Influenza viruses have infiltrated most parts of the United States, with 43 states experiencing “widespread” flu activity and six others reporting “regional” flu activity, according to the Centers for Disease Control and Prevention.
Hawaii was the only state where flu cases were merely “sporadic” during the week that ended Dec. 27, the CDC said in its latest FluView report.
One week earlier, California had also been in the “sporadic” category and Alaska and Oregon reported “local” flu outbreaks. Now all three states have been upgraded to “regional” flu activity, along with Arizona, Maine and Nevada. The rest of the states are dealing with “widespread” outbreaks, according to the CDC.
At least 601 people in the U.S. died of influenza or pneumonia during the 52nd week of the year, down from 837 the previous week, according to data collected by the CDC’s 122 Cities Mortality Reporting System. The 601 deaths accounted for 6.8% of the 8,893 total deaths in the last full week of the year, just missing the 6.9% threshold to qualify as an epidemic.
H3N2 flu viruses continued to dominate as 2014 came to a close, accounting for 99.6% of the 1,641 influenza A viruses that were subtyped during week 52. When H3N2 strains are more common than H1N1 strains, the flu usually causes more severe illnesses and deaths, warned Dr. Tom Frieden, director of the CDC.
About two-thirds of the 268 H3N2 viruses analyzed by the CDC since Oct. 1 are similar to the A/Switzerland/9715293 strain that was first detected in the U.S. in March, the FluView report said. By then, the CDC had already picked a different type of H3N2 to be the target of the North American flu vaccines.
Most of the other influenza viruses the CDC has analyzed since the start of the flu season were covered by this year’s vaccines, including the H3N2 strain known as A/Texas/50/2012 and the H1N1 strain called A/California/7/2009.
All of the flu viruses tested for signs of drug resistance have been vulnerable to the drugs Tamiflu (oseltamivir), Relenza (zanamivir) and Rapivab (peramivir), the CDC said. However, the health agency warned that “rare” cases of drug resistance among H1N1 and H3N2 viruses have been reported elsewhere in the world.
The overall hospitalization rate since the start of the flu season rose to 12.6 per 100,000 Americans, up from 9.7 per 100,000 Americans a week earlier. Senior citizens continued to have the highest hospitalization rate (51.8 per 100,000 people), followed by children under the age of 5 (16.5 per 100,000 people).