| The Basic Surveillance Network was started in 2000
and is one of the networks on infectious diseases funded by the European
Commission. The network collects and makes readily available basic surveillance
data on infectious diseases from all the 'old' (pre-2004) European Union
member states. The aim is to provide easy access to descriptive data that
already exist in national databases, so that it is possible to monitor
and compare incidence trends for infectious diseases in the EU member
states.
The list of diseases covered by the network has recently been expanded
from 10 initial 'pilot' diseases to over 40 diseases listed by the EU
to be under surveillance. In the near future, the new member states
will be invited to participate in the network.
Data are case-based and comprise date of onset of disease, age and
sex. Only a very short list of disease specific additional variables,
such as country of infection or immunisation status, is collected. Classification
of cases ( possible, probable, confirmed) is specified according to
EU case definitions.
The participants of the network have access to an internal web site
were all the data is presented in tables and graphs. An open website
is available for the public at
https://www.eubsn.org./BSN/
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Introduction
In September 1998, a proposal from the European Commission was adopted
as a Decision of the European Parliament and Council (2119/98/EC) to set
up a network for the epidemiological surveillance and control of communicable
diseases in the European Community.
With this legal document as a background, several projects to develop
designated surveillance networks (DSN) have been funded by the Commission
and they are now operating at the European level (for diseases such as
salmonellosis, legionellosis, tuberculosis and HIV/AIDS). Each one of
them is collecting data at a detailed level and most of them have objectives
beyond routine surveillance (surveillance that only includes information
collected on a regular basis in a majority of European Union (EU) countries
and by methods used by regular national surveillance systems). Some examples
of these extended objectives used in different networks include: the collection
of strains for the further study of resistance mechanisms; surveillance
of antibiotic resistance; and to function as an early warning system for
outbreaks in travellers [1-3]. To fulfil this type of detailed surveillance,
a considerable input is often needed from the member states. Epidemiologists
at the reporting institutes have to fill in manually questionnaires sent
out by DSN at a regular basis. The different networks' case definitions
may differ both from the one proposed by the EU and from the one used
nationally. Age grouping can also vary between, for example, the World
Health Organization and a DSN for the same disease.
A later EU decision listed some 40 diseases that should be under surveillance
[4]. Today there is no single source of routine surveillance data for
these diseases; many of them are not covered by a specific network and
even when covered the data does not necessarily mirror the national surveillance
data. An easy one-step access to simple descriptive data on numbers and
incidences would be useful.
To conclude, there is a need for a surveillance network at the European
level that handles rare diseases and also collects basic or 'generic'
information on the other listed infectious diseases using the three-level
system for case definitions (possible, probable, confirmed).
The Swedish Institute for Infectious Disease Control (SMI) applied for
funding of a project to establish this network, and an agreement between
the Commission and SMI was reached whereby SMI was to coordinate the formation
of a Basic Surveillance Network (BSN). BSN was started in 2000.
Objectives
The key objective of the BSN project is to create a standard, passive
system for sharing basic surveillance data, in order to detect and monitor
incidence trends for infectious diseases in Europe. A long term objective
is to promote activities that make national data more comparable than
they are today. An example is the use of EU case definitions.
Method
One epidemiologist and one database manager have been identified at
each national institute for infectious disease control in the (then)
15 EU member states plus Iceland, Norway and Switzerland. Together with
these designated participants, a programme to fulfil the objectives
has been developed. The following are the main principles of this programme
that the participants have agreed on. The guiding principle has been
to find a level of detail and frequency that is as low as possible,
yet still useful:
· BSN collects data that already exist in national databases.
· Data are case-based, and include age, sex, report date.
Classification of cases are specified (possible, probable, confirmed),
based on the EU case definitions. If case-based data are unavailable,
aggregated data will be collected.
· Only a short list of additional variables for each disease
is collected [TABLE 1].
· The BSN database is updated on a monthly basis.
·Data collection: data are transferred from the national
databases in a predefined format in xml or comma separated files. Before
data are added to the common database, they are checked for consistency
and adherence to the predefined format, and all exceptions found are
clarified. The data are first published on the participating country's
private web page,on the BSN internal website, where only the sending
country can review them. During the first week of the following month,
the new data are added to the common database.
· Aggregated data from the common database are accessible
for all network members via the internal website. A module for standardised
output to a public website has been created. To increase the interpretation
of data, countries can add comments to the graphical presentation of
the aggregated data, shown on the public website.
Activities
Annual meetings of all participating partners are held to discuss principles
of operation and collaboration. Several temporary and one permanent
working group have worked on various epidemiological and data management
issues. Ten pilot diseases have been chosen for reports [TABLE 1]. They
were selected to represent a wide range of different epidemiological
characteristics, not in terms of public health priority, but primarily
to test the feasibility of the collection and transfer protocols set
up.
Data has been collected since 2000 and some countries have also reported
historical data in monthly aggregated format since 1995. Historical
data make the time series longer and facilitate detection of trends.
There is a variation between the members of the network on how many
diseases can ben reported to the network, and how often. Some can deliver
data on all ten diseases, others on six or three, and others on none
[see TABLE 2]. There are several reasons behind these differences. It
may be that a specific disease is not under surveillance in the country,
that the information is not stored in a computerised database, that
the data are not stored at national but at county level or other reasons
that make reporting impossible.
The designated participants of the network have access to an internal
website where surveillance data are presented in various ways. The BSN
focuses on numbers and incidence rates and their trends over time.
Discussion
One of the main benefits of the network is that once the monthly transfer
of the standardised data is in place, incidence trends on more than
40 infectious diseases from all European countries are easily available
within a short time delay. This is not currently possible to find, as
most of the dedicated (disease specific) surveillance networks do not
collect data on all national cases, but rather on a subset. This means
that BSN will provide health professionals and the public with descriptive
data on reported diseases. The network will not be a tool in itself
to answer more complicated questions such as 'why has the incidence
for hepatitis A in country X increased between 00-02?. It can, however,
be a positive stimulus for professionals to initiate further investigative
and analytical work, and furthermore provide them with information on
incidence trends in other EU countries when they experience changes
in their own countries.
There are numerous additional benefits that have been identified during
the development of the network. Bringing database managers from the
national institutes together for the first time made it possible to
examine a number of questions from a new angle. Several of the countries
were at different stages of developing new or updated versions of computerised
reporting systems when the project started. The meeting of the database
managers made it possible to exchange ideas and facilitated and improved
the development of some of these systems.
Among epidemiologists, discussion on interpretation of data has been
possible in a new forum, and detection of major shifts in trends and
difference between different countries can be identified and analysed
at a multinational level.
As with all surveillance networks, there are a number of inherent problems.
When pooling incidence of diseases from individual countries based on
data from their national surveillance systems, there are a number of
obstacles to be faced regarding case definitions and other factors that
will influence the number of cases reported. Although there are common
case definitions for the infectious diseases under surveillance specified
in Decision 2002/253/EC (19.3.2002), this only solves a small part of
the problem. Other, more country specific factors, such as the tendency
of people to seek medical care, different diagnostic methods in use,
and the percentage of physicians sending in notifications probably have
an impact on the numbers reported.
Another problem is that it takes time before data series become long
enough to make trends in disease incidence obvious. Before this output
can be produced, there is a risk that countries providing data and using
the services will not perceive the output as valuable, and might therefore
discontinue their data transfers. Despite such problems, BSN is becoming
a useful part of the common surveillance system laid down by Decision
2119. Two main expansions of the network are planned for the future.
The first, already is in progress, is to expand the number of diseases
reported from the ten pilot diseases to all diseases included under
Decision 2000/96/EC [TABLE 1]. The other is to invite the new members
of the EU to join BSN. We foresee that with basic incidence rates for
the member states published on a single website, BSN will continue to
be a platform for collaboration and exchange of ideas.
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