HIV and other sexually transmitted infections

1. Key messages

Despite a recent decrease, the total number of new HIV diagnoses remains high. This calls for a more intensive implementation of the combined preventive strategies available in Belgium.

The HIV epidemic in Belgium mainly affects two populations: men who have sex with men (MSM), mainly of Belgian or other European nationality, and men and women who have contracted the virus through heterosexual relations, mainly from sub-Saharan Africa. The rate of new HIV diagnosis is higher in Brussels than in the other regions, reflecting the fact that HIV is mainly an urban phenomenon. 69% of the new HIV cases were diagnosed in men. Most HIV cases were diagnosed in the 25-49 age group.

Chlamydia is the most common sexually transmitted Infection (STI) in Belgium, followed by gonorrhea and syphilis. The number of reported cases of these three STIs has increased almost threefold in the past 10 years, reflecting more an increase in testing and screening practices, than an increase in incidence. However, there has been an increase in unsafe sexual practices, which is more pronounced among certain groups such as MSM, possibly resulting in some increase in the number of STI cases.

2. Background

Sexually transmitted infections (STIs) are spread primarily through person-to-person sexual contact. Some STIs, particularly HIV can also be transmitted through blood products and tissue transfer, and from mother to child during pregnancy.

Several STIs, such as HIV, chlamydia, and syphilis, can be present without symptoms, which can facilitate their transmission. STIs may however also lead to severe long-term consequences: HIV is one of the most serious communicable diseases in Europe. It is an infection that can lead to serious morbidity (AIDS) and high costs of preventive treatment and care. Chlamydia and gonorrhea may lead to complications such as infertility, chronic inflammation, and ectopic pregnancy. Untreated syphilis can damage any organ and cause severe neurological complications.

HIV and other STIs are avoidable infections since the transmission is largely preventable by behavioral measures (safe sex, safe injection). Therefore their incidence in a defined population is an indicator of the success/failure of control strategies. Since 2017, the use of pre-exposure prophylaxis to HIV (PrEP) is reimbursed in Belgium. While this may have a positive effect on the incidence of HIV, it may lead to an increase in the incidence of other STIs due to relaxing of vigilance.

The modes of epidemiological surveillance of HIV and other STIs are different, and are therefore described separately.

The epidemiological surveillance of HIV and AIDS in Belgium dates from 1985 and is carried out by Sciensano on the basis of the registration of the new HIV and AIDS diagnoses. These data come from two sources: on the one hand the registration and reporting of the AIDS patients by the clinicians, and on the other hand the registration of the HIV diagnoses by one of the seven AIDS reference laboratories that perform the confirmation tests. In addition to recording the number of newly diagnosed HIV positive, the laboratories also collect basic epidemiological data on gender, age, nationality, possible route of infection, and clinical stage at the time of diagnosis.

The slow progressive nature of the disease allows the existence of a "hidden" epidemic consisting of undiagnosed people living with HIV. Sciensano therefore also estimates the number of people living with HIV, including those who have not yet been diagnosed [1]. For this, it uses an instrument developed by the European Center for Disease Prevention and Control (ECDC), called the ECDC HIV Modeling Tool [2].

ECDC and the WHO Regional Office for Europe jointly coordinate HIV/AIDS surveillance in Europe. The surveillance data on HIV and AIDS diagnoses are collected and submitted annually by the national HIV/AIDS surveillance programs in the Member States to The European Surveillance System (TESSy). The international comparability is however poor, since the national surveillance systems in different countries may differ in levels of underreporting and reporting delay.

The surveillance of other STIs in Belgium is mainly done via the Sciensano's sentinel network of medical laboratories, which covers about 50% of the laboratories. Since the surveillance of STIs is based on reported cases, the trends do not represent the true incidence. Indeed, since STIs are often asymptomatic, only a part of them are detected and notified. As a result, changes in notification rates can be affected by changes in both the underlying incidence and the proportion of cases being detected (due to an intensification of the screening or to more performant tests). To help interpret these trends, Sciensano compares the evolution of the number of reported cases of chlamydia and gonorrhea to that of the total number of tests for these STIs reimbursed by National Institute for Health and Disability Insurance (RIZIV-INAMI).

The routine surveillance of the laboratory network is completed by the clinical sentinel network to identify the most important behavioral risk factors and evaluate the impact of prevention campaigns. This clinical network is not suited to follow the evolution of the number of cases of the predominant STIs, but can help to describe factors that influence the transmission of STIs.

3. HIV

Situation in 2018

Belgium

In 2018, 882 new diagnoses of HIV infections were made in Belgium (7.8 new diagnoses per 100,000 inhabitants, or on average 2.4 cases a day). Among those, 69% were men. 68% of the HIV cases were diagnosed in people aged 25-49.

In 2018, 49 cases of AIDS were notified. 59 deaths were notified among the people living with HIV. This number includes deaths from any cause (not only related to HIV); from the cause of death register, it appears that HIV is mentioned as underlying cause of deaths in about two-thirds of the deaths where an HIV infection was mentioned.

Number of new reported HIV diagnoses by age and sex, Belgium, 2018
Source: Epidémiologie du SIDA et de l’infection à VIH en Belgique, Sciensano, 2019 [1]
Regional specificities

In 2018, of the 882 new diagnoses, 235 were reported in Brussels, 414 in Flanders, 170 in Wallonia, and 63 cases were of unknown residence.

When related to the number of inhabitants, the diagnostic rates in Flanders and Wallonia are quite comparable, while the one in Brussels is much higher. This difference is not surprising, since a high HIV prevalence is typically an urban phenomenon. The Brussels Capital Region can indeed be considered as a big city – with the socio-cultural characteristics of an urban context – while the two other regions mix rural, semi-urban, and urban contexts.

Rate of new HIV diagnoses per 100,000 by region, Belgium, 2018
Source: Own calculations from Epidémiologie du SIDA et de l’infection à VIH en Belgique, Sciensano, 2019 [1]

Trends

Belgium

In 2018, the number of new HIV diagnosis has decreased by 2% compared to 2017 and by 28% compared to 2012.

Between the start of the outbreak in the early 1980s and the end of 2018, a total of 31,695 persons were diagnosed with HIV, a total of 5091 cases of AIDS were reported, and 2751 people had died with HIV. Not all of those deaths were due to HIV. From the cause of death register, it appears, that since 1998, about 1000 deaths were declared having HIV as the direct cause of death (the code of death for HIV did not exist before).

Number of new diagnoses of HIV, AIDS, and deaths reported, Belgium, 1982-2018
Source: Epidémiologie du SIDA et de l’infection à VIH en Belgique, Sciensano, 2019 [1]
Regional specificities

Between 2012 and 2018, the number of new HIV diagnoses decreased in Flanders and Wallonia, but remained quite stable in Brussels. However, it should be noted that the availability of information on region of residence of HIV cases has greatly improved in recent years, from 75% in 2015 to 93% in 2018. The large number of cases with unknown region or residence in the past has resulted in an underestimation of the number of cases in each region, which complicates interpretation of trends.

Number of new HIV diagnoses by region, Belgium, 2009-2018
Source: Epidémiologie du SIDA et de l’infection à VIH en Belgique, Sciensano, 2019 [1]

Modes of infection

The HIV epidemic in Belgium mainly affects two populations: men who have sex with men (MSM), mainly of Belgian or other European nationality, and men and women who have contracted the virus through heterosexual relations (95% of the HIV-infected women and 28% of the men), mainly from sub-Saharan Africa.

A decrease in the number of new HIV diagnoses occurred in both key populations. The proportion of new infections in injecting drug users (IDUs) is limited and tends to decrease further. Finally, it is also important to note that there is a significant proportion of new infections for which the mode of transmission is unknown (25% in 2018).

Number of new HIV diagnoses by probable mode of infection, Belgium, 1999-2018
Source: Epidémiologie du SIDA et de l’infection à VIH en Belgique, Sciensano, 2019 [1]
Nationality by mode of infection

In 2018, 50% of the HIV cases diagnosed among MSM were of Belgian nationality. This proportion has strongly decreased in the last few years (73% in 2009 and 62% in 2016 and 2017). Among people infected by heterosexual contact, 43% were of sub-Saharan nationality in 2018 (compared to 61% in 2009 and 50% in 2017).

  • MSM
  • Heterosexuals

Number of new HIV diagnoses in MSM by nationality, Belgium, 1995-2018
Source: Epidémiologie du SIDA et de l’infection à VIH en Belgique, Sciensano, 2019 [1]

Number of new HIV diagnoses in heterosexuals by nationality, Belgium, 1995-2018
Source: Epidémiologie du SIDA et de l’infection à VIH en Belgique, Sciensano, 2019 [1]

Estimation of the HIV prevalence in Belgium

Sciensano estimates the prevalence of HIV in Belgium based on a tool developed by ECDC [1,2]. The number of people living with HIV in Belgium in 2018 was estimated at 19,213. Among those, 1747 were not diagnosed. This implies that 9.1% of all people living with HIV in Belgium are not aware of their seropositivity.

Note: the prevalence estimated by the model is lower than the total number of people diagnosed with HIV since the beginning of the epidemic (31,695). This difference is mainly due to deaths and people who have left the territory. In addition, some duplication cannot be excluded due to the old personal identifier. Finally, it should be noted that these estimates have been calculated on the basis of available data, and that missing data may affect accuracy.

4. Other sexually transmitted infections

Situation in 2018

Belgium

Chlamydia is the most common STI in Belgium with 80 reported cases per 100,000 in 2018. Chlamydia infections are more frequent in women, with the highest notification rate among women aged 20-24.

Gonorrhea and syphilis are less common, with respectively 19 and 14 reported cases per 100,000 in 2018. Most gonorrhea and syphilis cases are registered among men, especially among men who have sex with men (MSM). The highest number of gonorrhea and syphilis cases are reported among men aged 25-29 and 30-39, respectively.

  • Chlamydia
  • Gonorrhea
  • Syphilis

Reported cases of chlamydia by age and sex, Belgium, 2016
Source: Surveillance des infections sexuellement transmissibles, Sciensano, 2020 [4]

Reported cases of gonorrhea by age and sex, Belgium, 2016
Source: Surveillance des infections sexuellement transmissibles, Sciensano, 2020 [4]

Reported cases of syphilis by age and sex, Belgium, 2016
Source: Surveillance des infections sexuellement transmissibles, Sciensano, 2020 [4]

Trends

Between 2002 and 2018, the chlamydia notification rates increased from 9.5 cases/100,000 in 2002 to 80.2 cases/100,000 in 2018, while the notification rates of gonorrhea and syphilis increased to a lesser extent.

A similar increase is observed in the test intensity for chlamydia and for gonorrhea, (except in 2015 where the testing rate of gonorrhea evolved faster than the reported rate of the cases). These similar evolutions in both the testing rates and the reported infections suggest that the apparent rise in reported cases could be a consequence of an intensified testing rather than an increase in incidence. Indeed, for chlamydia infection, it is generally accepted that the actual incidence has remained stable over time. Also for gonorrhea, the incidence does not seem to have increased at the level of the general population. However, additional information provided by the STI clinical network suggests that unsafe sexual practices have become more common in certain population groups (especially MSM), leading to a focused increase in the incidence and reinfections with gonorrhea and syphilis in this group.

5. Read more

View the metadata for HIV

View the metadata for STI

Sciensano: HIV/AIDS surveillance

Sciensano: STI surveillance

Sciensano Epistat: Determinants of Sexually Transmitted Infections 

Definitions

HIV/AIDS
HIV infection and AIDS are the acronyms of "Human Immunodeficiency Virus" (HIV) infection and "Acquired Immune Deficiency Syndrome" (AIDS). Initial HIV infection is most often asymptomatic, while people may experience influenza-like symptoms. This is followed by a prolonged period with no symptoms. If the infection progresses, it interferes more with the immune system, increasing the risk of developing infections such as tuberculosis, as well as other opportunistic infections, and tumors which are rare in people who have normal immune function. These late symptoms of infection are referred to as AIDS. Since the late 1990s, efficient antiretroviral treatment exists that can slow down the progression of the disease.

References

[1] Epidémiologie du SIDA et de l’infection à VIH en Belgique. Situation au 31 décembre 2018. Brussels: Sciensano; 2019. https://doi.org/10.25608/k6sn-n789

[2] European Centre for Disease Prevention and Control. HIV Modelling Tool. 2015. https://www.ecdc.europa.eu/en/publications-data/hiv-modelling-tool

[3] European Centre for Disease Prevention and Control/WHO Regional Office for Europe. HIV/AIDS surveillance in Europe 2019 – 2018 data. Stockholm: ECDC; 2019. https://www.ecdc.europa.eu/sites/default/files/documents/HIV-annual-surveillance-report-2019.pdf

[4] Surveillance des infections sexuellement transmissibles. Données pour la période 2014-2016. Brussels: Sciensano; 2020. https://www.sciensano.be/sites/www.wiv-isp.be/files/surv_sti_1416_fr.pdf