SAN JOSE — If you’re going to get a lesson in hand-washing, say San Jose Unified School District officials, it might as well be fun — and even glow in the dark.

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Stomach-flu outbreak hits students in Santa Clara County That’s how several classrooms at Anne Darling Elementary School learned about the importance of hand-hygiene on Wednesday, following a recent outbreak of viral gastroenteritis within the school district that has jumped from 202 students on Tuesday to a total of 242 on Wednesday — including at least 27 cases at Anne Darling.

Viral gastroenteritis attacks a person’s intestines and often causes nausea, vomiting or diarrhea. Last month, the same illness also hit 106 students at Rosemary Elementary School in Campbell and 23 students at Jackson Academy of Music and Math in Morgan Hill.

But Santa Clara County public health officials say the illness — its onset, duration and quick recovery — all point to norovirus, though the county has not yet confirmed that in a laboratory test.

By now, however, many of the San Jose children who were sick have returned to school — after waiting the prescribed 48 hours following their recovery — said Melinda Landau, a manager with the San Jose Unified School District.

Anne Darling officials weren’t taking any chances. So on Wednesday, starting with Kiera Strockis’ second-grade class, school district nurse Coryne Wong applied a lotion mixed with Glo Germ powder on the hands of all 28 kids, who were then instructed to rub their hands together.

The visual tool for teaching proper hand-washing — to both kids and adults — was invented by then-Costa Mesa resident Dean Luxton in 1968, according to the company’s website. The product contains proven safe ingredients formulated to be the same size as bacteria, or 5 microns in size, the website says.

With the use of ultra-violet light, Glo Germ simulates the spread of germs, teaching kids how quickly germs can spread in a short period of time.

Under black lights, school district nurses Wong and Kera Cowley inspected every pair of hands where suddenly tiny dots, or “glowing germs” appeared on the students’ palms and the backs of their hands.

The youngsters next had to line up at the classroom sink and take turns washing their hands — spending the same amount of time washing as singing the “Happy Birthday” song.

Then came the real test: the nurses inspected the hands of the children again with the same black light to see if all of the dots had disappeared. If they hadn’t, it was back to the sink for another hand washing.

Eight-year-old Brian Tapia made it through with only one trip to the sink.

“It was fun because I got to wash my hands and learn about germs so we don’t get sick,” said Brian, still clasping his hands where he had counted eight germs after the first black light test.

Brian was proud to say he already washes his hands “seven times a day,” starting just before breakfast, to right after he’s played with his dog, and then throughout the day at school where Strockis makes sure the kids are cleaning their hands often.

His classmate Khang Fung called Wednesday’s exercise “perfect” because he got to see nine germs on his hands “like under a microscope,” which he also successfully washed off the first time. “It feels good and very nice,” added Khang.

Strockis said two students in the class had come down with the illness — one was still at home recovering, while another had returned, but only after waiting the prescribed 48 hours.

“At the beginning of school, we talk a lot about hand-washing,” Strockis said. “We wipe down our desks every day — I’m pretty adamant about it. And I also make sure they use hand sanitizer just before going to the computer lab or the cafeteria.”

Public health officials say hand sanitizers are not as effective as soap and water, which Strockis acknowledged.

“It’s hard to have 28 kids wash their hands — it takes a lot of time,” she said. “It’s easier to use hand sanitizer. And I’d rather that they had something rather than nothing.”

The Glo Germ hand-washing lessons will be repeated in several more classrooms on Thursday, said Anne Darling Elementary school principal Ronald Hammond.