Cook, Robert L. MD, MPH*; Clark, Duncan B. MD, PhD†
DOES CONSUMPTION OF ALCOHOL increase the risk of acquiring a sexually transmitted disease (STD)? The association may appear to be obvious and has been reported throughout history. In 1901, a study in the Journal of the American Medical Association concluded that alcoholic indulgence was related to over half of newly diagnosed syphilis infections,1 and in 1910, government officials took multiple steps to limit access to alcohol among active duty troops in an effort to prevent venereal diseases.2 More recently, a report from the Institute of Medicine implicates alcohol consumption as a primary factor associated with STDs among young persons.3 Yet, on closer examination, relatively few research studies have specifically examined the relationship between alcohol consumption and STDs, and many of those have not found a significant association.
A major limitation of much of the existing research on the relationship between alcohol consumption and STDs is the frequent use of very general measures of alcohol consumption (e.g., “any alcohol consumption” or “ever drank alcohol”). Such broad-based measures combine persons with many types of drinking, and one can readily imagine that drinking to intoxication at parties could lead to a very different risk of STDs compared with drinking an occasional glass of wine with dinner. Because different drinking patterns are unlikely to have a similar impact on current risk of STDs, combining all types of drinking behavior in a single measure could lead to erroneous conclusions.
Although problem drinking has been associated with other adverse health risks and behaviors, clinicians counseling persons about STD prevention may neglect to discuss alcohol consumption or mention it only casually. Without convincing evidence that problematic alcohol consumption is indeed a significant risk factor for STDs, clinicians and prevention experts have little incentive to aggressively screen for alcohol problems and incorporate alcohol drinking into prevention messages. We therefore conducted a systematic review of the literature to evaluate whether there is sufficient evidence to conclude that there is an established association between alcohol consumption and STDs, and whether this relationship appears to vary by gender or by specific patterns of alcohol consumption.
Our primary search strategy sought articles that assessed for any risk factor for any STD, regardless of whether alcohol consumption was mentioned in the title, abstract, or MESH terms. The primary search was conducted on MEDLINE (Ovid) dating from 1995 to March 2003. Specifically, our search combined terms on STD detection (medical subject heading [MESH] terms: chlamydia infections [epidemiology], gonorrhea [epidemiology], condylomata acuminata [epidemiology], genital diseases, female [epidemiology], genital diseases, male [epidemiology], sexually transmitted diseases [epidemiology], sexually transmitted diseases, bacterial [epidemiology], Trichomonas vaginitis [epidemiology], trichomonas infections [epidemiology], herpes genitalis [epidemiology], or syphilis [epidemiology]) together with articles that assessed for risk factors (MESH terms: risk factors, prevalence, incidence, multivariate analysis, odds ratio, or cross-sectional studies). This search strategy identified 1744 titles of articles published in English. An additional 33 candidate articles were identified through review of article references dating back to 1991, providing a total of 1777 articles and abstracts.
From the 1777 identified articles, we excluded 1562 articles from further consideration because of: 1) the absence of clinical outcome data (e.g., editorials, reviews, commentaries, mathematical models, decision analyses); 2) the outcome was not a STD (e.g., sexual behavior, Chlamydia pneumoniae infection); 3) the STD was one often acquired through nonsexual means (e.g., HIV, hepatitis B, bacterial vaginosis); 4) the article focused on a diagnostic test or microbiology assessment; or 5) the study did not assess any risk factors. We then examined the full text of 205 articles and excluded an additional 163 because the study did not include a measure of alcohol consumption, alcohol consumption could not be clearly distinguished from other drug use, or the study included the same participants from another identified article. The final 42 articles were then assessed in further detail.
From each article, we extracted data on study population characteristics (number, age, gender, race/ethnicity), study setting, alcohol consumption measure, and STD outcome measure. Study results were generally reported as unadjusted or adjusted odds ratios or risk ratios. If data were not presented in this manner, we used original data from the article and STATA 7.0 (College Station, TX) to calculate odds ratios or risk ratios with corresponding 95% confidence intervals. When available, we obtained results for specific subgroups of participants (e.g., gender, type of STD, or pattern of alcohol consumption). If an article reported results for increasing levels of alcohol consumption, we extracted data comparing the highest level versus all lower levels of alcohol involvement.
All studies were grouped into 1 of 4 types of alcohol consumption measures: 1) “any alcohol” (yes/no), 2) quantity and/or frequency, 3) alcohol use in a specific situation, or 4) a measure of problem drinking. Measures in the first 3 categories were considered to be general consumption measures that combined both problem drinking and nonproblem drinking. Problem drinking included any specific drinking pattern that has been shown to be associated with harmful clinical or social outcomes. Specifically, problem drinking was defined as binge drinking (5+ drinks for men, 4+ drinks for women),4 high quantity/frequency (>7 drinks/week for women, >14 drinks/week for men),5 being drunk or intoxicated, or having alcohol-related problems or disorders.
The identified studies were very heterogenous in terms of alcohol consumption pattern, STD outcome, and study population; thus, we did not calculate any summary estimates using metaanalysis. Instead, we present summaries of all eligible studies, together with additional detail of the studies that included specific alcohol measures consistent with problem drinking.
Eleven articles included specific measures of problem drinking (Table 1).6–16 Eight of these found a significantly increased risk of at least 1 STD among problem drinkers, and the other 3 studies found no statistically significant increase or decrease. Details of these 11 studies follow.
Shafer et al. conducted a cross-sectional study of 414 male adolescents in a youth detention center; the majority were black (65%).6 All participants were asked whether they had “ever had an STD” (self-report), and the majority (65%) underwent current testing for chlamydia and gonorrhea (urethral culture), syphilis (serology), hepatitis B (serology), or genital warts (clinical examination). Alcohol consumption was assessed using the quantity and frequency of standard drinks consumed in the previous 3 months. Compared with youth who did not drink, those reporting daily drinking (13% of the sample) were more likely to have a current or past STD (odds ratio [OR], 3.53; 95% confidence interval [CI], 1.61–7.2). In a multivariate analysis controlling for lifetime number of sexual partners and low condom use, heavy drinking (20 or more drinks per week) was associated with an increased risk of STD, compared with nondrinkers (OR, 2.23; 95% CI, 1.08–4.62). One limitation of the study was the combining of self-reported STD together with objective clinical and laboratory data, because the self-reported data may decrease the validity of the outcome measure.
Ericksen and Trocki analyzed data from the 1990 National Alcohol Survey, which used a probability sample of adults in the 48 contiguous United States.7 The sample included 882 men and 979 women. STDs were assessed by the question “Have you ever had a sexually transmitted (venereal) disease (for example, syphilis, gonorrhea, genital herpes, genital warts, chlamydia)?” The survey also included several alcohol assessment measures, including binge drinking (5 or more drinks in 1 sitting on at least a weekly basis over the past year) and problem drinking (having 3 or more of 8 major symptoms associated with alcohol abuse or dependence). Binge drinking was associated with an increased risk of STD in men, but not in women; the increased risk in men did not persist in multivariate analysis. However, having ≥3 symptoms of drinking was associated with an increased risk of STD in both men and women, and these results remained significant in multivariate analysis. Limitations in this study included a self-reported measure for STD and difficulty determining the temporal relationship between current drinking and a lifetime STD.
Ellen et al. conducted a cross-sectional study of 1442 heterosexual men and women attending public STD clinics in 3 U.S. cities.8 In this sample, 61% were male, 70% were black, and the mean age was 27. Participants all received laboratory and clinical assessments for gonorrhea and syphilis, and all reported how often they were drunk from alcohol during sex in the prior 3 months. Men who reported being drunk before sex were slightly more likely to be diagnosed with gonorrhea (OR, 1.14; 95% CI, 1.02–1.29), but this result did not remain significant in multivariate analysis. There was no relationship between being drunk during sex and syphilis among men, or for gonorrhea or syphilis among women. Limitations in this study include the somewhat limited generalizability of this high-risk population (over one fourth of the sample were current users of crack cocaine), lack of reliability and validity information on the alcohol variable (being drunk before sex in the previous 3 months), and a sample size that may not have been sufficient to detect moderate differences in syphilis infections (fewer than 5% of the subjects had syphilis).
Zhang et al. conducted a cohort study using data from 16,797 women aged 25 or older who attended a screening program for cervical cancer in China between 1974 and 1985.9 The presence of trichomonas was determined by Pap smears obtained at baseline and then every 2 years (each woman had an average of 3.5 screenings). Alcohol consumption was measured at baseline according to the number of drinks per week (0, 1–9, 10 or more) and the number of years of drinking (0, 1–9, 10 or more). Compared with women who did not drink at baseline, the relative risk (RR) of an incident trichomonas infection was 1.7 (95% CI, 1.30–2.23) among women who drank 1 to 9 drinks per week and 0.69 (95% CI, 0.22–2.15) among women who drank 10 or more drinks per week. It was not clear why the risk of trichomonas appeared to be greater among moderate drinkers compared with heavier drinkers. Limitations in the study include the relatively low sensitivity of Pap testing to detect trichomonas and the potentially large time difference between baseline assessment of alcohol consumption and incident trichomonas infection (detected up to 9 years later).
Chokephaibulkit et al. conducted a case–control study among a group of pregnant adolescents in Tennessee.10 Cases (n = 67) were pregnant adolescents who were diagnosed with chlamydial infection (by culture) at their first prenatal visit. Pregnant adolescents of similar age and socioeconomic background who presented for their first prenatal visit on the same day, but were not infected, served as controls (n = 53). All participants completed a questionnaire that assessed for “alcohol abuse”; no specific details of the measure were included. The prevalence of alcohol abuse was 33% in the cases and 39% in the controls, a difference that was not statistically significant. The study’s limitations include a relatively small sample size and an unclear definition of “alcohol abuse.”
Wilson et al. conducted a prospective study among 677 women, 232 of whom had HIV infection.11 All were recruited from clinical and community-based settings in Brooklyn between 1990 and 1994; the mean age was 32 years and the majority (86%) were black. Participants were tested for chlamydial and gonococcal infections (cervical culture) and trichomonas infection (vaginal culture) at baseline and then every 6 months during follow up. Incident infections were defined as new infections in persons with a prior negative test result, and the incidence rate for new STDs was approximately 13 per 100 person-years. Alcohol consumption was defined by the self-reported number of times per week participants drank alcohol measured on a 7-point scale ranging from “never” to “more than 4 times a day” (based on a 1-year time period). In a Cox regression model predicting STD incidence, there was a slightly increased risk of a new STD with each consecutive level of alcohol consumption frequency, although this result was not statistically significant (RR, 1.09; 95% CI, 0.97–1.22).
Miranda et al. conducted a cross-sectional study among 121 women in a prison in Brazil (mean age, 30 years).12 All participants received assessments for STDs, including gonorrhea (cervical culture), chlamydia (enzyme-linked immunosorbent assay), syphilis (Venereal Disease Research Laboratory [VDRL] screening with confirmation), human papillomavirus (HPV; assessed by the presence of squamous intraepithelial lesions on a Papanicolaou smear from the cervix), and trichomonas (vaginal wet mount). Participants completed a survey that assessed whether the participant “ever abused alcohol”; 49% of the sample responded affirmatively. Having “ever abused alcohol” was significantly associated with syphilis infections (OR, 2.0; 95% CI, 1.1–5.5), but not with chlamydia, gonorrhea, trichomonas, or HPV. The study has several methodologic limitations, including the small sample size, limited generalizability, vague definition of alcohol abuse, and use of Pap testing to assess for HPV infection.
Mehta et al. conducted a study among male and female patients who attended an urban emergency department in Baltimore for medical treatment of any nature.13 Participants provided a urine sample that was used to test for gonorrhea and chlamydia using ligase chain reaction (LCR). Patients were also administered the 4 CAGE questions (a screening test for alcohol abuse and dependence). In analysis restricted to participants aged 18 to 31 years old, 2 alcohol questions were associated with an increased risk of STD in men: “ever been annoyed by others criticizing your drinking” and “ever had a drink first thing in the morning.” The second question remained a significant predictor in men in multivariate analysis. None of the alcohol questions were predictive of STD in women. Limitations of the study include difficulty with temporal relationships (“ever” having alcohol problems vs. “current” STD).
Miller et al. conducted a cohort study of 1034 Aboriginal people from a central Australian community; 53% were female and 60% were currently married.14 The sample included all persons aged 12 to 40 who were seen at least twice between 1996 and 1998 for STD testing at any of 9 public clinics. All received laboratory testing for chlamydial and gonococcal infections (using a urine-based polymerase chain reaction assay) and syphilis (serology). Incident STDs were identified among those who had a previous negative result or who had received treatment for STDs at least 4 weeks previously. Alcohol abuse was defined as “binge drinking or regular heavy use” according to Aboriginal health workers, and 36% of the population was classified as abusing alcohol. Persons with alcohol abuse were significantly more likely to have an incident gonococcal infection (RR, 1.46; P = 0.007), but there was no significant association with chlamydial infections (RR, 1.18; P = 0.28) or syphilis (RR, 0.63; P = 0.42). The limitations of this study include its limited generalizability outside Aboriginal communities and the unclear reliability and validity of the alcohol consumption measure.
Thomas et al. conducted a cross-sectional study among 299 U.S. Navy-enlisted women in southern California.15 The mean age was 26 years; 61% were white and 51% were married. All participants received chlamydial testing by a urine-based LCR assay, and the overall prevalence was 4.7%. Problem drinking, defined as “consuming alcohol until you passed out or vomited” within the previous 30 days, was reported by 5.4%. The prevalence of chlamydia among women with and without this drinking pattern was 21.4% versus 4.6%, with an odds ratio of 6.6 (95% CI, 1.6–27.8) after adjusting for current pregnancy.
Cook et al. conducted a cross-sectional study among 240 young men and women participating in a longitudinal study of adolescents with alcohol use disorders.16 Participants were recruited from clinical and substance abuse treatment settings, together with a control sample recruited from the general population. Participants each completed a clinical diagnostic interview to assess alcohol abuse or dependence, and provided a serum sample that was initially stored and later assayed for herpes simplex virus type 2 (HSV-2) infections. The prevalence of HSV-2 among 120 young women was 19%; none of the 120 young men were seropositive for HSV-2. The adjusted odds ratio for HSV-2 among women with an alcohol use disorder was 8.1 (1.5–44.8). Limitations of the study include the use of serology to assess STD, because the STD could have been acquired many years earlier, the relatively small sample size, and the absence of HSV-2 infection in male subjects.
Studies With General Alcohol Measures
Thirty-one studies were identified that assessed general measures of alcohol consumption (Table 2).17–47 Eight studies used very general measures of “any alcohol use.” Of these, 5 found a significant association with at least 1 STD,20–24 whereas the other 3 found no significant association.17–19 Sixteen studies reported on quantity and/or frequency. Nine of these found a significant association with at least 1 STD,27,28,30,31,33,34,36,38,40 6 found no significant association,25,26,29,32,37,39 and 1 found alcohol consumption to be associated with a decreased risk of STD.35 Eight studies reported on situational measures of alcohol consumption; 4 of these found an increased risk of STD28,43,46,47 whereas 4 found no significant association.41,42,44,45 As noted in Table 2, there was no significant pattern of risk according to the study population (e.g., gender, setting) or STD assessed, although alcohol consumption was associated with chlamydial infection in only 1 of the 7 studies that reported separate results for chlamydial infection.
The purpose of this review was to systematically evaluate the literature on the relationship of alcohol consumption to STDs. Although hazardous drinking has already been linked to several adverse health and behavioral consequences,3 clinicians evaluating patients at risk for STDs and HIV infection often fail to address this common behavior. Moreover, the precise relationship between alcohol and STDs was unclear, because several individual studies had not found a significant association between alcohol and STDs. A final goal of the article was to identify strengths and limitations in the current literature (such as problems with measurement) and to inform future research in this area.
We identified 42 articles that assessed the relationship of alcohol consumption and STDs.6–47 Of these, only 11 included a measure of alcohol consumption that could be used to identify problem drinking and thereby be sufficiently informative to make a reasonable conclusion about the relationship of problem drinking to STDs.6–16 Eight of these 11 studies found an increased risk of STD,6–8,12–16 and the other 3 found no significant association.9–11 Of these 3, 1 had a very small sample size,10 another used a very insensitive measure of STD,9 and the third just missed achieving statistical significance.11 Taken together, these results suggest that problem drinking is clearly associated with an increased risk of STDs across a wide variety of populations. The results from the studies with general measures of alcohol consumption were similar, with the majority finding a significant association with at least 1 STD.
The 42 articles we reviewed included over 30 different types of alcohol measurement descriptions, making it difficult to come up with clear conclusions about which particular pattern of alcohol consumption is associated with the greatest risk. Many articles used very general measures of alcohol consumption such as “any” versus “none.” These general measures combine persons with true problem drinking together with persons who occasionally drink or who may have small amounts of alcohol with their meals. These general measures are grossly inadequate to test the hypothesis on whether problematic alcohol consumption influences STD risks. Some of the measures assessed drinking in specific situations related to sexual activity (e.g., ever drank before sex), but most of these were also classified as general, because they inquired about any such activity over a period of time. Even among those studies that did use a specific measure, only 1 used a structured clinical interview with published sensitivity and specificity.16
Is the Association Causal?
Alcohol consumption might directly cause an increased risk of STD by its effects on behavior,48 sexual arousal,49 or by adverse effects on the immune system.50 It is also possible that both alcohol consumption and STDs are linked to a third, confounding variable (e.g., “sensation-seeking”) that represents the true causal factor.51 Typically, the strongest evidence of a cause–effect relationship comes from randomized, controlled trials. However, both practical and ethical reasons limit the ability to conduct randomized trials to directly assess the impact of alcohol consumption on STD outcomes. To date, all of the literature on this topic has used an observational study design, including cross-sectional, case–control, or cohort study.
To further assess the extent to which cause–effect relationships may be inferred here, we considered principles first proposed by Hill52 and later modified by an expert panel within the U.S. Public Health Service.53 These principles include: 1) temporality (Does the exposure proceed the outcome of interest?), 2) biologic plausibility (Is the suspected cause–effect relationship biologically plausible?), 3) consistency (Have the observed associations been repeated by different investigators?), 4) Alternative explanations (Have alternative explanations for an association been sufficiently explored?), 5) dose–response relationship, 6) strength of association between the exposure and the clinical outcome, and 7) experiment (Does removal of the exposure prevent the outcome of interest?).
The issue of temporality is very difficult to assess in the current literature, because one would ideally like to know whether alcohol consumption immediately preceded the specific sexual situation during which an individual contracted an STD. Many studies inquired about lifetime alcohol consumption or lifetime acquisition of STDs, making temporal assessments nearly impossible. Even cohort studies that assess the relationship between drinking at 1 time point and STD acquisition at a future time point cannot prove that alcohol consumption directly proceeded disease acquisition. Similarly, an affirmative response to situational question such as “Have you been drunk during sexual intercourse in the past 6 months?” does not mean that the person acquired the STD during that particular sexual event.
For biologic plausibility, one can identify several possible mechanisms by which alcohol consumption could directly lead to an increased risk of STD. Although alcohol consumption does not by itself cause an STD, it can directly affect risk either by increasing the risk that one is exposed to an STD through risky sexual behavior or selection of high-risk partners.48,54–56 Another plausible mechanism is that alcohol consumption might increase the biologic susceptibility to an STD if exposed, through adverse effects on the immune system or other direct biologic changes.50,57 Consistency is 1 criteria that is demonstrated by the present review: alcohol consumption has been associated with an increased risk of STD among a variety of population characteristics, including gender, clinical setting, drinking pattern, and STD type. Many of the studies we reviewed assessed for alternative explanations by conducting multivariate analyses that controlled for other drug use, specific sexual behaviors, and other population characteristics. Controlling for these factors had an inconsistent impact on the association of alcohol and STDs, with some associations becoming nonsignificant and others remaining significant after controlling for these other factors.
A few studies examined for a possible dose–response relationship by calculating risks associated with increasing quantity and/or frequency of alcohol consumption. In general, these studies did not show any consistent findings of a biologic gradient, but the absence of this does not rule out the possibility of a causal relationship. The strength of the relationship varied among studies, with some studies finding no significant association, and others finding significant associations with odds ratios ranging from 1.1 to 8.1. We are not aware of any study that has evaluated the impact of cessation of alcohol consumption on future outcomes related to STDs. Such evidence would be very important in the assessment of a true causal link between problem drinking and STDs.
If alcohol consumption does not have a cause–effect relationship with STDs, the observed associations could be explained by a common third variable such as a personality trait (e.g., general risk-taking, sensation-seeking); or the association may reflect a more global association of problem drinking to social and sexual networks and partnerships58–60 or to neighborhood characteristics.61 Indeed, 1 study found a strong association between the number of alcohol beverage sales outlets and rate of gonorrhea.62
Implications for Research
Although we could not uniformly assess study quality, bias related to study design, measurement, and publication could impact the findings. Very few studies used measures of alcohol consumption with known reliability or validity, and only 1 used a validated clinical assessment for alcohol abuse or dependence.16 Future research on this topic should use clearly defined, specific measures of problematic alcohol consumption.63 Measures of STDs also varied in their reliability and validity, and included laboratory assessments of current infections, serology to assess antibodies to an STD (which documents lifetime acquisition of an infection), and self-report (which occasionally has poor validity). The majority of studies were cross-sectional, which limits the ability to determine whether alcohol consumption proceeded acquisition of an STD. Several investigators have used event-specific analyses to examine situational links of alcohol consumption to risky sexual behavior (such as nonuse of condoms). In general, these analyses have had inconsistent conclusions.55,64 To our knowledge, none of the studies to date have applied an “event-specific” approach to the association of alcohol consumption with STD acquisition; instead, all the studies report only on general associations.
Regardless of whether alcohol consumption is the true risk factor, or a marker for some other behavior, the literature to date suggests that persons with higher levels of alcohol consumption are generally at higher risk for STDs. Therefore, interventions may be helpful in reducing their risk. The next series of research studies should focus on identifying the specific mechanisms by which alcohol consumption does lead to an increased risk of STD and on developing effective prevention interventions. To date, we are not aware of any results from a randomized, controlled trial showing that a decrease in alcohol consumption will lead to a reduced risk of future STDs. Results from such a trial would contribute substantially to our understanding of the potential causal link between alcohol consumption and sexually transmitted infections.
Implications for Prevention and Treatment
Alcohol consumption is restively common among young persons, is widely perceived to be associated with STDs, and represents a potentially modifiable risk factor. Although hazardous alcohol consumption is recognized to be harmful by many clinicians and public health officials, many clinicians fail to address alcohol consumption as part of their STD/HIV prevention strategies. This may be especially true in settings such as STD clinics or family planning clinics where the focus has traditionally been on a single health issue. The finding that problematic alcohol consumption is associated with an increased risk of STDs in a variety of populations and settings should be seen as a wakeup call to clinicians who see patients at risk for STDs and HIV, regardless of the type of clinical venue. As concluded in a recent review, “despite the high coincidence of substance abuse and sexual activity, including risky and violent sexual activity, remarkably few public or private prevention, treatment and counseling programs attend to the connection.”48
In summary, the available literature consistency confirms that problematic drinking is associated with an increased risk of STDs, and this risk is present for both men and women. Prevention interventions can be implemented to target individuals, clinicians, healthcare systems, or communities. Individuals who drink alcohol can be educated about the particular risks that may lead to increase STD risk and be encouraged to develop a plan or a buddy system to avoid unwanted sexual contacts when drinking alcohol. Clinicians should screen for alcohol problems among persons at risk for STDs, educate about the potential health benefits resulting from decreased consumption, and suggest treatment options for those who are seriously impaired. The healthcare system can assist by easing the ability to screen for alcohol problems in a variety of settings and combining services for alcohol problems together with STD services in a variety of healthcare environments such as STD clinics. Community-based interventions that reduce alcohol consumption could impact on STD rates (e.g., raising beer prices, reducing the number of alcohol outlets, banning alcohol in campus dormitories), but such interventions have not been evaluated in a systematic manner. As noted in a recent assessment by the Institute of Medicine, a multipronged approach may be most effective.3
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