At least 30 students have been admitted at PCEA Chogoria and Magutuni sub-county hospitals with cholera-like symptoms.
About 300 others were treated in Maara Sub County, Tharaka-Nithi County, and discharged.
Out of 11 girls from Iruma Girls' Secondary School admitted at PCEA Chogoria Mission Hospital, two tested positive for cholera.
"Two girls have tested positive while stool samples from the rest, who were also experiencing severe diarrhoea, have been taken for further screening," said Dr Hildah Nabiswa.
Twenty pupils from Kieni Mixed Secondary, Kiurani Boys and Jediel Kiraithe Boarding Primary School have been admitted at Magutuni Sub County Hospital.
Dr Nabiswa, who said in the last one month, the hospital had treated three other cases of cholera, urged the public to remain cautious.
County Director of Education Bridget Wambua told the media that the students had been complaining of severe abdominal pains.
Ms Wambua said 100 boys from Kiurani Secondary School were on Tuesday treated and discharged at Magutuni Hospital, while 76 others were on Wednesday morning rushed to the hospital for treatment.
She added that 50 girls from Kieni Mixed and 51 from Iruma Girls were treated and discharged while others were still receiving treatment.
"New cases are still being reported in the four schools and my officers and those of county public health department are following up the matter," said Ms Wambua.
She said they suspected that either the students had cases of food poisoning or they had drunk contaminated water.
County Health Executive Dr Gichuiya Nthuraku said the number of affected students had been growing since Tuesday evening.
"We are investigating reports of snacks being sold to students in some of the affected schools," said Dr Nthuraku.
He added that public health officers had been dispatched to the affected areas in effort to trace the cause of the disease.