Washington pertussis outbreak is very, very bad

By PHIL PLAIT - BAD ASTRONOMY
Added: Thu, 02 Aug 2012 16:32:17 UTC

This is one of the scariest graphs I’ve seen in a long time.

This plot, from the CDC, shows probable and confirmed cases of pertussis – whooping cough – in the state of Washington from 2011 through June 2012. Last year’s numbers are the short, light-blue-grey rectangles, and this year’s are the dark blue. The plot is by week, so you can see the 2011 numbers slowly growing across the year; then this year’s numbers suddenly taking a huge leap upward. They are reporting the new rate as 13 times larger than last year. Note that 83% of these cases have been confirmed as being pertussis, while 17% are probable. The drop in recent weeks is due to a lag in complete reporting of cases.

Got that? There are 13 times as many people – more than 2500 in total so far – getting pertussis right now as there were last year at this time in Washington.

Some of this increase may be attributable to the pertussis bacterium growing a resistance to the vaccine and booster. However, it’s curious that Washington state has seen such a large jump; the incidence of pertussis overall in that state is nine times higher than the national average.

Why would this be? Well, it so happens that the antivax movement is quite strong in Washington state, and it also so happens that parents are choosing not to vaccinate their children in higher numbers there than the rest of the nation.