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Wednesday, February 28th 2007

Prevalence of HPV

Two studies in this weeks JAMA are getting major media attention. One of them on how antioxidant supplements actually increase your likelihood of death is interesting but the real gem is a look at the prevalence of human papillomavirus in women. And what do you know the article is free on JAMA’s website.

The Real Question: How Long Until The FDA Regulates It?

Off topic: How many other medical students out there who are AMA members actually read their copies of JAMA (which collect on my coffee table). I’m actually using it as bathroom reading recently, which I think is actually a good thing. Probably TMI.

Anyway, what is the prevalence of the HPV infection in women?

The overall HPV prevalence was 26.8% (95% confidence interval [CI], 23.3%-30.9%) among US females aged 14 to 59 years (n = 1921). HPV prevalence was 24.5% (95% CI, 19.6%-30.5%) among females aged 14 to 19 years

So let’s put the statistics above in perspective.

1) Nearly one-fourth of teenage girls 14 and over have HPV. However, the vast majority of these carriers aren’t carrying type 16 or 18.

2) Still, that is a pretty amazing statistic because this was a point in time study. Most HPV infections are cleared, meaning at the single moment of collection of the sample for this study a quarter of teenage girls have a current HPV infection. This just reiterates the claim that the vast majority of women will get an HPV infection (even if asymptomatic) very soon after becoming sexually active.

The incidence of high risk types 16 and 18 is much less,

The overall prevalences of high-risk HPV types 16 and 18 were 1.5% (95% CI, 0.9%-2.6%) and 0.8% (95% CI, 0.4%-1.5%), respectively.

That may not look large but consider how it plays out when applied to the general public.The Merck vaccine protects against types 6 and 11 (the most common cause of genital warts) and 16 and 18 (found in the majority of cervical cancers).

Including those who were infected with types 6 and 11, by the study’s estimate more than 3 million women are infected with HPV type 6, 11, 16, or 18. More than 7 million women are infected with some HPV type at any one time. Obviously the vaccine could dramatically reduce the incidence of this.

As further circumstantial evidence of the sexual risks taken by teenagers – which is the argument for this vaccine – consider that other types which, while having less of a relationship to cervical cancer than types 16 and 18, were still classified as “high risk” by the researchers. Of all the “high risk” types of HPV (remember: the vaccine is not protective for all of these types), including types 16 and 18, the prevalence was more than 15% in girls aged 14 to 19.

Something to chew on at least.