Parainfluenza, influenza, adenovirus and
RSV. Bacteria: B pertussis, H influenza, Mycoplasma and Chlamydia
pneumonia.
• Chronic bronchitis caused by S pneumonia and nontypable H influenza.
• Dx: Nasopharyngeal specimens are used in direct fluorescent antibody and
PCR assays. Gram stain and culture and sensitivity when purulent sputum
produced. Serodiagnosis in the case of Mycoplasma and Chlamydia
pneumonia.
• Rx: humidified air and oxygen. Specific antimicrobic therapy (bacterial
only).
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Diseases Caused by Microorganisms Affecting the
Upper and Lower Respiratory Tract
• A number of infectious agents affect both the upper
and lower respiratory tract regions
• Most well-known: whopping cough, respiratory
syncytial virus (RSV), and influenza
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Pneumonia
• Anatomical diagnosis
• Inflammatory condition of the lung in which fluid fills the alveoli
• Can be caused by a wide variety of different microorganisms
• Viral pneumonias are usually milder than bacterial
• Community-acquired vs. nosocomial pneumonias
• Begin with upper respiratory tract symptoms, including runny nose and congestion
• Headache common
• Fever is often present
• Onset of lung symptoms follows: chest pain, fever, cough, discolored sputum
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Pneumonia
• Histological/Radiological– Lobar vs bronchopneumonia
– Lobar vs. interstitial
• Microbiological– Bacterial, viral, fungal
• Clinical/ Microbiological– Atypical vs. typical
• Clinical/epidemiological– Community acquired vs. nosocomial
• All have clinical relevance though none is absolute
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Clinical Presentation
• Cough (productive vs. non-productive)
• Fever
• Dyspnoea
• Fatigue
• Headache
• Nausea, vomiting, diarrhoea
• Myalgia
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Predisposing factors
• Age
• COPD
• Diabetes
• Heart failure
• Immunocompromised status
• Alcoholism
• Smoking
• Travel/occupational/recreational exposure
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Physical signs
• Tachycardia
• Tachypnoea
• Hypotension
• Crepitation
• Bronchial breathing
• Fever
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Investigation
• Chest X-ray
• CBC
• CRP
• U&E’s
• ABG’s
• Sputum culture
• Blood culture (+ve in 1-16% of pt’s requiring admission)
• Serology/PCR/antigen
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S pneumoniae
C pneumoniae*
Viral
M pneumoniae
Legionella spp
H influenzae
G- Enterobacteria
C psittaci
Coxiella burnetii
S aureus
M catarrhalis
Other
PNEUMONIA AETIOLOGY
0 5 10 15 20 25 30Percentage of Cases
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Aetiology
• Community Acquired
– S. pneumoniae
– H. influenzae
– Atypicals
– S. aureus
– Kleb. pneumoniae
• Hospital Acquired
– Gram negatives
• E.g. E.coli, Klebsiella,
Pseudomonas
– S. aureus
– Atypicals infrequent
– S. pneumoniae rare
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Pathogens
• S. pneumoniae
• Gram +ve diplococci
• Almost all S to penicillins, cephalosporins (R more common is southern Europe and S. Africa)
• Most S to erythromycin
• H. influenzae
• G –ve cocco-bacilli
• S to amoxycillin
• 25% produce B-lactamase, thus Amoxy R.
• S to Co-Amoxyclav, ceph’s, Ciprofloxacin
• R Eryth
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Pathogens
• S. aureus
• Seen classically after flu
• Severe necrotising pneumonia in young adults
seen in PVL (toxin) producing strains-
emerging pathogen
• Rx flucloxacillin, eryth.
• Vancomycin, linezolid for MRSA
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Atypical pneumonia
• Caused by organisms that will not grow under routine culture conditions
• Non-productive cough
• Negative culture
• Clinical signs often do not match severity of clinical (and radiological) presentation
• Legionella, Mycoplasma, C. psittacci, C. pneumoniae, C. burnetii, viruses (esp. influenza)
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Aspiration pneumonia
• Occurs in patients with abnormal gag reflex (altered
consciousness, CVA…)
• Combination of chemical (acid) injury, bronchial
obstruction and bacterial infection.
• Bacteria involved will reflect oropharyngeal flora-
anaerobes and Streps & haemophilus (community) or
gram neg’s (nosocomial)
• Rx often broad spectrum B-lactam e.s. co-amoxyclav
or pipperacillin/tazobactam +/- metronidazole
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Diagnosing Atypical Pneumonia
• Clinically
• Laboratory:– Culture-not likely to be useful
– Serology-detects antibody response• Usually take time
• Requires demonstration of a single high level or 4-fold rise (after 10-14 days)
• Immunocompromised patients?
– Antigen detection• Good strategy but only available for Legionella
– PCR• Detects DNA/RNA of organism
• Potentially excellent strategy
• Only available in reference centres currently
• Will likely be method of choice in future
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Treatment-Specific organisms
S. pneumoniae• Benzylpenicillin or amoxycillin
S. aureus• Flucloxacillin
Legionella• Clarithromycin (or a quinolone e.g. Cipro)
Psitacosis or Q fever• Doxycycline
Mycoplasma• Clarithromycin
C. pneumoniae• Clarithromycin
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Resources
• https://www.youtube.com/watch?v=GoRhRJXp0j8&t=6s
• https://www.youtube.com/watch?v=IAQp2Zuqevc
• https://www.youtube.com/watch?v=dzJNabJAPaE&t=13s
• https://www.youtube.com/watch?v=eup3_i_5uaw