Lecture 25 Influenza Lalji

INFLUENZA TYPES

Type A Type B

Potentially severe illness

Humans & animals

Epidemics & pandemics

Usually less severe illness

Humans only

Epidemics only

Classified into different strains or subtypes based on two proteins or antigens on virus surface o Hemagglutinin (H) o Neuraminidase (N)

Classified into two antigenically distinct lineages o Yamagata-like o Victoria-like

INFLUENZA NOMENCLATURE:

ANTIGENIC DRIFT & SHIFT:

Drift: mutations in the proteins

ex// H1S H1P

Retain immunity

Shift: mixing of viruses MAJOR change

ex// H1 H5

Lose immunity

COMPLICATIONS:

Direct complications (respiratory) o Asthma & COPD exacerbations o Ear/sinus infection o Bronchitis & pneumonia

Indirect complications (multi-organ systems) o TRIGGER FOR: acute MI, ischemic heart

disease, cerebrovascular disease o EXACERBATION OF: hypertension, renal

disorder, diabetes RISK FACTORS:

Children < 2 years and adults ≥ 65 years

Chronic conditions/comorbidities

Immunocompromised / suppressed

Pregnant or postpartum 2 weeks

< 19 years receiving long-term aspirin

First Nations

Morbidly obese (BMI ≥ 40)

Residents of long term care facilities

MODES OF TRANSMISSION:

Respiratory droplet transmission

Droplets (when sick person coughs/sneezes) inhaled or lands on mouth/nose of others

Contact transmission

Touch a surface/object contaminated with the virus and then touches their mouth or nose

SYMPTOMS: FLU VS. COLD Flu Cold

Fever High, sudden onset, 3-4 days Rare

Headache Common Rare

Muscle aches, pains

Common – often severe Sometimes – mild

Tiredness & weakness

Common – severe (2-3 weeks) Sometimes, mild

Extreme tiredness

Early onset, can be severe Unusual

Runny, stuff nose

Common Common

Sneezing Sometimes Common

Sore throat Common Common

Coughing Common – can be severe Sometimes – mild to moderate

GI symptoms Sometimes Unusual

DIAGNOSIS:

Viral culture: gold standard; accurate; takes 3-10 days to get results

RT-PCR: done in lab; accurate; takes 1-8 days to get results

Rapid Influenza Diagnostic Tests (antigen detection tests) or Rapid Molecular Assay (viral RNA detection) or immunofluorescence: takes <30 mins; done at bedside; not very accurate

o Sensitivity 50-70% and specificity 90-95% = false negatives occur more commonly than false positives o A negative RIDT result does NOT exclude a diagnosis of influenza in a pt with suspected influenza

NOTE: when there is clinical suspicion of influenza & antiviral treatment is indicated, antiviral txt should be started asap without waiting for results of additional influenza testing

Lecture 25 Influenza Lalji

TREATMENT: antiviral txt for influenza must be started within 48 h (or less) of onset of sx for max. effectiveness

Drugs of choice are neuraminidase inhibitors (NI) – effective against influenza A & B, and not much resistance

Recommended as early as possible for any pt with confirmed or suspected influenza who: o Is hospitalized o Has severe, complicated, or progressive illness o Is at higher risk for influenza complications

Use Age Dose Duration Adverse Events

Oseltamivir Recommended drug of choice for both prophylaxis and treatment in an influenza outbreak

Treatment Any age C: ??? A: 75 mg bid*

5 days CNS: seizure, abnormal behavior, delirium, hallucinations, agitations, anxiety, altered LOC, confusion, nightmares, delusions

Cardiac: arrhythmia

GI: NV, hepatitis, abnormal LFTs

DERM: rash, dermatitis, urticaria, eczema, toxic epidermal necrolysis, Stevens-Johnson Syndrome, erythema multiforme

METABOLIC: aggravation of diabetes

DRUG INTERACTION: LAIV vaccine (not TIV)

Prophylaxis ≥ 3 mo C: ??? A: 75 mg daily

7 days

Zanamivir Used when predominant circulating strain is resistant to Oseltamivir

Treatment ≥ 7 yrs C/A: 10 mg inh bid

5 days Anaphylactic allergy

Confusion, delirium, self-injury (RARE)

Headache, dizziness, NVD, fever, chills, joint pain, ear pain, sinusitis, nasal s/s, bronchitis, cough, ENT infxn

NOT RECOMMENDED: in people with underlying respiratory disease

Prophylaxis ≥ 5 yrs C/A: 10 mg inh daily

7 days

Peramivir (IV) Used in hospitalized patients who cannot take oral meds by mouth or nasogastric tube

Amantadine & rimantadine Effective against influenza A only; also resistance is >99% by H3N2 and H1N1 (type A) not used clinically

EVIDENCE:

Duration of illness: reduces duration of uncomplicated influenza A & B by approx. 1 day when administered within 48 h of illness onset

Preventing serious influenza-related complications & hospitalizations: data limited & unclear

Hospitalized patients: improved survival & reduces severe clinical outcomes EVEN among those starting treatment more than 48h after symptom onset

PREVENTION:

Hand hygiene/respiratory etiquette

Vaccine

Chemoprophylaxis for ppl who have had recent, close contact with an influenza case

To prevent outbreaks in LTCF

Direct contacts who are at higher risk for influenza complications but not yet vaccinated

Unvaccinated HCWs who have occupational exposures & didn’t use adequate personal protective equipment

VACCINES: recommended for everyone ≥ w/o contraindications

Potential gap in vaccine effectiveness for those ≥ 65 yrs, therefore give extra protection: o FLUZONE high-dose (4x more) vaccine

60 mcg hemagglutinin of each influenza strain per 0.5 mL dose

Trivalent, inactivated, split-virus influenza vaccine

No adjuvant, antibiotic, gelatin, or perseverative

o FLAD (contains adjuvant)