Human Papilloma Virus is a common double stranded DNA virus affecting both men and women. There are over 100 different types of HPV, of which 40 types of HPV will affect the ano-genital region. Although the virus is “transmitted sexually” through direct genital contact and sexual relations it has not been viewed as a traditional STI. HPV establishes productive infection in keratinocytes only (skin and mucous membranes) and is largely asymptomatic. Eight out of 10 sexually active women will come into contact with the virus at some stage in their lives; with most being unaware they have been affected as the virus is usually temporary. An individual’s cellular immunity usually allows for the virus to be cleared spontaneously and thus has little long term significance. There is currently no treatment for HPV infection, although its consequences may be managed.
Testing for HPV involves examining the genetic material extracted from the cells obtained during routine cervical cytology specimens. In October 2008, the NHS Cervical Screening Programme introduced liquid based cytology (LBC) sampling. This implementation significantly improved the accuracy of sampling and provided the simultaneous opportunity to test for HPV and thus women would not have to undergo additional invasive testing. HPV testing was incorporated into NHS Cervical Screening Programme in April 2011 after a successful pilot programme.
HPV testing has been shown to be a more accurate screening tool than cytology alone, with the sensitivity of HPV testing being 95%, and thus better than cytology at detecting high grade CIN or CGIN at colposcopy. However, HPV testing has been shown to have a low specificity, due to the infection often only being present temporarily. For example, a large number of women may test positive but will not have significant cytological abnormalities as the test can pick up transient infection.1 A positive HPV test indicates infection with a high risk HPV subtype (e.g 16, 18, 31, 33, 39, 45, 51, 52, 56, 58, 59, 66, 68, 73) that is linked to cervical cancer.
Laboratory diagnosis of HPV positivity can lead to significant psychological distress in the woman, even after a careful, factual and sympathetic explanation of HPV and sexual transmission. In the majority of cases, HPV infection will have been confirmed at the same time as an abnormal smear result is received thus reinforcing that cervical cancer is caused by a sexually transmitted virus.
The NHS cervical Screening Programme aims to utilise HPV testing to triage cytology referrals to colposcopy. HPV testing can help distinguish between women who have an increased risk of having high grade cytology from those women who have a lower risk. A further development for the UK cervical screening programme is the introduction of “HPV test of cure”. This aims to test for HPV in women following treatment for CIN.
The disadvantage of HPV testing is that in the majority of women HPV infections can spontaneously resolve within one to two years and may not have health implications.
Is HPV a true STI?
HPV infections occur in the 15 to 25 year age group and spontaneous regression is common. However, a positive diagnosis carries with it the stigma of a STI and many young people will focus on the embarrassment of HPV positive test result and the subsequent difficulties that comes with confronting a partner.2 Partners usually share HPV. A study has shown that there is minimal difference between male to female (3.5 per 100, 95% CI 2.7-4.5) and female to male (4 per 100, 95% CI 3-5.5) transmission rates. Transmission was also found to be similar across HPV subtypes and oncogenic risk categories.3
HPV infection has been shown to be highest after the onset of sexual activity. If the first episode of sexual intercourse occurs within one year of menarche, there is a significant increased risk of cervical cancer. This is possibly due to the exposure to HPV occurring at a time of rapid changes to the cervix at a cellular level or due to behavioural patterns that may include multiple sexual partners and thus exposure to multiple subtypes of HPV (including 16 and 18).
In many populations a second peak occurs in 45 to 50 year olds. The question that is raised is this late peak due to re-activation of a prior infection or due to a new infection acquired through sexual activity with a new partner.4 A study has shown that natural immunity does not play a role in controlling the extent of re-infection with a different type of HPV indicated by the fact that initial infection rates were lower than those of re-infection with a different type.
The role of condoms in the prevention of HPV
Condoms may lower the chances of transmission, but need to be used with every type of sexual act and for the entire duration. However, it should be noted that HPV can infect areas not covered by a condom. Winer et al found that 9.7% of women who reported sexual contact not involving intercourse tested positive for HPV DNA.5 A further study by Manhart et al illustrated that it is not possible to make an exact estimation of condom protection against HPV (range 0% to 80%).6 The same study found that although condoms may not prevent HPV infection, condom use may lower the risk of genital warts, high grade dysplasia and invasive cervical cancer. The study concluded that it is unlikely that condoms offer the same level of protection against genital HPV as they do against HIV and other sexually transmitted infections. Winer at al showed that consistent use of condoms for more than 50% of sexual acts significantly reduced the risk of cervical and vulvavaginal HPV infection by 50% compared to partners who used condoms 5% of the time (95% CI 0.3-0.9).5
Condom use in HPV positive women may help with CIN regression because the cervix is not repeatedly being exposed to a HPV positive partner.7 Davis et al found condoms could offer 87% protection against HPV.8
Condom use can promote the regression of HPV related lesions in men whose partners are found to have CIN. Bleeker et al found the median time for regression of flat penile lesions was 7.4 months for condom users