Orthodox Jewish communities in Brooklyn are seeing an outbreak of whooping cough, a disease fatal to infants that can be prevented by vaccines. View Full Caption Getty/Justin Sullivan

WILLIAMSBURG — An outbreak of whooping cough has hit the Orthodox Jewish community in Williamsburg and Borough Park — largely among children and infants without vaccines, the Health Department said.

Between October 2014 and April 2015, there have been 21 cases of pertussis, or whooping cough, a highly contagious bacterial infection that causes violent coughing and can be fatal for infants, according to an alert from the New York City Department of Health and Mental Hygiene.

Eighteen of those cases were children and three of the cases were adults. Twelve of the children were unvaccinated, and two had vaccines but not the updated pertussis vaccine, the agency said.

The other four children with confirmed whooping cough had the proper vaccines. Ten of the children were less than 1 year old.

Whooping cough can lead to pneumonia, the brain inflammation disease encephalitis and death for infants, the department said. Adults could potentially suffer rib fractures and persistent coughs.

Children and adults with whooping cough will show non-specific symptoms for some seven to 10 days before the coughing fits begin, the Health Department said.

The cough could last weeks to months if not treated.

The Health Department is recommending people stay up to date with their vaccine schedules, which can be found here. Pregnant women also need to be vaccinated with Tdap — which prevents whooping cough — during each pregnancy.

An alert sent to all of the city's doctors encouraged them to notify the city immediately of potential whooping cough cases. A delay in reporting them caused a delay in recognizing that cases had increased, the agency said.