It’s Just Not the Flu Anymore Rick Hong, MD Associate Chairman CCHS EMC Medical Director, PHPS.
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Transcript of 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