The mumps outbreak first reported in early February at Cedar Hill High School, when three cases were reported, has grown to 23 infected students and staff, according to Dallas County health officials Wednesday.


Health officials note that an additional nine cases are under investigation.

All of the students diagnosed with mumps infections have had documentation of two prior doses of mumps-containing vaccine.

Dallas County Health and Human Services is recommending that all students and staff at the school receive an additional third booster dose of MMR (measles, mumps, and rubella) vaccine.

North Texas has been continuing to experience an increase in mumps cases over the past few months, including unrelated outbreaks in other counties in the region and an ongoing outbreak in Johnson County.

Mumps is transmitted through respiratory droplets or saliva, and can be spread within 3 to 6 feet when an infected person coughs or sneezes

Symptoms typically start 12 to 25 days after exposure, and include fever followed by unilateral or bilateral parotitis lasting for more than 2 days. Up to 20% of mumps infections are asymptomatic.

Persons are considered infectious from 2 days before symptom onset to 5 days after parotid swelling begins.

Severe complications of mumps are rare but can include orchitis, oophoritis, deafness, and meningoencephalitis. All cases in this current outbreak have presented with parotitis or orchitis.

Mumps can occur even in vaccinated persons, since the effectiveness of the mumps vaccine is approximately 88% after two doses. During outbreaks, a third booster dose of MMR in the highest risk populations may further protect individuals in the event of future exposure to mumps, and limit the size and duration of mumps outbreaks.