influenza

Saturday, May 29, 2010

INFLUENZA

Jaime A. Santos

Influenza

• commonly called “the flu”

• a contagious respiratory illness caused by influenza viruses

• Infection with influenza viruses can result in illness ranging from mild to severe with life-threatening complications

1918 Spanish flu pandemic: 20 to 50 million people may have died worldwide

Viral Titers Peak Early

“Flu” symptoms

Fever/ chills

Headache

Nasal congestion

Sore throat

Dry cough

Myalgia/ body aches

GI symptoms

Malaise/ tiredness

Influenza - Clinical Signs and Symptoms

• incubation period for influenza is 1--4 days, with an average of 2 days

• Adults - infectious from the day before symptoms begin through approximately 5 days after onset

• Children - infectious for > 10 days, and young children can shed virus for < 6 days before their illness onset

• immunocompromised persons can shed virus for weeks or months

• resolves after a limited number of days for the majority of persons, although cough and malaise can persist for >2 weeks

• young children can have initial symptoms mimicking bacterial sepsis with high fevers– < 20% of children hospitalized with

influenza can have febrile seizures

• Influenza infection has also been associated with encephalopathy transverse myelitis Reye syndrome myositis myocarditis pericarditis

Influenza - Hospitalization and Deaths• Population at risk for complications,

hospitalizations, & deaths:> 65 years old– young children– persons of any age with certain

underlying health conditions: cardiovascular and pulmonary (including asthma), metabolic e.g. DM, Hgbpathies, immunosuppression

– receiving long term ASA

“U” Shaped Epidemic Curve of Influenza During the Interpandemic Period

Visits/100ARD Hospitalizations/10,000P&I Mortality/100,000

Age group

< 5 5–9 10–14 15-19 20-24 25-34 35-44 45-54 55-64 > 640

120 Visits/100ARD Hospitalizations/10,000P&I Mortality/100,000

Age group

< 5 5–9 10–14 15-19 20-24 25-34 35-44 45-54 55-64 > 640

Age group

< 5 5–9 10–14 15-19 20-24 25-34 35-44 45-54 55-64 > 640

Age group

< 5 5–9 10–14 15-19 20-24 25-34 35-44 45-54 55-64 > 640

Age group

Influenza Responsible for Substantial Disease

Deaths36,0001

Hospitalizations114,0002

Direct medical costs$1-$3 billion4

Infections and illnesses50–60 million3

Physician visits25 million3

1. Thompson WW et al. JAMA. 2003;289:179-186.2. CDC. MMWR Recomm Rep. 2003;58(RR-8):1-34.3. Couch RB. Ann Intern Med. 2000;133:992-998.4. Patriarca PA. JAMA. 1999;282:75-77.

Seasonal

• In colder countries flu is largely seen during colder months and they vaccinate prior to this season (e.g. October)

• In tropical countries flu is seen all year round

Flu Season in the Philippines Southern Hemisphere PatternCumulative Data: RITM Influenza Surveillance Data Feb. 1998 – Oct. 2004

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Influenza virus types

• Three : Influenza A, B, and C• Influenza types A or B viruses cause

epidemics; influenza A may cause pandemics

• Getting a flu shot can prevent illness from types A and B influenza but not from type C

• Influenza type C causes mild respiratory illness ; not thought to cause epidemics

Influenza Virus: Segmented genome

Influenza A virus divided into subtypes based on HA and N proteins on surface

• 15 HA, 9 N• Nomenclature based

on: site of origin isolate number year of isolation subtypeExample:influenzaA/

Johannesburg/33/94(H3N2)

Drift or shift

• “Antigenic drift" - small changes in the virus that happen continually (influenza A and B)

• “Antigenic shift” - abrupt, major change in the influenza A viruses, resulting in new H &/or new H and N proteins that infect humans (influenza A only)

Influenza subtypes in humans

• current subtypes of influenza A viruses found in people are A(H1N1) and A(H3N2)

• Influenza B virus is not divided into subtypes

• Influenza A(H1N1), A(H3N2), and influenza B strains are included in each year's influenza vaccine

• Protection is serotype specific

Domestic poultryDomestic pig:

Mixing vessel

Migratory water birds

Domestic poultryDomestic pig:

Mixing vessel

Migratory water birds

Avian Influenza

• Caused by 15 subtypes of influenza A virus subtype of avian influenza

• Low pathogenicity avian influenza (LPAI)

• Highly pathogenic avian influenza (HPAI) – First recognized in Italy in

1878– Extremely contagious in

birds – Rapidly fatal, high

mortality (almost 100% in a few days)

Avian Influenza Infections in HumansConfirmed instances of avian influenza viruses infecting humans since 1997

• 1997: Hong Kong, avian influenza A (H5N1)• 1999: Hong Kong, avian influenza A(H9N2)• 2003: 2 cases of avian influenza A (H5N1)• 2003:H9N2 infection was confirmed in a child

in Hong Kong• 2003: Avian influenza A (H7N7) infections

among poultry workers / families in the Netherlands (> 80 cases )

Characteristics of Avian Influenza Infections in Humans

• reported symptoms of avian influenza : typical influenza-like symptoms (e.g., fever, cough, sore throat and muscle aches) to eye infections, pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications

• It is believed that most cases of H5N1 infection in humans have resulted from contact with infected poultry or contaminated surfaces

Current Avian Flu (H5N1) Strain

– genetically sequenced: all bird origin– antiviral resistance to amantadine and

rimantadine– oseltamavir and zanamivir should still be

effective

Avian Influenza (Bird Flu) Outbreak Why H5N1 is of particular concern

• H5N1 mutates and acquires genes rapidly from other species

• Documented to cause severe disease in humans• avian influenza virus could change so that it could

infect humans and could spread easily from person to person

• no immune protection against them in the human population

• If an avian virus were able to infect people and gain the ability to spread easily from person to person, an “influenza pandemic” could begin

4 days

Vaccines

Some antiviral drugs

60 million?

FLU PANDEMICS: THEN AND NOW

2005WHAT COULD HAPPEN

1 9 1 8WHAT HAPPENED

1.8 billion

Troop ships,railroad

4 months

Gauze masks,disinfectants

Bed rest,aspirin

20+ million

7 billion

World Population

Primary mode of transportation

Preventive measures

Time for virus to circle the globe

Treatments

Estimated deadJanet Englund, MDPIDSP Feb. 2005

Treatment of Influenza

• Antiviral Medications: – antiviral drugs: adamantanes: amantadine,

rimantadine neuraminidase inhibitors: zanamivir,

oseltamivir

– Antiviral treatment lasts for 3-5 days and must be started within the first 2 days of illness.

Antiviral treatment and prophylaxis

• amantadine [4.4-8.8 mg/kg/day, not to exceed 150 mg/day] can be given for 3-5 days; for treatment of influenza A

• oseltamivir [2 mg/kg/dose BID] can be given for 5 days for treatment of influenza A and B.

Its use for treatment and prophylaxis of household contacts has been effective for children > 12 years old

Do I Need A Flu Shot?

Target Groups For Vaccination

1. Those with increased risk of complications:

• Persons age 50 yrs old and above • Children from 6 to 23 months old• Adults and children with the following risk

factors:– Chronic cardiovascular disease (e.g. congestive

heart failure, Hypertensive cardiovascular disease, valvular heart disease, rheumatic heart disease, stroke)

– Chronic lung disease (e.g COPD, asthma, bronchiectasis, malignancies, chronic PTB)

• Chronic metabolic disease (diabetes mellitus)• Chronic renal dysfunction• Hemoglobinopathies • Immunosuppressed (e.g.HIV, malignancies,

immunosuppressive drugs, radiation therapy, transplant patients)

• Children and adolescents who are receiving long-term aspirin therapy

• Residents of nursing homes and other chronic care facilities

• Pregnant women on their 2nd or 3rd trimester who have not received their flu vaccine within the last 12 months.

Target Groups For Vaccination

2. Those who can transmit the disease to others

• Health care workers and other personnel of out patient care settings, hospitals, nursing homes, and chronic care facilities.

• Household contacts (including children) and caregivers of person at high risk.

When Should You Give the Flu Shot?Highlights Influenza Consensus – Flu TWG Oct. 2004

• Data from the five-year epidemiologic data (February 1998 – September 2003) shows increased influenza activity June to November.

• Vaccination should be given once a year preferrably from February to June

• The Southern Hemisphere vaccine which is made available starting February of each year is recommended to cover the expected increase in influenza activity from June to November.

Vaccine dosage by age group

Age Dose No. doses Route

6 – 35 mos 0.25 ml 1 or 2* IM

3 – 8 yrs 0.5 ml 1 or 2* IM

= or > 9 yrs

0.5 ml 1 IM

* 2 if receiving vaccine for 1st time, 1 month apart

Thank You!

influenza

shaped epidemic curve

flu shot

clinical signs

household contacts

domestic pig

target groups

nursing homes

hong kong

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