Review
Oral sex and the transmission of viral STIs
Sarah Edwards, Chris Carne
Objective: To review the literature on the role of oral sex in the transmission of viral sexually
transmitted infections (STIs).
Method: A Medline search was performed using the keywords oro-genital sex, and those specific
to each infection. Further references from each article identified by Medline were also included,
as were relevant references from “Current contents”.
Conclusions: Oral sex is a common sexual practice among both heterosexual and homosexual
couples. The evidence suggests that HIV transmission can take place through oro-genital sex
from penis to mouth and vagina to mouth. Case reports describe apparent transmission from
mouth to penis although this appears less likely. The risk of oro-genital transmission of HIV is
substantially less than from vaginal and anal intercourse. Receptive oro-genital sex carries a small
risk of human papillomavirus infection and possibly hepatitis C, while insertive oro-genital con-
tact is an important risk factor for acquisition of HSV 1. Oro-anal transmission can occur with
hepatitis A and B. The transmission of other viruses may occur but is unproved. The relative
importance of oral sex as a route for the transmission of viruses is likely to increase as other,
higher risk sexual practices are avoided for fear of acquiring HIV infection.
(Sex Transm Inf 1998;74:6–10)
Keywords: oral sex; viral STIs
For the purposes of this review the term oral
sex is taken to include oro-genital and oro-anal
sex but to exclude kissing. Oral sex is a
common practice in both heterosexual and
homosexual relationships.
1
Vaginal intercourse
remains the most commonly reported activity
between heterosexual couples, although 72.9%
of men and 66.2% of women had experienced
cunnilingus, while 69.4% of men and 64% of
women had experienced fellatio.
1
This com-
pares with much lower rates found by Kinsey in
the 1940s and 1950s.
23
Contemporary culture
is approving of oro-genital sex, and during the
1970s and 1980s premarital oral sex has
increased dramatically
4
and in one study more
adolescent girls had received oral-genital
stimulation than had vaginal intercourse.
5
Among homosexual men there is evidence of
declining rates of anal intercourse as a response
to the HIV epidemic,
6
and recent homosexual
contact is more likely to be oro-genital or non
ano-penetrative.
1
Oral sex has therefore be-
come a relatively more important route for the
transmission of sexually transmitted infections
(STIs). This and a subsequent article aim to
review the literature on oral transmission of
viral and non-viral STIs.
Human immunodeficiency virus (HIV)
HIV is found in semen,
7
vaginal secretion,
8
and, at much lower levels, in saliva.
9
Apart from
the level of HIV in saliva, other factors which
may influence rates of transmission of HIV by
oral sex are, firstly, the finding that other com-
ponents of saliva inactivate the virus
10
and, sec-
ondly, a lack of expression of potential
receptors for HIV in oral mucosa.
11
Thirdly, the
presence of other pharyngeal infections may
act as a cofactor in transmission.
12
Although no
clear evidence exists, it seems likely that
inflammation of the mucosa and blood staining
of saliva (which are particularly common with
some oral manifestations of HIV) will influence
the risk of transmission. Finally, microscopic
physical trauma during oro-genital contact
may also be important.
HOMOSEXUAL TRANSMISSION
Male to male
The original reports on the sexual transmis-
sion of HIV came from the early years of the
American epidemic among homosexual men,
when unprotected anal sex was common, and
HIV infection was a virtual certainty if there
was unprotected receptive anal intercourse
with six or more diVerent partners.
13–15
These
studies concluded that there was negligible
risk of HIV acquisition from oro-genital sex,
however it may be that the risk was obscured
by the frequent practice of higher risk
activities. Behaviour has changed since that
time,
6
and there is an increasing number of
case reports of transmission following oro-
genital sex between men. Seroconversion has
occurred during receptive oro-genital sex both
with
16 17
and without
18 19
ejaculation. Receptive
oro-genital sex was a risk factor in three out of
the five cases reported by Rozenbaum et al.
20
However the other two patients denied any
contact other than insertive fellatio and “deep
kissing”. Two further cases of HIV infection
following insertive oro-genital sex have been
reported; in one of these cases phylogenetic
analysis supports the epidemiological data.
21
In a study of primary HIV infection Schacker
et al found that four of the 46 patients enrolled
in the study reported having only unprotected
oro-genital contact, including a documented
case of infection after performing fellatio.
22
If
true, it seems that blood stained saliva must
Sex Transm Inf 1998;74:6–106
Department of
Genitourinary
Medicine,
Addenbrooke’s
Hospital, Hills Road,
Cambridge CB2 2QQ
S Edwards
C Carne
Correspondence to:
Dr Sarah Edwards.
Accepted for publication
9 October 1997
have been involved. In the Amsterdam cohort
study of 102 homosexual men, 11 men only
admitted to oro-genital contact before sero-
conversion, although two of these changed
their history at interview.
23
The authors felt that
the high proportion of men infected by this
route was partly as a result of underreporting of
higher risk activities in a group who were well
informed about safer sex. This phenomenon
has subsequently been found by others.
24
The
largest study of oral sex as a potential HIV risk
was of 741 homosexual men in the
Netherlands, which suggested that oro-genital
contact alone was a risk for HIV acquisition,
although this result was not statistically
significant.
25
However, Darrow et al were
able to demonstrate that participants in a hepa-
titis B study had a higher risk of HIV infection
from both oro-genital and oro-anal contact.
26
Female to female
Perry et al have reported oro-genital transmis-
sion of HIV between women.
27
However, it may
be that not all cases of apparent female to
female oral transmission are genuine as there
appears to be underreporting of bisexual
activity.
28
HETEROSEXUAL TRANSMISSION
Fischl et al evaluated heterosexual partners of
adults with AIDS and found higher reporting
of oral sex among infected partners, but did
not diVerentiate between male:female and
female:male exposure.
29
Male to female
In heterosexual intercourse there is a diVeren-
tial in transmission between the sexes, with a
higher risk of women acquiring the infection.
30
Two cases of HIV transmission by fellatio
(without ejaculation) with a seropositive drug
user have been reported in Italy,
31
while a larger
study by Padian et al showed increased risk of
transmission with increasing numbers of sexual
contacts, irrespective of whether the contact
was vaginal or oral.
32
Female to male
Although there is known to be a lower overall
risk of transmission from female to male,
30
there is little information on the relative risk of
diVerent sexual practices. Cases of infection
following oral sex have been reported,
33 34
one
of which involved an impotent diabetic man
infected by fellatio from a prostitute.
33
Herpes simplex virus
Historically, genital herpes was predominantly
caused by herpes simplex virus type 2 (HSV
2),
35 36
but more recently there have been
reports of both a rising incidence of new
cases,
37 38
and a rise in the proportion due to
HSV 1 in various centres in the United
Kingdom.
38–40
This trend has also been re-
ported in other countries with high or rising
rates of genital herpes—for example, Japan,
41
and also in the United States—a study by Wald
et al published in 1994
42
found 32% of primary
herpes infections to be due to HSV 1 compared
with the data from Corey et al in 1983 in which
HSV 1 was isolated from only 10% of primary
herpes.
43
The increase in isolation of HSV 1 has
been predominantly in women, and accounted
for up to 79% of female isolates and 39% of
male cases in one series.
38
This would be com-
patible with the fact that both sexes report
greater experience of cunnilingus than fellatio.
1
However, further data from SheYeld suggest
that misdiagnosis of mild HSV 1 infection in
men may partly explain this discrepancy.
44
Although some studies have reported that
transmission of either viral type may be via
oro-genital contact since concomitant pharyn-
gitis may occur with primary genital
infection,
45
none has specifically looked at the
role of oral contact as the sole route of
transmission. The development of an acute
HSV 1 pharyngitis in a homosexual man
Table 1 Evidence for the transmission of viral STIs by oral sex
Infection Nature of risk Evidence References
HIV Fellatio: Case reports:
oral partner with ejaculation 16, 17, 20
without ejaculation 18, 19, 22, 31
penile partner Case reports 20, 21, 33, 34
Cunnilingus Case report (between lesbian women,
NB possible
under-reporting of bisexual behaviour)
27
oro-genital/oro-anal contact
(general)
Cohort studies 23, 25*, 26
Higher reporting of oral contact between infected
partners
29
HSV to genital partner Rising cases due to HSV 1 (esp women) 38, 39, 40, 41, 42, 48
Case report after receptive fellatio 46
Documented orogenital contact in HSV 1 cases 47, 48
HPV to oral partner Case reports of oral warts 62, 63, 68
Genital HPV types in oral mucosa 64, 65, 66, 67, 74, 75
Studies suggestive of risk 50, 62, 67, 61
Case report of oral bowenoid papulosis 77
to genital partner Inc risk of cervical cancer with cunnilingus/fellatio 69
Hepatitis B Risk to oral partner in oro-anal sex Cohort study of prevalence and factors associated with
transmission
82
Rectal lesions and HBsAg 85
Cohort study 81
Hepatitis A Risk to oral partner in oro-anal sex Higher rates of seropositivity in homosexual men 90
Epidemics among homosexual men 91, 92
Hepatitis C Risk with oro-genital contact Cohort study—marginal risk for oral sex with >25
partners
81
Molluscum contagiosum To oral partner in oro-genital sex Facial molluscum in AIDS patients 97
Kaposi’s sarcoma (HHV8) Oro-anal sex Association found in one study 99
*Study shows borderline significance.
Oral sex and the transmission of viral STIs 7
following insertive oral sex has recently been
reported.
46
Reports of HSV 1 transmission
suggest that oral sex is the predisposing factor,
although information on the practice of
oro-genital sex is often absent from the case
notes.
47 48
The role of genito-genital spread of
HSV 1 is probably less significant as genital
HSV 1 infection recurs less often
45
and is asso-
ciated with less subclinical shedding of virus.
49
Human papillomavirus (HPV)
Genital warts form a large proportion of the
workload for many genitourinary medicine
clinics, and are generally thought to be sexually
transmitted. The seroprevalence of HPV anti-
bodies rises with increasing numbers of sexual
partners,
50 51
and the incidence of HPV lesions
on the cervix is also correlated with greater
numbers of sexual partners and earlier age of
coitarche.
52
However, studies of virgins have
shown conflicting results, with no HPV de-
tected either on analysis of tampons from
virginal women
53
or in a longitudinal serological
study.
54
HPV DNA was detected by Pao et al in
premarital checks of virgins raising the
possibility of transmission by mechanisms other
than penetrative intercourse, although in this
series no HPV DNA was detected in the
husbands to be.
55
Transmission by fomites is
plausible as HPV DNA has been isolated from
equipment after examination of patients with
genital warts,
56
but transmission via this route is
not proved and is thought to be unlikely.
57
Hand-genital transmission is thought to occur
58
and oro-genital transmission is therefore plausi-
ble. Vertical transmission (and viral persistence)
is known to occur
59
and is linked to juvenile res-
piratory papillomatosis.
60
In a study comparing
juvenile respiratory papillomatosis with adult
onset disease, aVected adults reported a higher
frequency of oral sex than controls.
61
The
development of oropharyngeal warts is
uncommon
62 63
but when present a large
proportion are due to “genital” HPV types—
that is, 6, 11, 16, 18.
64–67
One case report also
temporally relates the development of an oral
condyloma to cunnilingus with an infected
partner.
68
Some studies suggest oro-genital
transmission
50 62 67
while another study found a
slight increase in the risk of cervical cancer with
fellatio and cunnilingus, although this may be
confounded by the increased number of part-
ners in the group reporting oral contact.
69
Asymptomatic HPV is well recognised in
genital sites
50
and it is likely that asymptomatic
infection in the mouth is commoner than
manifest disease. Acetowhitening of the oral
mucosa has been shown to be non-specific and
should not be regarded as a diagnostic criterion
for oral HPV infection,
70
but HPV DNA has
been identified in the mouth.
71 72
HPV types 6
and 16 were identified in up to 24% of exfoli-
ated oral mucosal cells in both normal children
(suggesting persistence after perinatal infec-
tion) and in adults,
71
and HPV was found in
five out of 12 biopsies of normal tissue in
another series.
72
However, this was not con-
firmed in a further study in which 65 men and
111 women showed no evidence of oral HPV
infection.
73
HPV can also cause malignant change in the
oral cavity and genital types (especially HPV
16) have been isolated from these lesions.
74 75
However, HPV is clearly not the sole risk factor
for oral cancer. Indeed, one study found a
lower incidence of oral sex in cancer suVerers
than in controls.
76
Further evidence of oral
pathology associated with HPV comes from the
case report of a man being treated for
Hodgkin’s disease who had bowenoid papulo-
sis on his penis and proved HPV associated
severe epithelial dysplasia in his mouth, which
the authors described as the first reported case
of oral bowenoid papulosis.
77
Hepatitis viruses
HEPATITIS B
Hepatitis B positivity has been known to be
more frequent in STD clinic attenders, homo-
sexual men, and prostitutes for many years,
78–80
and is commoner in patients with more sexual
partners or a past history of STI in both
homosexual
81–83
and heterosexual groups.
83
An-
tigen has been found in both semen and
saliva,
84
and also in faeces,
85
although this has
not been confirmed by all investigators.
86
Experimental transmission of hepatitis B has
followed intradermal inoculation of saliva (in
gibbons), but not after oral inoculation.
87
Although sexual transmission is felt to be an
important route for the spread of infection in
heterosexuals
88
the nature of the contact has
not been addressed. More information is avail-
able on the relative risks of diVerent sexual
practices in homosexual men. The role of oro-
anal contact is probably important as a risk for
transmission from anus to mouth.
82 85
Trans-
mission may be from faeces or from asympto-
matic rectal bleeding which has been reported
in homosexual men
85
and this would correlate
with Kingsley and colleagues’ finding of a
higher risk from insertive than receptive anal
intercourse.
89
Receptive oro-genital contact
with more than 25 partners was associated with
hepatitis B infection in another series
81
al-
though the risk of transmission in this group
may be confounded by the large number of
partners. Kingsley et al
89
and Schreeder et al
82
failed to find an association between receptive
oro-genital sex and HBV infection.
HEPATITIS A
As hepatitis A is an enteric pathogen and is
excreted in the stools in high concentrations, it
is not surprising that rates of infection are
higher among homosexual men who report
oro-anal contact. In Seattle the annual inci-
dence was found to be 22% among seronega-
tive individuals and there was a correlation
between acquisition of hepatitis A and oro-anal
contact, and also with increasing numbers of
partners.
90
Epidemic outbreaks aVecting ho-
mosexual men have occurred
91 92
and these also
suggest that the oral role in oro-anal contact is
the predominant risk, while oro-penile contact
is unimportant.
HEPATITIS C
Sexual transmission in hepatitis C infection is
uncommon.
93 94
Transmission is linked to the
8 Edwards, Carne
presence of both hepatitis B and HIV which
may act as cofactors, and a slightly higher
prevalence of infection has been reported in
homosexual men in one study.
95
Receptive oro-
genital contact with more than 25 partners was
marginally associated with infection (OR 2.4),
with a similar association with more than 50
partners per year (OR 2.1) and more than 25
anal receptive partners (OR 1.9).
81
Miscellaneous
MOLLUSCUM CONTAGIOSUM
These are commonly found on the genitalia in
adults,
96
and are frequently found on the face in
homosexual men with AIDS.
97
This could rep-
resent spread from the skin around the genital
area during oro-genital contact.
KAPOSI’S SARCOMA
A new herpes virus designated human herpes
virus 8 (HHV8) has been isolated from patients
with Kaposi’s sarcoma.
98
One study has found
oro-anal contact to be a risk factor for Kaposi’s
sarcoma in homosexual men.
99
Conclusion
It is biologically plausible that transmission of
HIV takes place through oro-genital sex from
penis to mouth and vagina to mouth. This
conclusion is supported by case reports.
Further case reports suggesting transmission
from mouth to penis are open to question on
the basis that they are biologically less plausible
unless blood stained saliva was involved.
Epidemiological evidence indicates that oro-
genital sex poses substantially less risk of HIV
infection than vaginal and anal intercourse.
Receptive oro-genital sex is also a risk factor
for acquisition of human papillomavirus and
possibly hepatitis C. Insertive oro-genital sex is
a risk factor for acquisition of HSV 1 on the
genitalia. Oro-anal sex, with transmission to
the mouth, occurs with hepatitis A and B.
Transmission of other viruses by oral sex is
plausible but unproved.
The use of condoms or dental dams should
be discussed with patients to minimise their
risk of acquiring infection.
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10 Edwards, Carne
