9.13 Sexually transmitted infections
Oxford Textbook of Public Health
Sexually transmitted infections
Michael Adler and Frances Cowan
What are the diseases/organisms?
Consequences/sequelae of STIs
The pattern and distribution of STIs around the world
Interaction of STIs with HIV
Mass treatment/presumptive treatment
Special services for core groups
Failure to control STIs
Sexually transmitted infections (STIs) are those infections whose primary mode of transmission is through sexual contact. They present a major public health problem, and are among the most common causes of illness and even death in the world. STIs have far-reaching health, social, and economic consequences. The distribution of STIs within a community is dependent on the sexual behaviour of individuals within that community as well as the efficiency of transmission and the duration of infectiousness of the STI. The recognition that the presence of an STI, particularly those causing genital ulceration and/or inflammation within the genital tract, can enhance both the acquisition and transmission of the human immunodeficiency virus (HIV) has resulted increasingly in the development of integrated control programmes for HIV and STDs (Cohen et al. 1997; Fleming and Wasserheit 1999). Over and Piot (1991) reported that 70 per cent of HIV infection in Africa is found in patients with a sexually transmitted disease (STD) with lower, but increasing, levels of 15 to 30 per cent in Thailand amongst STD patients.
STIs (as well as HIV/AIDS) have a major demographic, economic, social, and political impact, particularly in sub-Saharan Africa and increasingly in Asia. The World Bank (in 1993) estimated that for those aged 15 to 44 years, STIs (excluding HIV) were the second most common cause of healthy life lost in women after maternal morbidity and mortality (Fig. 1).
Fig. 1 Top ten causes of healthy life lost, ages 15 to 44 years: (a) females; (b) males.
What are the diseases/organisms?
The types of disease spread by sexual contact will vary in their incidence and clinical manifestations throughout the world. Traditionally, the venereal diseases comprised three bacterial infections, chancroid, syphilis, and gonorrhoea. However, over the last 30 years more and more micro-organisms have been recognized as spread by sexual intercourse or contact (Table 1).
Table 1 Micro-organisms that can be sexually transmitted
Chlamydial infection, genital warts, herpes, and trichomoniasis have become increasingly common and important causes of morbidity throughout the world. On the other hand, scabies, pediculosis pubis, and vaginal candidiasis are often diagnosed in STD clinics although they are not usually acquired sexually. Similarly, sexually transmitted hepatitis (A, B, and C) is becoming more common. The incidence of chancroid, granuloma inguinale, and lymphogranuloma venereum is low in the developed as opposed to developing countries, where such conditions are still common.
Consequences/sequelae of STIs
Untreated STIs result in major consequences to health, particularly in women (Table 2). These include cancers (e.g. cervical, vulval, and penile), reproductive health problems, particularly pelvic inflammatory disease (salpingitis), tubal infertility, and ectopic pregnancy, and pregnancy-related problems such as premature rupture of membrane, preterm delivery, postpartum infection, and low birth weight. In addition, infection can be transmitted to the newborn either during pregnancy or at the time of delivery, resulting in conjunctivitis (Chlamydia trachomatis, Neiserria gonorrhoeae), pneumonia (Chlamydia trachomatis), neonatal herpes, and congenital abnormalities (syphilis).
Table 2 Major sequelae of STDs
The pattern and distribution of STIs around the world
The pattern and distribution of an STI within a population are dependent on the sexual behaviour of individuals within that community (including rate of partner change, extent of mixing between high- and low-risk populations, and barrier contraceptive usage), as well as the transmissibility and the duration of infectiousness of the micro-organism. The pattern and distribution can be expressed mathematically as set out below. The case reproduction rate R0 represents the average number of new infections that result from an infected individual over the infectious period within a population:
R0 = bcD
where b is the transmission probability, c is the average rate of acquiring partners (c is not the mean number, but is the mean m plus the variance-to-mean ratio s2/m of the relevant distribution of partner-change rates), and D is the duration of infectiousness.
It is possible to use this formula to predict or model the likely course of an STI epidemic, given various parameters, and to predict how altering these parameters might influence the epidemic. For example, in communities where the duration of infection is prolonged because of poor access to treatment facilities, an infection can be sustained, despite lower rates of partner change, than in a population where duration of infection is typically shorter. If the case reproduction rate R0 is greater than unity, then the incidence of infection theoretically increases within the population while if it is consistently less than unity the incidence decreases and the infection disappears from the population.
While the mean rate of partner change is important, data from observational studies and mathematical models suggest that STI/HIV epidemics are sustained or exacerbated by ‘core groups’ of men and women who have very high rates of sexual partner change, such as commercial sex workers (CSWs). In a population in which a few people have very high rates of partner change and the majority have very low rates, STIs including HIV will spread more quickly than if the same average number of partners were distributed more equally across the entire population. Clearly, the extent of mixing between high- and low-risk populations is important. In populations where there is little mixing between high- and low-risk populations (assortative), infection will remain confined to the core group. More commonly, however, there is disassortative mixing (Garnett and Anderson 1996).
The pattern and distribution of bacterial and viral STIs reflect differences between their natural history and response to treatment. The bacterial infections are curable with appropriate antibiotic therapy, if available. Even if untreated, individuals infected with bacterial STIs will become uninfectious to others with time. Therefore it is theoretically possible to reduce the incidence and prevalence of these infections and their sequelae through intensive screening and treatment initiatives which result in a decrease in the duration of infectiousness. Indeed, in many developed countries, the rate of the bacterial STIs has dramatically reduced over the last 20 years. However, in developing countries, with few resources for screening and treatment, infected individuals remain infectious for longer and rates of bacterial STIs and their sequelae remain high.
In contrast, the non-curable viral STIs are chronic and persist over years, in some cases for life, with those infected remaining potentially infectious to others over prolonged periods. In this circumstance, without effective primary prevention of infection either through behaviour modification or vaccination, the prevalence of viral STIs continues to rise in both developed and developing countries.
The recognition given and resources spent on control programmes and notification for STIs varies throughout the world. The World Health Organization (WHO) has been responsible for a series of estimates of the size of the problem represented by STIs, and they suggest an annual total of 333 million new infections per annum. The major focus for these is Southeast Asia, with an estimated 150 million new cases per year, and sub-Saharan Africa with 65 million. In Eastern Europe and Central Asia, the estimate is 18 million, and for Western Europe 16 million (Fig. 2). The estimated prevalence and incidence of STIs by region shows considerable variation. For example, the difference in prevalence and incidence rates between sub-Saharan Africa and Western Europe is fourfold and threefold respectively (Table 3).
Fig. 2 Estimated new cases of curable STDs among adults (1995).
Table 3 Estimated prevalence and incidence of STDs by region
Although notification of STIs is required in many European countries, the accuracy of this information is variable, and often suffers from the reluctance of private doctors or general practitioners, who in many European countries see the majority of patients, to notify these. For example, in Italy it is estimated that for each case of syphilis notified, 2.3 are not, and for each case of gonorrhoea notified, two are not. In The Netherlands under-reporting of gonorrhoea has been estimated in the past to run at 66 per cent. Because of these gross limitations it is difficult to obtain accurate data. Some countries have set up alternative systems for collecting this information which may not give total coverage. For example, STD clinics (United Kingdom, France, Italy), laboratory systems (Denmark, Sweden), and sentinel general practitioner systems (Belgium). However, these statistics do not cover patients who are treated in other facilities, for example family planning, gynaecology, and primary care. The majority of these surveillance systems are, however, only able to detect symptomatic STIs in individuals who present for clinical care. Many STIs are asymptomatic and are therefore unrecognized, particularly in women.
The lack of good data and notification systems has often been overcome by prevalence studies in particular countries. Such information is useful but is often of limited value as it is rarely based on a truly random sample of the community being studied. More often it is obtained from atypical, high-risk, and usually consulting groups of individuals and/or patients. Figure 3 indicates the prevalence of the common STDs in women in Africa in different settings. In CSWs, the prevalence of gonorrhoea can reach nearly 50 per cent and the prevalence of syphilis ranges from 2 to 30 per cent for acute or previous infection. Levels of Chlamydia trachomatis can be as high as 30 per cent. In the developing world, prostitution is a driving force for STDs and HIV. For example, in Kenyan urban STD clinics, 60 per cent of men with a gonococcal urethritis or chancroid reported commercial sex exposure as the probably source of infection. Other high-risk groups studied are men and women attending STD clinics, and, as expected, levels of infection are found to be high. Unfortunately, levels of infection can also be high in what can be termed as ‘low-risk’ groups, namely women attending antenatal clinics. One finds very high levels of gonococcal and chlamydial infection from various studies in other continents apart from Africa, for example Latin America and South and Southeast Asia. Studies of herpes simplex virus seroprevalence indicate very high levels of infection in many developing countries. For example, in Mwanza, Tanzania, over 40 per cent of teenage girls have evidence of infection with herpes simplex virus type 2 (HSV-2) (Obasi et al. 1999). Additionally, two random population studies from the United States indicate that the prevalence of HSV-2 antibody in non-institutionalized Americans has risen from 16.8 per cent in the period 1976–1978 to 21.2 per cent in 1988–1992 (Fleming et al. 1997). Studies from Europe suggest lower infection rates than those in the United States and developing countries.
Fig. 3 STDs in women in Africa.
Even though rates of STIs tend to be lower in Europe, there has been increasing concern over major epidemics of gonorrhoea and syphilis in Eastern Europe in the newly independent states of the former Soviet Union. Figure 4 indicates the high rates of gonorrhoea, the highest rates are seen in Estonia (166), Russia (139), and Belarus (125) per 100 000. Incidence rates for syphilis are now below 5 per 100 000 in nearly all Western European countries. However, Eastern Europe has not experienced this decline, and recently, as with gonorrhoea, there has been considerable concern about the epidemic of syphilis. In these countries, syphilis incidence in 1996 was between 140 and 254 per 100 000 (Fig. 5); increases are considerable in all age groups but particularly in older adolescents. Between 1986 and 1996, the incidence of syphilis in 18- to 19-year-old Russians increased from 6 to 607 per 100 000 in men and from 20 to 1321 per 100 000 in women. The increase between 1992 and 1996 was 20-fold in Russia, sixfold in Estonia, 12-fold in Latvia, and 14-fold in Lithuania (Fig. 6). It is unlikely that the epidemic is restricted to syphilis and gonorrhoea, and it is highly likely that there is also an epidemic of HIV infection. With recent outbreaks of HIV infection among intravenous drug users, particularly in Belarus, Russia, and Ukraine, and the very high incidence of syphilis and other STIs in the region, the stage is now set for a potentially rapid spread of HIV.
Fig. 4 Gonorrhoea rates per 100 000 Eastern and Central Europe (1996).
Fig. 5 Incidence of syphilis in Belarus, the Russian Federation, Moldova, and Ukraine during the period 1990 to 1998.
Fig. 6 New cases of syphilis in Russia and the Baltic States in the period 1992 to 1996 (rates per 100 000).
Interaction of STIs with HIV
There is strong evidence that STIs facilitate the transmission of HIV. Studies have shown that genital HIV viral shedding increases significantly in the presence of acute STIs, returning to preinfection levels following effective treatment (Cohen et al. 1997; Schacker et al. 1998a,b). In addition there is strong experimental evidence from the community-randomized trial in Mwanza, Tanzania, that it is possible to substantially reduce the incidence of HIV infection among adults by introducing effective STI control in the form of syndromic treatment for symptomatic bacterial STIs (Grosskurth et al. 1995). There is increasing evidence from cross-sectional studies and a few prospective studies of a strong association between HSV-2 infection and acquisition/transmission (Gwanzura et al. 1998; Fleming and Wasserheit 1999). In communities with high rates of STIs, it is likely that a considerable proportion of HIV infections are attributable to the effect of STIs on HIV transmission.
Control requires a broad-based approach which addresses prevention and low-cost/low-technology approaches to diagnosis, treatment, and care, which are often delivered by non-medical personnel in rural settings. The social, demographic, and economic causes and consequences of STDs need addressing since they have major consequences on productivity, social, and family structures. It follows from this that the medical model is too limited in controlling STDs. It is pointless to develop strategies for control if appropriate systems and public-sector financing are not in place for the delivery and adoption of services, health education, new technologies, etc. The institutional and infrastructural issues of public-sector financing, community development, and capacity building are pivotal to any control programme.
Particular issues for the control of STIs are as follows:
high rates of infection among young adults, adolescents, and certain groups (CSWs and truck drivers)
long-term morbidity, particularly in women
increased acquisition of HIV in transmission
women are disadvantaged/disempowered
the complex mix of social, political, cultural, demographic, and economic factors.
The principles of effective control of STDs are:
to prevent new infections
to treat those with symptoms of infection
to identify and treat those without symptoms by screening and partner notification
to motivate health-seeking behaviour among people who may know they are infected but who delay or avoid seeking treatment.
These principles and aims can be achieved or attempted through two approaches.
provision of condoms
social, cultural, and economic interventions.
promotion of health-care-seeking behaviour
early detection and treatment of symptomatic/symptomatic infections.
Clearly it is best to avoid infection in the first place. The advent of AIDS has been a major influence in the increased awareness of the need for health education and the public acceptance of explicit messages and images. Programmes aimed at safer sexual practices and increased condom use have been widely advocated and implemented in both developed and developing countries. The success of such programmes is often difficult to assess and, sadly, initial modifications in behaviour are not always maintained over longer periods of time. This has been seen within both the United Kingdom and United States: initial and profound changes in sexual behaviour in homosexual men led to lower levels of STDs, but unfortunately this alteration in behaviour has not been universally sustained.
Programmes to market and encourage the use of condoms have been at the heart of many control programmes and are particularly useful since they reduce acquisition and transmission of both traditional STDs and HIV infection. In Africa there has been encouraging evidence that increased condom use has been accepted by high-risk groups such as CSWs and their clients, and that this has altered levels of infection. Examples of this have been reported in Africa and Southeast Asia. A 3-year programme of condom promotion and STD control in Zaire saw an increase in consistent condom use from 0 per cent to 68 per cent amongst CSWs (Laga et al. 1994). Social marketing of condoms in Zaire saw sales increasing from 20 000 to 18 million in a period of 3 years (Kyungu 1992). Multiple outlets were used, such as street traders, night clubs, CSWs, and pharmacists. In parallel with the increased condom use in CSWs, the incidence of gonorrhoea, trichomoniasis, genital ulcer disease, and HIV declined. In Zimbabwe a community intervention at a cost of $85 000 resulted in the distribution of 5.7 million condoms, with a suggested resulting decline in STDs ranging from 6 to 50 per cent in different areas. CSWs were found to have increased condom usage from 18 per cent prior to the programme to 72 per cent with their last client (World Bank 1993). In Thailand, an education programme advocating the use of condoms by CSWs and clients was followed by increased usage from a baseline of 14 per cent to 94 per cent (Hanenberg et al. 1994). A concurrent decline in bacterial STDs was seen over the same period.
Even though these results are promising, as indicated previously experience in developed countries suggests that such changes are hard to sustain. Repeated reinforcement and monitoring are required. Also, social and economic issues need to be addressed. Often women are so poor and disempowered that they have sex on a commercial basis against their will and are unable effectively to negotiate the use of condoms by clients. Economic programmes may be required that help reduce the necessity for women to earn or supplement their incomes by prostitution. At the same time women need to be taught skills that help them negotiate safer sex with clients and regular partners. This is particularly difficult with the latter since husbands and regular partners can see such negotiation as a reflection of themselves at the same time as suggesting that the woman has herself had multiple partners. The recognition of the substantial shift in cultural attitudes that are still necessary to establish wider condom use has led research workers to explore the use of vaginal virucides. Such an agent(s), if effective, would allow women more control. Raising the status of women in the developing world would be a crucial factor in the control of STDs and HIV, and can only be achieved through equality in the fields of education and employment.
Vaccination of susceptible individuals within a community is the other potential mechanism for primary prevention. To date the only effective vaccines for infections that are sexually transmitted are for the viral hepatitides. Concerted research efforts are underway to develop and test vaccines for other STIs, most notably for human papillomavirus infection and herpes simplex virus infection. For STIs, however, there is at least the theoretical possibility that an incompletely effective vaccine (which all vaccines are to some extent) could reassure vaccinees and result in increased sexual risk-taking, with all its adverse consequences.
It is self-evident, but often overlooked, that providing screening and diagnostic services, however good and client friendly, is of no use within a control programme unless utilized. It is an essential part of a health education programme to point out the symptoms associated with a possible STD but also to reinforce an understanding that many diseases are asymptomatic, particularly in women. It should be pointed out that, ideally, once symptoms develop further sexual contact should cease and care be sought, and that those who are at high risk (e.g. have multiple partners) should, regardless of symptoms, seek regular screening. Waaler and Piot (1969)) have highlighted this basic issue of health-care-seeking behaviour (Fig. 7). Their cascade for tuberculosis has been used to conceptualize STD control, and illustrates that only half of women with an STD symptom recognize its significance and only half of these present for treatment, of whom a further half receive adequate treatment. Health-care-seeking behaviour is influenced by a large number of factors apart from knowledge and awareness. For example, economic structural adjustment programmes have been criticized, since the introduction of fees for medical care, which are forced upon governments to fulfil these programmes, affects uptake of services (Lurie et al. 1995). A documented example of this occurred in Nairobi’s large STD clinic, where the introduction of fees was followed by a reduction in attendance of 60 per cent among men and 35 per cent among women (Moses et al. 1992).
Fig. 7 Health-care-seeking behaviour in women with STDs.
Clinical services and case management
Once a client presents with an STI symptom, different methods of case management are available. Whichever method is used they should share the common objectives of providing diagnosis and treatment based on a clinical, laboratory, or syndromic approach, as well as promoting reduction of risk-taking behaviour and treatment of sexual partners. Whatever the chosen method of case management, it is essential to create a non-judgemental, sensitive, and user-friendly environment which encourages clients to utilize services, whether they are provided in the formal or informal sector.
Vertical services for control
In resource-rich countries, the traditional approach to the diagnosis of a presumed STI is through aetiological diagnosis, established by microscopy and laboratory cultures and run by specialist doctors. This vertical approach has both advantages and disadvantages (Table 4). The main advantages are that the services provided by those who are specialists, well trained, and motivated to provide good services that are supported by accurate laboratory diagnoses to which appropriate treatment can be tailored. Such specialized facilities also offer the ability for good training, monitoring, surveillance, and research. However, this type of service has disadvantages, particularly in resource-poor settings, in that it is expensive, the use of laboratories for the definitive diagnoses inevitably means that there can be delays and therefore patients may not return for appropriate therapy, and that such services, usually based in urban settings, are of limited availability and do not give total coverage of the population. Since such services are usually specialist, they can create stigmatization. However, in countries such as the United Kingdom, this is no longer a major problem. A much more fundamental issue is that the expense of specialist vertical services mean that they are unsustainable in a resource-poor setting.
Table 4 Vertical services for STDs
Thus it can be seen that the concepts for models of case management used in resource-rich countries are usually inappropriate for implementation in developing countries. In such situations care is provided in an integrated non-specialist manner through an array of services and individuals, including general hospital outpatient clinics, primary health centres, clinics, maternal and child health centres, family planning clinics, private practitioners, pharmacists, traditional healers, unqualified practitioners, and street vendors. Few of those providing STI care have specialist training or medical qualifications. As with vertical services, there are both advantages and disadvantages to the integrated approach (Table 5). The major advantages are immediate diagnosis by the non-specialists and an inexpensive service managed in a standardized way. The disadvantages relate to low sensitivity and specificity and the detection of asymptomatic infection, which is discussed under the section on syndromic case management.
Table 5 Integrated services for STDs
Whilst all of these services and providers can work together in a complementary fashion, it is important that strategic decisions are taken about the most appropriate system to form the core and backbone of a control programme in any one country. It is likely that in the resource-poor countries, a different model from the vertical one described above will have to be used, and that is why the integrated approach using all types of potential providers is more sustainable and has led to the development of the syndromic approach.
WHO has placed increasing emphasis on integrated approaches, especially at the primary health centres level, using a syndromic approach for patient management (WHO 1991, 1994). This approach recognizes the limitation of resources for health-care and of specialist trained medical personnel. It is advocated for use particularly in high prevalence areas where there are inadequate laboratory facilities, lack of trained staff and large distances between rural primary health centres and specialist/laboratory facilities.
Syndromic case management The syndromic approach uses algorithms based upon commonly presenting signs and symptoms, for example genital ulcers or urethral and vaginal discharge (Fig. 8), where laboratory support may or may not be present. Counselling, education, condom use, and partner notification are an integral part of this approach.
Fig. 8 An example of an algorithm used in syndromic case management.
The algorithm for genital ulcers works on the basic premise that the two most common causes of such a sign/symptom are syphilis and chancroid, or a combination of both, and that with no laboratory support and the difficulty of establishing an accurate clinical diagnosis it is appropriate to give therapy for both conditions. The algorithm for urethral discharge assumes that the aetiology could be gonococcal and/or chlamydial and that therapy appropriate for both should be utilized. Both these algorithms have been evaluated and shown to be robust and sensitive.
Unfortunately, the algorithm for vaginal discharge does not discriminate easily between vaginal infections and vaginal plus cervical infections (gonorrhoea and chlamydia). Whilst vaginal infections are usually successfully covered by most available algorithms, they are not sensitive to gonococcal and chlamydial infections which are dangerous and often asymptomatic. Attempts to improve this algorithm have been made by incorporating a risk assessment which includes symptoms in the partner, number of partners, age, and marital status. Assessment of the use of such scores in Tanzania and Malawi has shown a low sensitivity of approximately 50 per cent (Mayaud et al. 1995a,b). Unless this level can be improved, a dilemma exists between only treating vaginal infections and missing and undertreating some patients with gonorrhoea and chlamydia, or overtreatment by prescribing for vaginal and cervical infection when some patients will not have infection at both sites.
The recent Mwanza Intervention Trial demonstrated the importance of an integrated STI programme in rural communities on HIV incidence (Grosskurth et al. 1995). This community randomized trial showed that improved STI care integrated at primary health centre level resulted in a reduction of HIV incidence of 42 per cent over the 2-year period of the study. The study also demonstrated a significant reduction of active syphilis and of symptomatic male urethritis. The study confirms the effect of STIs on HIV acquisition and transmission and that the integrated non-specialist and syndromic approach can be very effective.
The role of specialist centres The use of an integrated and syndromic approach does not preclude specialist and reference clinics. The Mwanza Intervention Trial evaluated the role of the reference clinic in support of an integrated STI control programme (Mabey et al. 1995). The reference clinic played an important role in identifying appropriate treatment regimens, monitoring treatment outcomes and the development of antibiotic resistance (particularly in Neisseria gonorrhoea), training staff from rural health units, and monitoring the underlying aetiologies of STI syndromes. It played a minimal role as a referral centre.
Therefore, in general, the diagnosis and management of STIs in developing countries, both in rural and urban environments, is not best achieved through specialist centres. Syndromic management should be offered in an integrated way in both urban and rural settings. The large number of clients seen in cities is not adequately managed in specialist clinics, for both economic and cultural reasons. The stigma associated with STI clinics is still a strong disincentive to attendance. Therefore the use of the syndromic approach in a non-specialized integrated way using general outpatient services and other agencies (e.g. family planning clinics, maternal and child health centres, and antenatal clinics) is the major way in which STIs can be managed in both rural and urban environments.
Traditional healers and other agencies As indicated earlier, substantial numbers of clients use a variety of non-medical personnel to treat symptoms. These include traditional healers, pharmacists, unlicensed practitioners, street vendors, and herbalists. Mulder (1994) and colleagues in Uganda studied a rural cohort in the general population and reported that 30 per cent of individuals with genital ulcer disease, and 19 per cent with vaginal or urethral discharge, sought care from the informal sector.
Those working in the informal sector are important in providing education and care. Traditional healers often advise on health, cultural, and spiritual matters and have considerable respect in the community, enabling them to influence beliefs and behaviour. Additionally, women may feel more able to access services within the informal sector. Studies in Zambia have shown that partnerships between traditional healers and the formal sector can be achieved, particularly in the field of education and condom distribution (Anyangwe et al. 1995; Nzima et al. 1995). Similar results have been reported in South Africa (Rutayuga 1995) and Uganda (Lutakome et al. 1995). Health practitioners in the informal sector must be recognized as an integral part of an STI prevention and treatment programme. These workers should be included in training programmes to improve their understanding of STIs and the efficacy of treatment protocols, and should be given guidance on the referral of clients when necessary. Unfortunately, this can be difficult to put into practice. However, innovative ways of gathering data on STI management practices by pharmacists have been reported (Garcia et al. 1998).
Asymptomatic infection is substantial with regard to STIs and a control strategy needs to devise ways in which asymptomatic individuals are identified and treated. Asymptomatic infection is found in both women and men. It is well established that 60 to 70 per cent of gonococcal and chlamydial infections in women can be asymptomatic. More recently, data have appeared showing that the levels of asymptomatic infection in men are higher than previously thought. Grosskurth et al. (1996) reported from a population-based study carried out in rural Tanzania where 500 men aged 15 to 54 years were selected from 12 rural communities. The prevalence of gonorrhoea was 2.2 per cent and that of chlamydia was 0.7 per cent. Most alarming, in terms of control, was the fact that 85 per cent of those with either of these conditions had no symptoms. More recently, data have emerged suggesting high levels (approximately 10 per cent) of trichomonas infection in African males, of which about 80 per cent are asymptomatic (Jackson et al. 1997). With regard to viral infections, advances in laboratory techniques have allowed more detailed description of these infections. Clinical studies of individuals seropositive for HSV-2 demonstrate that the majority of infection is unrecognized. Importantly, individuals with unrecognized asymptomatic herpes infection shed virus intermittently from their genital tract and therefore are potentially infectious to their sexual partners. Perhaps of more importance is the increasingly apparent role that herpes simplex plays in transmission/acquisition of HIV. Likewise, studies of human papillomavirus infection indicate that infection is clinically apparent in the minority of infected individuals.
At present, very little screening for asymptomatic STIs is undertaken in public clinics in developing countries. The main exceptions are testing for syphilis and gonorrhoea in some specialist and private clinics. Although antenatal testing for syphilis is well established in some countries, a number of studies have shown that many women who test positive fail to receive appropriate treatment unless it is carried out on-site on the same day. The main challenges to the improvement of STI case-finding are increasing case-finding where no laboratory is available, and making more effective use of resources where it is. The simplest form of screening can be undertaken by health workers who are trained to be more aware of STIs, to have the confidence to enquire about present or past STI symptoms and risk exposure, and to offer genital examinations when appropriate. Staff working in antenatal clinics, family planning clinics, and maternal and child health centres can be given additional training in recognizing and treating vaginal discharge, genital ulceration, mucopurulent cervicitis, and pelvic infection among clinic attenders. Where basic laboratory facilities are available, STI case-finding can easily be increased by testing more patients with STI symptoms for syphilis and by looking for evidence of trichomonas infection in a wet preparation from anyone undergoing speculum examination.
Partner notification (also known as contact-tracing) is the process of contacting the sexual partners of an individual with an STI and advising them that they have been exposed to infection. By this means people at high risk of an STI, many of whom are unaware that they have been exposed, are contacted and encouraged to attend for screening and treatment. Partner notification endeavours to reduce the burden of asymptomatic disease in the community and to shorten the average period of infectiousness for a given disease, in the expectation that this will reduce disease transmission within the population. It constitutes one aspect of STI control, alongside education and screening and treatment of cases. The rationale behind partner notification for bacterial STDs is that individuals who have been exposed to an STD but are asymptomatic can be identified and cured of their infection reducing both their morbidity and duration of infectiousness, thereby breaking the chain of transmission of infection. In this scenario both the individual and the community can be seen to gain from partner notification. Traditionally, little emphasis was placed on health education or promoting safer sexual behaviour for bacterial STI control, on the basis that this might discourage people from attending STD clinics for screening and treatment.
For viral STIs, including HIV, the rationale for partner notification is less clear. Asymptomatic contacts may have less to gain personally as a result of being notified; if infected, they cannot be cured of their infection.
From an epidemiological perspective, partner notification for viral STDs, including HIV, is only worthwhile if people who become aware of their infectivity modify their behaviour to reduce their risk of further disease transmission. There is limited evidence to suggest that this happens. For example, in the European Study of heterosexual transmission of HIV infection, around half of the 245 couples taking part continued to have unprotected sexual intercourse despite repeated counselling (de Vincenzi et al. 1994). Vaccine studies for prevention of genital herpes demonstrate continued transmission despite awareness of serodiscordance between sexual partners and counselling about condom use. Therefore, for viral STDs, there may be less to gain for both the individual and the community than for partner notification of bacterial STDs. Thus primary prevention (preventing acquisition of infection), either through vaccination or changing sexual behaviour, must remain the cornerstone of viral STD control in contrast with secondary prevention (preventing transmission of infection by treatment) for bacterial STDs. Effectiveness of partner notification as a means of detecting STIs has been examined in a systematic review by Oxman et al. (1994).
Partner notification can be undertaken in a variety of different ways.
Patient referral—the index patient is encouraged to contact his or her sexual partners and advise them to seek appropriate medical care. This process can be assisted by health-care workers who spend time educating the patient about the importance of contact-tracing, give out contact cards or using telephone or mail reminders.
Provider referral—the health-care workers involved in the index patient’s care can notify the sexual partners without naming the patient concerned.
Conditional referral—the health-care worker of the index cases obtains names of their sexual partners but allows patients a period of time to notify partners themselves. If the partners are not notified within this time period the health-care professional notifies their sexual partners without naming the patient concerned.
This can be carried out by the use of clinical examination, with or without laboratory tests. Such an approach in resource-poor countries is unlikely to be feasible given the expense generated by the special facilities and mobile teams, with or without laboratory support, which would be required.
The real challenge for total population screening is to develop an inexpensive, non-invasive, simple, available, diagnostic test which can be used widely to screen large sections of the population who would not be identified by opportunistic case finding in antenatal clinics, family planning clinics, and primary health centre clinics. The leucocyte esterase dipstick test has been evaluated in men using ‘first catch’ urine but in the developed work its sensitivity has been found to be low (McNagny et al. 1992).
Newer techniques such as the ligase chain reaction have been evaluated in the detection of chlamydial infections. It has been demonstrated that the ligase chain reaction on urine taken from infected women yielded a sensitivity of 96 per cent compared with cervical cell culture and ELISA, which gave sensitivities of 78 per cent and 56 per cent respectively (Bassiri et al. 1995). The drawback of this approach currently is that it is much more expensive than other techniques. Thus even in developed countries wide-scale population screening in men is not currently possible and, as indicated below, is neither feasible nor cost effective in women.
Mass treatment/presumptive treatment
An alternative and much more radical approach to reducing the high numbers of people infected with STIs in developing countries, and one which has the particular advantage of addressing infection in asymptomatic individuals, is to administer treatment to the entire population.
For example, in pursuit of the eradication of congenital syphilis, the WHO has advocated a target of syphilis testing to be made available by the year 2000 to all women attending antenatal clinics. Proposals have also been made for a campaign for the global elimination of syphilis.
The potential advantages and disadvantages of adopting a mass treatment approach to STI control are listed in (Table 6). Mass treatment is not currently a formal component of any established STI control programme and so far there is very little evidence to judge its potential effectiveness. As evidence accumulates that effective STI control can have a substantial impact on HIV transmission, there is renewed interest in the efficacy and costs of mass treatment. Some experts have voiced serious doubts about the sustainability and long-term effectiveness of mass treatment for STIs, and fear that such programmes could accelerate the development of antibiotic resistance and produce a situation where bacterial STIs can only be treated with new and expensive antibiotics. The recently reported Rakai study (Wawer et al. 1999), in which mass treatment with ciprofloxacin, azithromycin, and metronidazole was delivered to adult men and women in rural Uganda every 10 months over a 20-month period, failed to reduce HIV incidence despite good coverage in the study population. The failure of this programme has been attributed to the fact that the HIV epidemic in Uganda is already mature and that STIs in such an epidemic are unlikely to have an important facilitatory role. It is worth noting, however, that although coverage of the population was excellent at over 80 per cent, the intervention may still have excluded those at highest risk of infection. For example, truck drivers and CSWs may well not have been in the community when treatment was delivered. In addition, only limited reductions in STIs were found. It is possible that the dosing interval was too wide in the absence of other treatment services for STIs within the study communities.
Table 6 Potential advantages and disadvantages of employing mass treatment to control STIs
Special services for core groups
Mathematical models suggest that preventing STI/HIV infection in someone with a high rate of partner change will avert many more future infections than preventing infection in a person with fewer sexual partners. If this is so, then STI/HIV prevention programmes which are targeted at high-risk individuals (core groups) are likely to have a much greater impact than the same programmes applied to the general population. The World Bank, the Joint United Nations Programme on HIV/AIDS, and others argue that in developing countries interventions targeted at core groups may prove to be a more sustainable and cost-effective means of controlling the spread of HIV in the general population, even in countries with mature epidemics (Plummer et al. 1991; Over and Piot 1993; Kahn 1996; World Bank 1997). However, reliable empirical data are required, as at present this hypothesis is supported by mathematical models for different hypothetical populations (Moses et al. 1991; Over and Piot 1993; Woolhouse et al. 1997), and data from few observational studies. There are no experimental studies to support this approach and these are urgently required if scarce resources are to be used appropriately.
Programmes targeting CSWs have been implemented in many parts of the world, with some apparent successes. The Thai 100 per cent condom programme was referred to earlier. The Sonagachi Project in Calcutta has used CSW peer educators to promote clinic attendance and condom use and has succeeded in maintaining low seroprevalences of HIV. In South Africa, monthly presumptive periodic treatment for bacterial STIs has apparently resulted in decreased prevalences of STIs in both the CSWs themselves and their male clients. Of note, CSWs in many parts of the developed world, notably Europe and Australia, have very low rates of STIs, probably because of outreach programmes which encourage condom use, hepatitis B vaccination, and regular STI screening and treatment. Programmes targeting other core groups such as truck drivers are also widespread within the developing world, and again largely focus on encouraging appropriate treatment of STI syndromes and promoting condoms.
Failure to control STIs
Given the increasing incidence and prevalence of STIs throughout the world, and the associated morbidity, it is clear that control programmes are often inadequate. The reasons why there is a failure to control these infections are varied. Often they are of low priority within countries and are not given a strong political lead by politicians, policy makers, and planners. In addition, the models of care delivered are sometimes inappropriate. For example, they tend to concentrate more on symptomatic than asymptomatic infection, service delivery is all too often not integrated, and there is a lack of availability of antibiotics. Finally, primary prevention, even though recognized as being important, is not given the priority that it should be.
Control programmes are frequently evaluated in terms of process and outcome. While process evaluation is clearly important in order to ascertain whether and how a programme is being delivered, social, economic, and temporal factors external to the programme under evaluation can impact on the prevalance and incidence of STIs. It is therefore difficult to draw conclusions about the effectiveness of such programmes in the absence of experimental evidence. However, trials of effectiveness are difficult and expensive to undertake. That said, policy-makers, particularly those in resource-poor countries, must carefully consider the probable benefits of a given programme before diverting resources from elsewhere. For example, the results of the Mwanza trial demonstrated a clear benefit of delivering syndromic STI treatment through primary health clinics and has had a major impact on STI control policies around the world.
STIs are a major public health problem around the world, both in terms of morbidity and mortality in their own right and in relation to their facilitatory role in the acquisition and transmission of HIV. A successful STI control programme, by reducing both the incidence and prevalence of STIs, will obviously reduce the morbidity, suffering, and economic cost associated with these diseases. By eliminating STIs as a facilitating factor in HIV transmission and by contributing to behavioural changes towards safer sex, it would also play a significant role in the prevention and control of HIV infection and AIDS.
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