Nightly News | July 19, 2012
>>> good evening. as we said at the very top of the broadcast, there is troubling health and medical news tonight. for most people this comes out of nowhere. it's about whooping cough making a big comeback in this country. this is ontrack to be the worst year in five decades. there have been 18,000 reported cases just this year. that's more than double last year's number. it's highly contagious. it has already caused nine deaths. doctors seem to know what's behind this sudden rise. it's where we begin our coverage tonight with our chief science correspondent robert bazell .
>> reporter: the cdc says the u.s. is ontrack to have the greatest number of whooping cough cases in some 50 years. 12-week-old marco is part of the epidemic. he spent much of his life in intense i ever care.
>> we even had him baptized because we just didn't think he was going to make it.
>> reporter: whooping cough , a bacterial infection known as pertussis usually causes this characteristic wheeze recorded in a home video posted on youtube.
>> it can be very serious in children under a year especially under six months of age. they can develop pneumonia, seizures.
>> reporter: there were several outbreaks but the biggest is in washington state where through july 14th there were more than 3,000 cases, a 1300 % increase over the same period last year. so far nationwide there have been nine deaths. marco was still too young to have his first shot which protects against pertussis but was almost certainly infected by an older child or adult. that is a tragically common story. protection from the vaccine that's been used since 1997 often wanes over time so children and adults can get infected even if they got their baby shots. usually they don't get too sick but can put infants at risk. scientists want a better vaccine but meanwhile the key to containing outbreaks is to get booster shots for both children and adults. in washington state and other outbreak sites people have been lining up to get their boosters. i'm jeff gordon warning parents about pertussis.
>> reporter: while the march of dimes and other organizations are putting out the message.
>> ask your health care provider about the pertussis vaccine.
>> reporter: there is evidence the boosters are bringing the outbreaks under control, but experts say new cases will continue to pop up until all infants, children, and adults are properly immunized. robert bazell , nbc news, new york.