SAN DIEGO -- A fourth student at a San Diego area charter school has contracted measles -- the county's first outbreak of the disease since 1991, health officials said Wednesday.

The infected student is home and recovering, according to the San Diego County Health and Human Services Agency.

Earlier this week, county health officials announced that three other children at the San Diego Cooperative Charter School got measles. None had been vaccinated for the disease.

Two of the students contracted measles while traveling abroad.

"We are continuing surveillance and we urge parents to vaccinate their children for measles and other vaccine-preventable diseases," said Dr. Wilma Wooten, the county's public health officer.

"Measles is one of the most infectious diseases among humans and is easily spread by coughing, sneezing or close contact with an infected person," Wooten added.

According to the HHSA, the best way to prevent measles is by getting the measles, mumps and rubella, or MMR, vaccine.

Parents should get their children the MMR vaccine at 12 months, and again between 4-6 years old.

Measles causes a high fever, cough, runny nose and watery eyes, followed by a rash. Symptoms usually last for one to two weeks. Complications from measles, which can be fatal, are most common in children younger than 5 and adults over 20.