Fraser Health is urging all Chilliwack adults in regular contact with young children to get a vaccine for whooping cough, which continues to spread throughout the Fraser Valley. Pregnant women and their partners are also encouraged to get vaccinated.

Health officials say they have detected 140 suspected or confirmed cases of whooping cough since December, but that the real number of those affected is likely much higher.

"Certainly we are seeing numbers this year we haven't seen for five or six years now," said Fraser Health spokesman Roy Thorpe-Dorward. "We know the real count is signifi-cantly higher because so many cases go unreported."

The outbreak began in Hope last year and spread to Chilliwack and Agassiz early this year. There were 80 confirmed cases in Hope between August 2010 and Jan. 11.

Since then, other cases have been identified in Langley, Surrey and Maple Ridge. The Fraser Health Authority put out an advisory on Feb. 20 that "the pertussis outbreak . . . may be spreading more broadly."

Since then, Thorpe-Dorward said, it has spread again to White Rock, Burnaby, Abbotsford and Coquitlam.

Most of the cases have been in children. Thorpe-Dorward said there have only been three confirmed cases in children under a year old and no fatalities.

Whooping cough, or pertussis, is a bacterial infection of the lining of the respiratory tract. It is extremely contagious and spread through the air or contact. It often starts like a cold then develops into the distinctive "whoop" cough which can last from six to 12 weeks.

Most children are vaccinated for the illness, but the vaccine wears off within a decade, so adults can contract it as well. It is not usually fatal, except occasionally in infants with their small, weak lungs.

"Pertussis in very young children can lead to hospitalization and even death," Fraser Health's chief medical officer of health Dr. Paul Van Buynder said in a release. "The best protection against pertussis is to get vaccinated."

On Thursday, Fraser Health announced it is expanding the breadth of those who are eligible for the free whooping cough vaccine.

A free vaccine will now be available to all adults and youth who have not had a booster in the past five years and who are in regular contact with young children.

Free immunizations for children are offered through local public health clinics.

According to Health Canada, "whooping cough is the most frequently reported, vaccine-preventable disease in Canada."

Health Canada states that in the past decade, an average of 2,400 to 10,000 cases are reported each year, mostly due to the vaccine fading. Between one and three infants die of the disease in Canada each year, usually unvaccinated children.

Anyone with symptoms should stay home until they have taken antibiotics for at least five days, to prevent spreading the illness. Without antibiotics, the health authority warns people can be infections for up to three weeks after the onset of the cough.

Preventive antibiotics are advised for women in their third trimester of pregnant and babies under a year of age and their caregivers.

According to Carol Swan at the BC Centres for Disease Control, there are no other major whooping cough outbreaks in the province at this time.

Washington state has also reported higher than normal numbers of cases this year.