While much is known about the natural history of cervical HPV infection and its consequences, including cervical intraepithelial neoplasia and cervical cancer, relatively little is known about the natural history of genital HPV infection and diseases in men. In part this reflects difficulties in penile sampling and visual assessment of penile lesions. Although HPV is transmitted sexually and infects the genitals of both sexes, the cervix remains biologically more vulnerable to malignant transformation than the penis or anus in men. However, as more precise and sensitive methods become available and wider studies are performed, the number of HPV-associated pathologies has also increased 
. Understanding male HPV infection is therefore important in order to reduce HPV pathology and its transmission 
The HPV infection rate increased steadily throughout the years of the study in the male population in our area. In the first years of the study (2002–2005), it was 28.3% to 43% in 2007–2009. This rate remained stable in the latest years after solving some issues related to sample types and sample gathering, and improving the assessment of individuals with a potential pathology. The 36.3% incidence rate in men attending a STI clinic is close to the highest values described 
; hence, we can state that men constitute a critical link in the transmission of HPV infection 
, especially if those men have multiple sexual partners and are in contact with risk groups 
Data on infection incidence take into account the results of the urethral and paraurethral swabs. As other authors have already described, paraurethral swabs exhibited a greater diagnostic performance, which facilitates the performance of this type of studies, since these samples can be easily obtained 
In this study, swabs obtained from anal lesions or penile condylomata were also processed. The performance of these types of samples was lower than expected (50%), but it must be taken into account that no biopsies were carried out. Biopsies would be the preferred samples to perform an etiologic diagnosis of lesion samples 
No evident influence of age on infection rate has been found in the published literature on HPV infection in men 
. In the U.S., Stone et al.
found a higher prevalence rate in the 30–39 age range. Our series, however, reveal a decrease in the infection rate as age increases, just as described for the female population 
; however, the percentages are always higher than those found in women, in any age range 
The more frequent viral genotypes in the male population were the vaccinal genotypes, notably HPV-6 and HPV-11, a fact already mentioned by other authors 
. In this study, low-risk oncogenic genotypes were found with a 47% frequency, a value that contrasts with other publications in which LR genotype prevalence was between 2.3% and 24%. Further more, HPV 6 was found more frequently in men younger than 35 years old. As opposed to the findings of most other studies in which the HPV-16 is the most frequent genotype 
. In this series HPV-16 was only more frequent in men older than 35 but not significantly. A possible explanation of this fact would be that many of these men featured subclinical lesions, all caused by low-risk HPV (6 and 11), as revealed by peniscopy. In keeping with this, Partridge and Koustky 
concluded that the epithelium of the penis seems to be less receptive to high-risk genotypes.
According to these results, male vaccination with the tetravalent vaccine would be more effective than with the bivalent one, since it could reduce the risk of anal-genital warts, which, although not a severe pathology, do cause significant psychological morbility.
In the present study, to 2007 a 3.1% of mixed infections were detected. The prevalence of multiple-type HPV has been reported to be between 2.1% and 34.8% in men 
. Technical limitations may condition the results. However, a large-size fragment amplification was carried out, and the genotyping was performed by hybridization techniques which allow for the detection of minuscule populations more efficiently than sequencing techniques, although the number of probes was limited to the most common genotypes found in our environment. This limited amount of probes may underestimate the amount of mixed infections with uncommon genotypes. From 2007, when seven probes were added, the prevalence of multiple-type HPV raises 20%. The 97.5% mixed infections were composed by high-risk genotypes, but only less than half of the cases (38.8%) corresponded to the genotypes included in the FDA-approved quadrivalent vaccine for men 
The individuals from this study that would have benefit by the bivalent vaccine will be 15.9% and by the quadrivalent vaccine 40%.
The virus was more frequently detected in those men showing a clinical presentation compatible with HPV infection than in those who did not. In these cases, however, the percentage of HPV found was not higher than 51%. Obtaining cellular samples by exfoliation of the keratinized epithelium was difficult in those instances, thus compromising the diagnosis 
The risk of contagion is related to sexual behaviour (number of sexual partners, both throughout life and simultaneous), sexual intercourse with risk groups (prostitution), polygamy, having suffered other STDs and parenteral drug use. In our study, none of these factors seemed to be involved in the increase of the HPV infection rate, with the exception of marital status: single or divorced individuals were associated to a higher HPV infection rate. These males also exhibit a sexual behaviour different to that of married men.
Although many males get infected with HPV, most of such infections do not develop into cancer. It is thus probable that other co-factors, such as tobacco usage, alcohol intake and coinfection with other sexually transmitted diseases play a role in the pathologic process. No relationship between these co-factors and the presence of oncogenic genotypes was established in this study.
On this study, urethral and paraurethral swabs are not collection simultaneously, and clinical and pathological data were reviewed only from 151 patients due to the medical history confidentiality. These limitations could have any influence in the data.
To sum up, although HPV infection do have worse consequences for women, men play an active role in it, as the high incidence rates found demonstrate. Men are involved in its reservoir and transmission, and the virus may end up causing major disorders and severe consequences. The high prevalence in this collective suggests the need of more exhaustive assessments, even though most individuals do not feature high-risk oncogenic viruses. Most countries have only included girls in their national vaccinations programs 
, and MSM will not be indirectly protect. Inclusion of men in the national HPV vaccination program may reduce their burden of HPV-related disease and reduce transmission of the virus to non-vaccinated women.