Please note that there are different definitions and guidelines available to describe long COVID. Based on the definition used, the results may be different. The COVIMPACT study in Sciensano was developed based on the definition of the National Institute of Health and Care Excellence (NICE): "symptoms persist or develop for more than 3 months after a COVID-19 infection and cannot be explained by another diagnosis” .
The epidemiological situation of COVID-19 in Belgium is followed via different monitoring systems.
47% of COVIMPACT participants infected with SARS-CoV-2 reported persistent symptoms of long COVID 3 months after infection and 32% 6 months after infection.
The risk factors for developing persistent symptoms 3 and 6 months after a SARS-CoV-2 infection are: being female, having a lower level of education, having a chronic disease, obesity, having at least one symptom during the acute phase of infection, and being hospitalized due to COVID-19.
The top 5 persistent symptoms of long COVID 3 and 6 months after SARS-CoV-2 infection were fatigue and exhaustion, headaches, memory loss, concentration problems, breathing problems, and sleep disturbances.
Participants with long COVID reported a lower health-related quality of life than those recovering from their infection.
2.Epidemiology of COVID-19
The coronavirus disease 2019 (COVID-19) pandemic started in December 2019 in the city of Wuhan, China. COVID-19 is caused by the virus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). On 11 March 2020, the Director-General of the World Health Organization declared COVID-19 a global pandemic.
The virus is transmitted from human to human by infectious droplets. People can remain asymptomatic or present with a broad spectrum of symptoms. The risk of severe disease increases markedly with age and previous underlying conditions. For the general public, vaccination, handwashing, social distancing, avoiding crowded indoor spaces, and wearing a face mask are the recommended measures to protect oneself. Vaccines are available in Belgium since January 2021; more information on vaccines can be found here.
An overview of the scientific information about COVID-19 based on updated literature monitoring is available in the Sciensano fact sheet.
In Belgium, COVID-19 is monitored by Sciensano
In Belgium, the first confirmed case was reported on 3 February 2020, in an asymptomatic person repatriated from Wuhan. The second case was registered almost one month later, on 1 March 2020. This case was followed by a rapid growth in the number of cases occurring after the Carnival holidays. Since then, the virus is widely spreading in the country.
The Belgian institute for health, Sciensano, monitors the epidemic based on the data collected by its surveillance networks and reports on the latest figures and trends.
Four key indicators are followed; for the three first ones a moving average is computed on the last 7 days and compared to the average of the 7 previous days:
the number of confirmed cases;
the number of new hospitalizations of laboratory-confirmed cases;
the number of deaths;
the number of ICU beds occupied.
Moreover, the reproduction rate, that is the average number of people infected by a person carrying the virus, is calculated. If the reproduction rate is over 1, the disease is spreading in the population. Additional indicators are followed as the number of occupied beds in hospitals and ICU, vaccination coverage, the number of tests performed, and the percentage of those that are positive (positivity rate).
Frequently asked questions related to the different COVID-19 surveillance, data collection, and ways of reporting are answered in a specific document.
International data on COVID-19 can be consulted on different platforms
Comparisons among countries should be interpreted with caution due to differences in testing strategy, in laboratory capacities, and in the effectiveness of the surveillance. Comparisons of COVID-19 deaths are also hampered by differences in the methodology of counting COVID-19 deaths.
Epidemiological International data can be consulted on several platforms:
In the COVIMPACT study, the overall occurrence of long COVID was 47% three months after a SARS-CoV-2 infection, and 32% after 6 months. These numbers are in line with the international literature, which reports a prevalence of 47% and 30% for long COVID at 3 and 6 months .
All age groups are affected by long COVID
Although the proportion of long COVID differs slightly according to age, it is not a significant risk factor. Among participants with an age between 18 and 25 years, 47% reported persistent symptoms 3 months after a SARS-Cov-2 infection. This is similar to participants aged between 26 and 45 years where 51% reported persistent symptoms, but higher compared to the other age categories 46-65 years (42%) and 66+ (36%). At 6 months, the prevalence of long COVID has decreased among all age categories to 27%, 26%, 37%, and 21% respectively .
Long COVID proportion by age and months after infection, Belgium Source: COVIMPACT study, Sciensano 
Women are more likely to report long COVID
In the COVIMPACT study, 37% of the participants were men and 63% of them were women. The proportion of long COVID at 3 months is higher amongst women (56%) in comparison to men (42%). After 6 months, the proportion decreased in women to 40% and men to 27%. Women are 1.4 times more likely to have long COVID than men at 3 and 6 months.
Long COVID proportion by sex and months after infection, Belgium Source: COVIMPACT study, Sciensano 
Participants with lower socioeconomic status are more vulnerable to long-COVID symptoms
Among participants with a lower educational status, 56% reported persistent symptoms 3 months after infection, which is slightly higher compared to patients with a higher educational level (47%). After 6 months, these proportions decrease to respectively 41% and 32%.
Long COVID proportion by socioeconomic status and months after infection, Belgium Source: COVIMPACT study, Sciensano 
The most prevalent symptoms of long COVID are fatigue and exhaustion
The most prevalent symptoms reported by participants with long COVID at 3 and 6 months post-infection are fatigue and exhaustion (49% and 50%), headache (27% and 32%), memory problems (26% and 32%), respiratory problems (21% and 27%), sleeping problems (19% and 22%), loss of smell (20% and 17%) and taste (14% and 13%).
Prevalence of long COVID symptoms among the proportion of participants with long COVID by months after infection, Belgium Source: COVIMPACT study, Sciensano 
Patients with long COVID report a reduced quality of life
The health-related quality of life has been assessed with the EQ-5D questionnaire, which contains questions on mobility, autonomy, daily activities, pain/discomfort, and anxiety/depression. After 3 months, 18% of participants with long COVID reported mobility problems, 4% autonomy problems, 30% had problems with daily activities, 48% had pain and 40% of them reported anxiety and depression. After 6 months, these proportions were respectively 21% (mobility), 5% (autonomy), 33% (daily activities), 56% (pain), and 49% (anxiety and depression).
Health-related quality of life score by the quality of life dimensions and months after infection, Belgium Source: COVIMPACT study, Sciensano 
The mean score of health-related quality of life was assessed among COVIMPACT participants before their SARS-CoV-2 infection, at the time of infection, and after 3 and 6 months. Before infection, the average quality of life score was 92.6/100 and it significantly decreased at the time of infection to 81.7/100. For the scores 3 and 6 months after infection, a comparison was made between people who recovered from their infection and those who had long COVID. People who recovered from the infection had a higher quality of life score 3 and 6 months after infection (95.7/100 and 95.8/100) than people with long COVID (86/100 and 83.6/100).
Health-related quality of life score by the mean quality of life score and months after infection, Belgium Source: COVIMPACT study, Sciensano 
Besides his mission of surveillance, Sciensano is also involved in scientific research projects on COVID-19. In collaboration with partners, Sciensano coordinates and participates in projects aiming to better understand the virus and its effects on population health. Here is an overview of the existing projects.
Specific aspects of COVID-19 monitoring, prevention, and control are competencies of the regions. Further information on these aspects is available via the following websites:
If you are a professional, you can find the procedures for managing COVID cases on the Sciensano website.
In Belgium and worldwide, at the beginning of the COVID-19 pandemic, the focus was on managing the acute phase of the disease. However, some people continue to experience symptoms beyond the acute phase of infection . This phenomenon is referred to as "long COVID" or "Post COVID-19 condition" .
There is currently no consensus on the definition of long COVID. Still, many studies apply the definition proposed by the National Institute of Health and Care Excellence: "symptoms persist or develop for more than 3 months after a COVID-19 infection and cannot be explained by another diagnosis .
In the COVIMPACT study, the two definitions used to describe long COVID 3 and 6 months after acute infection are (1) having at least one symptom related to the SARS-CoV-2 infection three months after it, (2) still have at least one persistent symptom related to the SARS-CoV-2 infection six months after it. The objective of the COVIMPACT project is to constitute a cohort of people who test positive for COVID-19 in order to:
study the long-term evolution of a SARS-CoV-2 infection on physical, mental, and social health
identify the groups at risk and the factors associated with a favorable/unfavorable evolution
COVIMPACT is a prospective online observational cohort study. The target group is people who have had a COVID-19 infection confirmed by a laboratory test. When a COVID-19 test is positive, the lab sends the information to a central database that is used by call centers to contact COVID-19 cases and trace their contacts. At the end of the call, the call center agents inform people aged 18 and over about our online survey and ask if they agree to receive a link by SMS for more information on the study, and potentially participate in the study and complete the first questionnaire. Follow-up questionnaires are sent by Sciensano every 3 months until the end of the study in April 2023. Depending on when participants entered the study, the follow-up varies from 3 months to 2 years. Between 29 April 2021 and 1 May 2022, 2092 people completed the first questionnaire and the two follow-up questionnaires (3 and 6 months after infection). Full details on the sample and design are described in the latest COVIMPACT study report. The following topics were assessed in the study: COVID-19, quality of life, breathing difficulties, fatigue, functional limitations, mental health, physical activity, employment, and economic status.
A confirmed case is defined as a person who has a confirmed diagnosis by molecular or antigenic test of COVID-19.
The COVIMPACT study in Sciensano was developed based on the definition of the National Institute of Health and Care Excellence (NICE): "symptoms persist or develop for more than 3 months after a COVID-19 infection and cannot be explained by another diagnosis”.
The moving average is calculated as the average number of deaths across the last 7 days. The reason to use the moving average is that it smooths the daily fluctuations, and therefore, allows for a more robust appreciation of trends than the number of deaths that occurred during the last day.
The average number of people infected by a person carrying the virus. If the reproduction rate is higher than 1, the disease is spreading in the population.
The positivity rate is the percentage of all COVID-19 tests performed that are positive.
Smith P, Charafeddine R, Drieskens S, De Pauw R, De Ridder K, Demarest S, Van Cauteren D. Etude COVIMPACT : Infection COVID-19 et ses implications physiques, mentales et sociales à long terme – Résultats du suivi à 3 et 6 mois suivant l’infection. Bruxelles, Belgique. Juin 2022. Numéro de dépôt : D/2022.14.440/36 DOI : /10.25608/gyzc-w673
Amdal, C. D., Pe, M., Falk, R. S., Piccinin, C., Bottomley, A., Arraras, J. I., Darlington, A. S., Hofsø, K., Holzner, B., Jørgensen, N. M. H., Kulis, D., Rimehaug, S. A., Singer, S., Taylor, K., Wheelwright, S., & Bjordal, K. (2021). Health-related quality of life issues, including symptoms, in patients with active COVID-19 or post COVID-19; a systematic literature review. Quality of Life Research. https://doi.org/10.1007/s11136-021-02908-z
Taquet, M., Dercon, Q., Luciano, S., Geddes, J. R., Husain, M., & Harrison, P. J. (2021). Incidence, co-occurrence, and evolution of long-COVID features : A 6-month retrospective cohort study of 273,618 survivors of COVID-19. PLOS Medicine, 18(9), e1003773. https://doi.org/10.1371/journal.pmed.100377
Please note that the following numbers should be interpreted in the context of COVID-19
Belgium is a low-incidence country for tuberculosis, with 7.6 new tuberculosis cases per 100,000 inhabitants in 2021.
There were important regional differences, with the Brussels Capital Region having the highest incidence.
The incidence of tuberculosis was higher in men, regardless of age, region or nationality.
More cases were reported in big cities with Liège reporting the highest incidence.
In Belgium, 62.7% of the tuberculosis cases occurred among people who did not have a Belgian nationality.
Belgium is a low incidence country for tuberculosis with 7.6 cases per 100,000 inhabitants in 2021
In 2021, 875 new cases of tuberculosis were reported in Belgium (7.6 cases/100,000 inhabitants). Men were approximately 2 times more often affected by the disease than women, with 68.2% of new cases occurring among men in 2021 in Belgium. Of all cases, 40.3% of the tuberculosis patients diagnosed in 2021 were aged 25-44 years.
Among the regions of Belgium, the Brussels Capital Region has the highest incidence of tuberculosis
Of the total number of new registered cases, 38.4% of tuberculosis cases were registered in the Flemish Region (n=336), 31.8% in the Brussels Capital Region (n=278) and 29.8% in the Walloon Region (n=261). Considering the number of inhabitants in each region, the incidence rate was 3.2 times higher in the Brussels Capital Region (22.8 cases/100,000) as compared to the Walloon Region (7.2 cases/100,000) and 4.5 times higher as compared to the Flemish Region (5.1 cases/100,000). The incidence rates in the Flemish Region and the Walloon Region were similar, with slightly higher rates in the Walloon Region.
Tuberculosis occurs more often among people with a foreign nationality
In 2021, 62.7% of the new tuberculosis cases occurred among people with a foreign nationality in Belgium. This proportion was higher in the Brussels Capital Region (69.7%) compared to the Walloon Region and the Flemish Region (respectively 60.1% and 58.9%). Among Belgians, the incidence rate was 4.7 times higher in the Brussels Capital Region (10.7/100,000) compared to the Flemish Region (2.3/100,000), and 3.3 times higher compared to the Walloon Region (3.2/100,000). Among non-Belgians, the incidence rate was 1.4 times higher in the Brussels Capital Region (44.8/100,000) compared to the Flemish Region (31.2/100,000), and 1.1 times higher compared to the Walloon Region (41.2/100,000).
The distribution of the incidence by age and sex was different according to nationality in 2021. Among Belgians, the incidence increased with age in men and is higher in men across all age categories. The overall male-female ratio tends to increase with age: the incidence rate was 3.3 times higher in men among people over 75 years. Among non-Belgians, the incidence was highest in age group 15-29 years and lower in older age groups. The incidence rate was 1.9-2.9 times higher in men compared to women across the younger age groups (0-14 years, 15-29 years, 30-44 years, and 45-59 years).
In 2021, the incidence of tuberculosis remained low
The number of new cases of tuberculosis is decreasing for more than 40 years, although the diminution is slowing down since the nineties and tends to stagnate over the last few years. The incidence rate dropped below the level of 10 cases/100,000 for the first time in 2007, ranking the country among low-incidence countries. In 2021, the incidence rate (7.6 cases/100,000; n=875) remained low and was only slightly higher compared to the incidence rate of 2020 (7.2 cases/100,000; n=830).
Since 1981, the incidence rate is decreasing in all three regions, with more variations in Brussels due to migration flows:
In the Walloon Region, the lowest rate ever in terms of incidence (5.6 cases/100,000) was recorded in 2020. In 2021, the incidence increased slightly to 7.2 cases/100,000.
In the Flemish Region, the incidence rate dropped from 5.4 cases/100,000 in 2020 to 5.1 cases/100,000 in 2021, which is the lowest incidence ever recorded.
In the Brussels Capital Region, the incidence rate decreased from 28.1 cases/100,000 in 2019 to 21.9 cases/100,000 in 2020, which was the lowest incidence ever recorded. In 2021, the incidence increased slightly compared to 2020 to 22.8 cases/100,000.
Despite being a low incidence country, Belgium is ranked third in terms of tuberculosis incidence among EU countries
In 2021, according to World Health Organization (WHO) , the estimated incidence rate in Belgium was above the EU-14 average, ranking the country 3rd in the EU-14 after Portugal and Spain.
International comparisons made on reported data must be interpreted with caution, since methods for collecting data are different depending on the country. That is why the WHO Global Task Force on TB Impact Measurement  has developed a methodology to take into account under reporting, over and under-diagnosis in tuberculosis estimates. This explains why the incidence rate in Belgium presented in this international comparison is different compared to the incidence rate extracted from the Belgian tuberculosis registry publication.
Tuberculosis incidence per 100,000, EU-14 countries, 2021 Source: WHO/ECDC 
Tuberculosis is a disease caused by a bacterium called Mycobacterium tuberculosis that usually affects the lungs.
According to the World Health Organization (WHO), there were 10.6 million new cases of tuberculosis in 2021. The disease is one of the top 10 causes of death worldwide. Belgium is situated among the “low-incidence countries” with less than 10 new cases of tuberculosis per 100,000 inhabitants per year .
Tuberculosis can nowadays be effectively treated with a success rate of 82.4% in 2020 in Belgium. In Belgium, treatment is free of charge for the entire population (even for people without health insurance). However, 9.5% of tuberculosis patients still die before the end of treatment (half of these deaths are linked to comorbidity) .
The main risk factors for tuberculosis are contacts with infected people, poverty, poor nutritional status and immunodeficiency. Some people are more likely to get infected with tuberculosis since they are more exposed to the risk factors, like health care professionals and vulnerable populations such as homeless people, prisoners and migrants originating from countries with high tuberculosis prevalence.
The incidence rate is calculated as the number of new cases divided by the number of people registered at the National registry. Incidence rate in non-Belgians is slightly overestimated, as cases in unregistered migrants are counted in the numerator, while the denominator could only include the registered migrants.
The EU-14 corresponds to all countries that belonged to the European Union between 1995 and 2004: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Portugal, Spain, and Sweden. We compare the Belgian health status to that of the EU-14 because these countries have similar socioeconomic conditions. Note: The United Kingdom is not included since they have left the EU.
According to the WHO-recommended definitions , a tuberculosis case is defined as a case of active tuberculosis clinically diagnosed by a clinician or other medical practitioner or bacteriologically confirmed. Clinically diagnosed cases include “cases diagnosed on the basis of X-ray abnormalities or suggestive histology and extrapulmonary cases without laboratory confirmation” .
The total number of new HIV diagnoses in 2021 has increased slightly compared to 2020. But compared to previous years the total number of new HIV diagnoses is still substantially lower.
In 2021, 74% of the new HIV cases were diagnosed in men. Most HIV cases were diagnosed in the 20-49 age group.
The increase in new diagnoses in 2021 was observed among Belgians, both men having sex with men (MSM) and heterosexuals; among non-Belgians, there was a decline or a stabilization.
The rate of new HIV diagnoses is higher in Brussels compared to the other regions, reflecting the fact that HIV infection is mainly an urban phenomenon.
2.New diagnoses of HIV infections in 2021
In 2021, 781 new diagnoses of HIV infections were made in Belgium (6.7 new diagnoses per 100.000 inhabitants, or on average 2.1 cases a day). Among those, 74% were men. 76% of the HIV cases were diagnosed in people aged 20-49.
New HIV diagnoses have increased in 2021 - but are still lower compared to previous years
The number of new HIV diagnoses has increased by 4.3% in 2021 compared to the previous year. But in comparison to previous years, the total number of new HIV diagnoses is still substantially lower (-17% compared to 2019).
Between the start of the epidemic in the early 80s and the end of 2021, a total of 34.010 persons were diagnosed with HIV, and a total of 5,296 cases of AIDS were reported.
Brussels has a higher diagnosis rate compared to the rest of Belgium
In 2021, of the 781 new diagnoses, 251 cases were reported in the Brussels Capital Region, 354 in the Flemish Region, 161 in the Walloon region, and 14 cases were residing abroad.
When accounting for the number of inhabitants, the incidence rates in the Flemish Region and in the Walloon Region are comparable, while the rate in the Brussels Capital Region is much higher. This difference is not surprising since a higher HIV prevalence is a common phenomenon in a big city. The Brussels Capital Region can indeed be considered a big city - with the socio-cultural characteristics of an urban context – while the two other regions mix rural, semi-urban, and urban contexts.
A decrease in new diagnoses has been observed in Brussels, while for Flanders and Wallonia, the number of diagnoses increased
In 2021, the slight decrease in the number of new HIV diagnoses in the Brussels Capital Region that has been observed in the previous years has continued. There was a large decrease in the number of diagnoses in the Flemish Region and the Walloon Region in 2020, this was followed by a slight increase in 2021.
Diversification in the 2-key populations in Belgium
Since the start of the HIV epidemic in Belgium, two key populations have been particularly affected: men who have sex with men (MSM), of Belgian nationality, and heterosexual men and women from sub-Saharan Africa.
However, among both MSM and heterosexuals, the distribution of nationalities is changing significantly over time. Among people infected by heterosexual contact, the share of people of sub-Saharan nationality is decreasing (64% in 2012 to 45% in 2021). Among MSM, a decreasing share of new diagnoses in Belgian was observed since 2013. However, HIV transmission appears to have increased among Belgian MSM in 2021, as suggested by the increase in the number of acute infections among this group in 2021, reaching approximately the same number as in 2019.
More than a thousand people in Belgium live with an undiagnosed HIV infection
In 2021, Sciensano has estimated the number of people living with undiagnosed HIV based on a tool developed by ECDC . 1,155 people living with HIV in Belgium were not aware of their seropositivity. Based on the ECDC tool the number of people living with undiagnosed HIV in Belgium seems to decrease. In 2020, 1585 people in Belgium were unaware of their HIV infection.
Sexually transmitted infections (STIs) such as human immunodeficiency virus (HIV) are spread primarily through person-to-person sexual contact. Additionally, HIV can be transmitted through blood products and tissue transfer, and from mother to child during pregnancy or breastfeeding.
HIV can be present without symptoms, which can facilitate transmission. It is one of the most serious communicable diseases in Europe. Infection with the virus can, if antiretroviral treatment (ART) is not initiated, lead to serious morbidity (Acquired Immunodeficiency Syndrome (AIDS)) and requires life-long treatment.
HIV is an avoidable infection since the transmission is largely preventable by behavioural measures (safe sex, safe injection). Therefore HIV 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.
Surveillance of HIV in Belgium
The epidemiological surveillance of HIV in Belgium dates from 1985 and is carried out by Sciensano on the basis of the registration of new HIV diagnoses. These data are reported by the seven AIDS reference laboratories that perform all confirmations of positive HIV screening tests. In addition to recording the number of newly diagnosed HIV positive, the laboratories also collect basic epidemiological data on gender, age, nationality, probable route of infection, and clinical stage at the time of diagnosis. Sciensano also collects data on the people living with HIV (PLWH) in Belgium (HIV cohort data) from the AIDS reference laboratories and the HIV reference centres.
Besides the newly diagnosed cases, Sciensano also estimates the number of people living with HIV: those who have not yet been diagnosed  and those living with a diagnosed infection. To estimate the undiagnosed population an instrument developed by the European Center for Disease Prevention and Control (ECDC), called the ECDC HIV Modeling Tool  is used. And HIV cohort data are used to estimate the number of people living with a diagnosed infection.
ECDC and the WHO Regional Office for Europe jointly coordinate HIV/AIDS surveillance in Europe . The international comparability has some limitations since the national surveillance systems differ in levels of underreporting and reporting delay.
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 tumours which are rare in people who have a 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.
The following page reports data on influenza and influenza-like illness during the season 2018-2019. Due to the increase of the workload related to COVID-19, final data for the seasons 2019-2020, 2020-2021, and 2021-2022 are not yet published. In the meantime, we invite you to consult:
On average, around 600,000 people are affected by influenza-like illness (ILI) each year in Belgium, i.e., about 5% of the total population. About 50-60% of these cases are actual influenza cases.
While ILI is in most cases a benign illness, about 2% to 3% of influenza cases require hospitalization. Of the hospitalized cases, 13% develop severe complications, including 6% who die in the course of hospital stay; usually more than 80% of these deaths occur in people of 65 years and over.
The Belgian flu epidemic of the 2018-2019 season lasted 8 weeks, which was average compared to previous seasons. An estimated 506,000 Belgians consulted their GP for flu-like symptoms. The severity indicators indicated that this flu epidemic was relatively no more serious than in previous seasons.
Influenza-like illness (ILI) is a medical diagnosis of possible influenza or other illness causing a set of symptoms. These symptoms commonly include fever, shivering, chills, malaise, dry cough, loss of appetite, body aches, and nausea, typically in connection with a sudden onset of illness. In most cases ILI is a benign illness, but for elderly people, pregnant women and people with chronic diseases, the complications of flu can be dangerous.
ILI is caused by a variety of respiratory pathogens, including, amongst others, influenza virus, parainfluenza virus, adenovirus, RSV, and Mycoplasma pneumoniae. The influenza A(H1N1) and A(H3N2) viruses as well as the influenza B virus are the cause of seasonal influenza epidemics in Belgium and circulate every year to different extents. Vaccination remains the best way of preventing transmission, complications and hospitalization of flu.
Sciensano coordinates sentinel networks of general practitioners and hospitals to ensure the permanent surveillance of ILI and influenza activity, intensity and severity of epidemics and impact on the population. The epidemic threshold is the minimum number of GP consultations for flu-like symptoms per 100,000 inhabitants per week needed to officially speak of an epidemic. This number is calculated by the European Centre for Disease prevention and Control (ECDC), and varied between 135 and 157 GP visits/100,000 inhabitants over the last 5 years. Sciensano also hosts the National Reference Centre (NRC) for influenza virus.
At the international level, influenza surveillance and pandemic preparedness is coordinated by ECDC and the World Health Organization.
The Belgian flu epidemic of the 2018-2019 season lasted 8 weeks, which was average compared to previous seasons. The epidemiological threshold was exceeded from week 4/2019 (January 21 to January 27, 2019) to week 11/2019 (March 11 until March 17, 2019). The epidemic was of medium activity.
From week 40/2018 to week 18/2019, respiratory samples from patients diagnosed with ILI were collected by the sentinel network of general practitioners and analyzed at the National Influenza Center. Of these samples, 53% were positive for influenza viruses.
Based on surveillance through the sentinel network of general practitioners, it was estimated that about 506,000 Belgians consulted their GP for flu-like symptoms and, if they were all systematically tested, about 307,000 of them would actually be infected with the flu virus.
All age groups were affected at the approximately same weeks during the epidemic, with peak incidences in weeks 7/2019 and 8/2019.
Although there were many hospital admissions for a severe acute respiratory tract infection (SARI) during this intense season, the severity indicators of the confirmed flu cases (estimated through the network of 6 sentinel hospitals) indicated that this flu epidemic was relatively no more serious than in previous seasons.
The average length of stay for a serious flu infection during this season was 8.8 days (varying in age from 3.6 days in the age of 0-4 to 13.3 days in persons aged 85 years and older). This is comparable to the other seasons.
About 2% to 3% of people with influenza were hospitalized. Among those, 13% had serious complications, which were fatal in 6% of hospitalized patients; these indicators are however similar to those observed in the previous seasons. The vast majority of patients who suffered from severe complications had pre-existing comorbidity (91%).
Deaths were only observed in people aged 54 and over and 90% of these deaths were in patients with one or more comorbidities. The median age of death of patients without comorbidities was 87 years (range: 71-90 years) and the median age of death of patients with comorbidities was 79 years (range: 54-97 years).
The observations in Belgium were in line with those in the rest of Europe.
At European level, influenza activity started in week 49/2018, peaked in week 7/2019 and returned to baseline levels in week 17/2019. Influenza viruses started circulating at high levels in week 52/2018 until week 12/2019.
Intensive care unit (ICU) cases were mainly aged 65 years and older, but in certain countries there was a substantial number of hospitalizations in persons aged 40–64 years.
Each year, between 300,000 and 900,000 people visit their GP because of influenza-like illness in Belgium. Among these, the annual number of influenza infections is estimated between 116,000 and 472,000.
ILI can be caused by a variety of microbial agents other than influenza viruses. Influenza infection causes a clinical syndrome not easily distinguished from other respiratory infections. ILI is defined by the World Health Organization as an acute respiratory infection with: measured fever of ≥ 38 C°; and cough; with onset within the last 10 days.
Severe acute respiratory tract infection (SARI)
SARI is defined by the World Health Organization as an acute respiratory infection with: history of fever or measured fever of ≥ 38 C°; and cough; with onset within the last 10 days; and requires hospitalization. The SARI definition aims to capture both the influenza-related pneumonias and influenza-related exacerbations of chronic illnesses such as asthma or heart disease.