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H3N2 Influenza Leads to More Severe Flu Cases Around the United States

JAN 11, 2017 | EINAV KEET
Influenza activity is now categorized as widespread in at least 12 states as the flu season continues to hit the United States, with some regions already experiencing epidemic-level outbreaks resulting in severe illness, a number of hospitalizations, and even deaths.

In its annual surveillance of flu season activity, the Centers for Disease Control and Prevention (CDC) categorizes the level of flu activity in each state as either sporadic, local, regional, or widespread. In a new influenza surveillance map detailing surveillance data for the 2016 -2017 flu season, the CDC has reported widespread virus activity in California, Connecticut, Idaho, Massachusetts, New Hampshire, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Virginia, and Washington. So far this season, public health laboratories around the country have collected 3,793 influenza positive specimens, of which 3,193 are influenza A (H3N2). Despite the slow start to this season, the predomination of this strain of the virus has led to more severe illnesses.

Officials from California’s Department of Public Health (CDPH) have reported that widespread flu activity in the state has led to at least three influenza-related deaths and 29 severe cases of infection that resulted in patients under 65 years of age being hospitalized. Laboratories in the state have collected at least 1,488 specimens that tested positive for the flu, and CDPH officials noted that the specimens closely match the components of the 2016-2017 flu vaccine. The San Francisco Health Department is reminding local residents who have not yet received the influenza vaccination, that it’s not too late to receive a flu shot; this warning comes on the heels of a widespread flu outbreak that led to three deaths in the Bay Area.

In Washington state, health department officials have reported 24 lab-confirmed influenza deaths so far this flu season, as the Pacific Northwest continues to be hit hard by the epidemic. The CDC’s weekly FluView report noted that Region 10—which includes Washington, Oregon, and Alaska—has the country’s highest rate of respiratory specimens having tested positive for the flu, with 27.4% of all specimens now flu-positive versus a low of 5.5% of specimens in Region 5. Influenza A (H3N2) and influenza A viruses that have not been subtyped have been most prevalent in the state, according to laboratory results from World Health Organization/National Respiratory and Enteric Virus Surveillance System (WHO/NREVSS). Washington’s Snohomish and Walla Walla counties as well as the Puget Sound region are just some of the areas that have reported a spike in flu-related hospitalizations and deaths.

On the East Coast, New York State’s Department of Health surveillance reported 2,784 laboratory-confirmed influenza reports and 845 patients hospitalized with the flu for the week ending December 31, 2016. Across the state, flu-related hospitalizations grew by 186% over the previous week, but there have been no cases of pediatric influenza-associated deaths.

With flu activity now at its peak, state officials are urging residents to receive the seasonal flu vaccine in order to prevent further spread of the virus, as the flu season can last as late as May.
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Influenza A (H3N2) has caused most of the illnesses in this severe flu season, but influenza B is becoming increasingly responsible for more infections as the flu season continues to hit the United States.