Update on S-OIV or A (H1N1) Influenza (formerly Swine Influenza) - May 1, 2009

Until further notice, I am going to devote my blog to updates on the A (H1N1) influenza situation. I will post again about outdoor medicine once the flu situation settles.

The following post is derived from information provided by the Santa Clara County (California) Health Department:

We are now referring to "swine influenza" or "swine flu" as influenza A (H1N1) or S-OIV (swine-origin influenza virus).

As of May 1, 2009, the United States has confirmed 141 cases of S-OIV. In contrast to the cases reported from Mexico that have been more severe, the majority of U.S. cases have thus far been characterized as mild. Because of evidence of sustained human-to-human transmission, the World Health Organization raised the pandemic alert level to Phase 5. The outbreak strain of swine-origin influenza A (H1N1) virus (S-OIV) is susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza), but resistant to amandatine and rimantadine.

Because of the high number of patients who are concerned about whether or not they are suffering from S-OIV and the mild profile of the vast majority of U.S. cases, it is becoming necessary in certain locations to prioritize testing for patients in high risk settings for whom a positive result would necessitate a public health action or decision (such as school closure) or for patients who are seriously ill, in order to help doctors, public health officials, and epidemiologists understand disease patterns and severity.

It is currently being recommended to test patients for S-OIV if they are:

• Hospitalized persons with influenza-like illness (fever greater than 37.8°C [100°F] AND at least two of the following: runny nose or nasal congestion, sore throat, or cough; OR if they suffer from pneumonia. Some instructions use a slightly higher temperature (38°C [100.4°F]) as an indicator.
• Non-hospitalized persons with influenza-like illness if they are in a congregate setting: such as school, daycare, or university; jail; homeless shelter; or long-term-care facility.

The usual test is a nasal swab to test for influenza virus. This is not a test specifically for S-OIV, but only for influenza A or B. False negative tests for influenza A are possible. If the test if positive for influenza A, the sample must be further tested ("typed") to determine the presence or absence of S-OIV. A rapid influenza test that is positive for influenza B is of some reassurance, because concurrent S-OIV (a form of influenza A) infection is unlikely.

When a person is suspected or known to have S-OIV infection, and the case is mild (e.g., does not require hospitalization), then the patient is instructed to self-isolate at home, and asked not to attend work or school for 10 days after the start of illness, or until all symptoms have resolved (whichever is longer).

Guidance for care at home of persons with A (H1N1) influenza can be found at
http://www.cdc.gov/swineflu/guidance_homecare.htm

The Centers for Disease Control (CDC) considers the definition of a confirmed case of S-OIV infection to be a person with an influenza-like illness with laboratory confirmed S-OIV infection at the CDC by reverse transcriptase polymerase chain reaction (RT-PCR) or viral culture. A probable case of S-OIV infection is defined as a person with an influenza-like illness who is positive for influenza A, but negative for H1 and H3 by influenza RT-PCR. A suspected case of S-OIV infection is defined as a person with influenza-like illness:

• with onset within 7 days of close contact with a person who is a confirmed case of S-OIV infection, or
• with onset within 7 days of travel to a community either within the United States or internationally where there are one or more confirmed cases of S-OIV, or
• who resides in a community where there are one or more confirmed S-OIV cases.

The estimated incubation period for S-OIV infection is unknown and could range from 1 to 7 days, and more likely from 1 to 4 days. Persons with S-OIV infection are assumed to be shedding virus (and to be contagious) from the day prior to illness onset until resolution of symptoms. Persons with S-OIV infection should be considered potentially contagious for up to 10 days following illness onset. Persons who continue to be ill longer than 10 days after illness onset should be considered potentially contagious until symptoms have resolved. Children, especially younger children, might be contagious for longer periods.

When indicated, antiviral treatment should be initiated as soon as possible after the onset of symptoms. Evidence for benefits from treatment in studies of seasonal influenza is strongest when treatment is started within 48 hours of illness onset. However, some benefit, including reduction in mortality or duration of hospitalization, may be seen even for patients whose treatment is started more than 48 hours after illness onset. Recommended duration of treatment is five days.

It is important to remember that seasonal human influenza A strains (both H1 and H3 subtypes) and influenza B continue to circulate in some communities. Seasonal influenza A/H3 and influenza B are sensitive to oseltamivir (Tamiflu) and zanamivir (Relenza). However, seasonal influenza A/H1 is resistant to oseltamivir (Tamiflu). S-OIV is sensitive to oseltamivir (Tamiflu) or zanamivir (Relenza). Recommendations for use of antivirals may change as data on antiviral susceptibilities and effectiveness become available.

Antiviral chemoprophylaxis (pre-exposure or post-exposure) with either oseltamivir or zanamivir is recommended for the following individuals [with reference to A (H1N1) influenza]:

1. Household close contacts of a confirmed or probable case, who are at high-risk for
complications of influenza.
2. Health care workers or public health workers who did not use appropriate personal protective equipment during close contact with an ill confirmed, probable or suspect case of swine-origin influenza A (H1N1) virus infection during the case’s infectious period.

Persons at high risk for complication of influenza include the following:

• persons aged > 50 years of age;
• children < 5 years of age;
• pregnant women;
• persons with chronic diseases such as diabetes mellitus, asthma, heart disease (excluding hypertension), kidney diseases, severe anemia, cancer, and weakened immune systems due to immunosuppressive medications (corticosteroids, anti-TNF alpha medicines, etc.) or HIV infection;
• children aged six months to 18 years who are on long-term aspirin therapy;
• persons with any condition (e.g., cognitive dysfunction, spinal cord injuries, seizure disorders, or other neuromuscular disorders) that can compromise respiratory function or the handling of respiratory secretions or that can increase the risk for aspiration;
• residents of nursing homes and other chronic care facilities

Antiviral chemoprophylaxis with either oseltamivir or zanamivir can be considered for the following:

1. Household close contacts of a suspected case, who are at high-risk for complications of influenza.
2. Children attending school or daycare who are at high-risk for complications of influenza and who had close contact (face-to-face) with a confirmed, probable, or suspected case.
3. Health care workers who are at high-risk for complications of influenza who are working in an area of the healthcare facility that contains patients with confirmed swine-origin influenza A(H1N1) cases.
4. Travelers to Mexico who are at high-risk for complications of influenza.

For Healthcare Providers:

You may consult CDC guidelines for current recommendations for dosing and duration of chemoprophylaxis. These recommendations can be found at http://www.cdc.gov/swineflu/recommendations.htm

Pregnant women should consult their primary provider regarding use of influenza antiviral medications. The CDC has recently issued guidelines for the use of influenza antivirals in pregnancy, which can be found at http://www.cdc.gov/swineflu/clinician_pregnant.htm. The FDA has recently approved oseltamivir (Tamiflu) for treatment and prophylaxis of young children, including infants. Further information on the use of influenza antivirals in young children, including dosing guidelines, can be found at http://www.cdc.gov/swineflu/childrentreatment.htm.

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