it’s just not the flu anymore rick hong, md associate chairman cchs emc medical director, phps

It’s Just Not the Flu Anymore

Rick Hong, MD

Associate Chairman CCHS EMC

Medical Director, PHPS

The “Flu”

• Contagious respiratory illness • Caused by influenza viruses• Can cause mild to severe illness, even death• In US (yearly):

– 5% to 20% incidence– more than 200,000 hospitalized – about 36,000 deaths

• High risk population– the elderly– young children– co-morbidities

Influenza Viruses

3 Types

“A” – Various Animals

(Pandemic)

“B” – Human (Epidemic)

“C” – Human (Mild Infection)

Type “A” Influenza VirusesIdentified by 2 Surface Protein StructuresCombinations

“H” - Hemagglutinin (1 – 16)Entry into Cell

“N” - Neuraminidase ( 1- 9) Exit from Cell

144 Possible combinations

Current Avian or Bird Flu Strain: A (H5N1)High Pathogenic and Low Pathogenic

Viral Replication

What’s the Problem?

Antigenic Drift• Variants from frequent point

mutations during replication• Less frequently in Influenza B• Antibody against one influenza

virus type/subtype confers limited or no protection against another type/subtype

• Antibody to one antigenic variant may not protect against a new antigenic variant of the same type/subtype

• Virologic basis for seasonal epidemics and the incorporation of one or more new strains in each year's influenza vaccine

Antigenic Shift

• More dangerous, less frequent mutations

• Emergence of a novel influenza virus

• Not “recognized” by immune system

• Can cause epidemics/pandemics

Definitions

• Seasonal Flu– respiratory illness transmitted person to person– some human immunity; vaccine available

• Pandemic Flu– virulent human flu that causes a global outbreak– easily spread from person to person– little natural immunity; no vaccine– no pandemic flu currently

• Avian Flu– influenza viruses occurring naturally among wild birds– H5N1 variant lethal to domestic fowl – transmitted from birds to humans (human-to-human?)– no human immunity; no vaccine

Influenza Pandemics 20th Century

A(H1N1)A(H2N2) A(H3N2)

1918: “Spanish Flu” 1957: “Asian Flu” 1968: “Hong Kong Flu”

20-40 Million deaths

675,000 U.S. deaths

1-4 Million deaths

70,000 U.S. deaths

1-4 Million deaths

34,000 U.S. deaths

• Abrupt onset of constitutional and respiratory signs and symptoms – fever (3-5 d)– myalgias (3-5 d)– headache– malaise (2 w)

• Typically resolves after 3-7 days• Cough and malaise can persist for >2 weeks• Secondary bacterial pneumonia or primary

influenza viral pneumonia• Difficult to distinguish from other respiratory

illnesses (70% accurate)

Case Definition

–nonproductive cough (2 w)–sore throat–rhinitis– otitis media, nausea, vomiting

Transmission

• Incubation period of 1-4 days• Via respiratory droplet (e.g., cough, sneeze)

• Viral shedding from the day before symptoms through 5-10 days after illness onset (longer in children and the immunocompromised)

Lab Testing• Preferred specimen: nasopharyngeal/nasal swab, wash, aspirate• Rapid influenza tests

– Results within 30 minutes– May determine type (A vs. B)– High false negative results (30%)

• Viral culture– Results in 3-10 days– Determine specific subtype or strain– reference standard of diagnosis

• Not necessary to test all patients– May not affect clinical decision-making– Expensive– Labor intensive– Cohort hospitalized patients– Outbreaks

Prevention

• Vaccination– two types of vaccines:

• "flu shot”– an inactivated vaccine (containing killed virus) – people older than 6 months, including healthy people and

people with chronic medical conditions. • nasal-spray flu vaccine (LAIV for “Live Attenuated Influenza

Vaccine”) – live, weakened flu viruses – approved in healthy people 5 years to 49 years of age who are

not pregnant.

– contains three influenza viruses-one A (H3N2) virus, one A (H1N1) virus, and one B virus

• strains based on surveillance and estimations about which types and strains of viruses will circulate in a given year

– development of antibodies after 2 weeks

Prevention

• “Health Habits”– avoid close contact– stay home when you

are sick– cover your mouth and

nose with a tissue– wash your hands– avoid touching your

eyes, nose, or mouth

Antivirals

• NOT a substitute for vaccination• Must be taken each day for the duration of

influenza activity in the community (8 weeks)• 4 licensed influenza antiviral agents available

– M2 ion channel inhibitors (amantadine, rimantadine)• only protects against Influenza A• high levels of resistance• not recommended by CDC and ACIP

– neuraminidase inhibitors (Influenza A & B)• oseltamivir (Tamiflu): ages > 1 year• zanamivir (Relenza): ages >5 years.

Treatment

• In general, supportive care only

• Antivirals– Influenza A virus resistance to amantadine

and rimantadine – neuraminidase inhibitors for both influenza A

and B viruses• oseltamivir for treatment of persons aged >1 year• zanamivir for treatment of persons aged >7 years