Influenza

Question 1

Influenza Presentation

Answer 1

• INCUBATION PERIOD: 2 - 4 DAYS (range 1 - 7 days)
  
  • ABRUPT FEVER: up to 41° C (commonly 38 - 40° C), which LASTS 3 DAYS (range 1 - 5 days)
  • • ≥ 2: COUGH, (SORE THROAT, RHINORRHOEA), MYALGIA, HEADACHE, MALAISE
  • PREDOMINANCE of SYSTEMIC SYMPTOMS
  • LESS COMMON SYMPTOMS: NAUSEA, VOMITING, DIARRHOEA

Question 2

Seasonal Flu vs. Pandemic Flu

Answer 2

Seasonal:

EVERY WINTER - AFFECTS 10 - 15% of POPULATION

UNPLEASANT, usually NOT LIFE-THREATENING

Pandemic:

SPORADICALLY (~ 3x per century & can occur at any time of year) - AFFECTS 25% + of POPULATION

MORE SERIOUS + MORE COMPLICATIONS

Question 3

Antigenic Shift vs. Antigenic Drift

Answer 3

Antigenic Shift:

* ABRUPT MAJOR CHANGE = resulting in new H/N COMBINATIONS
* GENETIC CHANGES enable FLU STRAIN to JUMP BWTN ANIMAL SPECIES
* REASSORTMENT of VIRAL GENE SEGMENTS
* NEW ANTIGENIC PROPERTIES = UNPROTECTED POPULATION AT RISK = PANDEMICS

Antigenic Drift:

* MECHANISM of GENETIC VARIATION W/I VIRUS
* Occurs CONTINUALLY OVER TIME = SMALL ONGOING POINT MUTATIONS in GENES CODING for ANTIBODY-BINDING SITES
* May CHANGE ANTIGENIC PROPERTIES & eventually IMMUNE SYSTEM LESS EFFECTIVE at COMBATTING VIRUS
* Causes WORSE THAN NORMAL EPIDEMICS & VACCINE MISMATCH

Question 4

Influenza Investigations

Answer 4

General: pulse oximetry, RR
Bloods: U+E, FBC, CRP, blood culture
Imaging: CXR
Other: viral nose + throat swabs for PCR

Question 5

Influenza Common Complications

Answer 5

Acute bronchitis
Secondary bacterial pneumonia (urgent CXR for influenza symptoms + fever > 4 days; CURB 65; S. pneumonia, S. aureus, H. influenzae)

Question 6

Influenza Less Common Complications

Answer 6

Respiratory: primary viral pneumonia

Cardiac: pericarditis, myocarditis

CNS: transverse myelitis/Guillain-Barre, myositis, myoglobulinuria

Question 7

High risk groups for complicated influenza

Answer 7

• NEUROLOGICAL, HEPATIC, RENAL, PULMONARY & CHRONIC CARDIAC DISEASE
  
  • DM
  • SEVERE IMMUNOSUPPRESSION
  • AGE > 65 YRS
  • PREGNANCY (incl. up to 2 weeks post-partum)
  • CHILDREN < 6 MONTHS
  • MORBID OBESITY (BMI ≥ 40)

Question 8

Influenza-like Illness Presentation

Answer 8

• FEVER ( > 38° C) + COUGH + ONSET W/I LAST 10 DAYS

* If requires hospitalisation = defined as SARI (SEVERE ACUTE RESPIRATORY INFECTION)

Question 9

Influenza Management

Answer 9

Use ASAP + W/I 48 HRS of SYMPTOM ONSET (however in COMPLICATED ILLNESS = ALWAYS GIVE, NO MATTER HOW LONG AFTER ILLNESS ONSET e.g. LRTI, CNS involvement, sig. exacerbation of underlying medical condition)

NEUROAMINIDASE INHIBITORS: OSELTAMIVIR, ZANAMIVIR

Question 10

When does an individual become non-infectious?

Answer 10

Immunocompetent adults: 24hrs after last symptoms (fever, cough)/completion of anti-viral therapy

Immunocompromised/young children: consider each case separately

Question 11

PPE for influenza

Answer 11

Most pt. w/ influenza = surgical face mask, plastic apron, gloves

Pt. receiving nebuliser/NIV (aerolised virus) = face fit FFP3 respirator mask