Forty children have died of whopping cough, a respiratory infection also called pertussis, since this year, the Philippines' Department of Health (DOH) has reported.

The DOH said in a statement on Wednesday that cases have continued to increase since the start of this year, recording 568 cases from Jan. 1 to March 16.

"The total number of cases for the same period in 2023 was only 26, making this year's tally more than 20 times from last year," the DOH said.

The DOH said that 356, or 62.7 percent, of the total recorded pertussis cases, were infants under six months old.

Among those infants, 270, or 75.8 percent, were either unvaccinated or had an unknown vaccination history, while 384, or 67.6 percent of the total number of cases regardless of age, were under similar conditions, it said.

Quezon City and Pasig City in Metro Manila, as well as Iloilo City in the central Philippines have so far declared a pertussis outbreak.