H1N1 Treatment

Antiviral Guidance for Suspected, Probable or Confirmed H1N1 Influenza

The Centers for Disease Control and Prevention (CDC) emphasizes early, empiric antiviral treatment for hospitalized patients and high-risk outpatients with suspected, probable or confirmed H1N1 influenza.

Preliminary information indicates that some hospitalized patients with H1N1 influenza have not been treated with antivirals or that treatment with antiviral agents was delayed until confirmatory testing was completed. In particular, some patients with chest X-ray evidence of pneumonia and influenza symptoms have not received antivirals early. While data from seasonal influenza indicates that early antiviral treatment is most effective (within 48 hours of symptom onset), some studies have reported a benefit in treating hospitalized patients. Therefore, initiating therapy at the earliest possible time is desirable, including at hospital admission, if patients were not previously treated.

Clinicians should be aware that influenza virus infection can cause primary viral pneumonia and early treatment of people with influenza-related pneumonia is desirable. Additionally, empiric treatment with influenza antiviral medications does not preclude empiric treatment for bacterial co-infections. Specific influenza testing should be performed for any hospitalized patient with suspected H1N1 influenza.

Accordingly, the CDC would like to emphasize antiviral treatment for the following:

• All hospitalized patients with suspected, probable, or confirmed H1N1 influenza should be empirically treated with oseltamivir or zanamivir as early after illness onset as possible.
  
  No comparative studies have been done to assess whether higher doses or longer treatment courses might be more effective for severely ill patients. However, a longer duration of treatment should be considered for severe illness that persists at the end of the usual five day course. Some experts also recommend higher treatment doses (e.g., 150 mg oseltamivir twice per day), based on concerns about the potential for lower oseltamivir absorption, higher viral loads and reduced delivery of oseltamivir to damaged tissue among severely ill patients. Patients who have received higher treatment doses or longer treatment durations have tolerated these regimens without substantial increase in adverse events, based on limited data.
• All outpatients with suspected H1N1 virus infection who are at higher risk for influenza complications should be empirically treated with oseltamivir or zanamivir as early after illness onset as possible.
• Groups with a higher risk for influenza complications:
  
  a. Children younger than five years old. The risk for severe complications from seasonal influenza is highest among children younger than two years old.
  b. Adults 65 years of age and older
  c. Persons with the following conditions: chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, hematological (including sickle cell disease), neurologic, neuromuscular or metabolic disorders (including diabetes mellitus), immunosuppression, including that caused by medications or by HIV, pregnant women, persons younger than 19 years of age who are receiving long-term aspirin therapy, residents of nursing homes and other chronic-care facilities

Antiviral Chemoprophylaxis for H1N1 Influenza

For antiviral chemoprophylaxis of H1N1 influenza, either oseltamivir or zanamivir are recommended (view recommendations). Duration of antiviral chemoprophylaxis post-exposure is 10 days after the last known exposure to H1N1.

The indication for post-exposure chemoprophylaxis is based upon close contact with a person who is a confirmed, probable or suspected case of H1N1 virus infection during the infectious period of the case. The infectious period for persons infected with the H1N1 virus is assumed to be similar to that observed in studies of seasonal influenza.

With seasonal influenza, studies have shown that people may be able to transmit infection beginning one day before they develop symptoms to up to seven days after they get sick. Children, especially younger children, might potentially be infectious for longer periods. However, for this guidance, the infectious period is defined as one day before until seven days after the case’s onset of illness. If the contact occurred with a case whose illness started more than seven days before contact with the person under consideration for antivirals, then chemoprophylaxis is not necessary. For pre-exposure chemoprophylaxis, antiviral medications should be given during the potential exposure period and continued for 10 days after the last known exposure to a person with H1N1 virus during the cases infectious period. Oseltamivir can also be used for chemoprophylaxis under the Emergency Use Authorization (EUA) for children less than one year of age.

Post-exposure antiviral chemoprophylaxis with either oseltamivir or zanamivir can be considered for the following:

1. Close contacts of cases (confirmed, probable or suspected) who are at high-risk for complications of influenza
2. Health care personnel, public health workers or first responders who have had a recognized, unprotected close contact exposure to a person with H1N1 influenza (confirmed, probable or suspected) during that person’s infectious period. Information on appropriate personal protective equipment might be updated frequently as additional information on transmission becomes available.
   
   Pre-exposure antiviral chemoprophylaxis should only be used in limited circumstances, and in consultation with local medical or public health authorities. Certain persons at ongoing occupational risk for exposure who are also at higher risk for complications of influenza (e.g., health care personnel, public health workers or first responders who are working in communities with H1N1 outbreaks) should carefully follow guidelines for appropriate personal protective equipment or consider temporary reassignment.

Adapted for the Web by the American Medical Association.
Source: Centers for Disease Control and Prevention.