||Over 100, of which over 30 are sexually transmitted
Cervical, anal, penile, and other cancers
|Treatable / curable
||90% of cases clear within two years with no intervention
Many cases are curable
||Yes, moderately effective
||Yes, but of limited usefulness
||75% of adults contract HPV at some point during their lives
27% of adults are infected with HPV at any given time
||Skin to skin contact, including indirectly via hands
Oral transmission is possible but less common
Probably not transmitted by fluids
||Very highly transmissible. Exact transmission rates are unclear.
||Condoms probably provide significant protection
Gloves may provide limited protection
||If you can afford it, get vaccinated with Gardasil regardless of your age and sex.
Women: Get regular Pap tests. Consider asking for DNA testing for HPV at the same time.
Men who have sex with men: Consider getting regular anal Pap tests.
||Always use condoms for penetration.
Consider using gloves for all genital contact (not just penetration).
Consider being careful about casual non-penetrative genital contact.
Consider using condoms and dams for oral contact.
||Maintain a sense of perspective. HPV is very transmissible, but it’s also very common
and usually not very severe.
HPV is the most widespread STD in the United States, with most sexually active individuals contracting at least one strain at some point in their lives. Most infections produce few if any symptoms and naturally disappear within 1 to 2 years. A significant minority of cases, however, produce significant symptoms, and some may persist indefinitely.
HPV spreads very efficiently and there are no reliable ways to prevent transmission.
Symptoms and progression
There are more than 100 known strains of HPV, over 30 of which are sexually transmissible. The sexually transmissible strains are distinct from the strains that cause warts elsewhere on the body.
Sexually transmitted strains are classified as either high-risk (can cause cancer but will not cause warts) or low-risk (do not cause cancer, but may cause warts). Two high-risk strains (16 and 18) are believed to be responsible for 70% of all cervical cancer, while two low-risk strains (6 and 11) are believed to be responsible for 90% of all genital warts.
Most infections are asymptomatic. In those that are symptomatic, initial symptoms may appear anywhere from weeks to years after the initial infection. Once symptoms have appeared, they often disappear and reappear in cycles.
In healthy individuals, 70% of infections naturally disappear within one year and 90% within two years. Up to 10% of cases may persist indefinitely, however. Once an individual has cleared an infection, they are usually immune to further infection by that particular strain of the virus, but they are still susceptible to infection by other strains. While an individual is infected, the infection can spread to new areas of their body.
Long-term HPV infections can ultimately lead to cancer, especially of the cervix, anus, and penis. These cancers typically take many years to develop and are highly treatable if caught early (typically by a Pap test). It appears that oral HPV infection can cause some head and neck cancers as well.
Men who have sex with men (MSM) have relatively very high rates of anal cancer (about 35 times the rate in the general population), probably because of exposure to HPV.
Two vaccines are available, both of which are highly effective against certain common strains of HPV. Neither vaccine provides complete protection, and neither provides any protection against existing infections.
Gardasil protects against HPV types 16 and 18 (which cause about 70% of all cases of cervical cancer), and types 6 and 11 (which cause about 90% of all cases of genital warts).
Cervarix protects against types 16 and 18, but not against types 6 and 11. Cervarix includes an additional adjuvant, which may increase the strength or duration of the protection it provides.
Both vaccines are given as three shots over six months. A complete course costs between $350 and $500.
The vaccine is effective and approved for use in both men and women. The vaccine is most commonly given to women (who are at risk of cervical cancer) and gay men (who are at risk of penile and anal cancer).
The vaccine is currently only approved for use in individuals between the ages of 9 and 26, even though it appears to be safe and effective in older individuals. This decision is based largely on cost-effectiveness: it is believed that older individuals are likely to have had prior exposure to HPV, that they are less likely to contract new infections, and that new HPV infections in older women are less likely to progress to cervical cancer.
While the current recommendations may be appropriate from a public health perspective, it is my opinion that they are not appropriate for responsible individuals with multiple sexual partners. I strongly recommend that everyone get vaccinated with Gardasil, regardless of age, sex, or sexual history.
Testing and diagnosis
There are no generally available tests that can detect all strains of HPV.
The Pap test is a routine screening test that looks for pre-cancerous changes in the cervix. Widespread use of the Pap test is credited with dramatically reducing the number of deaths caused by cervical cancer in the US. All women who have had sex should have regular Pap tests, although the frequency of testing is the subject of some controversy.
For women, a DNA test is available which tests for the presence of high-risk HPV. This test is often administered at the same time as a Pap test. Although the test can identify the presence of high-risk HPV, it cannot identify which strains are present.
There are no approved tests for detecting high-risk HPV in men.
There has been increasing interest in recent years in giving MSM regular anal Pap tests. Although this seems like a reasonable strategy, there is insufficient data to say whether it is effective. One might speculate that anal Pap testing might also be appropriate for women with an extensive history of receptive anal intercourse.
Warts caused by low-risk HPV are generally diagnosed by visual inspection, sometimes with the use of acetic acid. This procedure is somewhat haphazard and cannot detect asymptomatic infections.
A variety of treatments are available. These are moderately effective at alleviating symptoms and clearing the infection, and probably reduce the risk of transmission.
Over the counter treatments for common and plantar warts are not appropriate for use on genital warts.
Unfortunately, there isn’t much definitive data about the transmission of HPV. What data does exist often has methodological issues that make it hard to make definitive statements about real-world transmission. However, it is possible to make some general observations.
HPV is very efficiently transmitted. Very few studies have attempted to quantify the rate of transmission, and none has produced definitive results. My best wild guess based on the very limited data available is that a heterosexual couple having regular unprotected sex for a year have a significantly greater than 50% chance of passing any given HPV strain from an infected partner to an uninfected one. It is possible that HPV spreads more efficiently from women to men than from men to women.
HPV transmission occurs via virus shed from the skin, not via fluids. It can affect the genitals, anal area, groin, and oral area, and can be spread when an infected area comes in contact with any susceptible area. It can also be transmitted indirectly. For example, an infected man is likely to have HPV on his fingertips. He may infect the surface of a condom while applying it, and the condom may subsequently infect his partner. Transmission has also been observed from casual, non-penetrative contact (for example, from a woman’s anus to her partner’s scrotum).
In men, the penile shaft appears to be the primary source of the virus, and in women the cervix appears to be the primary source.
It is likely that transmission is more efficient when the infected partner exhibits visible symptoms, and it is also likely that oral transmission is less efficient than genital transmission.
It is possible (and probably quite common) for HPV to spread from one site on a person’s body to others.
The data on the efficacy of condoms at preventing HPV transmission is very scant and somewhat contradictory. It is likely that they provide some protection, especially against the development of genital warts. My personal impression from reading the research is that while older studies and studies with poor methodology tend to find little benefit associated with condom use, more recent, high-quality studies have frequently found significant benefit. I’m afraid the jury is still out on this one, although it is clear that condoms do not provide anything like complete protection.
It is reasonable to assume that using gloves for genital contact will reduce the rate of HPV transmission, but there is no data to confirm this.
References and technical discussion that you probably don’t care about
If you’re old enough to be having sex, you’re old enough to know how to use Google and Wikipedia. Most of the facts in this document are well known and uncontroversial, and can be found in the excellent Wikipedia article on HPV, which includes extensive references. There are a few specific papers, however, that I want to comment on.
Transmission of human papillomavirus in heterosexual couples.
Hernandez et. al., June 2008
This fascinating paper examines the spread of HPV within monogamous heterosexual couples. The authors performed regular DNA testing of multiple sites on each subject, and observed the migration of specific HPV strains between partners and between sites on the same individual. What they found is that HPV spreads amazingly efficiently. They observed frequent events of transmission between partners via penetration, casual non-penetrative contact, indirect transmission via hands, and self-innoculation (i.e., transmission between different sites on the same person).
The study’s methodology makes it hard to calculate overall transmission rates because they focus on transmission events (i.e., spread of the virus from one site to another) and not on the initial infection of a previously uninfected individual. However, if you dig into the numbers, they found an overall male to female infection rate of 4.5% per month (58% per year) and a female to male infection rate of 13.7% per month (83% per year).
In addition, this study found a strong protective effect from condom use. Condoms were used always by 3% of the couples that experienced transmission and by 56% of the couples that did not experience transmission.
Finally, it’s worth noting that this study regularly detected HPV in the urine of male and female subjects, and in the semen of male subjects.
Do condoms prevent genital HPV infection, external genital warts, or cervical neoplasia?
Manhart et. al., November 2002
There are a number of published studies that examine the efficacy of condoms in preventing HPV transmission, but this is the only meta-analysis that I’ve found. Studies of this subject tend to be hampered by substantial methodological problems, so the following data aren’t as definitive as one might like. Looking at the existing literature as of 2002, the authors found evidence that condoms provide significant protection (60% relative risk reduction) against the development of genital warts in both men and women, but no clear evidence that they reduce HPV infection as measured by DNA testing, or that they protect against cervical cancer and its precursors.
Genital Human Papillomavirus Infection: Incidence and Risk Factors in a Cohort of
Female University Students
Winer et. al., February 2003
Condom Use and the Risk of Genital Human Papillomavirus Infection in Young Women
Winer et. al., June 2006
It’s interesting to compare these two papers, written by the same investigators and looking at similar pools of subjects. The first paper found that “Always using male condoms with a new partner was not protective.” The second, paper, however, which was specifically focused on condom use and which used a much stronger methodology, found that condom use was highly protective against HPV infection. Women in the second study who always used condoms developed new HPV infections at a rate of 38% per year, whereas women who never used condoms developed new HPV infections at a rate of 89% per year.
It is my unproven belief that many of the studies that failed to find that condom use reduces HPV transmission had similar methodological flaws, and that condoms do in fact significantly reduce HPV transmission.
The first paper has some useful data about the spread of HPV via nonpenetrative sexual contact:
“Infection in virgins was rare, but any type of nonpenetrative sexual contact was associated with an increased risk. Detection of oral HPV was rare and was not associated with oral-penile contact. The data show that the incidence of HPV associated with acquisition of a new sex partner is high and that nonpenetrative sexual contact is a plausible route of transmission in virgins.”
“Of 72 virginal women reporting nonpenetrative sexual contact (and completing at least two visits), seven tested positive for HPV DNA (9.7 percent) whereas only one of 76 women(1.3 percent) reporting no such contact (and completing at least two visits) tested positive.”