Some 20 students of Ihiga Secondary School in Kangema have developed a strange disease characterised by swelling of joints.
On Friday, parents were called to collect the children and take them to hospital after the complications got serious.
It is the second time this ailment has struck the school this year. In February, about 60 students developed similar symptoms and had to seek treatment.
In the last incident, some students said they suspected the disease could have been caused by congestion in hostels.
County Director of Education Victoria Mulili said a team of health experts has been sent to the school to investigate the disease.
School administration said health experts had inspected their food and water and given them a clean bill of health.