CDC: H1N1 Flu Numbers Represent a "Very Great Underestimate"

May 9, 2009 — The confirmed numbers of influenza A (H1N1) cases reported are likely to fall far short of the actual numbers occurring within the community, according to a US Centers for Disease Control and Prevention (CDC) spokesperson.

"The individual numbers are likely a very great underestimate of how much virus is circulating or how many people are becoming ill from it," said Anne Schuchat, MD, the Director of the CDC's National Center for Immunization and Respiratory Diseases, speaking at a media briefing today.

The latest numbers from the CDC include 2254 confirmed cases and 722 probable cases in 45 states and the District of Columbia, representing an increase of 494 cases since yesterday, according to Dr. Schuchat. To date, 2 deaths and 104 hospitalizations have been reported in the United States. However, she added that "we are still seeing quite a few of the hospitalized cases having underlying disease."

According to Dr. Schuchat, transmission in the United States is ongoing, and "this is a very easily transmissible virus, similar to the seasonal influenza viruses."

This week, the CDC's online map of influenza-like activity in the United States was updated. The map is an aggregate of all influenza-like activity, both the seasonal and new H1N1 influenza viruses, and "the trends from this particular illness are showing up," Dr. Schuchat said.

"The virus is continuing to spread.... Fortunately, the severity of illness that we are seeing at this point doesn't look as terrible as a category 5 pandemic...but influenza virus is unpredictable," she said. "It can change over time."

Currently the CDC is preparing the vaccine candidate strain to hand off to researchers in industry, and a vaccine should be available in the fall.

"We have heard in the media and from partners that the 'all clear whistle' has gone off or we're 'out of the woods,' but I do want you to know that here at CDC and in the public health community, active efforts are still ongoing," she said.

Dr. Schuchat told Medscape Infectious Diseases during the briefing that the antivirals oseltamivir and zanamivir should be used only for the most severe cases and for those with underlying health conditions. "Other people can probably get away with self-care at home," she added. In addition, the antivirals should be used for "treatment not prevention," she said.

"We have seen changes in resistance very quickly for seasonal flu viruses, and this is one of our big concerns," she said. "We really want to make sure that we are tracking resistance because things could change rapidly."