March 31, 2003
NHANES III oversampled children under age 5, persons age 60 and above, Mexican Americans, and blacks. Prevalence estimates were weighted to represent total U.S. population and accounted for oversampling and nonresponse to household interview and physical examination.
Of the 9,629 subjects selected to participate in the survey in the 12-59 age group, 7,476 (77.6 percent) agreed to examination; from them, 7,218 serum samples were available for testing. HPV-16-specific IgG antibody was detected by use of an HPV-16 virus-like particle ELISA.
Overall, 13 percent of study participants had antibodies to HPV-16. Seroprevalence was significantly higher in women (17.9 percent) than in men (7.9 percent), yielding a female:male prevalence ratio of 2.3. Seroprevalence was 12.5 percent among whites, 19.1 percent among blacks, and 8.9 percent among Mexican Americans. With increasing age, HPV-16 seroprevalence increased in women to 24.7 percent at ages 20-29 years and then declined to 11 percent after age 49 years. In men, seroprevalence peaked later, at ages 30-39 years (11.5 percent) and was sustained throughout older age groups.
In men, HPV-16 seropositivity was significantly associated with several variables, including age, race/ethnicity, marital status, poverty index, urban residence, age at first intercourse, years of sexual activity, number of lifetime sex partners, number of sex partners during the last year, and having sex with a man. In the logistic model, variables that remained statistically significant were age, urban residence, race/ethnicity, age at first intercourse, years of sexual activity, and having sex with men. No other variables appeared to be confounders. Although age was no longer statistically significant, it appeared to be confounded with years of sexual activity.
The most likely explanation for higher HPV-16 seropositivity in women is that women and men have fundamental differences in immune response after exposure. In men, HPV infections may be more transient, and infection often involves keratinized epithelium that may be less likely than mucosal epithelium to induce humoral immune response. Anorectal mucosal exposure may be more likely to produce a detectable immune response and could contribute to the high seropositivity in MSM. The strong association between HPV-16 seropositivity and number of lifetime sex partners and no association with number of recent partners suggest seropositivity is a measure of lifetime rather than recent exposure.
"Our national data on seroepidemiology of naturally occurring HPV-16 infection," researchers concluded, "is useful to establish baseline HPV-16 seroprevalence in demographic groups, to highlight differences in humoral immune responses between men and women, and to document a high burden of infection with this single HPV type. Moreover, a system for monitoring seroprevalence over time will be valuable to assess effectiveness of vaccine programs."
Journal of Infectious Diseases
11.15.02; Vol. 186; No. 10: P. 1396-1402; Katherine M. Stone; Kevin L. Karem; Maya R. Sternberg; Geraldine M. McQuillan; Alysia D. Poon; Elizabeth R. Unger; William C. Reeves