COSTA MESA ( — The flu is back and getting worse by the week.

“I’m achy. I can’t even sleep. The pain is that bad,” said Phillip Martin, a flu patient.

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Martin and his mother Renee walked out of an urgent care center in Costa Mesa and drove straight for Rite Aid to pick up Tamiflu, an antiviral treatment for the flu.

They weren’t the only ones.

In fact, a pharmacist there says there is now a nationwide shortage of it.

“In the last couple weeks, huge upswing,” said Dr. Tom Le. “We’ve seen at least 15 cases already.”

That’s confirmed cases of the flu.

Le, who runs the Coastline Urgent Care in Santa Ana, says there are a lot more patients who opt not to get the diagnostic test for the flu, but who are suffering from the same symptoms.

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“They get pretty severe symptoms,” he said. “A lot of body aches. A lot of them are having GI upset, fevers, chills.”

Le says so far the only patients he has seen did not get their flu shots.

In a statement provided to CBSLA, Genentech spokeswoman Tara Iannuccillo denied there was any shortage of Tamiflu.

“We produced enough supply of all Tamiflu formulations to be prepared for a severe flu season and are working with distributors and national retail pharmacies to optimize access to Tamiflu across the country,” said Iannuccillo.

And even though the Centers for Disease Control and Prevention says it’s not too late for a flu shot, Le says it takes two weeks to work.

Those who haven’t gotten the flu shot are urged to wash their hands regularly and steer clear of those who are symptomatic.

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“Once one person gets the flu, you can pretty much bet the rest of the people in the workforce is gonna get it so that’s a lot of lost time in productivity,” he said.