acute bacterial infections of the respiratory tract
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Acute Bacterial Infections of the Respiratory Tract - University of AdelaideTRANSCRIPT
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Acute Bacterial Infections of the Respiratory Tract
Dr Celia Cooper Clinical Director of Pathology & Head,
Microbiology & Infectious Diseases, WCH Site, SA Pathology
Upper & Lower Respiratory Tract
• Upper respiratory tract – The airway above the
glottis or “vocal chords” • The nose, nasal cavity and
paranasal sinuses • The pharynx • The larynx
• Lower respiratory tract – The respiratory tract from
the trachea to the lungs
Upper Respiratory Tract Infection Aetiology
• VIRAL – “Common Cold” – Pharyngitis – Otitis media – Sinusitis – Laryngitis – Acute
laryngotracheobronchitis “croup”
• BACTERIAL – Pharyngitis – Otitis media – Sinusitis – Epiglottitis
Pharyngitis • An inflammation of the pharynx caused
by several different groups of micro-organisms
• The commonest infectious disease presentation to general practice
• Most common cause is viral
• Most important bacterial cause is group A ß haemolytic streptococci (Streptococcus pyogenes)
• Important to diagnose bacterial pharyngitis to determine appropriate treatment. Antibiotics will be ineffective in viral pharyngitis but necessary in Streptococcus pyogenes pharyngitis to prevent rheumatic fever and glomerulonephritis
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Microbial Causes of Acute Pharyngitis
• Viral – 40% • Bacterial – 30%
– Group A ß-haemolytic streptococci – 20% – Group C and G ß-haemolytic streptococci – 5% – Rare causes e.g. Neisseria, Corynebacterium – 5%
• Unknown 30%
ß-Haemolytic Streptococci and Acute Pharyngitis
• Pharyngeal carriage of S. pyogenes is common in asymptomatic people
• ? Strain-related virulence factors (toxins) determine development of disease
• Marked erythema and oedema of the fauces and uvula and a greyish-yellow tonsillar exudate
Severe local complication of acute bacterial pharyngitis
• Peritonsillar abscess – quinsy
• Associated with severe pharyngeal pain and dysphagia
• On examination – inflammation and swelling of the tonsillar area and medial displacement of the tonsil
Diagnosis • The primary objective is to distinguish between viral and bacterial pharyngitis
to avoid unnecessary antibiotic treatment
• Usually not possible on clinical grounds alone, but clues include: – Tonsillar exudate rare in pharyngitis due to viral tonsilitis unless due to
EBV or adenovirus – Skin rash associated with Streptococcus pygenes, sometimes EBV – Associated conjunctivitis – adenovirus – Features that increase the likelyhood of S. pyogenes infection are: fever >
38, tender cervical lymphadenopathy, tonsillar exudate and no cough
• Microbiological sampling using a cotton-tipped swab – sent directly to the laboratory or in transport media if there will be a delay in treatment
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Treatment • Treatment of S. pyogenes pharyngitis/tonsillitis is necessary to avoid:
– Non-suppurative complications – rheumatic fever, glomerulonephritis
– Suppurative complications – quinsy, acute otitis media, acute sinusitis
– Prolonged illness
• S. pyogenes remains highly susceptible to penicillin, can use roxithromycin if penicillin allergic, steroids may be used if severe swelling obstructing swallowing is present.
Otitis Media • Fluid in the middle ear accompanied by
signs and symptoms of acute inflammation
• Very common cause of GP visits
• The peak incidence occurs in the first three years of life – 2/3 children have at least one episode by age 3, 1/3 children have 3 or more episodes by age 3
• Less common in school-aged children, adolescents and adults
• Significantly more common in indigenous than non-indigenous children
• Associated with blockage of the eustachian tube and lack of drainage of fluid from the middle ear.
Microbial Causes of Acute Otitis Media
• 40% - Commonest bacterial cause is Streptococcus pneumoniae (pneumococcus)
• 30% - Haemophilus influenzae (non-typable)
• 10% - Moraxella catarrhalis
• 20% - other bacteria
• Viruses often present as well – dual bacterial and viral infection is common
Pneumococcus and Acute Otitis Media
• Commonest bacterial cause is Streptococcus pneumoniae (pneumococcus).
• 6 distinct serotypes are responsible for most cases of OM.
• The conjugate pneumococcal vaccine introduced early this century covers approximately 70% of responsible strains
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Severe Local Complications of Acute Otitis Media
• Temporary hearing loss associated with middle ear effusion – subsequent impact on speech,
language and cognitive abilities
• Mastoiditis – inflammation and infection of the mastoid sinus connected to the middle ear by a small channel – Can result in associated
temporal lobe cerebral abscess or cavernous sinus thrombosis
– Rare – 1:1,000 cases of untreated OM in high income countries
Diagnosis • Symptoms – ear pain, ear discharge, hearing loss, fever, lethargy and irritability
• Signs – redness, however redness may just indicate inflammation of the entire upper respiratory tract as
occurs in viral infection – Middle ear effusion
• Bulging of tympanic membrane • Limited movement of tympanic membrane by varying air pressure using pneumatic
otoscope • An air-fluid level behind the tympanic membrane • Perforation of tympanic membrane with discharge of middle ear fluid
• Most patients will be treated with empirical antibiotic therapy without microbiological sampling
• Microbiological sampling by needle aspiration of the middle ear (tympanocentesis) should be considered if patient is critically ill, if no response to initial therapy in 48 – 72 hours and still febrile and unwell or if immunosuppressed
Treatment • Antibiotic therapy provides modest benefit – Need to treat 16 children to prevent one
child experiencing pain at 2-7 days – Benefit most likely in children younger than 2 years especially those younger than 6
months – Benefit also greater in systemically unwell children with fever and vomiting
• Antibiotic chosen must be active against Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis
– Amoxil, if treatment failure – amoxil plus B lactamase inhibitor
• Broader spectrum antibiotic cover should be used if immunosuppressed or if associated mastoiditis
• Pain relief should always be given, decongestants and antihistamines of no benefit
• Surgery maybe necessary in chronic OM but not covered here.
• Pneumococcal vaccine as prevention - modest reduction only (6-7%)
Sinusitis • The paranasal sinuses are air-filled cavities in
the facial bones connected to the nasal cavity via small tubular passages (infundibula)
• The sinuses are lined with ciliated epithelium containing goblet cells which produce a mucous blanket
• The ciliated epithelium sweeps the mucous blanket out through the infundibula and the mucous blanket changes 2-3 times each hour
• Mucus does not normally accumulate in the sinus cavities
• While the nasal passages are colonised with bacteria, the paranasal sinuses are sterile under normal conditions
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Microbial Causes of Sinusitis • The “common cold” caused by a number of respiratory viruses plays an important role in
initiating Acute Bacterial Sinusitis
• “Colds” are associated with swelling of the nasal mucosa, increased mucus production and frequent obstruction of the sinus infundibula
• The act of “nose blowing” causes a transient increase in intranasal pressure that does not occur with sneezing or coughing
• “Nose blowing” can propel nasal fluid and bacteria into the sinus cavity
• The bacteria commonly associated with Acute Bacterial Sinusitis are the same as those colonising the nasal passages and the nasopharynx – Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus
• Other less common causes are Moraxella catarrhalis (in children) and mixed anaerobic organisms (in adults)
Microbial Causes of Acute Sinusitis Organism Adults Children Viruses 23% 4%
Streptococus pneumoniae 33% 36%
Haemophilus influenzae 24% 23%
Viridans Streptococci 9% -
Moraxella catarrhalis 8% 19%
Anaerobic bacteria 6% -
Staphylococcus aureus 4% -
Streptococcus pyogenes 2% 2%
Gram negative bacteria 9% 2%
Severe local complications of Acute Bacterial Sinusitis
• Meningitis, brain abscess, subdural emyaema
• Caverous sinus and cortical vein thrombosis
• Orbital cellulitis, subperiosteal abscess of frontal bone (Pott’s puffy tumour) and orbital abscess
Diagnosis • Symptoms and Signs
– Often indistinguishable from the underlying “cold”
– Purulent nasal discharge can occur with a “cold”
– fever >38, facial pain, tenderness, swelling, erythema and duration of symptoms > 7 days – characteristic of bacterial sinusitis but not always present
– Exclude – foreign body, dental infection, immunodeficiency and cystic fibrosis
• Investigations – Sinus cavity culture obtained by
puncture and aspiration – CT/MRI scanning – Only in unusually severe cases or
where cerebral or orbital extension
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Treatment • Analgesics
• Nasal saline sprays
• Nasal corticosteroid sprays
• Nasal decongestants (<5 days, not in young children)
• Antibiotics can shorten the duration of illness but spontaneous resolution of symptoms in 2 weeks occurs in patients given placebo
• Use antibiotics (in conjunction with nasal corticosteroid sprays) if severe sinusitis symptoms for more than 5-7 days and any one of the following: high fever, unilateral maxillary sinus tenderness, severe headache, worsening of symptoms after initial improvement
Acute Epiglottitis • Cellulitis of epiglottis and adjacent
structures
• Has the potential for causing abrupt, complete airway obstruction
• Most important bacterial cause is Haemophilus influenzae type B (HiB)
• Previously most common in male children between the ages of 2 – 4 years, almost all cases due to HiB
• Since introduction of an effective vaccine routinely given as part of the childhood immunisation schedule, the disease is now most common in adult males (only 25% due to HiB, the remainder due to other bacteria).
Microbial causes of Acute Epiglottitis
• Haemphilus influenzae type B – 100% children – 25% adults
• Other bacteria – Streptococcus pneumoniae, other streptococci, Staphylococcus aureus
• Not viruses
Haemophilus influenzae and Acute Epiglottitis
• Haemphilus influenzae type B is found in blood cultures of up to 100% of children with Acute Epiglottitis
• Effectively prevented by a conjugate vaccine given as part of the routine childhood immunisation schedule. This has lead to a 99% reduction in childhood cases
• Replacement of HiB with other strains of Haemophilus influenzae was feared but has not occurred
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Severe complication of Acute Epiglottitis
• A fulminating course e.g. a patient progressing from being asymptomatic to complete airway obstruction in 30 minutes
• Visualising the airway is necessary to make a diagnosis but can precipitate complete obstruction and therefore should only be performed when prepared to immediately secure the airway i.e. intubate the patient
• This severe course is associated with infection due to HiB, epiglottitis due to other bacteria is less severe.
Diagnosis • Generally a short history of fever,
irritability, dysphonia and dysphagia
• Patient observed to sit forward, drooling oral secretions, tentative respirations
• Epiglottis appears oedematous and “cherry red” but care must be taken as examination of the epiglottis can precipitate complete airway obstruction
• Blood film shows a raised white cell count, cultures of epiglottis and blood are generally positive for Hib
• Xray of lateral neck can show characteristic changes but false positive and false negative results are common
Treatment • Immediate steps to maintain an adequate airway i.e. intubation,
mortality of children who obstruct is 80%
• Manage as a medical emergency, take steps to minimise stress or anxiety in the child
• Intravenous antibiotic therapy with a 3rd generation cephalosporin e.g cefotaxime or ceftriaxone
• Intubation is generally only required for 12-48 hours until oedema in the epiglottis and surrounding structures has resolved.
Lower Respiratory Tract Infection Aetiology
• VIRAL – Acute bronchitis – Chronic bronchitis – Bronchiolitis – Pneumonia
• BACTERIAL – Chronic bronchitis – Pneumonia – Empyema – Lung Abscess
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Pneumonia • The most common cause of infection –
related mortality
• Infection of the lung
• The lower respiratory tract (LRT) is usually sterile
• Microbes gain entry to the LRT through:
– Aspiration of upper respiratory tract resident flora
• Altered level of consciousness – Inhalation of an infectious aerosol
• E.g. Legionella pneumophila – Secondary infection seeded from
the blood stream • E.g. Staphylococcus aureus
Microbial causes of Pneumonia
• Viral • Bacterial • Rickettsia • Mycoplasma and
Chlamydia • Mycobacteria • Parasites • Fungi
Bacterial Causes of Pneumonia • Common
– Streptococcus pneumoniae – Staphylococcus aureus – Haemophilus influenzae – Mixed anaerobic bacteria – Enterobacteriaceae
• Escherichia coli • Klebsiella pneumoniae • Enterobacter spp. • Serratia spp.
– Pseudomoas aeruginosa – Legionella spp
Streptococcus pneumoniae and Pneumonia • Leading cause of acute community-
acquired pneumonia, though less common than in the past
• Risk factors: old age, cigarette smoking, diabetes, splenectomy, chronic illness
• Symptoms – cough, fatigue, chills, sweats and shortness of breath
• Signs – fever, tachycardia, tachypnea, localising chest signs
• Pleural effusion +/- empyaema
• Lung abscess is rare
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Staphylococcus aureus and pneumonia
• Causes < 10% of cases of community-acquired pneumonia but 20 – 30% of cases of hospital acquired pneumonia
• May follow influenza infection
Staphylococcus aureus and Pneumonia
• Symptoms – severe – cough, shortness of breath, pleuritic pain, haemoptysis
• Signs - high fever, hypotension, widespread chest signs
• Multiple lung abscesses
• Common cause of empyaema
Klebsiella pneumoniae and Pneumonia
• Gram negative bacillus
• Outer polysaccharide capsule that is responsible for virulence
• Often resistant to multiple antibiotics through chromosonmal and plasmid related resistance
Klebsiella pneumoniae and Pneumonia
• Classically causes pneumonia in hospitalised or debilitated patients e.g. alcoholics
• K. pneumoniae pneumonia is also known as “Friedlander’s disease”
• Characterised by: – Severity, upper lung lobe
involvement, “red currant jelly sputum, the bulging fissure sign on chest X ray and abscess formation
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Mixed Anaerobic Bacteria and Pneumonia • Numerous species of anaerobic bacteria are part of the normal flora of the oral cavity –
Fusobacterium, Prevotella, Bacteroides, Peptostreptococcus
• Aspiration of oral contents during a period of depressed consciousness can result in anaerobic pneumonia, lung abscess and empyaema
• Usually due to a mixture of anaerobic organisms +/- aerobic organisms
• Tend to be associated with tissue necrosis or abscess cavities where the oxygen tension is low
• Later in the course of the infection (after 1 week) the expectorated pus may become foul-smelling
• Gram stain of the pus reveals numerous organisms but failure to grow under normal culture conditions (i.e. in air) can be a clue to anaerobic infection
• Signs of severe sepsis are rare. The patient usually has a low grade fever, lethargy, loss of appetite and a cough productive of sputum
• Treat with broad spectrum antibiotics which include anaerobic cover
Summary • A very quick “Cook’s Tour” of the bacterial causes of
Respiratory Tract Infections
• Each topic could be the subject of a lecture in itself
• Represent some of the most common and serious infections in medicine
• Will be encountered in almost every medical career so well worth knowing about!