CDC Updates Guidelines on Management of 2009 H1N1 Influenza

Laurie Barclay, MD

September 09, 2009

September 9, 2009 — The US Centers for Disease Control and Prevention (CDC) have updated its guidelines on the reporting and management of the 2009 influenza A (H1N1) virus, according to a media briefing yesterday. Topics covered include characteristics of 2009 H1N1 influenza based on ongoing surveillance and guidance regarding use of antiviral agents for 2009 H1N1 influenza and seasonal influenza.

Although the recommended drugs and groups of patients requiring antiviral treatment remain unchanged from the previous update, the latest recommendations include a "watchful waiting" option for prophylaxis and emphasize the need for prompt treatment in high-risk patients.

"[The 2009 H1N1 influenza virus] never went away this summer — it's still around, and we need to pay attention," said Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases. "The good news is that the spectrum of illness doesn't seem to have changed, but we really don't know what the trajectory will be. Our principal prediction is that it will be a busy and long season, and we need to be prepared."

The most recent increase in 2009 H1N1 influenza activity appears to be centered in the southeastern states, including Georgia, Mississippi, Alabama, and Florida. On September 4, 24 primary and secondary schools in Georgia, Indiana, Missouri, and Tennessee announced that they had sent home a total of 25,000 students with flu-like illness thought to be caused by the H1N1 strain.

The reason for this geographic predilection is unclear, but 2 important factors may be that schools in the southeastern states resume classes earlier than do schools in other regions and that the southeastern states had relatively less H1N1 activity in the spring.

"We expect more variability in the H1N1 virus going into next spring," Dr. Schuchat said. "But the good news is that the virus is unchanged in its appearance so far, so that the vaccines that have been prepared against this strain should still be effective."

Compared with CDC guidance issued on May 6, 2009, the latest guidance differs in the following ways:

  • Additional context and guidance for clinicians is provided to help ensure that antiviral drugs are prescribed appropriately this season and that they are administered quickly to those in greatest need. As before, the priority for use of antiviral drugs is for patients who are hospitalized with influenza-like illness and for those patients who are ill with influenza-like illness and who are at high risk for influenza-related complications.

  • To shorten possible delays between illness onset in high-risk patients and treatment, clinicians should consider providing prescriptions for antiviral medications ahead of time for such patients. Should the patient develop symptoms, he or she could call the clinician for guidance about whether to fill the prescription.

  • More information is given concerning the appropriate (and limited) situations in which antiviral medications should be used for chemoprophylaxis. Antiviral agents should not be used for prevention in healthy persons based on community exposures. Rather than immediately treat all persons at high risk who have been exposed to H1N1, it may be appropriate in some closely monitored patients to watch expectantly, giving antiviral agents immediately if symptoms develop, but not as prophylaxis in asymptomatic individuals.

  • The new recommendations emphasize using antiviral drugs for early treatment instead of for prophylaxis to provide clinicians with the information needed to reach those at greatest risk with appropriate and timely treatment, to lower the risk of developing antiviral resistance, and to recognize the importance of clinical judgment in making patient-specific decisions regarding treatment and chemoprophylaxis.

Thus far, there have been "only a handful" of cases of reported H1N1 resistance to antiviral agents, according to Dr. Schuchat.

As the CDC recommended previously, all persons with suspected or confirmed influenza requiring hospitalization should be treated with oseltamivir or zanamivir, as should those who are at increased risk for complications (children younger than 5 years, adults aged 65 years and older, pregnant women, persons with certain chronic medical or immunosuppressive conditions, and persons younger than 19 years who are receiving long-term aspirin therapy).

"Timing of antiviral therapy is important, and it should be started in high-risk patients within 48 hours of symptom onset," Dr. Schuchat said. "But clinical judgment is still important, and we want clinicians to customize their care for each patient."

The latest guidelines emphasize starting treatment as early as possible in hospitalized patients or in those at high risk for complications, because studies have shown that treatment started within 48 hours of illness onset is more likely to provide benefit. Treatment should not be delayed pending laboratory confirmation of influenza, because a negative rapid test for influenza does not rule out influenza and sensitivity ranges from 10% to 70%.

In addition to hospitalized patients and those at high risk for complications, any patient with suspected influenza presenting with warning symptoms or signs should promptly receive empiric antiviral treatment. These "red flag" findings include dyspnea, tachypnea, fever, unexplained oxygen desaturation, and/or lower respiratory tract illness.

Clinicians should educate their patients about these warning symptoms and encourage them to seek treatment as soon as possible if the symptoms are present. In infants and young children, additional warning signs are lethargy, irritability to the point of not wanting to be held, and symptoms initially appearing to improve and then getting worse.

Persons who are not at higher risk for complications or do not have severe influenza requiring hospitalization generally do not require antiviral medications for treatment or prophylaxis.

"Antivirals are a critical part of our tool kit in countering influenza, both H1N1 and other strains," Dr. Schuchat said. "But a key point is that most children, adolescents, and adults do not need antiviral medication if they develop a flu-like illness. Giving these medications when they are not needed could actually make things worse by promoting viral resistance."

The reporting and management guidelines are available on the CDC's H1N1 Flu Clinical and Public Health Guidance page.

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