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

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

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

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

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

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

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

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

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

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!