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FLU (Epidemiology (Type A categorized into subtypes based on changes in…
FLU
Epidemiology
Causes significant morbidity and mortality esp among young children and elderly adults
25-30 million cases, 600,000 hospitalizations and 50,000 deaths annually in US
More ppl die of flu than only other vaccine preventable disease every year
Influenza virus types A, B, and C are orthomyxoviridae family - affect humans, pigs, horses, birds. A and B cause human infection. A responsible for seasonal flu epidemics. B associated with sporadic outbreaks particularly in nursing facilities
Type A categorized into subtypes based on changes in surface antigens - hemagglutinin and neuraminidase
Hemagglutinin allows flu virus to enter host cells by attaching to sialic acid receptors - major antigen to which antibodies are directed - 16 types
NA allows release of new viral particles from host cells by catalyzing cleavage of linkages to sialic acid - 9 types
Antigenic Drift and Shift - immunity to one antigenic variant may not confer protection against others - antigenic variants made by point mutations (antigenic drift) - this is the basis for seasonal epidemics of influenza and reason for changes in annual vaccine and basis behind anual vaccination. Antigenic shift occurs when influenza virus acquires a new HA or NAvia genetic reassortment rather than point mutations - occurs when animal that supports multipl esubtypes of influenza is concurrently infectied with two subtypes - result in emergence of novel flu virus and carries potential for pandemic - Spanish flu 1918, Asian flu 1957, Hong Kong flu 1968, Avian Flu, Swine Flu 2009
Clinical Presentation
Complications may include exacerbation of comorbidities, primary viral pneumo, secondary bacterial pneumo, resp illnesses, encephalopathy, transverse myelitis, myositis, myocardiits, pericarditis, Reye's syndrome
rapid onset fever, myalgia, HA, malaise, nonproductive cough, sore throat, rhinitis
N/V and otitis media commonly reported in children
S/sx typically resolve in 3-7 days although cough and malaise may persist 2 weeks
Diagnosis
CBC and chem panel obtained to assess overall status of pt
Gold standard diagnostic is reverse-transcription polymerase chain reaction (RT-PCR) or vial culture - can identify strain and subtype but takes a week to develop to not clinically relevant
rapid influenza diagnostic test can be done at point of care for rapid detection - allowed for prompt diagnosis and initiation of antiviral therapy
Cultures of potential sites of infection obtained if coinfection, superinfection or secondary infection suspected - chest radiograph is pneumonia suspected
Etiology
Can occur at any time of year - most common in fall and winter
highest rate of infection in children - highest rate of severe infection/hospitalization/death in elderly, young children, underlying medical conditions (pregnancy, cardiopulmonary disorders)
Deaths associated with flu result from secondary bacterial pneumonia, primary viral pneumonia, and/or exacerbation of underlying conditions
Treatment
Pharm
NA inhibitors - oseltamivir, zanamivir, peramivir for ppx and treatment of flu
peraminvir is only IV form - fewer ADRs
Neuraminidase inhibitors that have activity against influenxa A ans B - without NA release of virus from infected cells is impaired to replication decreased
Adamantanes - no longer recommended for use due to high resistance - block M2 ion channel which is specific to influenza A and inhibit viral uncoating
Non-pharm
APAP for fever
Antihistamine for rhinitis
Sleep and low level of activity - stay home for work/school, fluid intake, cough/throat lozenges, warm tea, soup
General Approach
early and definitive diagnosis is crucial - antivirals most effective if started within 48 hours of onset
Sooner anti-virals started the more effective they are - shorten duration of illness, provide symptom control
Prevention
Vaccination is primary method of prevention
recommended for ppl 6months and older
ideal time for vaccine is Oct or Nov to allow development and maintenance of immunity during peak flu season
inactivated influenza vaccine, live-inactivated flu vaccine
infection control measures - wash hands, cover cough, resp mask, contact voidance
chemoprophylaxis useful in certain situations
Pathogenesis
Transmitted via person-to-person inhalation of respiratory droplets (from cough and sneeze) or contaminated objects
incubation period is 1-7 days (avg 2 days) - transmisison can occur as long as infected person is shedding virus from respiratory tract
typically infectious within 1 day before and 7 days after onset of illness
Goals
Control symptoms, prevent complications, decrease work/school absenteeism, prevent spread