SAN DIEGO -- A 9-year-old student in Imperial Beach and a 10-year-old in La Mesa have been diagnosed with whooping cough, the San Diego County Health and Human Services Agency announced Thursday.

The infected children attend Oneonta Elementary and Murray Manor Elementary, according to the HHSA.

County health officials said letters have been sent to parents whose children may have come into contact with the ill student.

"We are seeing whooping cough cases across the county," said Dr. Wilma Wooten, the county's public health officer. "This is a highly contagious disease and parents should consult their primary care physician about testing for whooping cough if they notice symptoms such as severe coughing spells."

Whooping cough, also called pertussis, usually starts with flu-like symptoms, such as a runny nose, sneezing, fever and mild cough. The symptoms may be mild and brief, or last up to two weeks, but are often followed by severe coughing fits that may be associated with vomiting.

There were 51 cases of whopping cough reported in the county last year. So far this year, there have been 50 cases.