At least 30 children at an elementary school in California's affluent Orange County have come down with a mysterious rash - and no one knows why.

An outbreak of bites and blisters at Lake Forest Elementary School has left children itching through the night, and worried parents searching for answers.

Ten staff members at the school have also come down with the rashes and five new cases in the Saddleback Valley Unified School District have since been reported.

The outbreak is reportedly appearing as rashes, bites and welts, on anywhere from faces to arms, feet, backs, chests and waistlines, according to parents.

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Thirty children at Lake Forest Elementary School in California's affluent Orange County have come down with this mysterious rash - and the cause remains unknown

Mosquitoes, fleas, spiders, mites and mice have all been ruled out as the source, said Jared Dever of the Orange County Mosquito and Vector Control.

Dever said bed bugs are also unlikely the cause, as they are noticeable and tend to strike when people are asleep or immobile, he told NBC Los Angeles.

Dozens of traps have been laid out in the last week and Dever said they are now looking for a 'wide variety of biting or stinging insects'.

But for now they still aren't any closer to finding the cause of the outbreak.

Mosquitoes, fleas, spiders, mites and mice have all been ruled out as the source

'At this time, we have not been able to collect anything that would give us a clue as to what caused these bites,' Dever told CBS Los Angeles.

The school's entire campus, including inside classrooms and outside on its two fields, was sprayed with pesticide last weekend.

But new cases have continued to appear and thus the school will be sprayed again this weekend out of 'an extreme abundance of caution', said District Superintendent Assistant Tammy Blakely.

Lake Forest Elementary closed its fields last Friday after discovering all 10 staff members affected in the outbreak were involved with the after-school program.

The program is held in a portable building next to one of the school's fields, which have since been reopened.

Staff members have continued to keep the students off the fields this week out of caution, but children are still coming home with new bites.

Darnell Grunkemeyer said her affected fifth-grade son was not exposed to the school's fields and is not involved in the after-school program.

The mother found two new bites on him Tuesday, as week after he came home with a rash on his arm.

Mosquitoes, fleas, spiders, mites and mice have all been ruled out as the source of the outbreak and officials are now looking for a 'wide variety of biting or stinging insects'

The district said it was first notified of the outbreak on September 15.

But Grunkemeyer, who at first thought the issue was bed bugs, said the school didn't notify her about the problem until September 24.

'They don't seem to be looking out for (the kids') best interests at this point,' she told the Orange County Register.

'I don't feel comfortable with my kids going there now.'

Many parents were outraged that it took the school more than a week to inform them of the outbreak.

Blakely said that district officials at first believed the problem was merely linked to individual cases of mosquito bites or bed bugs.

'This has been a learning process for all of us,' she said. 'We're trying to determine what is accurate information.'

But Lake Forest council member Adam Nick has found the school's lack of transparency to be 'unacceptable', he told KTLA.

'Students are still coming to school,' he said.

'Maybe they should have shut down the school.'