Brenna Swift, The Union Democrat

The flu and other illnesses have made for a rough winter at Mother Lode schools.

Avery Middle School staff said 56 students - about one-fourth of the student body - were absent Thursday morning. Public health officials cautioned that only some absences are due to influenza, but they've been expecting a severe flu season.

"This could be the upswing that we've been anticipating," said Calaveras County Public Health Officer Dr. Dean Kelaita.

Nationwide, the flu took an unusually heavy toll this winter. New York State and the city of Boston both declared public health emergencies earlier this month.

The U.S. Centers for Disease Control and Prevention announced a flu epidemic Jan. 11, and its most recent "FluView" report shows widespread flu activity in California.

Influenza is a contagious respiratory illness caused by Influenza A or Influenza B viruses. A third type, Influenza C, is not thought to cause epidemics. Influenza A currently has two subtypes found in people, H3N2 and the new version of H1N1 known as the "swine flu."

Tuolumne County Public Health Officer Dr. Todd Stolp said H3N2 has been the predominant strain this year, both nationally and locally.

The good news is that this year's flu vaccines are a good match for the H3N2 strain driving the epidemic, he said.

The Calaveras County Public Health Department sent out a letter to parents Jan. 30, advising them that influenza cases are on the rise and that children can still get vaccinated.

But this flu season has also taken a heavy toll on people 65 and older, according to the CDC. They are prone to flu complications such as pneumonia and bronchitis.

Kelaita said Mark Twain Medical Center in San Andreas has been at or near capacity for the last two weeks, with more elderly people being admitted for respiratory infections.

Sonora Regional Medical Center has seen its share of flu cases, too, said spokeswoman Gail Witzlsteiner. The emergency room went through about 70 flu testing kits in three days, and it distributes face masks to patients who show symptoms of respiratory infections or colds.

Emergency room staff stressed that patients should manage their symptoms at home and avoid going to the hospital unless their symptoms are severe, since staying home helps prevent the spread of flu.

It's important to keep sick children out of school, said Joyce McMahon, a school nurse who works for the Tuolumne County Office of Education. But many parents have difficulty finding childcare and end up sending children to school before they're better.

The flu has shown up at local schools in clusters and had an impact on school attendance. Avery Middle School even postponed an upcoming ski trip because so many students have been sick.

Last week, Curtis Creek Elementary School had an average student absence rate of 15 percent, far above the 4 to 5 percent absence rate that other local schools reported.

On Jan.18, 19 percent of Sonora Elementary students were absent. The school's absenteeism rate has since decreased.

"We are still in the thick of our influenza outbreak," Stolp cautioned. "It has hit harder this year than usual, although across the state, the increase seems to be tapering off.

"We're hopeful that the same will be true for Tuolumne County," he said.

As if influenza wasn't enough, Tuolumne County has also experienced an increase in norovirus cases. Noroviruses cause stomach illness that typically lasts about 24 hours. The primary symptoms are diarrhea, vomiting and nausea.

The illness spreads very quickly in residential facilities such as nursing homes. Earlier this month, Summerville Elementary dealt with an outbreak.

Stolp said regular handwashing, particularly after using the bathroom, is the best way to prevent transmission.

Vigilant handwashing also helps prevent flu transmission, but public health officials say the No. 1 prevention measure is the vaccine. No vaccines protect against noroviruses.

The flu vaccine is still available at the Tuolumne and Calaveras County public health departments. The Tuolumne County Public Health Department hosts a free flu vaccine clinic at its Sonora office starting at 1 p.m. Tuesdays.

The Calaveras County Public Health Department hosts immunization clinics at its San Andreas office every Monday from 3 to 5:30 p.m. and Thursday from 8 a.m. to 12 p.m. It also offers shots every third Tuesday of the month at Valley Springs United Methodist Church from 3 to 5:30 p.m.

The fee for immunizations at Calaveras County Public Health Department clinics is $16, but no one eligible for a vaccine is denied because of inability to pay.