Influenza (cont.)

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What is the prognosis (outlook) and complications for patients who get the flu?

In general, the majority (about 90%-95%) of people who get the disease feel terrible (see symptoms) but recover with no problems. People with suppressed immune systems historically have worse outcomes than uncompromised individuals; current data suggest that pregnant individuals, children under 2 years of age, young adults, and individuals with any immune compromise or debilitation are likely to have a worse prognosis. In most outbreaks, epidemics and pandemics, the mortality rates are highest in the older population (usually above 50 years old). Complications of any flu virus infection, although relatively rare, may resemble severe viral pneumonia or the SARS (severe acute respiratory syndrome caused by a coronavirus strain) outbreak in 2002-2003 in which the disease spread to about 10 countries with over 7,000 cases, over 700 deaths, and had a 10% mortality rate.

At the beginning of the recent 2009 H1N1 pandemic, the numbers of people with flu-like illness were higher than usual and the illness initially affected a much younger population than the conventional flu. As the pandemic progressed, more young children became infected than usual, but the mortality statistics became more similar to those of the conventional flu mortality with an older population (especially ages 50-64) having the highest death rate. The best news about the H1N1 swine flu is that the majority of people worldwide who has caught the H1N1flu recovered without medical treatment and had an excellent prognosis, but this is not always the situation as demonstrated by the 1918 flu pandemic.

What is the bird (avian) flu?

The bird flu, also known as avian influenza and H5N1, is an infection caused by avian influenza A. This virus is not the one that causes SARS, an acute respiratory syndrome caused by a coronavirus. Bird flu can infect many bird species, including domesticated birds such as chickens. In most cases, the disease is mild; however, some subtypes can be pathogenic and rapidly kill birds within 48 hours. Rarely, humans can be infected by these bird viruses. People who get infected with bird flu usually have direct contact with the infected birds or their waste products. Depending on the viral type, the infections can range from mild influenza to severe respiratory problems or death. Human infection with bird flu is rare but frequently fatal. More than half of those people infected (over 340 infected people) have died (current estimates of the mortality [death] rates in humans is about 60%). Fortunately, this virus does not seem to be easily passed from person to person. The major concern among scientists and physicians about bird flu is that it will change (mutate) its viral RNA enough to be easily transferred among people and produce a pandemic similar to the one of 1918. There have been several isolated instances where a person has been reported to get avian flu in 2010; the virus was detected in South Korea (three human cases) resulting in a quarantine of two farms, and in 2012, over 10,000 turkeys died in a H5N1 outbreak with no human infections recorded. Recent research suggests that some people may have had exposure to H5N1 in their past but had either mild or no symptoms.

In addition, researchers, in an effort to understand what makes an animal or bird flu become easily transmissible to humans, developed a bird flu strain that is likely easily transmitted from person to person. Although it exists only in research labs, there is controversy about both the synthesis and the scientific publication of how this potentially highly pathogenic strain was created.

Do antiviral agents protect people from the flu?

Vaccination is the primary method for control of influenza; however, antiviral agents have a role in the prevention and treatment of mainly influenza type A infection. Regardless, antiviral agents should not be considered as a substitute or alternative for vaccination.

As of Dec. 15, 2010, the CDC published the following concerning antiviral medications:

Antiviral medications with activity against influenza viruses are an important adjunct to influenza vaccine in the control of influenza.

  • Influenza antiviral prescription drugs can be used to treat influenza or to prevent influenza.
  • Oseltamivir and zanamivir are chemically related antiviral medications known as neuraminidase inhibitors that have activity against both influenza A and B viruses.

The following is the CDC recommended dosage for antiviral medications for the treatment of influenza (flu) for the 2012-2013 season:

Table 1 Recommended dosage and schedule of influenza antiviral medications * for treatment† and chemoprophylaxis§
Antiviral Agent Age Group (yrs)
    0-6 7-9 10-12 10-64 65 and older
Zanamivir Treatment, influenza A and B NA 10 mg (2 inhalations) twice daily 10 mg (2 inhalations) twice daily 10 mg (2 inhalations) twice daily 10 mg (2 inhalations) twice daily
Chemoprophylaxis, influenza A and B NA for ages 1-4 Ages 5-9 10 mg (2 inhalations) once daily 10 mg (2 inhalations) once daily 10 mg (2 inhalations) once daily 10 mg (2 inhalations) once daily
Oseltamivir Treatment, ** influenza A and B Dose varies by child's weight** Dose varies by child's weight** Dose varies by child's weight**
More than 40 kg = adult dose
75 mg twice daily 75 mg twice daily
Chemoprophylaxis, influenza A and B Dose varies by child's weight†† Dose varies by child's weight†† Dose varies by child's weight††
More than 40 kg = adult dose
75 mg once daily 75 mg once daily
Abbreviation: NA = not approved

* Zanamivir is manufactured by GlaxoSmithKline (Relenza --- inhaled powder). Zanamivir is approved for treatment of persons aged 7 years and older and approved for chemoprophylaxis of persons aged 5 years and older. Zanamivir is administered through oral inhalation by using a plastic device included in the medication package. Patients will benefit from instruction and demonstration of the correct use of the device. Zanamivir is not recommended for those persons with underlying airway disease. Oseltamivir is manufactured by Roche Pharmaceuticals (Tamiflu --- tablet). Oseltamivir is approved for treatment of persons aged 2 weeks and older and for chemoprophylaxis of persons aged 1 year and older. Oseltamivir is available for oral administration in 30 mg, 45 mg, and 75 mg capsules and liquid suspension. This information is based on data published by the Food and Drug Administration (FDA)

†Recommended duration for antiviral treatment is 5 days. Longer treatment courses can be considered for patients who remain severely ill after 5 days of treatment.

§Recommended duration of post-exposure chemoprophylaxis for high-risk patients is 7 days after the most recent known exposure if chemoprophylaxis can be started within 48 hours of exposure; however, early treatment if symptomatic is preferred. For control of outbreaks in long-term care facilities and hospitals, CDC recommends antiviral chemoprophylaxis for a minimum of 2 weeks and up to 1 week after the most recent known case was identified.

See Table 2 for information about use of oseltamivir for infants aged younger than 1 year. A reduction in the dose of oseltamivir is recommended for persons with creatinine clearance less than 30 mL/min.

** The treatment dosing recommendation for oseltamivir for children aged 2 weeks to younger than one year is 3mg/kg twice a day. The treatment dosing recommendation for oseltamivir for children aged 1 year and older who weigh 15 kg or less is 30 mg twice a day. For children who weigh more than 15 kg and up to 23 kg, the dose is 45 mg twice a day. For children who weigh more than 23 kg and up to 40 kg, the dose is 60 mg twice a day. For children who weigh more than 40 kg, the dose is 75 mg twice a day.

††The chemoprophylaxis dosing recommendation for oseltamivir for children aged 1 year and older who weigh 15 kg or less is 30 mg once a day. For children who weigh more than 15 kg and up to 23 kg, the dose is 45 mg once a day. For children who weigh more than 23 kg and up to 40 kg, the dose is 60 mg once a day. For children who weigh more than 40 kg, the dose is 75 mg once a day.

Table 2. Dosing recommendations for treatment or chemoprophylaxis of children aged younger than one year using oseltamivir*
Age Recommended treatment for 5 days† Recommended chemoprophylaxis†
Younger than 3 months 3 mg/kg dose twice daily Not recommended unless situation judged critical because of limited data on use in this age group
3-11 months 3 mg/kg dose twice daily 3 mg/kg dose once daily
* An Emergency Use Authorization (EUA) was issued by the FDA on April 28, 2009 , and expired on June 23, 2010. This EUA allowed use of oseltamivir for treatment or chemoprophylaxis of 2009 pandemic influenza A (H1N1) virus infection during the pandemic in infants aged younger than 1 year. Currently circulating 2009 H1N1, seasonal influenza A (H3N2), and B viruses are susceptible to oseltamivir.

†Current weight-based dosing recommendations are not appropriate for premature infants. Premature infants might have slower clearance of oseltamivir because of immature renal function, and doses recommended for full-term infants might lead to very high drug concentrations in this age group. Very limited data from a small cohort of premature infants suggested that oseltamivir concentrations among premature infants administered oseltamivir 1 mg/kg twice daily would be similar to those observed with the recommended treatment dose in term infants (3 mg/kg twice daily). Observed drug concentrations were highly variable among premature infants. These data are insufficient to recommend a specific dose of oseltamivir for premature infants.

  • Antiviral treatment is recommended as soon as possible for patients with confirmed or suspected influenza who have severe, complicated, or progressive illness, or who are hospitalized.
  • Antiviral treatment is recommended as soon as possible for outpatients with confirmed or suspected influenza who are at higher risk for influenza complications based on their age and/or medical conditions; clinical judgment should be an important component of outpatient treatment decisions.
  • Antiviral medications currently recommended include oseltamivir and zanamivir, based upon recent viral surveillance and resistance data indicating that >99% of currently circulating influenza virus strains are sensitive to these medications. Amantadine (Symmetrel) and rimantadine (Flumadine) should not be used because of high levels of resistance to these drugs among circulating influenza A viruses.
  • Oseltamivir should be used to provide treatment or chemoprophylaxis (prevention of the flu after exposure to the virus) for infants younger than 1 year of age when indicated.
  • Antiviral treatment can be considered for any previously healthy non-high-risk symptomatic outpatient with confirmed or suspected influenza who is not in the recommended groups, based upon clinical judgment, if treatment can be initiated within 48 hours of illness onset.
Medically Reviewed by a Doctor on 2/20/2013

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