Monday January 30 2012
Oral HPV infection was higher in men than women
Men are far more likely to have the sexually transmitted human papillomavirus (HPV) in their mouths than women, the Daily Mail has reported. The Mail has outlined research into the prevalence of HPV, which is a risk factor mouth cancer and other cancers. Researchers found that HPV was more commonly found in people who engaged in all kinds of sexual activity – including vaginal, anal and oral. The Mail reports that the researchers suggest that HPV vaccination for men needs investigating to see whether it could help stop oral HPV and, potentially, oral cancer.
Mouth cancer has risen more than 20% in the past 30 years. Tobacco use and prolonged, heavy alcohol drinking are the biggest risk factors, but the presence of oral HPV is also a clear risk factor for the disease.
The latest research set out to estimate the proportion of people infected with oral HPV in the United States, and any factors associated with infection. It found that approximately 7% of the US population aged 14 to 69 years were infected with this virus, and that men were more likely to be infected than women.
This study shows a marked difference in oral HPV infection between men and women in the US, but does not necessarily reflect how many people in the UK are infected. There are many different types of HPV, and not everyone who is infected will go on to develop cancer.
HPV is known to cause cervical cancer, and a vaccine campaign for girls aims to reduce its prevalence among women, and so reduce the number of cervical cancers. It remains unclear whether vaccinating men would have an effect on the presence of oral HPV or reduce the number of cancers.
Where did the story come from?
The study was carried out by researchers from Ohio State University, the US National Cancer Institute and a US company called Information Management Services. The research was funded by Ohio State University, the US National Cancer Institute, John and Nina Cassils and the pharmaceutical company Merck. Merck is the manufacturer of Gardasil, the cervical cancer jab that targets several strains of HPV, including type 16, which is most commonly associated with oral cancer.
The study was published in the peer-reviewed Journal of the American Medical Association.
This research was covered appropriately in the media, with the Daily Mail emphasising that the prevalence estimate was drawn from a US population, and pointing out that not all individuals infected with oral HPV will go on to develop oral cancer. The BBC was careful to point out that it is not known if the existing vaccines against HPV used for preventing cervical cancer are effective against oral HPV infection and that vaccination cannot be recommended for the primary prevention of oropharyngeal cancer.
What kind of research was this?
This was a cross-sectional study that examined the number of people aged 14 to 69 infected with oral HPV in the United States.
Cross-sectional studies are a useful way to generate estimates of the number of cases in a population. However, they only collect information at one point in time, and cannot tell us why things are related, or how things change over time. This study provides a snapshot of the number of infections in one time period (between 2009 and 2010), but it does not attempt to link these numbers to the risk of developing oral cancer.
Background information supplied by the researchers suggests that the number of cases of oral cancer has increased over the past 30 years in several countries, and HPV has been directly implicated as the underlying cause.
What did the research involve?
Researchers recruited a sample of individuals that was intended to be representative of the US population. They conducted interviews and a physical examination. During the interview, participants provided information about:
- sociodemographic factors – such as age, sex, education, socioeconomic status, sexual orientation and marital status
- substance use – including tobacco, alcohol and marijuana
- sexual behaviour – including ever having had sex, ever having performed oral sex, age at first sex, number of sexual partners and history of sexually transmitted infection
During the physical examination samples of cells were taken from the inside of the mouth. These samples were sent to a laboratory where researchers isolated DNA from the cells to determine whether the individual was infected with oral HPV and, if so, to identify the virus type. They tested for 37 HPV types, of which 18 were ‘high-risk’ DNA types.
The researchers then analysed the data, arriving at overall estimates of the number of infections in the US population. They also conducted an analysis that accounted for sociodemographic and behavioural factors.
What were the basic results?
There were 5,579 participants in the beginning of the study. Of these 5,501 (98.6%) were included in the analysis. The researchers found that overall:
- 6.9% of participants were infected with HPV (95% confidence interval (CI) 5.7% to 8.3%)
- 3.7% of participants were infected with a type of HPV classified as having a high risk of causing cancer (95% CI 3.0% to 4.6%)
- 3.1% of participants were infected with a low-cancer-risk type of HPV (95% CI 2.5% to 3.9%)
- the most prevalent type of virus detected was HPV-16 (1.0%, 95% CI 0.7% to 1.3%)
When the researchers accounted for sociodemographic and behavioural factors in their analysis, they found that the following variables were independently associated with oral HPV infection:
- Age: infections peaked at two distinct age groups - in those aged 30 to 34, and again in those aged 60 to 64. This pattern was stronger for men than women.
- Sex: men had more than twice the number of infections as women (10.1% male versus 3.6% female; prevalence ratio (PR) 2.33, 95% CI 1.66 to 3.26). When looking at the most common HPV type (HPV-16) this increased to a nearly fivefold difference (1.6% male versus 0.3% female; PR 5.41, 95% CI 2.12 to 13.83).
- Lifetime number of sexual partners: those with two or more partners had significantly more infections than those who had no sexual partners. The prevalence of infection increased with increasing numbers of lifetime partners.
- Current smoking intensity: those who smoked 10 or more cigarettes a day had significantly more infections than those who had never smoked or who no longer smoked. This association was stronger for women than for men.
Ethnicity, marital status and alcohol and marijuana use were not independently associated with oral HPV infection.
How did the researchers interpret the results?
The researchers concluded that approximately 7% of the US population between the ages of 14 and 69 were infected with oral HPV. They say that this is significantly lower than infection with genital HPV.
This was a relatively large cross-sectional study that estimated the number of oral HPV infections in the US among 14 to 69 year olds. These estimates cannot be directly generalised to the UK.
The researchers say that their data provide evidence that oral HPV infection is mainly sexually transmitted. This is because infection was uncommon among participants with no previous sexual partners, but was up to eight times higher among those with previous partners, and increased significantly as the number of partners increased. The researchers do point out, however, that their study did not collect information on possible non-sexual transmission methods.
While policy decisions regarding HPV infection generally focus on genital HPV among females, this research demonstrated that, at least in the US, men are more likely to be infected with oral HPV. As high-risk types of oral HPV have been shown to cause mouth cancer, this research may open up discussions on the need to address these risks. Options for reducing the risk of infection include targeting modifiable behaviours, such as smoking and sexual behaviour. Whether current vaccines against HPV can prevent oral cancer is unknown and this research does not provide any evidence as to how effective any vaccine might be.
All in all, this was a well conducted cross-sectional study that estimated the prevalence of oral HPV infections in the United States. However, it does not provide any information on the number of participants who went on to develop oral cancer. It is important to remember that there are many different types of HPV, and not everyone who is infected will go on to develop cancer. This study cannot tell us the rates of oral HPV infection in the United Kingdom, but may provide information on risk factors for infection that apply to populations outside the US.