Mumps cases in the developed world had been on the decline since the introduction of a vaccine in the early 1980s. But numbers appear to be once more on the rise for a couple of reasons, including waning immunity in a group of people who received only one mumps shot when they were children. Now young adults, they are the very age group involved in this outbreak.
Clusters of cases like this one raise inevitable raise questions about whether scarce public health dollars ought to be spent to give a second shot of vaccine to adolescents and young adults, to boost their immunity against a virus that can cause rare but unpleasant side effects, including infertility in males, deafness and viral meningitis.
"The question around the country that we need to ask is what do we now think about that one dose? Is it sufficient, like we thought it was? Or isn't it?" asked Dr. Gaynor Watson-Creed, medical officer for Capital Health, the public health authority serving Halifax.
The Halifax outbreak appears to have begun in mid-February, with the disease probably arriving from a neighbouring province, Watson-Creed said.
Where the earlier outbreaks, in 2005, were centred around the city's universities, this time the disease appears to have been spread in the city's very active bar scene.
Cases are university aged - the average age is 22 - but are not necessarily enrolled.
"They're not necessarily passing their disease through on-campus activities," she said. "It's about all of the things that that age group does off-campus."
The virus is spread in infected droplets.
"It really requires face-to-face contact, close enough that you could get droplets from somebody's nose or airway. Having said that, again, when you look at the population we're dealing with - which is largely a university population, in bars where they have to yell - it's not that hard to do."
