Approximately half of men of all ages were infected with genital human papillomavirus, according to a prospective study of three urban areas in the United States, Brazil, and Mexico.
In addition, men’s risk for acquiring HPV did not decline with age as it does in women, but appeared to remain stable throughout their lifetimes, said Dr. Anna R. Giuliano of the risk assessment, detection, and intervention program at H. Lee Moffitt Cancer Center and Research Institute, Tampa, and her associates.
The Lancet published the study online March 1.
The researchers examined the incidence and clearance of genital HPV among men because little is known about the subject. Optimal strategies for preventing the disease both in men and in their sexual partners cannot be devised until more is known about its epidemiology in men, they said.
The prospective HPV in Men (HIM) study involved 1,427 men in Tampa, 1,443 in Sao Paulo, Brazil, and 1,429 in Cuernavaca, Mexico, who were examined for HPV infection at 6-month intervals for a median of 27.5 months. The men were aged 18-70 years at baseline, with a median age of 32 years. All subjects were HIV negative and had no history of cancer.
At each visit, three specimens of penile and scrotal cells were obtained from the coronal sulcus, glans penis, penile shaft, and scrotum for the detection of HPV DNA and for HPV genotyping. Sociodemographic and sexual behavior data were obtained using a questionnaire.
Dr. Giuliano and her colleagues reported findings for a subgroup of the first 1,159 study subjects they assessed. The overall rate of infection with any HPV type was 50%. The overall prevalence of oncogenic HPV subtypes was 30% and that of nononcogenic subtypes was 38%, they said (Lancet 2011 March 1:[doi:10.106/S0140-6736(10)62342-2]).
The incidence of acquisition of a new HPV infection was 38.4/1,000 person-months and did not change appreciably according to subject age. The reason for the lack of an age association such as that seen among women is not yet known. In the study cohort, men in three age groups – 18-30 years, 31-44 years, and 45-70 years – reported having similar numbers of sexual partners and of new sexual partners. Thus, it is possible that they have continued exposure to HPV as they age, the researchers noted.
"Another possible explanation is sex differences in the HPV immune response," Dr. Giuliano and her associates said. "HPV infection of keratinized epithelium, such as the penile skin, might generate lower and weaker immune responses than infection of mucosal epithelium such as the cervix or anal canal."
If men remain at high risk of developing new HPV infections throughout their lives, "then vaccination of older men might be warranted," they noted.
Acquisition of a new HPV infection strongly correlated with the patients’ reported number of sexual partners, male or female. Compared with men who reported no more than 1 lifetime female sexual partner, men who reported they had 10-49 lifetime female sexual partners were 2.7 times as likely to be infected. Those who reported at least three male anal-sex partners in the past 3 months were 2.3 times as likely to develop an infection as those reporting no partners.
Similarly, acquisition of a new infection with an oncogenic HPV subtype correlated with the number of female sexual partners and of male partners who engaged in anal sex. Again, the risk was more than two times greater among men who reported 10 or more such partners than among those who reported no more than 1 partner. Those who reported at least three male anal-sex partners in the past 3 months were 2.6 times as likely to develop an oncogenic HPV infection as those reporting no partners.
The odds of clearing an existing HPV infection also showed a strong association with number of sexual partners. And, as has been reported among women, the odds of clearing an HPV infection in men varied according to HPV subtype. The median time to clearance for oncogenic HPV was 7.2 months, while the median time to clearance of nononcogenic HPV was 7.6 months. Infection clearance times shortened with increasing age.
"The results from this study provide much-needed data about the incidence and clearance of HPV infection in men; these data are essential for the development of realistic cost-effectiveness models for male HPV vaccination internationally," the investigators said.
The National Cancer Institute supported the study. Dr. Giuliano reported ties to Merck, the manufacturer of the HPV vaccine.