Sexually transmitted infections in women

Abstract

Sexually transmitted infections (STIs) are highly prevalent and cause a wide spectrum of disease. However, the majority of these infections may be unrecognized due to lack of overt signs or symptoms of infection. Asymptomatic infections remain significant as a result of the potential for long-term sequelae, predominately in women, and the risks of complications during pregnancy as well as mother-to-child transmission. Laboratory diagnostics play an important role in identifying infection and in public health efforts to reduce the prevalence of these diseases. Serologic diagnosis is appropriate for syphilis and, in some settings, for herpes infections. However, the organisms that cause discharge such as Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis and Mycoplasma genitalium are best diagnosed using molecular assays. Currently available molecular assays are suitable for use with non-invasively collected sample types, most notably vaginal swabs for women thus expanding the potential reach of STI control programs to include non-clinic based screening.

Key Words::

• Chlamydia trachomatis
• herpes simplex virus
• molecular diagnostics
• Mycoplasma genitalium
• Neisseria gonorrhoeae
• serology
• syphilis
• Trichomonas vaginalis

Introduction

Sexually transmitted infections (STIs) are caused by a variety of pathogens, including protozoa, bacteria and viruses, which share a common mode of transmission. As a result of this diversity in the number and type of organisms, the potential manifestations of disease are varied and the medical disciplines that manage these infections are also varied and include dermatology, obstetrics/gynaecology, family practice, reproductive health and infectious diseases. The World Health Organization (WHO) groups the curable STIs (Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis and syphilis) for surveillance purposes and routinely provides data regarding the estimated global prevalence of these infections. The most recent WHO report estimated that nearly 500 million cases of curable STI occurred worldwide in 2008, representing an 11.3 % increase compared to estimates from 2005 [1]. In addition to the curable STIs, herpes simplex virus (HSV) affects an additional 500 million people, nearly 300 million women have human papilloma virus (HPV) and over 35 million people are living with human immunodeficiency virus (HIV). Thus, STIs affect a substantial portion of the global population resulting in poor health and a burden on limited healthcare resources. Below I will describe the basic disease manifestations, epidemiology, and current diagnostic options for the infections listed above with the exceptions of HPV (this viral infection is discussed in detail in conjunction with cervical cancer in the article by Petry in this issue) and HIV (this is considered a separate discipline that would warrant an entire review dedicated specifically to this pathogen).

As a result of the mode of transmission, STI by definition affect both men and women. However, framing a discussion of STI in the context of women's health is appropriate for a number of reasons. First, these infections often cause disease differently in women than in men. For example, a number of infections are asymptomatic in women and thus less likely to be detected and treated in the absence of screening programs that test women on a routine basis. Second, with many STIs, women are at much higher risk of adverse consequences of untreated infection such as pelvic inflammatory disease and tubal factor infertility. Thirdly, STIs present risks for negative outcomes of pregnancy and mother-to-child transmission of infections during pregnancy or labor and delivery. Finally, STIs continue to be highly stigmatized infections in many cultures where women are particularly vulnerable to negative social outcomes when diagnosed with an STI. The common risk factors for infection with any of these organisms include non-condom use, increased numbers of sexual partners, and new sex partners. STIs have been historically linked to sex work or promiscuity. While men suffer very little from the intimation that they have had a large number of sexual partners or have had sex with a sex worker, women may suffer the risk of physical or legal harm. This risk is present even in the event that a monogamous woman obtained an infection from her partner (i.e. she may still suffer the blame regardless of her actual behaviors). One of the strategies that will minimize the negative outcomes of STI in women is to institute routine screening programs that provide diagnostics independent of behavioral risk such as during the first trimester of pregnancy, when providing cervical cancer screening, and during reproductive and family planning healthcare visits. Such screening programs will identify asymptomatic infections, avoid negative outcomes during pregnancy and begin to frame testing as a health maintenance activity. As a result of advances in molecular diagnostics for most STI, now is the time to implement such screening programs in many healthcare and community-based settings and to encourage self-directed screening using home-based sample collection options.

Genital ulcer disease

Genital ulcer disease (GUD) may be caused by a number of pathogens, most notably Treponema pallidum, the causative agent of syphilis; herpes simplex virus (types 1 or 2); Haemophilis ducreyi, the causative agent of chancroid; and C. trachomatis, lymphogranuloma venereum strains. The latter two infections are rare, particularly among women and will not be discussed in this review. For additional information see reviews by Lewis [2] and Mabey [3]. GUD, as a syndrome, has been strongly associated with substantially increased risk for HIV acquisition. Syphilis, while not highly prevalent, may have devastating consequences if left untreated while HSV is a highly prevalent virus which is an important biological risk factor for HIV acquisition. Identification and management is complicated by the fact that while, by definition, GUD requires the presence of lesions, and these infections remain present and transmissible even in the absence of symptoms.

Herpes simplex virus

HSV types 1 and 2 affect over 500 million adults globally [1]. The majority of infections (with either type 1 or 2) are asymptomatic leading to increased potential for transmission. When symptoms are present they include painful vesicles or pustules that evolve into ulcers. Primary infection may also cause dysuria or discharge (vaginal or urethral) and thus HSV primary infections may be misdiagnosed as one of the discharge-causing STI. Periods of latency are followed by recurrence of lesions over the course of the first year in almost all patients with reductions in the frequency and intensity of recurrences over time. Clinical diagnosis is complicated by the variability in appearance of the lesions with frequent misclassification in both directions: labeling non-herpes lesions as HSV and not recognizing lesions caused by HSV [4]. Thus, laboratory diagnostics provide necessary information for appropriate management of disease. Effective treatment is available that will not cure HSV infection, but can reduce the frequency and severity of outbreaks. Treatment is particularly important for pregnant women with primary herpes infections in order to prevent neonatal herpes; a potentially devastating, and in some cases, life-threatening disease.

Until recently, laboratory diagnosis has relied on culture from active lesions and serologic testing. Culture in traditional cell lines required that samples be transported in compliance with strict cold-chain requirements and up to 3 weeks to obtain a negative result. Enhanced culture methods using genetically engineered cell lines are more rapid and more sensitive (approximately 75 %) and easier to interpret microscopically. However, mixed infections can be identified only as HSV type 2. Given the increase in genital infection with HSV-1, and the potential for different management strategies based on strain types, accurate typing provides useful information to clinicians. Currently available serological assays suffer from a lack of specificity that varies by population. While serology is a potentially useful tool for epidemiologic studies, use for diagnostic purposes requires careful calibration within the local population to avoid positive results based on cross-reactive antibodies to other infections.

We now have access to molecular diagnostic methods that are highly sensitive and detect and distinguish both type 1 and 2 from samples of lesions [5]. As with most molecular assays, the samples are robust and do not require cold-chain transport from the collection site to the laboratory. Time to results is reduced from weeks to <8 hours of laboratory time. As molecular diagnostics in general move toward rapid, point-of-care formats, more women may be able to know their HSV status by accessing rapid diagnostics and therefore engage in appropriate protective behaviors. Given the approximately 4-fold increase in risk of HIV acquisition in women with HSV-2 [6], access to improved HSV diagnostics will allow targeted counseling for women regarding strategies to protect themselves against HIV and may have a measurable impact on HIV transmission world-wide [7]. Unfortunately, at this time molecular diagnostics for HSV are only available for patients with active lesions and thus not appropriate for asymptomatic screening. Additional development of new diagnostic tools, including improved serology, is needed in order to reduce the global burden of HSV and its impact on the HIV pandemic.

Syphilis

Syphilis is relatively uncommon compared to other treatable STIs, however the WHO estimates that 10.6 million cases occurred in 2008 [1]. The consequences of untreated syphilis may be severe and include genital ulcers; rash; alopecia; pulmonary, cardiac and neurologic complications; or spontaneous abortion. For clinical reviews, see Read and Donovan [8]. The frequency of mother-to-child transmission ranges from 10−>70 % depending on the stage of the disease. Congenital syphilis may result in grave birth defects and poor outcomes, including high infant mortality rates, for neonates [9]. Therefore, screening pregnant women should be a health priority in all settings.

Molecular diagnostics have been developed for detection of T. pallidum from genital ulcers, however, low prevalence of disease in most settings, poor sensitivity and the rarity of seeing ulcers during clinical visits have resulted in a lack of commercial interest in further development. Syphilis serology remains the most widely used diagnostic method and is usually a staged process. Syphilis diagnosis is complex due to the need to interpret the serological results within the context of individual behaviors. Serum is tested with a non-treponemal specific assay (usually the rapid plasma reagin (RPR) agglutination test or the Venereal Disease Research Laboratory (VDRL) slide test) which generally remain positive for life following a syphilis infection. High titres may provide an indication of recent or active infection, however false positive may also occur due to the lack of specificity of these tests. Therefore, RPR or VDRL results should be confirmed using a Treponema specific assay. Traditionally the T. pallidum Hemagglutination Assay (TPHA) or the Fluorescent Treponemal Antibody (FTA) tests, which are highly specific for T. pallidum have been used to confirm current infections since these assays will become negative in most people following successful treatment. With the availability of chemiluminescent assays specific for T. pallidum that can be run on automated platforms in batches of > 96 samples, many laboratories now follow a reverse algorithm for testing in which treponema specific assays are run first and confirmation of infection is performed using a non-Treponema specific assay. This allows high throughput screening which is essential for blood bank screening, but perhaps less relevant for screening pregnant women and women at risk for other STIs. Global efforts to provide improved screening options that can be used in settings with limited access to reference laboratories have resulted in a number of promising rapid, point-of-care (POC) assays [10,11], some of which are combined with a rapid HIV assay in a single cassette requiring a single finger-prick blood sample to provide both results. POC assays have advantages that may offset slightly lower specificity in the case of syphilis control. Among the important activities of syphilis control efforts are tracing sexual contacts, large-scale screening of populations of identified risk (the factors involved change with each outbreak) and testing of all pregnant women in areas experiencing high burden of disease. POC assays allow field-based testing with the possibility of immediate follow-up which may include treatment, sample collection for additional confirmatory testing and the opportunity to interview the patient immediately to identify sexual contacts who may be at risk. Such strategies may reduce the overall time of infectiousness and transmission events in the population. Syphilis elimination remains an achievable goal and improved diagnostic tests are tools that will be essential in this effort.

Discharge-causing diseases

Discharge-causing diseases that are sexually transmitted include C. trachomatis, N. gonorrhea, T. vaginalis and Mycoplasma genitalium. In women, these infections share common features such as abnormal discharge (either cervical or vaginal), pain on urination, itching, pelvic pain, and pain during coitus. However, these infections may often be asymptomatic, particularly in women. Furthermore, if left untreated, these infections, particularly C. trachomatis, may lead to pelvic inflammatory disease (PID), ectopic pregnancy, tubal factor infertility or complications during pregnancy. Gonococcal and trichomonal infections have both been strongly associated with increased risk of HIV [12]. Chlamydia and mycoplasma have been epidemiologically linked with HIV [7,13] although the association has not been as strong or consistent as the associations observed for gonorrhea and Trichomonas. Discharge may also result from an overabundance of C. albicans or the disruption of normal flora that results in bacterial vaginosis [14]. However, these discharge syndromes, while they may result from sexual activities, are not the result of sexual transmission of a single pathogen and thus will not be described in the sections below.

The molecular diagnostic era has created exciting opportunities for STI control. Recommendations from WHO, the Centers for Disease Control & Prevention (CDC) in the US and the European Centers for Disease Prevention & Control (ECDC) agree that molecular diagnostics should be used whenever possible for chlamydia and gonorrhea testing; both screening (testing asymptomatic populations) and diagnostic testing (determination of the cause of symptoms). This class of test is also optimal for both trichomonas and mycoplasma as these assays are becoming more widely available. The excellent sensitivity of molecular assays has allowed the expansion of acceptable sample types to include specimens that can be patient-obtained (i.e. vaginal swabs, urine, anorectal swabs and oropharyngeal swabs). Patient-obtained samples may be used for either home-based collection for annual screening or collection at non-clinic venues such as pharmacies, schools, detention centers and community-based health screening events. Testing of non-genital samples (anorectal and oropharyngeal) is becoming increasingly important as infections at these sites often go undetected due to the difficulty of specimen collection thus creating a reservoir of infections within the population.

Trichomonas vaginalis

T. vaginalis is the most common curable STI with WHO estimates of > 275 million cases per year. Interestingly the distribution of disease is different for trichomonas than what is routinely described for chlamydia and gonorrhea. Trichomonas age-specific prevalence appears to peak in women 40–50 years of age rather than in those 15–25 as seen for chlamydia and gonorrhea.[15] However, due to overall high prevalence, trichomonas is often more prevalent than chlamydia and gonorrhea even among younger women. Thus, screening for all three infections may be warranted in many settings.

Cases of trichomonal infection are observed in women approximately 4 times more often than in men. The reasons for this are both biological and related to sexual healthcare practices. The vaginal micro-environment is ideally suited for T. vaginalis to attached to the epithelium and reproduce successfully. The urethra is less suitable due to the fluid dynamics involved in urination. Once infection is established, it is more likely to persist in the vaginal environment. Further, men are rarely tested for trichomonal infection when presenting with non-specific urethritis. This is, in part, a reflection of the traditionally poor diagnostic capacity for detecting low organism loads from male samples (e.g. wet preparation microscopy). Cases in women are also under-diagnosed in many healthcare settings. The dogma that all women with trichomonas have symptoms has led to a strategy of only testing those women who have symptoms and thus, in a self-fulfilling prophecy, finding cases only in women with symptoms. This is also a reflection of poorly sensitive diagnostic methods that have served to discourage screening in asymptomatic women.

T. vaginalis may cause vaginal white, foamy discharge and, occasionally, the appearance of punctate cervical friability (a ‘strawberry cervix’). However, the discharge may be masked by concomitant disruption of the vaginal micro-environment such as yeast overabundance and bacterial vaginosis. Thus, clinical observation is often non-specific. When left untreated, trichomonas has been associated with PID and negative outcomes during pregnancy such as premature rupture of membranes and low birth-weight babies. Perhaps of most concern is the epidemiologic association between trichomonas and HIV. Numerous studies, primarily conducted in sub-Saharan Africa, have demonstrated increased odds of HIV acquisition (1.5–35 fold) in women regardless of the presence of symptoms [12]. In both men and women living with HIV, infection with trichomonas has been shown to increase the HIV viral load in the genital compartment [7], the single largest biological risk factor for transmission to an uninfected partner. The combination of high prevalence of infection with trichomonas and increased risk related to HIV suggest that improving trichomonas control efforts may be a useful strategy for reducing HIV risk in HIV-endemic areas of the world.

Accurate screening and diagnostic tests are clearly warranted for use in populations at risk for T. vaginalis infection, particularly HIV endemic populations. Diagnosis has traditionally relied on wet preparation microscopy of samples from women exhibiting symptoms. However, under ideal conditions wet prep detects only ∼50 % of infections, and conditions are often less than ideal. Culture has been improved by use of the InPouch culture system that is amenable to field collection and transportation to a reference laboratory for observation and assessment of growth. However, this system is time-consuming (up to 5 days for results) and relatively insensitive (∼70–75 %). Molecular assays are now available that can be performed using samples collected for chlamydia/gonorrhea screening. These include vaginal, endocervical and urine samples. Considering that this pathogen is often more prevalent than chlamydia and gonorrhea combined, it would appear reasonable to add this test to the menu of women's routine sexual health screening performed on a regular basis.

Chlamydia trachomatis

C. trachomatis remains the second most common curable STI in most settings (roughly 106 million new cases per year) [1] despite more than 30 years of global control efforts. Detection of infection is hampered by the frequency of asymptomatic infection (60–80 % in women). Clinical observations of chlamydia infection may include mucopurulent cervicitis or pelvic pain while patients may have complaints of itching, pain on urination, or coital pain. However, signs and symptoms are non-specific and are not present during the majority of infections. Thus, in many countries routine screening has been recommended for all women under the age of 26, women with a new sex partner since her last test, women in the first trimester of pregnancy, and women undergoing fertility evaluations.

Unrecognized, and therefore untreated, infections may result in PID, ectopic pregnancy and tubal factor infertility. Despite a lack of consistent and sustainable reduction in case rates, many countries have observed reductions in these sequelae [16] suggesting that infections are being identified and treated earlier and are resulting in fewer complications of infection. As mentioned above, the groups at highest risk for chlamydial infection are adolescents and young adults. Screening recommendations that target annual testing of women in this age range are likely responsible for reductions in complications resulting from untreated infections. However, the mixed impact of chlamydia control efforts, stable or increasing case rates but lower complication rates, may suggest that screening only one half of the population (women) in which the infection resides may not be as effective as desired.

All screening should be performed using molecular (DNA-or RNA-based) assays where resources to do so are available. Molecular diagnostics for chlamydia offer the advantages of multiple acceptable sample types, room temperature sample storage and transport, and excellent sensitivity and specificity. The CDC recommends use of vaginal swabs, and in particular self-obtained vaginal swabs, as the optimum specimen type for molecular STI diagnostics for women due to excellent sensitivity and acceptability to patients. Use of self-obtained samples allows programs to offer non-clinic based, including in-home, collection of samples which may encourage routine sexual health maintenance practices.

Molecular assays are now available on partially or fully automated platforms which support high throughput screening. However, these large platform assays are not optimal in every setting due to the cost, the instrumentation requirements and the time to results. In some settings, POC assays may offer substantial advantages over tests that have to be sent to a central laboratory. Unfortunately, we have limited choices of POC assays for chlamydia and many suffer from unacceptably low sensitivity and specificity [17,18].

Neisseria gonorrhoeae

Although N. gonorrhoeae had been the least prevalent of the commonly described discharge-causing STI, the estimates developed by the WHO in 2012 suggest that, with 107 million cases in 2008, these infections are once again on the increase [1]. In many populations the case rates are low enough that routine screening in the absence of symptoms is not warranted. Unfortunately, although most men with gonococcal infection exhibit symptoms related to urethritis, a significant proportion of infections in women are asymptomatic. When symptoms or clinical signs are present they are similar to those seen with chlamydia infection: mucopurulent cervicitis, pelvic pain, itching, pain on urination, or pain during coitus.

Untreated gonococcal infections have many of the same complications as untreated chlamydial infections: most significantly PID and negative outcomes of pregnancy. N. gonorrhoeae has also been linked epidemiologically to increasing the risk of HIV infection similar to the increase in risk seen with T. vaginalis. Fortunately, the substantially lower prevalence of gonorrhea makes this infection less of a risk factor than trichomonas, but identifying and treating infections may still serve as a tool in the fight against the spread of HIV.

Molecular assays are now the most common methodology for diagnosis of infection with N. gonorrhoeae although culture remains an important laboratory tool. Several first generation molecular diagnostic tests suffered from low specificity as a result of cross-reactive primers due to the similarity between N. gonorrhoeae and several closely-related species. However, the second generation assays, which are in use today in most settings world-wide, have substantially improved specificity and can be used without confirmation by a second assay. These tests are generally bundled with chlamydia testing in multiplex assays.

Despite very high specificity when using the second-generation NAATs, in very low prevalence populations the positive predictive value may be less than 50 % (i.e. fewer than 50 % of test positives are from infected people) Thus, screening for asymptomatic women should be carefully considered and performed predominately:

(1)	in populations with endemic HIV rates,
(2)	among women with known behavioral risk factors (e.g. sex workers or intravenous drug users),
(3)	among pregnant women for whom the potential for adverse outcomes of infection is high (e.g. populations where underlying prevalence of disease is high), or
(4)	in regions experiencing an outbreak.

Declining antimicrobial susceptibility has been described in N. gonorrhoeae and is a major public health concern [19]. Fluoroquinolone resistance has been well documented leading to the discontinuation of use of this class of drug. Surveillance of resistance to ceftriaxone is essential for monitoring potential resistance to this therapy as well. Currently, surveillance is dependent on culture of isolates and thus this diagnostic technique must remain available in public health laboratories. Patients returning with signs or symptoms of infection following treatment should be reevaluated for active infection and extra effort should be directed toward ensuring that sexual partners are treated as well. Obtaining cultured isolates from patients with persistently positive molecular test results is particularly important for surveillance of drug susceptibility.

Mycoplasma genitalium

M. genitalium is a more recent addition to the group of discharge-causing STIs; it was first described as associated with non-gonococcal urethritis in the early 1980s [20]. Since then many epidemiologic studies have shown that this pathogen is responsible for urethritis in men and cervicitis in women and is sexually transmitted. However, like the other pathogens that cause discharge, infection with mycoplasma may also be asymptomatic. Symptoms when present are similar to those seen in cases of chlamydia and gonococcal infection making clinical diagnostics a difficult task.

M. genitalium is a highly fastidious organism that requires 3 weeks or longer to isolate. Culture is rarely available outside of highly specialized research laboratories. Molecular diagnostics are becoming more available, but there are few licensed assays commercially available to detect this organism. Laboratory developed assays or assays for research use only have demonstrated high sensitivity and specificity when used on samples collected for chlamydia/gonorrhea screening.

Using molecular assays, this organism has also been epidemiologically linked to HIV acquisition among women in sub-Saharan Africa. There are preliminary data suggesting that mycoplasma infections may be related to adverse sequelae similar to those seen for chlamydial infection, but we still lack sufficient data to determine the outcome of untreated infections. Therefore, while diagnostics for mycoplasma in women with symptoms may be warranted, an evidence-based recommendation for screening in asymptomatic women (e.g. combining testing with trichomonas, chlamydia and gonorrhea screening) cannot be made at this time. As more data are collected using molecular diagnostics and combined with subsequent data regarding outcomes, recommendations for control of this infection will likely evolve.

Conclusion

STIs in women share certain characteristics. Infections are asymptomatic in a large proportion, often the majority, of cases. Risk of HIV is increased many fold with most of these infections making STI control critical in HIV endemic populations. Reproductive health consequences of unrecognized or untreated infections include PID, infertility, complications during pregnancy and risk of mother-to-child transmission. Social consequences of infection are more harmful for women than men. However, in many settings, the single greatest risk factor for a woman acquiring an STI, or HIV, is the behavior of her sex partner. Thus, strategies are needed to encourage routine screening to detect unapparent disease and prevent sequelae while protecting women's rights.

Provision of routine screening, which can be facilitated by patient-obtained specimens, should be offered in many settings to increase discretion while making the behavior a normative health maintenance activity. In the era of molecular diagnostics, we now have extremely powerful tools that can be utilized: from support of high-throughput screening using automated systems to POC assays that provide rapid results, and thus the potential for treatment during initial patient visits. We should not ignore other tools in our arsenal, for example Grams stain for male urethritis or wet mount microscopy of vaginal samples, but we should find the appropriate tools for each setting in order to maximize our opportunity to reduce the overall burden of these highly prevalent diseases.

Questions and answers

Q (Gronowski): Are there indications for trichomonas screening in asymptomatic women?

A (Van Der Pol): We are far away from including it in the routine process since it is not going to be a notifiable disease anywhere in the world in the near future, since there is no convincing data on the negative outcomes of untreated infection. However, locally we include it in our screening and find it a common condition. If a demonstration project can be undertaken locally, it is unlikely that clinicians will then want to lose it from the screening panel.

Declaration of interest: The author reports no conflicts of interest. The author alone is responsible for the content and writing of the paper.