In a letter to parents, the school principal says the incident was reported on Tuesday.
The child first started showing symptoms on Friday. He is now recovering at Children's Hospital of Philadelphia.
Some parents are concerned that a third grade boy at the school was diagnosed with a bacterial infection in his blood. It's the same bacteria that causes meningitis and both infections are potentially deadly and contagious.
"Now I'll be on the lookout for fevers, 24 hour symptoms and stuff," said Armani Gianni.
Officials with the Perkiomen Valley School District and Montgomery County Health Department are working with the school to identify and notify anyone who may be at risk.
"By the end of the day, we will feel confident that all of the close contacts will have been identified and all of the contacts that have previously been identified will be able to get the preventative medicine that they need to protect themselves," said Julie Paoline.
The bacteria is spread through direct contact with saliva, or nose or throat secretions such as by kissing, sharing drinks or sharing eating utensils.
"So there is no alarm for a child who just goes to school with this child," said Paoline.
Still as an extra precaution the school is disinfecting desks, chairs and doorknobs.
The infected child is too young for the vaccine. Health officials recommend that starting at age 11.