Contra Costa County investigators are trying to determine whether the deaths of two brothers in Moraga last month were caused by the flu.

The bodies of Gary Armstrong, 67, and Richard Armstrong, 65, were found Jan. 15 at a Moraga ranch by a friend, who had gone to check up on them.

A coroner’s official said the cause of their deaths is pending, but police called to the scene after their bodies were discovered were told the men had the flu and had not been feeling well for days, said Moraga Police Chief Jon King.

The brothers, King said, lived alone in a camper on a large ranch property that houses the Ranch House cafe on School Street and a number of barns and outbuildings.

“No one is saying they died of the flu,” King said Friday. “Whether that’s the cause of death or not, I don’t know.”

This year’s flu season has been particularly deadly. So far, there have been 30 confirmed flu deaths in California, although health officials only track flu fatalities for people under 65 years old. That’s due in part to the high volume of flu cases among older people and the difficulty in pinpointing the flu as a specific cause of death amid the multiple health complications that can accompany people with advanced age.

Contra Costa County has recorded seven flu deaths this season, said Victoria Balladares, a health services spokeswoman.

While flu-related deaths in California are above normal for this time of year, it’s too soon to say how the season compares to years past until it ends around April or May. Still, state officials have said current figures put this year’s season on track to be the worst in a decade.

“We’ve seen it peak a lot earlier. We’re seeing a lot more cases,” Balladares said. “But we really won’t know what kind of flu season we’ve had until we’ve ran through the season.”

Jenna Lyons is a San Francisco Chronicle staff writer. Email: jlyons@sfchronicle.com Twitter: @JennaJourno