Update on A (H1N1) Influenza (Swine Influenza) - May 5, 2009

Let's review basics, then cover a few updates:

First and foremost, what are the symptoms of A (H1N1) influenza? Most authorities concur that persons with influenza will suffer the following:

1. Fever (defined in some references as temperature greater than 37.8 degrees C [100 degrees F], and in other references as 38 degrees C [100.4 degrees F])

AND two or more of the following:

2. runny nose or nasal congestion, sore throat, cough

It is, of course, possible to manifest fever and only one symptom and be evolving a case of influenza, but note how similar the symptoms of influenza are to the common cold, or any other viral upper respiratory (tract) infection. Other symptoms that appear to be quite common with influenza include muscle aches, nausea, fatigue, abdominal pain, headache, diarrhea, shortness of breath, joint pain, and chills.

Because so many persons are presenting to emergency departments and other health care facilities desiring a test for A (H1N1) influenza, and because the ability to process all of these tests is limited, protocols are now in place to control the volume of testing at many health care facilities. Typical instructions are to test persons with influenza-like illness (defined above) or who have pneumonia AND are in a "congregate setting," such as school, day care, jail, shelter, long term care facility, and so forth.

Another update is that since more and more cases of confirmed A (H1N1) influenza do not have a travel history, influenza now appears to be a community-based illness; travel to Mexico is no longer included in the early case definition.

While the incubation period is 1 to 7 days, most cases occur in 1 to 3 days. Patients can be contagious for up to 10 days, and perhaps even longer for children and immunocompromised individuals, who tend to shed the virus longer.

In many locations, it has been difficult to obtain oseltamivir (Tamiflu) and/or zanamivir (Relenza), because pharmacies have been out of stock due to a rush on these medications, virtually all by persons who are not ill, but who wish to stockpile the drugs "just in case." We are beginning to see the medications become available for both treatment and chemoprophylaxis of high-risk individuals, including health care providers who have been exposed to a patient with probable A (H1N1) influenza.

Despite the fact that the number of victims worldwide, including the U.S. (403 persons - one death), continues to grow, there is beginning to be a sense that the rate of spread and magnitude of the pandemic potential are beginning to wane. The outlook in Mexico appears less severe than originally perceived. According to the CDC, the virus is not showing the virulence markers associated with more serious disease, and the typical clinical course does not show any sign of being more severe than the seasonal flu.

However, because the disease is now spread around the globe, there may be another wave of influenza, the severity to be determined. Flu season is getting ready to begin in the Southern Hemisphere. If A (H1N1) influenza becomes part of that season, its behavior will be important for us in the Northern Hemisphere to observe, because when our flu season rolls around this winter, we may face that version of swine flu.

Tags: A(H1N1) influenza, S-OIV, influenza, swine flu, flu, swine influenza, wilderness medicine, outdoor medicine, healthline

Labels: A (H1N1) influenza, flu, influenza, swine flu, swine influenza

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