Cases of influenza have continued to be reported in Washtenaw County well into this month, and officials say the illness likely will see a longer season than normal this year.

Nationally, the Centers for Disease Control and Prevention reports this flu season has particularly affected individuals older than 65, who are more at risk for contracting the illness -- a trend that has been reflected locally.

The flu is responsible for the deaths of six adults in Washtenaw County, three of which have occurred since Feb. 11.

All of the deaths occurred in individuals older than 65, and all had other underlying medical conditions, said Susan Ringler-Cerniglia, spokeswoman for Washtenaw County Public Health. There have been no deaths of children in Washtenaw County from influenza this season.

The health department started tracking flu cases at the end of September, and the season appeared to rapidly increase in December.

More than 160 people have been hospitalized during the flu season this year, about half of which were adults more than 65 years old, Ringler-Cerniglia said. About 80 percent of the people hospitalized with influenza had more than one medical condition, she said.

Reports of increasing instances of respiratory sickness are occurring at elementary schools throughout Washtenaw County.

There have been a steady number of hospitalizations due to influenza this month, "Normally by this time of the year we'd expect it to be dwindling more than it is," Ringler-Cerniglia said.

Typically, the flu season peaks in January and February in Washtenaw County.

Influenza, which Washtenaw County Health Department tracks, is a viral, contagious respiratory illness that causes symptoms including fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches and fatigue.

In some cases, more likely with children, the flu will cause vomiting and diarrhea.

Everyone is advised to get a flu vaccine to ward off the illness. The CDC estimates the flu vaccine is about 47 percent effective against Type A — which was the predominant strain this year — and about 67 percent effective against Type B.

Influenza commonly is confused with norovirus, which has symptoms people tend to refer to as the "stomach flu."

Norovirus is another contagious virus that causes gastrointestinal issues including diarrhea, vomiting, nausea and stomach pain, as well as fever, headaches and body aches.

The health department is not receiving reports of norovirus in group settings like day care centers or nursing homes, Ringler-Cerniglia said, but anecdotal evidence would suggest the illness is still actively in circulation.

Amy Biolchini covers Washtenaw County, health and environmental issues for AnnArbor.com. Reach her at (734) 623-2552, amybiolchini@annarbor.com or on Twitter.