CDC: Flu season's grip growing weaker

Apr 1, 2011 (CIDRAP News) – Flu activity in the United States continues to tail off, though newly reported pediatric deaths were twice as high as the week before, the US Centers for Disease Control and Prevention (CDC) said today.

The percentage of deaths from pneumonia and flu, however, remained above the epidemic level, the agency said.

The number of states reporting widespread geographic activity fell from 18 to 10 last week. Most of the states still reporting widespread activity are located in the northern tier, except for Nevada and Virginia.

For the first time since the first week of January, the percentage of doctor's visits from flu-like illness was below the national baseline of 2.5%. It dipped to 2.0% from the previous week's level when it was at baseline.

Twelve flu-related pediatric deaths were reported to the CDC, six more than the previous week, raising the season's total to 89. Of the most recent ones, four were associated with influenza B, four with the 2009 H1N1 virus, one with H3N2, and three with unsubtyped influenza A viruses.

Meanwhile, the percentage of all deaths from pneumonia and flu remained above the epidemic baseline for the ninth consecutive week, the CDC said. The level last week was 8.7%, up very slightly from 8.6% the previous week.

The percentage of respiratory samples that tested positive for influenza continued to fall, dropping from 19% to 13.9%. The CDC didn't note any big changes in circulating virus levels.

Almost 29% of the positive samples were influenza B, and 71.2% were type A. Of the type A isolates, 35.6% were H3N2, 21.7% were 2009 HN1, and 42.7% were not subtyped. The CDC has said that the predominant virus has varied by week, region, and even by states in the same region.

Routine testing by public health laboratories in six states on flu viruses for neuraminidase inhibitor resistance found two more 2009 H1N1 isolates that were resistant to oseltamivir (Tamiflu), raising the season's total to seven. No samples of any of the flu virus subtypes have tested positive for zanamivir (Relenza) resistance.

In Mexico's Chihuahua state, a recent 2009 H1N1 outbreak in the Juarez area near the Mexico-US border was linked to four deaths, which sparked a fresh round of vaccination, outreach programs, and school checks, according to a Mar 28 Agence France-Presse (AFP) story.

Earlier in the week Chihuahua state's governor Cesar Duarte told the Associated Press (AP) that a woman in the state's capital died from a 2009 H1N1 infection after returning from a trip to Texas, and that the state's illness spike was related to outbreaks across the border in Texas and New Mexico. Deaths also included two traffic police officers and a woman from Juarez.

On Mar 28 the El Paso Department of Health (EPDH) said in a statement that preliminary data for March showed a drop in flu illnesses: 126 confirmed infections in March compared with 302 in February, including those from the 2009 H1N1 virus.

The EPDH said that the virus was a secondary factor in the February death of a 76-year-old man who had underlying health conditions. It reassured the community that it was taking the investigation seriously, but said there was no reason for alarm in the region.

New Mexico's health department said in a Mar 29 statement that flu levels were declining from a peak in mid February and that a cross-border surveillance system that it manages with federal officials and colleagues in Mexico's Chihuahua state showed no increase in flu activity along the border in the past few weeks. The New Mexico Department of Health (NMDH) said it would continue monitoring flu activity along the border.

Dr Mack Sewell, New Mexico's state epidemiologist, said in the statement that Mexico, like the United States, has seen the H3N2 predominate, along with influenza B. "Following the 2009-2010 H1N1 pandemic, we are seeing H1N1 becoming another seasonal influenza strain," he said.

In other influenza developments, Trinidad's health ministry issued an advisory yesterday about recurrence of 2009 H1N1 influenza, Newsday, a newspaper based in Port of Spain, the capital of the Republic of Trinidad and Tobago, reported today. Dr Anton Cumberbach, the country's chief medical officer, said that since 2009 health officials have been prepared for waves of 2009 H1N1 infections, and he urged the public to focus their efforts on good hygiene practices to prevent infections.

See also:

Apr 1 CDC flu update

Mar 28 AFP story

Mar 28 EPDH press release

Mar 29 NMDH press release

Apr 1 Newsday story

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