KIMBERLY, Idaho -- The Kimberly School District is warning parents after an outbreak of the contagious illness pertussis - commonly known as whooping cough - sickened students at multiple schools.

The superintendent announced the outbreak Tuesday in a letter posted on the district's website.

According to Logan Hudson with South Central District Health, there have been a total of three confirmed cases of pertussis in Kimberly students. The health district has recorded a total of 12 cases in the counties they serve since the beginning of the year.

School has not been canceled in the Kimberly School District.

Superintendent Luke Schroeder said in the letter that any student or staff member who shows symptoms of whooping cough will be required to go home. Employees and students will need a letter from their health provider before they are cleared to return to school.

South Central District Health, which alerted the district to the outbreak, recommended that anyone who is not current on their pertussis vaccine update their immunizations as soon as possible.

Pertussis can be very serious, and even fatal. Babies and the elderly are at particularly at risk.

In its earliest stages, the illness often causes cold-like symptoms including a runny nose and mild cough.

Later symptoms of the illness can include a high fever, headache, body aches and pains, extreme exhaustion and violent coughing that may be followed by gasping for air - often producing the "whooping" sound from which the sickness draws its name.

Babies under a year old may develop pneumonia, have seizures, or suffer brain damage from whooping cough.

According to the Center for Disease Control, whooping cough spreads easily through the air when an ill person sneezes, coughs or sneezes.

Pertussis can be treated with antibiotics.

The Kimberly School District instructed anyone with questions about the illness to contact South Central District Health.