Every year, thousands of individuals develop flu or flu-like symptoms but never seek medical care. These mild and common episodes often go uncounted, obscuring the true circulation of respiratory viruses worldwide.

According to the acute respiratory infection surveillance system SiVIRA, managed by the Instituto de Salud Carlos III, between September and May 2025, influenza led to more than 33,000 hospital admissions, approximately 1800 intensive care admissions, and approximately 1800 deaths in Spain. These figures capture only the most severe cases that require medical care, leaving many mild infections unrecorded and limiting understanding of respiratory virus circulation.

To address this gap, researchers developed Epidemiradar, an online surveillance platform created by the Spanish National Research Council (CSIC) within the European Data Science Initiative EOSC-SIESTA, the Influenzanet network, and the CSIC Interdisciplinary Platform on Global Health.

Epidemiradar is part of the broader Influenzanet network in Spain and invites any resident of Spain to voluntarily participate in building a collaborative map of respiratory virus incidence and spread. After registering on the website, participants complete a short questionnaire and then receive weekly emails asking them to report their current health status, allowing the system to generate continuous population-level surveillance data.

Any resident of Spain can register and complete a short questionnaire on the Epidemiradar. Participants then receive weekly emails asking them to report their current health status, enabling the system to build a collaborative map of respiratory virus activity.

Speaking with Univadis Spain, part of the Medscape Professional Network, Jose J. Ramasco, PhD, researcher at CSIC’s Institute for Cross-Disciplinary Physics and Complex Systems (IFISC CSIC-University of the Balearic Islands) and head of Epidemiradar in Spain, said, “The traditional system for measuring the prevalence of infectious diseases relies on what are called sentinel physicians, which are reports coming from the health system about the cases that are observed.” According to the epidemiology expert, these cases are usually relatively severe “because if the illness is mild, patients don’t go to the doctor, and therefore some of the information that could be important for understanding the extent of the disease in the population is lost.”

Although the platform currently focuses on influenza and COVID, “some trials have been conducted, such as for dengue fever in Italy, and this same system can be used to monitor However, he noted that “Such platforms like Epidemiradar are better suited to diseases that are common in the population. Less common diseases are difficult to detect because the population sample is necessarily small.”

Standardised Surveillance

“Epidemiradar operates in several European countries, such as Italy, France, the UK, and Netherlands. It is important to emphasise the word ‘standardised’ because the questions about symptoms are agreed upon to obtain comparable information on diseases at a continental level,” he said.

“The first survey of each season asks about risk factors, and information is collected in case it can be used in specific studies beyond Epidemiradar’s normal activity, where this information is not published. Of course, these additional studies, like everything on the platform, must be approved by a certified ethics committee,” he continued.

Users who have already experienced COVID or the flu can also register on the platform. “Because they can get it again. Moreover, the important thing now is to build a community of people interested in collaborating on health,” Ramasco emphasised.

The tool’s responses are anonymised and aggregated weekly by region and province, generating maps that track the presence and evolution of flu-like symptoms across the country. These data help researchers detect early patterns and anticipate potential outbreaks, thereby improving the understanding of how respiratory viruses spread.

According to Ramasco, this information is valuable at various levels. “In infectious diseases like COVID or the flu, there is a wide range in the severity of symptoms. Some patients have mild symptoms or are asymptomatic. This is important because these patients do not feel extremely ill, continue with their normal activities, and contribute to the spread of the disease. This profile is fundamental for models that help predict when and how diseases spread.”

Ramasco also highlighted that “these models need to be calibrated, and it’s crucial to have as broad an understanding as possible of the infection’s spread within the population across geographic areas over time in order to do so.” He added that “in some diseases, such as emerging epidemics, there are community transmission mechanisms that are not as well understood, and this information, together with the models, can help characterise them. For example, with COVID-19, the significance of mass infections wasn’t clear until quite late in the pandemic.”

He further noted the adaptability of the platform. One of the most compelling features of Epidemiradar, he said, is that “it helps to get a snapshot of the situation, currently focused on influenza and COVID, but it can be expanded. However, its potential is enormous. It’s necessary to build a community interested in health and willing to collaborate, but with this same system, many more diseases, both infectious and non-infectious, can be monitored.” Ramasco emphasised that “having as many users as possible is fundamental.” He concluded that if a new pandemic were to emerge, “this tool could focus on monitoring that disease and help public health managers better understand the situation quickly. It would help prevent outbreaks by ensuring that the measures taken are more effective.”

The authors reported having no relevant conflicts of interest.

This story was translated from Univadis Spain.