Flu epidemic may be slowing, CDC says

Feb 29, 2008 (CIDRAP News ) This year's influenza epidemic showed signs of tapering off last week, but flu was still widespread in every state except Florida, the Centers for Disease Control and Prevention (CDC) reported today.

At the same time, the CDC issued a notice aiming to remind clinicians to consider prescribing the antiviral drugs known as neuraminidase inhibitors to treat or prevent flu.

For the week that ended Feb 23, 5.7% of visits to the CDC's network of sentinel healthcare providers were for influenza-like illnesses (ILI), a decrease from the 6.4% reported the previous week, the agency said. The percentage of visits for ILI decreased in seven of nine regions across the country, whereas it increased in six of the nine regions the week before.

Three flu-related deaths in children were reported last week, and one previously reported death was reclassified as not due to flu, the CDC reported. Twelve pediatric deaths attributed to flu were reported the previous week. The total for this season now stands at 24.

Laboratories in the CDC's surveillance network tested 7,726 specimens for influenza last week, of which 2,321 (30.0%) were positive, the report says. The previous week, 34% of 6,889 tested specimens were positive.

In an advisory sent via the CDC's Health Alert Network today, the agency stressed the value of oseltamivir (Tamiflu) and zanamivir (Relenza) for treating or preventing flu.

"Recent studies suggest a considerable protective effect against complications associated with influenza when neuraminidase inhibitors are used for treatment," the notice says. "These benefits include reducing the risk of death among older adults hospitalized with laboratory-confirmed influenza."

Treatment should begin within 48 hours after illness onset if possible, but treatment should be considered for patients who present later than that if they are very sick or have an increased risk of serious complications, the agency said.

Today's surveillance report says that 6.8% (38 of 557) of the flu viruses tested so far this season had a mutation that confers resistance to oseltamivir. All the resistant viruses were the H1N1 subtype. That's significantly higher than was observed last season, but in today's advisory the CDC said the overall resistance level is still considered low.

The agency continues to advise against using the two older flu drugs, amantadine and rimantadine, because of high levels of viral resistance.

The CDC has reported that two of the three flu types (H3N2 and B) in this year's vaccine are not closely matched to the viruses in circulation. The latest surveillance report provided further evidence of that.

In today's advisory, the CDC said, "Preliminary results from a rapid assessment of vaccine effectiveness suggest that currently available influenza vaccines provide some protection against influenza virus infection requiring medical care. However, the level of protection is likely to be lower than what is observed in seasons in which the vaccine strains are closely matched to circulating influenza virus strains."