Update on Swine Influenza

From the Centers for Disease Control (CDC):

Interim Guidance on Antiviral Recommendations for Patients with Confirmed or Suspected Swine Influenza A (H1N1) Virus Infection and Close Contacts

This information is intended to provide interim guidance on the use of antiviral agents for treatment and chemoprophylaxis of swine influenza A (H1N1) virus infection. This includes patients with confirmed or suspected swine influenza A (H1N1) virus infection and their close contacts.

Case Definitions for Infection with Swine Influenza A (H1N1) Virus

A confirmed case of swine influenza A (H1N1) virus infection is defined as a person with an acute respiratory illness associated with fever, with swine influenza A (H1N1) virus infection laboratory-confirmed at the CDC.

Infectious period
The infectious period for a confirmed case of swine influenza A (H1N1) virus infection is defined as 1 day prior to the case’s illness onset to 7 days after onset.

A suspected case of swine influenza A (H1N1) virus infection is defined as a person with acute respiratory illness associated with fever, with onset within 7 days of close contact with a person who is a confirmed case of swine influenza A (H1N1) virus infection, or within 7 days of travel to a community either within the United States or internationally where there are one or more confirmed swine influenza A (H1N1) cases, or the affected person resides in a community where there are one or more confirmed swine influenza cases.

Close contact is defined as within about 6 feet of an ill person who is a confirmed or suspected case of swine influenza A (H1N1) virus infection during the case’s infectious period.

Acute respiratory illness is defined as recent onset of at least two of the following: runny nose or nasal congestion, sore throat, and cough (with or without fever or feverishness).

It is too early to determine which persons are at high risk for complications from swine influenza A (H1N1) virus infection. This guidance will be updated as new information is available.

Clinicians should consider swine influenza A (H1N1) virus infection in the differential diagnosis of patients with respiratory disease associated with fever and who 1) live in areas in the U.S. with confirmed human cases of swine influenza A (H1N1) virus infection or 2) who traveled recently to Mexico or were in contact with persons who had febrile (associated with fever) respiratory illness and were in the areas of the U.S. with confirmed swine influenza cases or Mexico in the 7 days preceding their illness onset.

Special Considerations for Children

Aspirin or aspirin-containing products (e.g. bismuth subsalicylate – Pepto Bismol) should not be administered to any confirmed or suspected ill case of swine influenza A (H1N1) virus infection aged 18 years old and younger due to the risk of Reye syndrome. For relief of fever, other anti-fever medications are recommended. These include acetaminophen or non-steroidal anti-inflammatory drugs, such as ibuprofen.

Antiviral Resistance

This swine influenza A (H1N1) virus is sensitive (susceptible) to the neuraminidase inhibitor antiviral medications zanamivir (Relenza) and oseltamivir (Tamiflu). It is resistant to the adamantane antiviral medications amantadine and rimantadine.

Seasonal influenza A and B viruses continue to circulate at low levels in the U.S. and in Mexico. Currently circulating human influenza A (H1N1) viruses are resistant to oseltamivir and sensitive (susceptible) to zanamivir, amantadine and rimantadine. Currently circulating human influenza A (H3N2) viruses are resistant to amantadine and rimantadine, but sensitive (susceptible) to oseltamivir and zanamivir. Therefore, at this time antiviral treatment recommendations for suspected cases of swine influenza A (H1N1) virus infection need to consider potential infection with swine influenza A (H1N1) virus as well as human influenza viruses, and their different antiviral susceptibilities.

Antiviral Treatment for Suspected Cases

Empiric antiviral treatment is recommended for any ill person suspected to have swine influenza A (H1N1) virus infection. Antiviral treatment with either zanamivir alone or with a combination of oseltamivir and either amantadine or rimantadine should be initiated as soon as possible after the onset of symptoms. Recommended duration of treatment is five days. Recommendations for use of antivirals may change as data on antiviral susceptibilities become available. Antiviral doses and schedules recommended for treatment of swine influenza A (H1N1) virus infection are the same as those recommended for seasonal influenza.

Confirmed Cases

For antiviral treatment of a confirmed case of swine influenza A (H1N1) virus infection, either oseltamivir or zanamivir may be administered. Recommended duration of treatment is five days. These same antivirals should be considered for treatment of cases that test positive for influenza A, but test negative for seasonal influenza viruses H3 and H1.

Pregnant Women

Oseltamivir, zanamivir, amantadine, and rimantadine are all “Pregnancy Category C" medications, indicating that no clinical studies have been conducted to assess the safety of these medications for pregnant women. Only two cases of amantadine use for severe influenza illness during the third trimester have been reported. However, both amantadine and rimantadine have been demonstrated in animal studies to be teratogenic and embryotoxic when administered at substantially high doses. Because of the unknown effects of influenza antiviral drugs on pregnant women and their fetuses, these four drugs should be used during pregnancy only if the potential benefit justifies the potential risk to the embryo or fetus; the manufacturers' package inserts should be consulted. However, no adverse effects have been reported among women who received oseltamivir or zanamivir during pregnancy or among infants born to such women.

Antiviral Chemoprophylaxis

For antiviral chemoprophylaxis of swine influenza A (H1N1) virus infection, either oseltamivir or zanamivir are recommended. Duration of antiviral chemoprophylaxis is 7 days after the last known exposure to an ill confirmed case of swine influenza A (H1N1) virus infection. Antiviral dosing and schedules recommended for chemoprophylaxis of swine influenza A(H1N1) virus infection are the same as those recommended for seasonal influenza.

Antiviral chemoprophylaxis (pre-exposure or post-exposure) with either oseltamivir or zanamivir is recommended for the following individuals:

1. Household close contacts who are at high-risk for complications of influenza (persons with certain chronic medical conditions, elderly) of a confirmed or suspected case.
2. School children who are at high-risk for complications of influenza (persons with certain chronic medical conditions) who had close contact (face-to-face) with a confirmed or suspected case.
3. Travelers to Mexico who are at high-risk for complications of influenza (persons with certain chronic medical conditions, elderly).
4. Border workers (Mexico) who are at high-risk for complications of influenza (persons with certain chronic medical conditions, elderly).
5. Health care workers or public health workers who had unprotected close contact with an ill confirmed case of swine influenza A (H1N1) virus infection during the case’s infectious period.

Antiviral chemoprophylaxis (pre-exposure or post-exposure) with either oseltamivir or zanamivir can be considered for the following:

1. Any health care worker who is at high-risk for complications of influenza (persons with certain chronic medical conditions, elderly) who is working in an area with confirmed swine influenza A (H1N1) cases, and who is caring for patients with any acute febrile respiratory illness.
2. Non-high risk persons who are travelers to Mexico, first responders, or border workers who are working in areas with confirmed cases of swine influenza A (H1N1) virus infection.

Adverse events and contraindications

For further information about influenza antiviral medications, including contraindications and adverse effects, please see the following:
http://www.cdc.gov/flu/professionals/antivirals/side-effects.htm
http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5707a1.htm

From the Center for Biosecurity at the University of Pittsburgh Medical Center:

Today, the Director General (DG) of the World Health Organization (WHO) raised the influenza pandemic alert level from the current phase 3 to phase 4. This decision follows from advice given by the WHO’s Emergency Committee, which met this morning to consider "available data on confirmed outbreaks of A/H1N1 swine influenza in the United States of America, Mexico, and Canada . . . [and] reports of possible spread to additional countries.”

Based on the advice of the Committee:

The DG recommended that nations focus on measures to mitigate the spread of infection. In light of widespread presence of the virus, the WHO has deemed that “containment of the outbreak is not feasible.” The DG recommended against closing borders or restricting international travel. The WHO noted that it is “prudent for people who are ill to delay international travel and for people developing symptoms following international travel to seek medical attention.”

The DG said that “production of seasonal influenza vaccine should continue at this time, subject to re-evaluation as the situation evolves.”

The European Union (EU) Health Commissioner, Androulla Vassiliou, issued a travel advisory to the 27 EU member countries recommending that “non-essential” travel to affected parts of the U.S. and Mexico be suspended. According to Vassiliou, this is a travel advisory only and not a travel ban, and it is up to member countries to make their own determinations about whether to set travel and trade restrictions. The acting Director of the Centers for Disease Control and Prevention (CDC), Richard Besser, responded by commenting that the EU travel recommendation is not warranted: "At this point I would not put a travel restriction or recommendation against coming to the United States,” said Besser.

In the U.S., a total of 40 cases have been confirmed. Today’s increase in case number comes after 20 additional cases were confirmed in New York City at the St. Francis Preparatory School. All U.S. cases continue to report only mild illness.

Several updates have occurred since yesterday in the worldwide reports of suspected cases of swine flu:

New Zealand is now reporting 25 cases under suspicion.
Spain has confirmed 1 of its 6 suspected cases.
Australia’s 2 suspected cases have tested negative.
France’s 4 suspected cases have tested negative.
Italy has 1 case under suspicion.
England has also ruled out swine flu in 1 suspected case.
Scotland has confirmed 2 cases.
Columbia has 12 suspected cases.
Brazil has 1 suspected case.

Finally, the CDC has published an excellent document entitled "Interim Guidance for Swine influenza A (H1N1): Taking Care of a Sick Person in Your Home." This is very useful if you have someone in your household whom you believe to be suffering from swine influenza.


Preview the Annual Meeting of the Wilderness Medical Society, which will be held in Snowmass, Colorado July 24-29, 2009.

Join me from January 24 to February 2, 2010 for an exciting dive and wilderness medicine CME adventure aboard the Nautilus Explorer to Socorro Island, Mexico to benefit the Wilderness Medical Society.