APPLIED EPIDEMIOLOGY
Human Papillomavirus
Brianna Loeck
2/1/2013
Human Papillomavirus is the most common STI infection throughout the world. Though it has no health
effects, if left untreated it may lead to cervical cancer as well as other HPV-associated cancers. It is
known that the virus typically clears itself naturally within about two years. It does not just affect
women; it also affects males as well. HPV vaccines are recommended for men and women to receive
the vaccine between ages 9 and 26 years of age in order to protect themselves from the most common
HPV strains that can lead to genital warts and cancer.
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The Human Papillomavirus, also known as HPV, was first discovered in the 1950’s. A
group of scientists from different countries contributed to the identification of the virus.
However, it wasn’t until the 1970s and 1980s where other characteristics, common strains and
associations of this virus were discovered.
HPV is a group of small DNA viruses that causes warts and certain cancers and
precancers of the skin lining the lower genital tract, anus and mouth (ASCP, 2012). There is an
estimated 100+ HPV strains that have been fully identified and which they all slightly differ in
structure depending on the location and the type of lesion each type is likely to cause (ASCP,
2012).
HPV is categorized into low-risk and high-risk types. The low-risk types which include
strains: 6, 11, 42, 43, 44, 54, 61, 70, 72 and 81 are rarely found in cancers. High-risk types
include strains: 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 73 and 82 and which have been
found in cancers of the cervix, vagina, vulva, and penis. The majority of cervical cancers (80%)
are caused by just four HPV strains, which are 16, 18, 31, and 45 (ASCP, 2012).
HPV is extremely common; more common than people would like to think. It is
considered a sexually transmitted infection (STI) because it is primarily transmitted through
genital skin-to-genital skin sexual contact. It is estimated that 75-90% of sexually active adults
will contract HPV some point in their life (ASCP, 2012).
Most people with HPV do not develop symptoms or health problems from it, which
results to passing it to partners without knowing they have the virus. In 90% of cases, the body’s
immune system clears HPV naturally within two years. It is only when certain types of HPV
stay in the body for many years that it can cause these cancers. But there is no way to know
which people who get HPV will go on to develop cancer or other health problems (CDC, 2012).
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HPV does have some potential health problems such as genital warts, cervical cancer,
other HPV-related cancers, and RRP. Cervical cancer and other HPV related cancers such as
vulva, vagina, penis, anus and throat can all be prevented by regular screening exams.
“Screening tests can find early signs of disease so that problems can be treated early, before they
ever turn into cancer” (CDC, 2012). This is why it is extremely important for women to be
screened regularly to prevent such cancers from occurring. CDC offers a graph showing the
rates of HPV-associated cancers and median age of diagnosis among women in the United States
between 2004 and 2008 (Refer to Appendix, Figure 1).
The most common HPV-associated cancer is cervical cancer, and almost all cervical
cancer is caused by HPV. According to CDC (2012), all women are at risk for cervical cancer,
but it is rare in women younger than 30 years of age. The average age at diagnosis is 47 years
old. In 2007, 12,280 women in the United States were told they had cervical cancer, and 4,021
died from the disease. CDC provides a graph for cervical cancer incidence and death rates by
race and ethnicity in the United States per 100,000 from CDC (Refer to Appendix, Figure 2).
The graph shows that Hispanic women have the highest incidence rate of cervical cancer,
followed by black, white, and American Indian/Alaska Native, and Asian/Pacific Islander.
Overall, 7.9 out of every 100,000 women were diagnosed with cancer in 2007 (CDC, 2012).
However, black women have a higher death rate, followed by Hispanic, American Indian/Alaska
Native, white, and Asian/Pacific Islander women. Overall, 2.4 out of every 100,000 women died
from cervical cancer in 2007 (CDC, 2012).
In Figure 3 (refer to Appendix) shows a map of the worldwide HPV government reported
age-standardized cervical cancer incidence rate per 100,000 women per year. The map also
illustrates the most prevalent HPV types in each country. Africa has a prevalence rate of 22.9%,
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which happens to be the highest in the world. Central America and Mexico follow at 20.5%,
South America at 14.3%, North American at 13.8%, Asia at 8.3% and Europe being the least
affected at a rate of 6.6%. Out of all countries, number 16 tends to be the most common strain of
the HPV virus, which is labeled as a high-risk strain.
There are a number of risk factors that are known to increase the risk of HPV infection
progressing to cervical cancer, including HIV, smoking, poor hygiene, younger mothers, and
having many children. Low income and industrialized countries tend to have higher incidence
and death rates due to minimal access and availability to vaccines and screening equipment.
Unfortunately, there is currently no medical treatment for HPV. The safest treatment is
to be screened regularly to avoid future infections that lead to cancer. However, genital warts
and precancerous lesions from HPV can be treated such as cryosurgery (freezing that destroys
tissue), LEEP (removal of cervical tissue using a hot wire loop), surgical conization (surgery
with a scalpel or laser), and also laser vaporization conization (use of laser to destroy cervical
tissue (NCI, 2012).
There are ways to reduce the risk of contracting HPV. In 2006, Gardasil (HPV4), an
HPV vaccine was introduced to protect against the exposure to certain strains such as 16, 18, 6
and 11. It is strongly recommend that girls and women between the ages of 9 and 26 years old
receive the vaccination. “While the vaccine does not prevent infection with all types of HPV, it
provides protection against the HPV types associated with 70% of cervical cancers (16, 18), and
90% of external genital warts (6, 11)” (ASCP, 2012).
Another vaccine called Cervarix (HPV2) contains types 16 and 18, both high risk strains.
This vaccine is only for females to be taken. Both HPV vaccines are administered in a threedose series of injections. The second and third doses should be administered 2 and 6 months after
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the first dose. The third dose should follow the first dose by at least 24 weeks. Of course the only
way to fully prevent contracting HPV is abstinence.
Although much of HPV and cervical cancer center towards women, it also affects males.
There are several strains of HPV that can lead to genital cancer in men, such as the anus or penis,
though it is rare. According to WebMD (2013), “The American Cancer Society estimates about
1,570 men in the U.S. will be diagnosed with cancer of the penis in 2012. About 2,250 men are
estimated to have received a diagnosis of anal cancer in 2012 as well”. This proves that men are
too affected by HPV; it’s not just a “woman” thing. CDC shows a chart displaying the rates of
HPV-associated cancers and the median age at diagnosis among men in the United States
between 2004 and 2008. The most common HPV-associated cancer is oropharynx which is
located in the mouth (Refer to the Appendix, Figure 4).
Currently, there is no routine test for men to check for HPV, except the visual screening
of warts. WebMD (2013) mentions that some doctors are urging anal Pap tests for gay and
bisexual men, who are at higher risk of anal cancer caused by HPV. The doctor collects cells
from the anus and has them checked for abnormalities in a lab. Nonetheless, in 2009 the
Gardasil vaccine was approved for males between the ages of 9 and 26 years old for the
prevention of genital warts caused by the strains 6 and 11.
There is no known season variation in HPV infection. “HPV is presumably
communicable during the acute infection and during persistent infection. This issue is difficult to
study because of the inability to culture the virus. Communicability can presumed to be high
because of the large number of new infections estimated to occur each year” (CDC, 2013).
Some parents are against getting their children vaccinated, especially their daughters
because they believe it will lead to promiscuity of sexual activity. According to the Huffington
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Post, a new study was implemented and the results turned out that in fact, receiving the HPV
vaccination does not encourage promiscuity. Dr. Matthew Davis, an associate professor of adult
medicine and pediatrics at the University of Michigan C.S Mott Children’s Hospital, “led a poll
using a national sample that found that 40% of parents have moral or ethical concerns about the
HP vaccination, while 36% said they felt pre-tens girls were too young to get it” (Huffington
Post, 2012). Davis quotes, “Those [rates], to me, indicate that there remain concerns that
adolescent's choices will be influenced by this vaccination," (Huffington Post, 2012).
I believe vaccines are the most important solution to prevent more HPV infections.
These two vaccines protect us from the major, most common HPV strains out there and will
eventually decrease the amount of women and/or men becoming diagnosed with the HPVassociated cancers. Also, for women who are sexually active to receive regular Pap smear tests
to detect for any abnormalities. This is to prevent any types of cancer from developing, which
will cause a decrease in mortalities. I don’t foresee everyone in the world to practice abstinence,
so these must be the solutions for society to follow.
Technology is always growing and becoming more powerful throughout the years. I
would hope to see in the future, a much stronger vaccine that will eventually protect us from all
strains of HPV, so that this virus can be completely eradicated in the future to save more men
and women’s lives.
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Appendix
Figure 1
CDC, (2012)
Figure 2
CDC, (2012)
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Appendix continued
Figure 3
Crow, (2012)
Figure 4
CDC, (2012)
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References
American Society for Colposcopy and Cervical Pathology. (2012). Natural History of HPV.
Retrieved from
http://www.asccp.org/PracticeManagement/HPV/NaturalHistoryofHPV/tabid/5962/Default.aspx
Center for Disease Control and Prevention. (March, 2012). Human Papillomavirus (HPV).
Retrieved from http://www.cdc.gov/hpv/index.html
Crow, M. James. (August 2012). HPV: The global burden.
http://www.nature.com/nature/journal/v488/n7413_supp/full/488S2a.html
Huffington Post. (2012). HPV Vaccine Does Not Increase Sexual Activity: Study.
Retrieved from http://www.huffingtonpost.com/2012/10/15/hpv-vaccine-sexual-activitystudy_n_1959630.html
National Cancer Institute. (March 2012). HPV and Cancer. Retrieved from
http://www.cancer.gov/cancertopics/factsheet/Risk/HPV
WebMD. (2013). HPV/Genital Warts Health Center. Retrieved from
http://www.webmd.com/sexual-conditions/hpv-genital-warts/hpv-virus-men