Brenna Swift, The Union Democrat

Tuolumne and Calaveras county health experts are urging the public to get flu vaccination as soon as possible, given a nationwide spike in influenza cases.

"The tricky thing about this virus is how quickly it can become a Godzilla," said Tuolumne County Public Health Officer Dr. Todd Stolp. "It's for that reason we try to maintain control over it. At this point in time, the best tool for doing that is the vaccine."

According to the most recent "FluView" report from the U.S. Centers for Disease Control and Prevention, most of the country is suffering from high levels of influenza infection. California was one of the 10 states reporting "low to minimal" influenza levels as of Friday.

That pattern is holding true locally, with public health departments in Tuolumne and Calaveras counties noting no sharp increases in "influenza-like illness."

However, the higher national rates are still cause for worry, said Calaveras County Health Officer Dr. Dean Kelaita - especially since flu season tends to rise in January and run through April.

"Health officials are watching this and are concerned that influenza activity could increase locally as well," Kelaita said.

Influenza is a contagious respiratory illness caused by influenza viruses, with Influenza A and Influenza B as the two main types. Influenza A is further divided into two subtypes, H3N2 and the new version of H1N1 known as the "swine flu."

Influenza symptoms include cough, sore throat, stuffy nose, headaches, muscle or body aches, and fever, although not everyone infected will get a fever.

Young children, people 65 and older, and those with chronic health conditions are more prone to flu complications such as pneumonia and bronchitis. While most affected by the flu will recover in a few days to two weeks, it can be fatal in some cases.

The severity of influenza illnesses can vary greatly from season to season. Stolp compared the viruses' constant mutations to changes of "clothing."

"The influenza virus is very fickle in that it changes its clothing regularly," he said. "If our immune systems don't recognize the virus because it's changed its clothing, that's when you can have a pandemic."

The influenza pandemic of 1918 killed an estimated 20 million to 50 million people worldwide. Stolp said its present-day equivalent would kill 175 million to 300 million people worldwide, a figure approaching the entire population of the United States. For that reason, it's more than what he called an annual "nuisance villain."

To fight the risk, the CDC recommends annual flu vaccinations for everyone 6 months of age and older. On a local level, the Tuolumne County Public Health Department is launching a campaign to boost flu vaccination rates among healthcare workers.

Two vaccine types are available - one as a shot and another as a nasal spray. The nasal spray, available for most patients aged 2 to 49, has recently proven more effective for children than injected vaccines.

It uses a live version of the influenza virus that can only live in the nose, where it creates an immune response.

Injections use a deactivated virus and don't cause the flu, Stolp said. But they stimulate the immune system and can trigger a slight fever, aches and pains.

Availability of flu vaccines at private doctors' offices varies according to how much the doctor has ordered for the season, Kelaita said. Both the Calaveras County and Tuolumne County public health departments still have vaccines on hand.

Stolp recommends seeing a doctor if flu symptoms become severe, especially in cases where fevers don't subside. A severe or worsening cough, as well as shortness of breath, should also prompt a visit to the doctor.

Other illnesses will occasionally mimic flu symptoms but can be identified with tests. In Tuolumne County, instances of infection with coxsackievirus and norovirus have recently risen, Stolp said.

Coxsackievirus can cause flu-like symptoms, as well as viral meningitis and a range of other symptoms. Norovirus causes vomiting and diarrhea but typically lasts a short time.