As of this writing, Colorado was one of a handful of states experiencing local or regional influenza activity. While January and February are typically peak months for the flu, outbreaks can occur in late winter or early spring.
While not overly severe at this stage, the current flu season brings with it some troubling news. Preliminary data from the Centers for Disease Control and Prevention indicate circulating strains of influenza A are resistant to a common antiviral medication known as oseltamivir, or Tamiflu.
Typically, this pill medication is prescribed when influenza illness is diagnosed early. The medication can reduce the severity and duration of the illness and can be particularly useful in those people at highest risk, such as children, the elderly or the infirm. Occasionally, the medication can be used in high-risk people who are exposed to influenza to prevent illness.
The problem of Tamiflu resistance this year, seen in 98 percent of tested strains, comes after recent flu seasons in which the virus has been resistant to other common antiviral medications known as amantadine and rimantidine. In recent years, the CDC issued guidance to health care providers to suspend use of these medications in certain situations because of their ineffectiveness in light of this new resistance.
So why are flu strains becoming resistant to our antiviral treatments?
The reason is twofold. One aspect of the resistance relates to the use of the medications, which selectively weaken viral strains sensitive to their effects. The other is the problem of mutation among viruses. As viruses rapidly divide and move from one infected individual to another, their genetic material constantly changes, or mutates. The result is an altered virus.
Sometimes these alterations weaken the virus. Sometimes they make the virus stronger.
Examples of viral mutations that strengthen the flu virus are changes in its outer coat. This is where vital proteins are present that help the virus attach to the body's cells. These proteins also are where the immune system learns to recognize the virus. So when the virus mutates, the body may become susceptible again.
The lessons learned from these recent flu seasons in which antiviral resistance has become so commonplace among flu viral strains puts into perspective the potential use of these drugs in the future - not only for seasonal flu but also for future flu pandemics.
Meanwhile, while antiviral resistance may reduce the medication armamentarium for this flu season, flu vaccination still is recommended for all those who are not immunized. The good news this year is the vaccine formula seems to be right on target in protecting against the common flu strains causing illness.
Dr. Matthew A. Clark is a
board-certified physician in internal medicine and pediatrics practicing at the Southern Ute Health Center in Ignacio.