Flashcards in L60 – Upper Respiratory Tract Infections Deck (89):
Locations of upper respiratory tract infections?
Above larynx, tracheobronchial tube
Mainly in nasopharynx and larynx
Includes structures connected to nasopharynx: perinasal sinus,
middle ear, eye
What are some underlying conditions/ diseases that can lead to/ exacerbate URT infection?
How does age relate to the type of URTI?
How does time of year relate to URTI?
e.g. influenza – 1 peak in summer, winter
What are some innate defense mechanisms in the Nasopharynx?
- Nasal hairs
- Turbinates (bone in nose covered by moucosa)
- Mucociliary apparatus
- Secretory immunoglobulin A (sIgA) secretion
What are some innate defense mechanisms in the Oropharynx?
Sloughing of epithelial cells (layer of skin comes off)
What are some innate defense mechanisms in the Trachea and bronchi?
Cough, epiglottic reflexes
Sharp-angled branching of airways
Ig production (IgG, IgM, IgA)
How does sharp-angled branching of airways protect the respiratory tract from infections?
↑ surface area for gas exchange
Particles >5μm knock on bifurcation = trapped in mucous and phagocytosed
Particles <5μm: not filtered and can reach most distal terminal
What are some innate defense mechanisms in the Terminal airways and alveoli?
Alveolar lining fluid
What is the general assessment for URTI?
- Time of year
- Site of infection
- Clinical syndrome
- Underlying immune impairment/ diseases if any
Are antibiotics used to treat MOST cases of pharyngitis?
Dont use antibiotics
What is the incubation period of Group A streptococcal pharyngitis? What is the usual time before subside?
Usually subside in ~1 week
What is the transmission of Group A streptococcal pharyngitis? Is it always symptomatic?
Direct person-to-person contact
Facilitated by over-crowding
Can have asymptomatic carriage
How are the acute onset symptoms for Group A strep. pharyngitis?
What are the manifestations of Group A strep. pharyngitis on lymphoid organs and tonsils?
Redness, lymphoid hyperplasia of posterior pharynx
Hyperaemic tonsils + greyish white exudate
Tender lymph nodes (sensitive to pain)
What is the treatment of choice for Group A Strep. Pharyngitis?
Compare between viral and Streptococcal pharyngitis:
Strep = Abrupt
Viral = Gradual
Compare between viral and Streptococcal pharyngitis: Throat pain?
Compare between viral and Streptococcal pharyngitis: Cervical nodes?
Strep= Enlarged, tender
Viral= Not enlarged
Compare between viral and Streptococcal pharyngitis: Eyes and nose?
Strep= not affected
Viral= watery eyes + runny nose
Compare between viral and Streptococcal pharyngitis: Throat and tonsils?
Strep= Red, swollen, exudates
Viral= Red, vesicles, ulcers
What is the most definitive way to differentiate between viral and streptococcal pharyngitis?
1) Gold standard = throat swab >> bacteriological culture
2) Antigen detection tests for Strep. A antigen (e.g. put swab in commercial kit)
If culture and antigen detection for bacteria returns negative, then the infection must be viral
What are the 2 types of Streptococcal pharyngitis complications?
Suppurative (pus) and Non-suppurative (no pus)
Name some suppurative complications of Strep. A pharyngitis?
- Local abscess
- Bacteraemia with metastatic foci of infection
- Intracranial infections
What types of Local abscesses can form in suppurative complications of Strep. A pharyngitis?
>> all cause swollen sneck and obstruct airway
What types of intracranial infection can form in suppurative complications of Strep. A pharyngitis?
Acute otitis media in middle ear
Acute sinusitis in nose
What are the 2 Non- suppurative/ immunological complications of Strep. A pharyngitis?
Acute rheumatic fever
Post-streptococcal glomerulonephritis (PSGN)
What criteria is used to diagnose Acute rheumatic fever?
Recurrent attacks of acute rheumatic fever can lead to what?
Recurrent valvular damage > Chronic rheumatic heart disease > infective endocarditis
How does Strep. A bacteria cause acute rheumatic fever and evade host defense?
result of molecular mimicry:
heartreactive antibodies (HRA) cross-reacts with:
a) antigens on heart tissues
b) group A streptococcal antigens
>> body attack own tissue
similar mechanism in PSGN
What drugs are used as prophylaxis for recurrent attacks of acute rheumatic fever?
IM benzathine penicillin,
oral penicillin V,
What drugs are used as prophylaxis for infective endocarditis?
Oral amoxicillin (high dose)
IV ampicillin + gentamicin
What is the gram stain, hemolysis and morphology of Strep. pyogenes?
gram-positive, beta-hemolytic, in chains
What is the gram stain, sprouting, motility and morphology of Corynebacterium diphtheriae?
What does Corynebacterium diphtheriae cause?
What is the primary prophylaxis of Diphtheria?
vaccination with diphtheria toxoid
Good childhood immunization coverage
What are the 2 types of Diphtheria?
What are the unique, differentiating histological factors of Corynebacterium diphtheriae ?
1. ‘Chinese character’ palisades
2. Metachromatic granules
What are the 2 cultures of Corynebacterium diphtherniae? Which one is selective and which one isnt?
Loeffler medium (non-selective)
Potassium tellurite medium/ Hoyle's medium (selective)
What is the positive result for Corynebacterium diphtherniae in Hoyle's/ Potassium tellurite medium?
Potassium tellurite medium
>> gun-metal black / dark grey colonies
What are the transmission routes for Corynebacterium diphtheriae? Is it always symptomatic?
Direct contact with respiratory secretions
Asymptomatic carrier state exists
Diphtheria is a endotoxin or exotoxin mediated disease? What does the bacteriophage carry?
Bacteriophage carries tox gene
What is the action of C. diphtheriae exotoxins?
Diphtheria exotoxin inactivates elongation factor 2 (EF2)
inhibits protein synthesis > cause respiratory disease, systemic effect, cutaneous diphtheria
What respiratory disease is caused by C. diphtheriae?
sore throat >> inflamed, necrotic epithelium
form pseudomembrane (‘white throat’) and obstruct airway)
What systemic effects are caused by C. diphtheriae?
fever, myocardial depression, neuropathy
What is the manifestation of cutaneous diphtheria? Which social groups are most affected?
Typically manifests as chronic non-healing skin ulcers
Especially among the underprivileged
What are the treatment options for diphtheria?
Describe acute epiglottitis?
rapidly progressive cellulitis of epiglottis, adjacent structures
What is the classical and alternative cause of acute epiglottitis?
Classical = Haemophilus influenzae type b
Beta-haemolytic streptococci (S. pneumoniae, S. pyogenes)
How does age relate to the cause of acute epiglottitis?
Bhildren (2-4 yrs old) most commonly affected
Classical cause of Haemophilus influenzae type b affects CHILDREN
Alternative causes (e.g. Strep. aureus) affect ADULTS
What are some causes of non-infectious epiglottitis?
trauma, irradiation, caustic ingestion, inhalational injury
What are the rapid onset symptoms of acute epiglottitis?
Dysphonia = cannot speak
Dysphagia = drooling of saliva
Why is acute epiglottitis a medical emergency?
Swelling can suddenly lead to complete airway obstruction > respiratory distress and death
* hence acute epiglottitis is a medical emergency *
What is the procedure that follows clinical suspicion of acute epiglottitis? What precaution is taken?
Examine epiglottis only when immediate intubation is possible
may cause laryngeal spasm and airway obstruction >> may need to perform tracheostomy
What clinical confirmatory tests can be done to confirm acute epiglottitis?
Laryngoscopy: cherry-red epiglottis
Lateral neck X ray: thumb sign, narrowing of pharynx
What are the empirical antibiotics of choice for acute epiglottitis?
3rd generation cephalosporins
(e.g. ceftriaxone, cefotaxime)
What are the 4 paired paranasal air sinuses?
Frontal - lower forehead
Maxillary - cheekbones
Ethmoid cells - beside upper nose
Sphenoid - behind nose
What is the normal sterility and secretion drainage of the paranasal air sinuses?
Secretion normally drains into osteomeatal complex
What are the common and alternatice predisposing factors/ antecedent conditions for acute sinusitis?
Most common = Upper respiratory tract viral infection
Other factors = allergy, dental root infection of maxillary sinusitis (rare)
Explain the pathogenesis of acute sinusitis?
swelling of inflamed mucosal lining in nasopharynx (e.g. URTI, allergy)
>> obstruct / impair normal sinus drainage into osteomeatal complex
>> abnormal buildup of fluid in sinus + bacteria infection
What are the 4 categories of sinusitis?
1. Acute community acquired sinusitis
2. Chronic sinusitis
3. Nosocomial (hospital-acquired) sinusitis
4. Fungal sinusitis
In Acute community-acquired sinusitis, what are the common pathogens?
Respiratory virus (10%)
*sterile cultures in 25%*
Name the bacteria that causes Acute community-acquired sinusitis?
1. Streptococcus pneumoniae (~40%) (most common)
2. Haemophilus influenzae (~30%)
3. Moraxella catarrhalis (~20% in children)
Name the viruses that causes Acute community-acquired sinusitis?
What are the clinical features of acute sinusitis? (persistent and severe symptoms after URTI)
Purulent nasal and postnasal discharges
What are the 3 categories of complications of acute sinusitis?
Peri- orbital (can affect eyes)
What are the Intracranial complications of acute sinusitis?
Brain abscess, meningitis
Osteomyelitis of frontal bone:
- in frontal bone or ethmoid sinus
Apart from clinical symptomatology, physical examination, what 2 other procedures are done for clinical diagnosis of acute sinusitis?
Imaging: sinus X-ray and CT scans
Culture: sinus puncture and aspiration of sinus in complicated cases
*not routinely needed*
Is normal culture of nasal discharge used for diagnosis of acute sinusitis?
Culture of nasal pus / sinus exudates: not reliable
What is seen in the X rays and CT scans for acute sinusitis?
Sinus X rays: opaque = sinusitis
Normally air-filled = black; Fluid-filled = white
*CT is sensitive in picking up lesions in sinus*
What is the empirical antibiotic treatment for acute sinusitis?
Empirical antibiotic coverage against:
Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis
What drugs are used for acute sinusitis?
ampicillin-sulbactam, amoxicillin-clavulanate, cefuroxime
**need to Consider local pattern of antibiotic resistance**
When is surgery used to treat acute sinusitis? (think of the types of sinusitis that needs surgery)
-Severe / chronic sinusitis
-suspected intra-orbital / intracranial involvement
> surgery is used to drain sinus
Acute otitis media affects what age group of the population most?
primarily a disease of childhood
(peak incidence: 6-24 months)
What are some anatomical features that predisposes acute otitis media?
-cleft palate, cleft uvula
-physiological abnormalities of Eustachian tube
How does the structure of the Eustachian tube predispose acute otitis media? (Pathogenesis)
obstruct normal drainage of
fluids, secretions accumulate in middle ear (cannot drain to nasopharynx)
> increase risk of infection
Apart from anatomical defects and physiological abnormalities, what are the 2 other predisposing factors for acute otitis media?
-preceding viral upper respiratory tract infection: potential bacterial pathogens colonize nasopharynx
-Congenital / acquired immunodeficiencies
Acute otitis media is usually preceded by what?
37% of URTI leads to acute otitis media
What bacteria commonly causes acute otitis media? (same bacteria as acute sinusitis)
Streptococcus pneumoniae (20–30%)
Haemophilus influenzae (25–35%) (most common)
What are some uncommon pathogens causing acute otitis media?
Streptococcus pyogenes (2–4%)
What are some general and ear-related symptoms of acute otitis media?
- Ear pain
- Erythema of tympanic membrane (eardrum)
- Perforation > Ear drainage (e.g. pus)
- Hearing loss (e.g. unilateral)
How is erythema of trympanic membrane caused in acute otitis media?
Fluid accumulation in middle ear> pressure increases > erythemia of tympanic membrane > bulging with pus
What are some complications of acute otitis media?
intracranial spread to brain, mastoid complex
What is the empirical antibiotic coverage for acute otitis media?
Same as acute sinusitis:
What special consideration is given to neonates / immunosuppressed individuals with acute otitis media?
consider infection due to more resistant / unusual organisms
When is culture needed for acute otitis media? Is it normally needed?
Normally not needed
**Tympanocentesis > aspiration of the middle ear content
Only use if patient is critically ill, unresponsive to antibiotics, immunocompromised
Where is infection in otitis externa?
External auditory meatus
What are the pathogens that cause otitis externa?
Staphylococcus aureus >> acute localized
Pseudomonas aeruginosa >> malignant