May 15, 2009 (CIDRAP News) – An official from the US Centers for Disease Control and Prevention (CDC) said today that novel H1N1 influenza is expanding across the country, with 22 states reporting widespread or regional illnesses.
Dan Jernigan, MD, MPH, deputy director of the CDC's Influenza Division, said at a press briefing that the spike in flu activity is unusual for this time of year, when infections from seasonal strains have typically tapered off. The seasonal influenza strains are responsible for half of the spike, which Jernigan attributed to increased testing throughout the nation for the novel strain.
The CDC is seeing some geographic variation in illness patterns, he said, with highest activity levels in the Pacific Northwest and the Southwest.
Jernigan said the CDC is investigating more hospitalizations and deaths from the novel flu strain and was aware of illness clusters in New York City and Houston schools. Yesterday officials in New York closed three schools in the Queens neighborhood to slow community transmission of the disease. High numbers of sick students prompted the closures, and a staff member from one of the schools is hospitalized in critical condition with a novel H1N1 infection, the city's health department said.
In Houston, school district officials today closed one of the city's elementary schools until May 26 after 400 of the school's 712 students stayed home sick, the Houston Chronicle reported.
Though the number of confirmed and probable cases is growing quickly, the total number will become less meaningful, because case confirmations are evolving to mainly reflect just the severe cases that are now the target of testing, Jernigan said. The total likely underestimates the true number of novel H1N1 cases in the United States, which could be as high as 100,000, he said.
Jernigan said that although some afebrile novel H1N1 infections have been seen in Mexico, the CDC hasn't detected the lack of fever as a prominent feature of US infections.
CDC experts and their global partners are exploring the possibility of mutations in the new virus. Analyses of genetic sequences haven't identified any that would make the new strain more virulent so far, though the CDC will continue to monitor the virus, he said.
In response to a reporter's question, Jernigan said the agency is investigating whether another novel H1N1 virus may have been identified in three Mexican states.
In other developments, Martin Cetron, MD, director of the CDC's quarantine division, announced at the press conference that the CDC has downgraded its travel advice for people visiting Mexico from a warning to a precaution, focusing on people who have underlying health conditions such as pregnancy, cardiovascular conditions, and immunodeficiency diseases.
The upgraded travel advisory, recommending against nonessential travel to Mexico, had been in effect since Apr 27.
May 15 CDC travel advisory update