Microbiology SC037: Do I Really Need That Antibiotic?

Question 1

Antibiotic resistance

Answer 1

Prevalence increase with age-group:
Reasons:
1. Co-morbidity
2. Previous exposure to antibiotics

Question 2

Principles of Judicious use of antibiotics

Answer 2

Avoid underuse / overuse

1. Is it necessary?
2. When to start?
3. Which one?
4. What route?
5. What dose + frequency?
6. How long?

Question 3

Potential harm from antibiotics

Answer 3

Common

1. N+V
2. Diarrhoea

Rare + potential life-threatening toxicity:

1. Drug reaction (e.g. skin manifestations)
2. Rupture tendon (Fluoroquinolone)
3. Arrhythmia (Prolong QT) (Macrolide, Fluoroquinolone)
4. Massive damage / disturbance to microbiome balance on skin / GI tract
   - Obesity
   - Asthma
   - Allergy
   - Type 1 DM
   - Clostridium difficile secondary infection —> Pseudomembranous colitis

Question 4

Respiratory conditions

Answer 4

1. URTI
2. Acute bronchitis
3. Pharyngitis
4. Acute rhinosinusitis
5. Acute otitis media / Otitis media with effusion

Principles:

• Default: No antibiotics, Symptomatic treatment if necessary
• Diagnosis: Clinical (History + P/E)

Question 5

1. URTI

Answer 5

• ***Clinical diagnosis made on basis of clinical S/S
• aka **Common cold, **Nasopharyngitis

Etiology:

• **>20 viruses
• Rhinovirus (most common)
• Coronavirus (most common)
• Influenza, Parainfluenza, Adenovirus, RSV (10-15%)
• Unknown (25-30%)

Management:
- Do NOT use antibiotics for common cold (Non-specific URTI)
—> running nose mainly
—> sinus, pharyngeal, lower airway S/S not prominent
—> purulent secretions do NOT predict benefit from antibiotics (mucopurulent rhinitis (thick, opaque, discoloured nasal discharge caused by WBC inflammation frequently accompanies common cold))
—> antibiotics do not lead to general improvement in URTI
—> even if prolonged symptoms —> still not need antibiotics (viral infection may have prolonged symptoms anyway)

Question 6

2. Acute bronchitis

Answer 6

• Clinical diagnosis
• Abrupt onset of cough, +/- Retrosternal discomfort (∵ involvement of trachea + larger bronchi), fever, sputum production

Etiology:

• ***Viral mostly (influenza A, B; parainfluenza, coronavirus, RSV, rhinovirus)
• Bacteria: Mycoplasma pneumoniae, **Chlamydia pneumoniae, (*Bordetella pertussis)

Management:

• Most resolve with symptomatic treatment
• ***No evidence that antibiotics is useful, even when due to atypical bacteria such as Mycoplasma / Chlamydia
• Consider **Pernasal swab (aka Nasopharyngeal swab) to exclude **pertussis if **severe cough persist for **>2 weeks
• Do not use antibiotics for uncomplicated acute bronchitis unless >3 weeks

Concern of pneumonia:
Features:
- Asymmetrical lung sounds
- Evidence of focal consolidation
- Abnormal vital signs: HR >=100, RR >=24, Temp>=38

Question 7

3. Pharyngitis

Answer 7

Etiology:

• Viral
• GAS

S/S of GAS:

1. Sudden onset of sore throat
2. 5-15 yo (School children)
3. Fever
4. Headache
5. N+V, Abdominal pain
6. ***Tonsillopharyngeal inflammation
7. ***Patchy tonsillopharyngeal exudate (may not be possible to distinguish from viral (e.g. EBV, Adenovirus))
8. ***Palate petechiae
9. ***Anterior cervical adenitis (tender LN)
10. Winter / Early spring
11. ***History of exposure to Streptococcus pharyngitis (e.g. close contact)
12. Scarlatiniform rash (***Scarlet fever)

Management:
Clinical + Epidemiological features
—> Non-suggestive of GAS —> No investigations + Symptomatic treatment
—> Suggestive of GAS —> ***Throat culture / RAT —> Antibiotic +/- Adjuvant treatment if positive (No investigations + Symptomatic treatment if negative)

• **CENTOR score:
• Estimate probability that pharyngitis is GAS

(JC129:
CENTOR score:
Estimate probability that pharyngitis is Streptococcal (distinguish from Viral)
- Bacterial if not treated with antibiotics can present with complications

4 criteria (1 point for each positive criterion):
(記: Fever, Exudates, Lymphadenopathy, Absence of cough)
1. History of fever
2. Tonsillar exudates
3. Tender anterior cervical lymphadenopathy
4. Absence of cough

Modified CENTOR criteria (add patient’s age to criteria)

5. Age <15 (+ 1 point)
6. Age >44 (- 1 point)

Score range: -1 to 5

• -1 to 1: No antibiotic / throat culture necessary
• 2/3: Consider ***rapid strept testing / culture + Treat with antibiotic if positive result
• 4/5: Consider ***rapid strept testing / culture + Treat with antibiotic if positive result

SC038:
Treatment of GAS pharyngitis:
- **Single dose of IM / **10 days Oral Benzathine penicillin for patients who are unlikely to complete a 10-day course of oral therapy
- ***10 days Oral Erythromycin is acceptable for patients
allergic to penicillin (although high resistance to macrolide in HK —> Tetracycline / Fluoroquinolone))

Question 8

4. Acute rhinosinusitis

Answer 8

Etiology:

• Most **viral / **allergic: ~90% patients with cold have rhinosinusitis
• 25% may persist for >2 weeks (prolonged does not mean bacterial)
• Occasionally sinusitis patients are related to periapical or periodontal disease
• If underlying allergic rhinosinusitis + acute viral rhinosinusitis on top —> symptoms can be severe

Microbial cause of acute sinusitis:

1. Viral sinusitis (87% URTI has CT evidence of sinusitis)
2. Bacterial sinusitis (complicate only 0.5-2% of viral URTI)
   - Streptococcus pneumoniae 30%
   - Haemophilus influenzae 20%
   - Moraxella catarrhalis 10%
   - Anaerobes 6%

Management:
***No antibiotics unless:
1. Severe (>=3-4 days)
2. Worsening / Double-sickening (>=3-4 days)
(3. Persistent + not improving (>=10 days))
—> Empirical 1st line antibiotics (2nd line if risk of resistant bacteria)

Risk of resistant bacteria:

1. Age <2 / >65, day care
2. Prior antibiotics within past month
3. Prior hospitalisation past 5 days
4. Comorbidities
5. Immunocompromised

Question 9

5. Acute otitis media / Otitis media with effusion

Answer 9

Do NOT use antibiotics for initial treatment of OME

Otitis media should be classified as:

1. Acute otitis media (AOM)
2. Otitis media with effusion (OME) (can have many causes)

Management:

1. Antibiotics should be reserved for AOM
   - If S/S of acute local illness (otorrhoea, bulging, red TM with loss of light reflex, ear pain, air-fluid level, pus)
   - If Systemic illness (fever temp >38 / malaise)
   - If confirmed by myringotomy or tympanocentesis
   - **Borderline AOM infection spontaneously resolves in **80-90% of cases with most symptoms subsiding within 24 hours after presentation —> ***Watchful waiting appropriate (Reassess after 24 hours)
2. OME
   - Antibiotics may be indicated if persist >=3 months
   - Effusion is NOT an indication for re-treatment of AOM
   - Most OME after AOM resolve spontaneously (but may take time)
3. May need to refer to ENT for myringotomy / grommet insertion

Question 10

Key messages

Answer 10

1. Colds / Flu: Viral —> No antibiotics
2. Runny nose: Viral —> No antibiotics
3. Cough: Viral —> No antibiotics
4. Bronchitis: Viral —> No antibiotics
5. Sinus infection: Viral / Bacterial —> Antibiotics maybe
6. Ear infection: Viral / Bacterial —> Antibiotics maybe
7. Pneumonia: Viral / Bacterial —> Antibiotics usually
8. Strep throat: Bacterial —> Yes antibiotics

Question 11

Scarlet fever (from CPRS51)

Answer 11

• follows pharyngitis
• Day 2 rash: upper chest, diffuse red bluish rash, spread centrifugally
• Facial flushing with perioral pallor
• Pastia’s lines
• Strawberry tongue
• Eosinophilia