The isolated pocket of about 20 cases of whooping cough in Hope at the start of the year has travelled to nearby Chilliwack - and grown to more than 100 cases.
And there could well be significantly more cases that are going unidentified and unreported.
"The true number is probably about three times that," said Dr. Elizabeth Brodkin, medical health officer with the Fraser Health Authority.
She said that while most cases of whooping cough, or pertussis, are recognizable by an extremely persistent cough marked with a "whoop" noise when the patient tries to catch their breath, some cases don't develop that cough.
"It may not always be recognized . or not reported," she said. "It starts out exactly like a cold - aches, pains, cough. But the cough goes on and on and on and on in most patients."
Coughing can become so bad that it can lead to vomiting.
On top of the cases around Chilliwack, there have also been a handful of cases that have popped up in Abbotsford, Maple Ridge, Surrey and Burnaby, but it's not clear that those are part of the Fraser Valley outbreak.
"There are a few cases each year, so those may be part of the normal (annual) cases that we'd see anyway," she told The Record.
Brodkin says the outbreak is most likely due to reduced immunity in the population at large. Vaccination protection tapers off after about five years and most adults get a natural "booster" from being exposed to the disease but there hasn't been an outbreak in about 10 years.
Adult immunity is important to protect children - though it can be uncomfortable, and take a long time to recover from, pertussis is not typically fatal for adults. However, it can be particularly dangerous for infants and young children.
Brodkin says that about half of young infants who contract it will end up hospitalized; of all infant cases, between one to two per cent will be fatal.
"It can really be bad for infants; there is one infant (in Fraser Health Authority) that has been in ICU since before Christmas," said Brodkin.
In the Hope and Chilliwack area, the health authority has rolled a program to offer vaccination to adults to help protect infants who slowly devel op an increasing immunity to pertussis through a series of vaccinations over the first few months of life.
Though parents outside that area, like those here in New Westminster, are not able to access free vaccination like parents in Chilliwack and Hope, Brodkin said it may be a good idea for adults generally to look into getting a booster.
"If I was a parent of a young child, I'd be thinking about it," she said, noting that many family doctors and pharmacists are able to offer the vaccination by purchase.
In fact, the question of whether or not adults in B.C. should be routinely offered a booster for pertussis is being discussed right now by medical authorities, she says.
"There's a working group looking at that issue right now," she said.
Currently, pertussis immunizations are given to infants, to children in kindergarten and again for youth in Grade 9.
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