Clinical Guidance on Swine Flu

Swine Flu: CDC Offers Clinical Guidance, WHO Raises Alert Level Again

The CDC has released a series of flu-related interim clinical guidance documents. They include one on the care of infected children and pregnant women, another for emergency medical services, and a case-definition document.

With regard to infected children, the advisory says the signs of severe disease include apnea, tachypnea, dyspnea, cyanosis, dehydration, altered mental status, and extreme irritability. Pregnant women suspected of being infected "should receive empiric antiviral treatment."

The CDC clarified case-definition terms as follows:

• An acute febrile respiratory illness is characterized by a temperature of 100.4 degrees or higher and recent onset of one of the following: rhinorrhea, nasal congestion, sore throat, or cough.
• Cases are "confirmed" only by PCR or viral culture.
• "Probable" cases include those with acute febrile respiratory illness, positive for influenza A, but negative for H1 and H3 by PCR.
• "Suspected" cases include symptomatic patients with recent (within 7 days) travel to infected areas or contact with a known case.

WHO raised its pandemic alert level from 4 to 5 (on a 6-level scale), reflecting confirmed person-to-person spread and the imminence of the threat. Earlier on Wednesday, the CDC confirmed the first death in the U.S.

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Dr Marwah

Swine influenza

Swine influenza (also swine flu) refers to influenza caused by any strain of the influenza virus endemic in pigs (swine). Strains endemic in swine are called swine influenza virus (SIV).

Swine flu is common in swine and rare in humans. People who work with swine, especially people with intense exposures, are at risk of catching swine influenza if the swine carry a strain able to infect humans. However, these strains rarely are able to pass from human to human. Rarely, SIV mutates into a form able to pass easily from human to human. The strain responsible for the 2009 swine flu outbreak is believed to have undergone such a mutation.This virus is named swine flu because one of its surface proteins is similar to viruses that usually infect pigs however this strain is spreading in people and it is unknown if it infects pigs.

In humans, the symptoms of swine flu are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort. The strain responsible for the 2009 swine flu outbreak in most cases causes only mild symptoms and the infected person recovers fully in a few days.

Of the three genera of human flu, two are endemic also in swine: Influenzavirus A (common) and Influenzavirus C (rare). Influenzavirus B has not been reported in swine. Within Influenzavirus A and Influenzavirus C, the strains endemic to swine and humans are largely distinct.

The CDC recommends the use of Tamiflu (oseltamivir) or Relenza (zanamivir) for the treatment and/or prevention of infection with swine influenza viruses. The virus isolates that have been tested from the US and Mexico are however resistant to amantadine and rimantadine. If a person gets sick, antiviral drugs can make the illness milder and make the patient feel better faster. They may also prevent serious flu complications. For treatment, antiviral drugs work best if started soon after getting sick (within 2 days of symptoms).

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Dr Marwah